SCINTILLATORCANDIDATECOMPOUNDS
ByDavidMichaelSmiadak
ATHESIS
Submittedto
MichiganStateUniversity
inpartialfulÞllmentoftherequirements
forthedegreeof
MaterialsScienceandEngineering-MasterofScience
2015ABSTRACTSCINTILLATORCANDIDATECOMPOUNDS
ByDavidMichaelSmiadak
CrystalswithcompositionMgTa
2O6andCe:LuAGweresynthesizedusingthemicro-pulling-down
method.Thecrystalswerepreparedfrompowderedoxidesandtheresultswerecharacterizedwith
x-raypowderdiffraction,x-rayluminescence,scanningelectronmicroscopy,andenergy-dispersivex-ray
spectroscopy.
AnalysisconÞrmedsinglecrystalgrowthsofCe:LuAGwhiletwophaseswereidentiÞedinthe
MgTa
2O6growths.Productionparametersforthesecrystalgrowthsaredetailed.Furtherdevelopmentis
requiredinthecaseofMgTa
2O6asgrowthresultsdidnotproducedetectableemissionspectrarequired
ofscintillators.
ThegrowthofsinglecrystalCe:LuAGwasconÞrmedandthespectralanalysismatchedthoseof
publishedvalues.Ce:LuAGwasconÞrmedtobeanappropriatescintillatormaterialthatcanbegrown
within-houseequipmentatLawrenceBerkeleyNationalLaboratory.Scanningelectronmicroscopyand
energy-dispersivex-rayspectroscopytestingwereperformedatMichiganStateUniversity.
Copyrightby
DAVIDMICHAELSMIADAK
2015FormywonderfulwifeSaeeda
ivACKNOWLEDGEMENTSIwouldliketothankalloftheindividualsatbothMichiganStateUniversityandLawrenceBerkeley
NationalLaboratorywhomassistedmeinmypursuitofaMasterofScienceDegreeinMaterialsSci-
enceandEngineeringatMichiganStateUniversity.Dr.CarlBoehlerthasbeenbothgenerouswith
histimeandßexiblewiththisprojectÕsscope,allowingmetheopportunitytoextendmyworkfrom
LawrenceBerkeleyNationalLaboratorywithexperimentalanalysisatMichiganStateUniversity.His
technicalassistancehasbeeninvaluablewithshapingthescopeofthisproject.Iwouldalsoliketo
thankmythesiscommitteemembersDr.PhillipEisenlohrandDr.DonaldMorellifortheirtechnical
assistanceandadvice.IwouldliketothankbothDr.EdithBourret-CourchesneandDr.DidierPerrodin
atLawrenceBerkeleyNationalLaboratoryfortheirinvaluableassistanceandguidanceinthesynthesis
andcharacterizationofthescintillatorcandidatecompounds.IwouldalsoliketothankDr.Gregory
Bizarri,Dr.IvanKhodyuk,Dr.MartinGascon,andDr.TetianaShalapakaatLawrenceBerkeleyNational
Laboratoryfortheirbrain-stormingandresearchsuggestionsaswellasDr.PaulLecoqfromCERN.I
wouldliketothankChrisRosenforhisassistanceinpowdersynthesisandx-raypowderdiffraction
testingatLawrenceBerkeleyNationalLaboratoryaswell.IwouldalsoliketoacknowledgetheÞnancial
supportprovidedbytheDepartmentofHomelandSecurityÕsDomesticNuclearDetectionOfÞce.Finally,
Iwouldliketoexpressmyverygreatappreciationtomyparents,PamandMattSmiadakfortheir
unwaiveringloveandsupport.
vTABLEOFCONTENTS
LISTOFTABLES
ixLISTOFFIGURES
xiKEYTOABBREVIATIONS
xixIntroduction:ScintillatorPrinciplesandProperties
1InorganicScintillator:Properties
3PhysicalDensity
3Transparency
4ProductionandMachinability
4LightYield
4LinearityofLightOutput
5DecayTime
5Afterglow
6InorganicScintillator:Mechanisms
6Freeandimpurity-boundexciton
6Self-trappedexciton
6Self-activated
7Activatorions
7Core-valenceluminescence
8Charge-transfer
8InorganicScintillator:Applications&Requirements
8HistoricalDevelopment
81896-193981940-198091980-Present
9Background:SelectedCompoundsandMethods
11ScintillatorCandidate:Ce:LuAG
11AnalysisoftheLu
2O3-Al2O3PhaseDiagram
12ScintillatorCandidate:MgTa
2O613AnalysisoftheMgO-Ta
2O5PhaseDiagram
13PowderSynthesis
15Micro-Pulling-DownMethod
16InductiveHeating
17CrucibleandAfter-Heater
18Melt18DiameterControl
19GrowthChamber
20X-rayPowderDiffraction
20X-rayLuminescence
21ScanningElectronMicroscopy
21Energy-DispersiveX-raySpectroscopy
21viExperimentalProcedures
23PowderSynthesis:Ce:LuAG
23HydraulicallyPressed:Sample
123
ManuallyPressed:Sample
223
PowderSynthesis:MgTa
2O624LoosePowder:Sample
124
ManuallyPressed:Sample
224
ManuallyPressed:Sample
325
ManuallyPressed:Sample
425
Micro-Pulling-DownMethod
26ChamberTemperatureCurve
26SoftwareDevelopment
29CrystalSynthesis:Ce:LuAG
29HydraulicallyPressedSample
1,Trial
129
HydraulicallyPressedSample
1,Trial
230
HydraulicallyPressedSample
1,Trial
330
HydraulicallyPressedSample
1,Trial
431
ManuallyPressedSample
2,Trial
132
ManuallyPressedSample
2,Trial
233
ManuallyPressedSample
2,Trial
333
CrystalSynthesis:MgTa
2O634LoosePowderSample
1,MeltCheck
34LoosePowderSample
1,Trial
135
LoosePowderSample
1,Trial
236
LoosePowderSample
1,Trial
336
ManuallyPressedSample
3,Trial
137
ManuallyPressedSample
3,Trial
238
ManuallyPressedSample
3,Trial
339
ManuallyPressedSample
4,Trial
141
ManuallyPressedSample
4,Trial
242
ManuallyPressedSample
4,Trial
342
ManuallyPressedSample
4,Trial
443
ManuallyPressedSample
4,Trial
544
X-rayPowderDiffraction
45X-rayLuminescence
45CrystalMounting
46CrystalPolishing
46LBNLSample
1468.7M48Ce:LuAGSample
2,Trial
348
Ce:LuAGSample
1,Trial
250
MgTa
2O6Sample4,Trial
551
CrystalCoating
52ScanningElectronMicroscopy
52Energy-dispersiveX-raySpectroscopy
54ResultsandDiscussion
56CrystalResults:Ce:LuAG
56viiPressedPowder:Sample
1,Trial
157
PressedPowder:Sample
1,Trial
258
PressedPowder:Sample
1,Trial
359
PressedPowder:Sample
1,Trial
459
PressedPowder:Sample
2,Trial
159
PressedPowder:Sample
2,Trial
360
Ce:LuAGCrystalDiscussion
62CrystalResults:MgTa
2O663LoosePowder:MeltCheck
63LoosePowder:Sample
1,Trial
164
LoosePowder:Sample
1,Trial
264
LoosePowder:Sample
1,Trial
365
PressedPowder:Sample
3,Trial
366
PressedPowder:Sample
4,Trial
167
PressedPowder:Sample
4,Trial
368
PressedPowder:Sample
4,Trial
468
PressedPowder:Sample
4,Trial
571
X-rayPowderDiffraction
73MgTa
2O6:Sample
1,Powder
73MgTa
2O6:Sample
1,MeltCheck
73MgTa
2O6:Sample
1,Trial
374
MgTa
2O6:Sample
3,Trial
374
X-rayLuminescence
76Ce:LuAG:Sample
1,Trial
1+276
Ce:LuAG:Sample
1,Trial
3+476
MgTa
2O6:Sample
1,Trial
380
MgTa
2O6:Sample
4,Trail
1+380
ScanningElectronMicroscopy
83Ce:LuAG:LBNLSample
1482.7M83Ce:LuAG:Sample
1,Trial
283
Ce:LuAG:Sample
2,Trial
385
Ce:LuAG:LBNLSample
1468.7M85MgTa
2O6:Sample
4,Trial
585
Energy-dispersiveX-raySpectroscopy
86Ce:LuAG:Sample
2,Trial
386
Ce:LuAG:LBNLSample
1482.7M88MgTa
2O6:Sample
4,Trial
589
Conclusions91APPENDIX92BIBLIOGRAPHY115viiiLISTOFTABLES
Table
1Historicallyinßuentialscintillators.
10Table
2ConstitutivecompoundmeltingtemperaturesinMgTa
2O6.13Table
3Commonµ-PDcrucibleandafter-heatermaterials,meltingtemperatures,andgrowth
atmospheres.
19Table
4CompoundmixturefortengramsampleofCe:LuAG.
23Table
5CompoundmixtureforÞvegramsampleofMgTa
2O6.24Table
6Grindingpapersusedforpolishingceramicsamples.
47Table
7Photonenergies(keV),ofprincipalK-,L-,andM-shellemissionlines.Boldvaluesare
withinourdetectorrange.[
35]55Table
8Electronbindingenergies,inelectronvolts,ofselectedelements.[
35]55Table
9AdditionalCe:LuAGsamplessentfromLBNLfortesting.
56Table
10ResultssummaryforCe:LuAG
µ-PDgrowths.Sampletypeisthemethodofprepara-
tionwhichwaseitherhydraulically-pressed(HP)ormanually-pressed(MP).
56Table
11Ce:LuAGSample
1crystalcomparisonwithlength-to-weightratio.
62Table
12ResultssummaryforMgTa
2O6µ-PDgrowths.Sampletypeisthemethodofprepara-
tionwhichwaseithernon-pressed(NP)ormanually-pressed(MP).
63Table
13PeakemissionvaluesfrompublicationscomparedtotheexperimentallygrownCe:LuAG
crystals.
79Table
14eZAFSmartQuantitativeResultsfromTEAMsoftware.Area
1ofCe:LuAGSample
2,Trial
3growth.
86Table
15eZAFSmartQuantitativeResultsfromTEAMsoftware.Area
1ofLBNLCe:LuAGSam-
ple1482.7M.88Table
16DarkphaseeZAFSmartQuantitativeResultsfromTEAMsoftware.Area
1ofMgTa
2O6Sample4,Trial
5growth.
90Table
17LightphaseeZAFSmartQuantitativeResultsfromTEAMsoftware.Area
1ofMgTa
2O6Sample4,Trial
5growth.
90Table
18eZAFSmartQuantitativeResultsfromTEAMsoftware.Area
2ofCe:LuAGSample
2,Trial
3growth.
99ixTable
19eZAFSmartQuantitativeResultsfromTEAMsoftware.Area
3ofCe:LuAGSample
2,Trial
3growth.
101Table
20eZAFSmartQuantitativeResultsfromTEAMsoftware.Area
2ofLBNLCe:LuAGSam-
ple1468.7Mgrowth.
103Table
21eZAFSmartQuantitativeResultsfromTEAMsoftware.Area
3ofLBNLCe:LuAGSam-
ple1468.7Mgrowth.
105Table
22DarkphaseeZAFSmartQuantitativeResultsfromTEAMsoftware.Area
2ofMgTa
2O6Sample4,Trial
5growth.
106Table
23LightphaseeZAFSmartQuantitativeResultsfromTEAMsoftware.Area
2ofMgTa
2O6Sample4,Trial
5growth.
106Table
24DarkphaseeZAFSmartQuantitativeResultsfromTEAMsoftware.Area
2ofMgTa
2O6Sample4,Trial
5growth.
108Table
25LightphaseeZAFSmartQuantitativeResultsfromTEAMsoftware.Area
3ofMgTa
2O6Sample4,Trial
5growth.
108xLISTOFFIGURES
Figure
1Sketchofscintillatorconversionofahighenergy(HE)photon.[
14]2Figure
2Theafterglowmechanismwhereeitheranexcitationeventcreatesafreeelectronand
electron-hole.Theelectron-holeistrappedat
T2whiletheelectronistrappedat
T1,onlyar-
rivingat
T2afteradelay.[
7]5Figure
3Frenkelexciton,aboundstateofattractionbetweenanelectronandelectron-hole.
6Figure
4Self-trappedexciton.
7Figure
5AcubicCe:LuAGlatticestructurewithatomicpositionsoflutetium(green),aluminum
(brown),andoxygen(red)takenfromICDDÕsPDF-
4+database,CrystalStructureSource:LPF.
12Figure
6TheLu
2O3-Al2O3phasediagram.[
62]12Figure
7AtetragonalMgTa
2O6latticestructurewithatomicpositionsofmagnesium(green),
tantalum(blue),andoxygen(red)takenfromICDDÕsPDF-
4+database.
13Figure
8PreliminaryphasediagramofthesystemMgO-Ta
2O5.[4]14Figure
9Mortarandpestlemadefromagatestoneusedtomixpowdercompounds.
15Figure
10DensiÞcationwasaccomplishedwitha
12-tonforcemanualpress.
15Figure
11Schematicdiagramof
µ-PDsystemwithexternalinductiveRFheating.
16Figure
12Sequentialimagesofphotoelectriceffectwithphotonabsorptionandphotoelectronejec-
tion(top)followedbyßuorescentx-rayemission(bottom).
22Figure
13PressedsampleofMgTa
2O6,singlepressattemptwithsigniÞcantlossinprocess.
24Figure
14PressedsampleofMgTa
2O6,twodifferentpresseswereusedtobreakthesampleinto
amoremanageablesize.
25Figure
15Translationspeedcontrolswithlocal(programmed)andremote(user)adjustment.
26Figure
16Fracturedceramicinsulatorcapremovedfromchamberafterhightemperaturecycling.
26Figure
17Thewater-cooled
µ-PDtestchamberfromCyberstar.
27Figure
18MarathonMM
2MHpyrometer.
28Figure
19Set-pointtotemperaturecalibrationcurvefordoubleinsulated
µ-PDexperimentsat
thecruciblenozzle.
28Figure
20Applicationsplashscreen.
29Figure
21ImagecaptureapplicationwrittenforWindows.
29xiFigure
22Sampleoutputofaformattedsingleframe.
29Figure
23ContinuousbutunevenCe:LuAGcrystalgrowth(Sample
1,Trial
2).30Figure
24Ce:LuAGcrystalgrowthwithlargemoltenregionbetweenthecrucibleandordered
crystal(Sample
1,Trial
2).30Figure
25SmoothandstableCe:LuAGcrystalgrowth(Sample
1,Trail
3).30Figure
26Ce:LuAGcrystalgrowthwithhorizontallinedefectsvisible(Sample
1,Trail
3).31Figure
27Ce:LuAGgrowthfailureshortlyaftersuccessfulseeding.Withanabrupttemperature
increasethemeltpulledbackintothecapillarychannel(Sample
1,Trial
4).31Figure
28StableCe:LuAG
crystalgrowth(Sample
1,Trial
4).31Figure
29TheCe:LuAGmeltattachedtotheseed,pullingitfromtheseedrodholderbelow(Sam-
ple2,Trial
1).32Figure
30StableCe:LuAGcrystalgrowthwithlargercruciblenozzle(Sample
2,Trial
3).34Figure
31MeltcheckforMgTa
2O6.35Figure
32MgTa
2O6seedattempt(Sample
1,Trial
1).35Figure
33SecondMgTa
2O6seedattemptwithmoreemergingmelt(Sample
1,Trail
1).35Figure
34SeedusedforMgTa
2O6growthattempt,gluedtoceramicpostwiththermaladhesive.
35Figure
35MgTa
2O6seedattempt(Sample
1,Trial
2).36Figure
36SecondMgTa
2O6seedattemptafterseedtranslation(Sample
1,Trial
2).36Figure
37MgTa
2O6growthinitialization(Sample
1,Trail
3).36Figure
38IncreasingdiameterofMgTa
2O6growth(Sample
1,Trial
3).37Figure
39TheMgTa
2O6meltwouldnotadheretotheseedduetopoormaterialcompatibility
(Sample3,Trial
1).38Figure
40TheseedrodpressedagainsttheMgTa
2O6meltwithsufÞcientforcetorotatetheafter-
heaterandobstructviewing(Sample
3,Trial
2).38Figure
41TheMgTa
2O6meltdidnotattachtotheseedbutcontinuedtodischarge(Sample
3,Trial
3).39Figure
42TheMgTa
2O6dischargecoveredtheentireviewingwindow(Sample
3,Trial
3).39Figure
43TheendoftheMgTa
2O6dischargeemptiedthecrucible(Sample
3,Trial
3).40Figure
44TheMgTa
2O6dischargefromthelasttestmadeforacompatibleseed.
40Figure
45ThedriedMgTa
2O6seedneededtobesandeddownslightlypriortouse.
41xiiFigure
46VariablediameterMgTa
2O6growthseededonnewconstructedMgTa
2O6seed(Sam-
ple4,Trial
1).41Figure
47MgTa
2O6growthinitiatedatasmalldiameterbeforegrowinglargerandcoolingquickly
(Sample4,Trial
2).42Figure
48ThesmallinitialMgTa
2O6growthdiameterbrokeoncethemassaboveitwasseeded
again,pluggingthecapillarychannelwithrelativelycoolMgTa
2O6(Sample4,Trial
2).42Figure
49VariablediameterMgTa
2O6growth(Sample
4,Trial
3).42Figure
50MgTa
2O6sampletobeseparatedafÞxedonrubberÞxture.
43Figure
51VariablediameterMgTa
2O6growth(Sample
4,Trial
4).43Figure
52VariablediameterMgTa
2O6growthafterseedingrestart(Sample
4,Trial
4).43Figure
53Wiresawusedtoseparatesamplegrowthfrombrokenseed.
44Figure
54VariablediameterMgTa
2O6growth(Sample
4,Trial
5).44Figure
55PreparedsampleforXRPDanalysis.
45Figure
56RawXRPDoutput,priortopost-processing.
45Figure
57BuehlerPneumetImountingpress.
46Figure
58Bottomsurfaceofthemountthatwillactasthetopofthesampletobepolished.
46Figure
59BuehlerEcometIVPolisher/Grinder.
46Figure
60ZeissStemiSV-
6stereomicroscopeusedforobservingpolishedsamples.
47Figure
61Ce:LuAG(<
0.5mol%Ce)-
10mmlengthcrystalafterÞrstpolish.MAG:
5.0x,AE:
1.5ms,AG:
4.0x.48Figure
62Ce:LuAG(<
0.5mol%Ce)-
10mmlengthcrystalpriortodiamondpastepolishing.MAG:
5.0x,AE:
1s,AG:
3.9x.48Figure
63Ce:LuAG(
1mol%Ce)from
3mmODcruciblenozzle.Initialcrystalstateaftermount-
ing.MAG:
5.0x,AE:
300ms,AG:
2.8x49Figure
64Ce:LuAG(
1mol%Ce)from
3mmODcruciblenozzle.Crystalstateafterpolishwith
2400gritsandpaperfor
5minutesat
200rpm.MAG:
5.0x,AE:
150ms,AG:
4.0x49Figure
65Ce:LuAG(
1mol%Ce)from
3mmODcruciblenozzle.Crystalafterdiamondpastepol-
ishing.MAG:
5.0x,AE:
300ms,AG:
4.8x49Figure
66Ce:LuAG(
1mol%Ce)from
1mmODcruciblenozzle.Crystalpriortopolishing.MAG:
5.0x,AE:
30ms,AG:
4.0x.50xiiiFigure
67Ce:LuAG(
1mol%Ce)from
1mmODcruciblenozzle.Crystalafter
320gritsandpa-
per.MAG:
5.0x,AE:
200ms,AG:
5.6x.50Figure
68Ce:LuAG(
1mol%Ce)from
1mmODcruciblenozzle.Crystalafterdiamondpastepol-
ishing.MAG:
5.0x,AE:
200ms,AG:
5.6x50Figure
69MgTa
2O6from
1mmODcruciblenozzle.Initialcrystalconditionaftermounting.MAG:
5.0x,AE:
30ms,AG:
4.0x.51Figure
70MgTa
2O6from
1mmODcruciblenozzle.Crystalaftersecondperpendicularpolish
with4000gritpaper.MAG:
5.0x,AE:
200ms,AG:
5.6x.51Figure
71MgTa
2O6from
1mmODcruciblenozzle.Crystalafterrepeatedperpendicularpolishes.
MAG:5.0x,AE:
200ms,AG:
5.6x.51Figure
72Ce:LuAG(<
0.5mol%Ce)-
10mmlengthcrystalaftercoating,
1nmthicknesstungsten
coating.MAG:
5.0x,AE:
200ms,AG:
5.6x.52Figure
73LeicaEMMED
020modularhighvacuumcoater(ImagefromLeica).
53Figure
74MiraXMHelectronmicroscope(ImagefromTescan).
53Figure
75Compositeimageofthe
5mmCe:LuAGsamplessentfromLBNLforfurthertesting.
57Figure
76PositionofCe:LuAGcrystalseparationthatoccurredjustoutoftheviewingwindow
ofthe
µ-PDchamber(Sample
1,Trial
1).57Figure
77A25mmlongCe:LuAGcrystalwithanapproximatediameterof
1mm(Sample
1,Trial
1).57Figure
78RemainingCe:LuAGmeltcontainedinthecrucible(Sample
1,Trial
1).58Figure
79SmoothmoltenCe:LuAGwithincrucibleremainingaftercrystalgrowth(Sample
1,Trial
2).58Figure
80A100mmlongCe:LuAGcrystalwithanapproximatediameterof
1mm(Sample
1,Trial
2).58Figure
81A13mmlongCe:LuAGcrystalwithanapproximatediameterof
1mm(Sample
1,Trial
3).59Figure
82TheCe:LuAGcruciblemeltaftercrystalgrowth,contaminationisobservedonthetop
surfacefromtheiridiumcrucible(Sample
1,Trial
4).59Figure
83CrystallizedCe:LuAGmeltwithinthecrucibleaftergrowthattempt(Sample
2,Trial
1).59Figure
84InitializationoftheCe:LuAGcrystalattherightwithcontaminationappearingasdark
discolorationalongthecrystalexterior(Sample
2,Trial
3).60xivFigure
85Ce:LuAGcrystalgrowthwasapproximately
23mminlengthandwasbrokenduring
after-heaterremoval(Sample
2,Trial
3).61Figure
86The100mmlongCe:LuAGcrystalpulledatarateof
0.5mmmin(Sample1,Trial
2)com-
paredtotheshorterCe:LuAGcrystalgrownatarateof
0.1mmmin(Sample1,Trial
3).62Figure
87A103mmlongCe:LuAGcrystalgrownat
0.1mmmin(Sample1,Trial
4)comparedtoa
100mmlongCe:LuAGcrystalgrownat
0.5mmmin(Sample1,Trial
2).63Figure
88Topofcrucible,melttestforMgTa
2O6(Sample1).63Figure
89Semi-smoothmoltenMgTa
2O6withincrucibleafterthe
µ-PDexperiment(Sample
1,Trial
1).64Figure
90Bluediscolorationonquartzpedestalafterseedattempt(Sample
1,Trial
1).64Figure
91SmoothmoltenMgTa
2O6meltwithincrucible(Sample
1,Trial
2).65Figure
92LoweredMgTa
2O6crystalwithintestchamber,belowinductioncoil(Sample
1,Trial
3).65Figure
93TheMgTa
2O6meltwithincrucibleafterthe
µ-PDexperiment(Sample
1,Trial
3).65Figure
94MgTa
2O6crystalgrowth(Sample
1,Trial
3).66Figure
95MgTa
2O6dischargeattachedtotheseedrod,avoidingcontactwiththeseed(Sample
3,Trial
3).66Figure
96Compounddepositonsurroundingceramicinsulatorandlid(Sample
3,Trial
3).66Figure
97TheMgTa
2O6meltwithincrucibleafterthe
µ-PDexperiment(Sample
4,Trial
1).67Figure
98The8mmMgTa
2O6growthattachedtothenewlyconstructedMgTa
2O6seed(Sam-
ple4,Trial
1).68Figure
99TheMgTa
2O6meltinsidethecrucible(Sample
4,Trial
3).68Figure
100The12mmMgTa
2O6growthattachedtothenewlyconstructedMgTa
2O6seed(Sam-
ple4,Trial
3).68Figure
101The136mmMgTa
2O6growthattachedtotheseedstillinthe
µ-PDchamber(Sample
4,Trial
4).69Figure
102BrokenupMgTa
2O6growth,measuring
136mmtotal(Sample
4,Trial
4).70Figure
103MgTa
2O6meltwithinthecrucible,suspectedcontaminationfromtheiridiumcrucible
(Sample4,Trial
5).71Figure
104Theexteriorofthecrucibleafterthe
µ-PDexperiment,grainboundariesprominentaf-
terhightemperaturecycling(Sample
4,Trial
5).71Figure
105BrokenupMgTa
2O6growth(Sample
4,Trial
5).72xvFigure
106DiffractionpatterntakenfromtheMgTa
2O6powdersamplepriortorunningthemelt
checkcomparedagainstthepeakstandard(Sample
1).73Figure
107DiffractionpatterntakenfromtheMgTa
2O6meltaftercompletingthemeltcheck,com-
paredagainstthepeakstandard(Sample
1).74Figure
108HighlightedregionsofMgTa
2O6growthwhereXRPDsamplesweretaken(Sample
1,Trial
3).74Figure
109DiffractionpatterntakenfromtheMgTa
2O6headregioncomparedagainstthepeak
standard(Sample
1,Trial
3).75Figure
110DiffractionpatterntakenfromtheMgTa
2O6tailregioncomparedagainstthepeakstan-
dard(Sample
1,Trial
3).75Figure
111DiffractionpatternstakenfromtheMgTa
2O6growthusedforasaseedcomparedagainst
thepeakstandard.(Sample
3,Trial
3).75Figure
112Ce:LuAGcrystalspreparedforXRLtesting,Sample
1,Trial
3+4(top)andSample
1,Trial
1+2(bottom).76Figure
113XRLintensityforthecombinationofCe:LuAGcrystalgrowthsfromSample
1,Trial
1+2.77Figure
114XRLintensityforthecombinationofCe:LuAGcrystalgrowthsfromSample
1,Trial
3+4.78Figure
115XRLintensitycomparisonforthecombinationofCe:LuAGcrystalgrowthsfromSam-
ple1,Trial
1+2andSample
1,Trial
3+4.79Figure
116XRLintensityforthetailportionoftheMgTa
2O6growth(Sample
1,Trial
3).80Figure
117XRLintensityforthecombinationofMgTa
2O6growthsfromSample
1,Trial
1+3.81Figure
118Four-waycomparisonofXRLresults.TheMgTa
2O6testresultsarebarelydiscernible
alongthex-axiswhiletheCe:LuAGrelativeintensitiesdominate.
82Figure
119Ce:LuAGcrystal(LBNLSample
1482.7M).83Figure
120Ce:LuAGcrystal,MAG:
100x(Sample
1,Trial
2).83Figure
121Ce:LuAGcrystalundersecondaryelectrons(left)andback-scatterdetection(right),MAG:
2000x(LBNLSample
1482.7M).Bothimagesarefeaturelessoutsideofsomedustparticles.
84Figure
122Ce:LuAGcrystal,MAG:
100x(Sample
2,Trial
3).85Figure
123UncoatedCe:LuAGcrystal(LBNLSample
1468.7M).85Figure
124MgTa
2O6two-phasegrowth(Sample
4,Trial
5).85Figure
125HighlightedareaofEDSanalysis.Area
1ofCe:LuAGSample
2,Trial
3growth.
86xviFigure
126EDSoutputspectrumofArea
1ofCe:LuAGSample
2,Trial
3growth.
87Figure
127HighlightedareaofEDSanalysis.Area
1ofLBNLCe:LuAGSample
1482.7Mgrowth.
88Figure
128EDSanalysisofArea
1ofLBNLCe:LuAGSample
1482.7Mgrowth.
88Figure
129HighlightedareaofEDSanalysis.Area
1ofMgTa
2O6Sample4,Trial
5Growth.
89Figure
130EDSanalysisoflightphase(top)anddarkphase(bottom),notethediscrepancyinthe
MgKpeaks.
89Figure
131Ce:LuAGcrystal,undervariousmagniÞcations(LBNLSample
1482.7M).93Figure
132Ce:LuAGcrystal,undervariousmagniÞcations(Sample
1,Trial
2).94Figure
133Ce:LuAGcrystal,undervariousmagniÞcations(Sample
2,Trial
3).95Figure
134Ce:LuAGcrystal,undervariousmagniÞcations(Sample
1,Trial
2).96Figure
135MgTa
2O6crystal,undervariousmagniÞcations(Sample
4,Trial
5).97Figure
136HighlightedregionofEDSanalysis.Area
2ofCe:LuAGSample
2,Trial
3growth.
98Figure
137EDSoutputspectrumofArea
2Ce:LuAGSample
2,Trial
3growth.
98Figure
138HighlightedregionofEDSanalysis.Area
3ofCe:LuAGSample
2,Trial
3growth.
100Figure
139EDSoutputspectrumofArea
3Ce:LuAGSample
2,Trial
3growth.
100Figure
140HighlightedregionofEDSanalysis.Area
2ofLBNLCe:LuAGSample
1468.7Mgrowth.
102Figure
141EDSoutputspectrumofArea
2ofLBNLCe:LuAGSample
1468.7Mgrowth.
102Figure
142HighlightedregionofEDSanalysis.Area
3ofLBNLCe:LuAGSample
1468.7MGrowth.
104Figure
143EDSoutputspectrumofArea
3ofLBNLCe:LuAGSample
1468.7Mgrowth.
104Figure
144HighlightedregionsofEDSanalysis.Area
2ofMgTa
2O6Sample4,Trial
5growth.
106Figure
145EDSoutputspectrumoflightphase(top)anddarkphase(bottom),notethediscrep-
ancyintheMgKpeaks.Area
2ofMgTa
2O6Sample4,Trial
5growth.
107Figure
146HighlightedareaofEDSanalysis.Area
3ofMgTa
2O6Sample4,Trial
5growth.
108Figure
147EDSoutputspectrumoflightphase(top)anddarkphase(bottom),notethediscrep-
ancyintheMgKpeaks.Area
3ofMgTa
2O6Sample4,Trial
5growth.
109Figure
148Pythonprogramminglanguage.
111Figure
149VisualBasicprogramminglanguage.
112xviiKEYTOABBREVIATIONS
µ-PDmicro-pulling-down.
ACalternatingcurrent.
AEautoexposure.
AGanaloggain.
ATM
atmosphere.
BDBridgman.CBconductionband.
CCDchargecoupleddetector.
Ce:LuAGceriumdopedlutetiumaluminumgarnet.
Ce:YAG
ceriumdopedyttriumaluminumgarnet.
Ce:YAP
ceriumdopedyttriumaluminiumperovskite.
CTx-raycomputedtomography.
CVcore-valence.
CXcharge-transfer.
CZCzochralski.EDSenergy-dispersivex-rayspectroscopy.
EFGedge-deÞned-Þlm-fed.FPSframes-per-second.
FWHMfullwidthathalfmaximum.
FZßoatingzone.
HEhigh-energy.
HEPhigh-energyphysics.
HPhydraulically-pressed.
ICDDInternationalCentreforDiffractionData.
IDEintegrateddevelopmentenvironment.
IDLEIntegratedDeveLopmentEnvironment.
IRinfrared.
LBNLLawrenceBerkeleyNationalLaboratory.
xviiiLHCLargeHadronCollider.
LPFLinusPaulingFile.
LuAGlutetiumaluminumgarnet.
LVSEM
low-vacuumscanningelectronmicroscopy.
LYlightyield.
MAGmagniÞcation.MPmanually-pressed.
NPnon-pressed.
ODouterdiameter.
OEopticalexcitation.
OP-Soxidepolishingsuspension.
PCpersonalcomputer.
PETpositronemissiontomography.
PMTphotomultipliertubes.
PSIpoundspersquareinch.
RErareearth.
RFradio-frequency.
RPMrotationsperminute.
RTroomtemperature.
SAself-activated.
SEsecondaryelectrons.
SEMscanningelectronmicroscopy.
SPset-point.SSCSuperconductingSuperCollider.
SXself-trappedexciton.
TEAMTextureandElementalAnalyticalMicroscopy.
UVultraviolet.
VBVisualBasic.
VBvalencebands.
XRLx-rayluminescence.
XRPDx-raypowderdiffraction.
YAG
yttriumaluminumgarnet.
xixIntroduction:ScintillatorPrinciplesandProperties
Theobjectiveofthisstudywastoproducesinglecrystalsofde-
siredcompounds,evaluatethegrowth,anddrawconclusions
abouttheirfeasibilityasascintillator.Acrystalisasolidconsist-
ingofaregularperiodicarrangementofatoms.
Ascintillatorisamaterialpossessingluminescentcentersthat
absorbshigh-energyphotonsandemitslightinthevisibleor
near-visiblespectrum.Theenergylevelsinvolvedinthisradiative
transitionmustoccurintheenergygapsothattheemittedlightis
notlostthroughreabsorption.Thistransitionhasprovenusefulfor
detectingbothx-rayand
!-rayphotons.
11B.C.Grabmaier,W.Rossner,and
J.Leppert.Ceramicscintillatorsforx-ray
computedtomography.
PhysicaStatus
Solidi(a)
,130(2):K183ÐK187,April
1992Scintillatorsexistasorganics,inorganics,glasses,liquids,and
gases.Thisstudyfocusesoninorganicsinglecrystalscintillators
forapplicationsintheÞeldofhigh-energyphysics(HEP)particle
detection.Scintillatorsareusedinconjunctionwithphotosensitivedevices
thatareabletoquantifytheemittedvisiblelight.Thesedevices
includephoto-diodesandphotomultipliertubes(PMT).
Inordertobetterunderstandtheprocessofscintillation,itis
usefultoÞrstdescribethebandstructureofamaterial.Thisband
structureisdividedintothreecriticalregions:conductionband
(CB),valanceband(VB),andtheenergygap(E
g)thatseparates
them.TheCBconsistsofelectronsthathavesufÞcientenergytotravel
throughoutthecrystalwhiletheVBconsistsofelectronsthatare
boundtothelatticestructure.TheCBandtheVBareseparatedby
theenergygapwherenoelectronstatesexist.
ElectronscanbepromotedtotheCBbyabsorbingenergyfrom
radiationinteractions.Thisisthedrivingmechanismbehind
scintillation.Directde-excitationthroughphotonemissioncan
beinefÞcient,withtheresultantphotoncarryingenergybeyond
thevisiblespectrum.Thisexcessenergycannotbecountedby
photo-detection.Hereiswheretheneedforscintillatorsarises,to
shiftthewavelengthofthephotonintothevisibleornearvisible
spectrum.Inordertoenhancephotonemission,asmallamountofimpu-
ritycanbeintroducedintothelattice.Thisimpurityisreferredto
asanactivatorordopant.Theseactivatorscreatespecialenergy
siteswithinthelatticewherethenormalenergybandstructureis
modiÞed.Thesespecialenergysitescanbewithinthetraditionally
forbiddenenergygapwhereelectronscande-excitetotheVB.
1Figure
1:Sketchofscintillatorconver-
sionofahighenergy(HE)photon.[
14]2Duetothesmallerenergyoftheseactivatorsites,transitions
betweenthesesitesandtheVBresultinphotonswithloweren-
ergies.Thislowerenergybringsthesephotonsintothevisible
ornear-visiblespectrumofemissions.Theseactivatorsitesare
referredtoasluminescencecentersorrecombinationcenterswhen
theyresideintheenergygap.
Thistrappingofelectronsisusefulbecausetheselocalizeden-
ergylevelsresideintheenergygapandavoidrecombinationwith
thelattice,allowingforlighttoescapethescintillatormaterial.
ElectronsinthisstatebecometemporarilyremovedfromtheCB.
22S.Kasap.
PrinciplesofElectronic
MaterialsandDevices
.McGraw-Hill
Education,thirdedition,March
2005Inorganicscintillationcanbedescribedinthreephases:
1.Ionizationeventthatcreatesaninnershellelectron-holeandan
energeticprimaryelectron.
2.Whentheelectronenergybecomeslessthantheionization
threshold,electronsandelectron-holesthermalize.Thisin
turntransferselectronstoexcitetheluminescentcentersinthe
energygap.
3.Excitedluminescentspeciesrelaxtothegroundstateand
emissionofscintillationlightoccurs.
Whileeachprocessoccurswithcharacteristictimeconstants.
theemissionofscintillationlightvarieswidelyduetothequan-
tumwave-functioncharacteristicsofthelevelsinvolvedinthese
transitions.3Duetothesecomplexities.predictivecomputational
3P.Lecoq,A.Annenkov,A.Gektin,
M.Korzhik,andC.Pedrini.
Inorganic
ScintillatorsforDetectorSystems:Physical
PrinciplesandCrystalEngineering
.Springer-Verlag,Þrstedition,
2006modelinghasproveddifÞcultindeÞningthesetimeconstants
withexperimentalistsexploringwellaheadofwhatcomputational
modelingcanreliablypredict.
44M.J.Weber.Inorganicscintillators:
todayandtomorrow.
JournalofLumines-
cence,100(1-4):35Ð45,2002InorganicScintillator:Properties
Inorganicscintillatorsarethefocusofthisstudy.Importantprop-
ertiesthatareconsideredwhenevaluatingscintillatorcandidate
materialsarephysicaldensity,transparency,productionand
machinability,lightyield,linearityoflightoutput,decaytime,and
afterglow.
PhysicalDensity
Highphysicaldensityiscriticallyimportantforhighenergy
applicationsduetoitsinherentlyhigherstoppingpowerprovided
bythehostlattice.ScintillatorsalsobeneÞtfromelementswith
higheffectiveatomicnumbers(Z
eff
),whichhavealargerphysical
sizewithinthelatticetostophighenergyparticleswithinthe
crystal.Additionally,ahigherdensityalsoreducesthephysical
sizeofadetectorwhichisimportantforÞeldapplications.
3Transparency
Thetransparencyofascintillatordirectlyrelatestoitsabilityto
transportphotonscintillationtoacoupledphoto-detector.Scintil-
latorstypicallyabsorbhigh-energyparticlesattheirentranceface
andthisenergymakesittotheothersideofthecrystalthrough
acombinationofreßectionsandscatteringbothatsurfacesand
withinthematerial.Minimizingthisvisiblephotonpathlength
iscritical.Longerphotonpathlengthscanbefurthersuscepti-
bletoopticalabsorptionandefÞciencychangesduetoradiation
damage.55C.GreskovichandS.Duclos.Ceramic
scintillators.AnnualReviewofMaterials
Science,27(1):69Ð88,August
1997ProductionandMachinability
Easeofproductionandmachinabilityareimportantwhendeter-
miningappropriatescintillatorcandidatematerials.SigniÞcant
costcanbeaccruedthroughequipment,productionandtheacqui-
sitionofrawmaterials.
Enduseofcrystalstypicallyrequirethemtobeinstalledin
detectorswithspeciÞcrepeatablecrystalgeometry.Cleavageof
singlecrystalscanalsobeaconcern.Incorrectorientationduring
machiningcanfractureasinglecrystalinunintendedways.
Additionally,acrystalmusthaveappropriatechemical,me-
chanical,andradiationhardness.Crystalsthatdonotundergo
phasetransformationordecomposeintoconstitutivecompounds
betweentheirmeltingtemperatureandRTarepreferredbecause
theyareeasiertoproduce.
LightYield
Ahighlightyield(LY),measuredinphotons/MeV,isdesirablefor
mostscintillatorapplications.Formedicalapplication,scintillators
withhighLYcanreducetheamountoftimeapatientisexposed
toradiation.ScintillatorLYislargelydrivenbytheprocessesthat
excitetheluminescencecentersofthescintillatingions.
Thenumberofvisible/UVphotons,
Nph,producedperenergy
canbeexpressedas,
Nph=E"EgáSáQ(1)where
Eisenergy,
"representstheaverageenergyrequiredto
produceonethermalizedelectron-holepair,
Egistheenergy
gap,SandQarethequantumefÞcienciesofthetransportand
luminescencestages,respectively.Theaverageenergyrequired
toproduceathermalizedelectron-holepair,relatestotheenergy
suchthat,
Ee-h="Eg(2)4with"!2"3.6TherelativeefÞciencyofascintillator,
#,canbe
6C.W.E.vanEijk.Inorganic-scintillator
development.
NuclearInstrumentsand
MethodsinPhysicsResearchSectionA:
Accelerators,Spectrometers,Detectorsand
AssociatedEquipment
,460(1):1Ð14,2001expressedas,
#=EgenNphE(3)where
EgenistheenergyoftheUV/visiblephoton.Oneofthe
mostefÞcientscintillatorscurrentlyproducedisZnS:Agwithan
efÞciencyof
#!0.2.Anotherfactortoconsiderwhenevaluatingascintillatorcandi-
dateistheenergyresolutionofthescintillatorandaccompanying
photodetectorneeded.Conventionalsolidstatesemi-conductors
orphotomultiplier-basedphotodetectorscandetectgeneratedvis-
ibleorUVlightwithhighsensitivity.
7Energyresolutionismost
7G.Dhanaraj.
SpringerHandbookof
CrystalGrowth
.Springer-Verlag,Þrst
edition,2010commonlydeÞnedasasystemÕsabilitytodiscriminatebetween
!-photonsofdifferentenergies.ThisenergyresolutionisdeÞned
bythefullwidthathalfmaximum(FWHM)ofthephoto-peakata
givenenergydividedbyitsenergy.Thisvalueisthusafunctionof
LY.
LinearityofLightOutput
Theidealscintillatormaterialwouldbeabletoconverteach
!-photontoaphotonofreducedenergyinthevisiblespectrum.
Eachcandidatematerialpossesseslessthanidealconversiondue
toaninhomogeneousscintillatormicro-structureandCompton
scattering.Comptonscatteringisthescatteringofaphotonbya
chargedparticle,typicallyanelectron.Thisdecreasestheenergy
andincreasesthewavelengthoftheaffectedphoton.
Additionally,discrepanciesinmicro-structurecanleadtospa-
tialdifferencethatleadtouniqueconversionefÞciencieswhere
Comptonscatteringproduceselectronsofvaryinglowerenergies.
Proportionalityiscriticallyimportantwhenitcomestodeter-
mineenergyresolutionsbecausenon-lineardeviationsinLYare
detrimentaltoscintillatorperformance.
DecayTime
Figure
2:Theafterglowmechanism
whereeitheranexcitationeventcreates
afreeelectronandelectron-hole.The
electron-holeistrappedat
T2whilethe
electronistrappedat
T1,onlyarriving
atT2afteradelay.[
7]Decaytime,alsoreferredtoasscintillatorresponse,isanimpor-
tantfactorindeterminingthetimeresolutionofascintillator.The
fasterthedecaytimeoftheluminescention,thebetterthetiming
resolution.Theradiativelifetime,
$,oftheluminescentcenteris
desiredtobeshortformedicalapplicationbecauseitcanlimitthe
timenecessaryforanindividualtobeexposedtotheradiation.
The4f-5dopticaltransitionproducedbyionssuchas
Ce3+exhibitatypicaldecaytimeof
10-60nsrange.
5Afterglow
Afterglowisthefractionofscintillatinglightpresentforagiven
periodoftimeoncetheionizingradiationhasstopped.Itisoften
desirableforthiseffecttobeminimizedoreliminatedcompletely.
IfnotcontrolledforaspeciÞcapplicationitwilltakemoretimeto
discriminatebetween
!-photons,decreasingtimingresolution.
88C.R.RondaandA.M.Srivastava.
Scintillators,chapter
5,pages
105Ð132.Wiley-VCHVerlagGmbHandCo.
KGaA,2007AfterglowcanbesigniÞcantlylongerthantheradiativelifetime
andoccursbecauseofdelayedradiantrecombinationofelectrons
andelectron-holesduetothetrappingofeitherasshowninFigure
2.Figure
3:Frenkelexciton,aboundstate
ofattractionbetweenanelectronand
electron-hole.
InorganicScintillator:Mechanisms
Manyofthescintillationmechanismsarerelatedtoexcitonswhich
canbedescribedasanelectricallyneutralquasiparticle.This
excitonstateoccurswhereanelectronandanelectron-holeare
attractedtoeachotherbyelectrostaticCoulombforcesasshownin
Figure
3.ExamplesofÞnalstageluminescenceinscintillatorsincludes
freeandimpurity-boundexcitons,andself-trappedexciton(SX).
Somescintillatorsareconsideredself-activated(SA)whileothers
useactivator/dopantions,core-valence(CV)luminescence,or
charge-transfer(CX)emission.
Intrinsicscintillatormaterialsareself-activatedandcaninvolve
electronandelectron-holerecombination.Additionalmechanisms
forself-activationinvolveexcitonluminescencebyeitherfree,
self-trappedordefect-trappedexcitonstates.
99S.E.Derenzo,M.J.Weber,E.D.Bourret-
Courchesne,andM.K.Klintenberg.The
questfortheidealinorganicscintillator.
NuclearInstrumentsandMethodsin
PhysicsResearchSectionA:Accelerators,
Spectrometers,DetectorsandAssociated
Equipment,505(1-2):111Ð117,2003Extrinsicscintillatormaterialsareexternallyactivated,typically
associatedwithadopantion.Examplesofthesedopantions
includeTl
+,Ce
3+,andEu
2+.1010M.J.Weber.Scintillation:mechanisms
andnewcrystals.
NuclearInstruments
andMethodsinPhysicsResearchSectionA:
Accelerators,Spectrometers,Detectorsand
AssociatedEquipment
,527(1-2):9Ð14,2004Freeandimpurity-boundexciton
Excitonsareformedwhenanionizationelectronandelectron-
holeareboundintopairstates.Thisislargelyconsideredalow
temperaturemechanismthatisboundasanentitytoanimpurity
atomordefect.Atroomtemperature(RT)thisemissiontypeis
weakbecausetheexcitonstateisquicklydisassociated.
Self-trappedexciton
TheSXcasedescribesanionizationelectron-holelocalizingonone
ormoreatomswithassociatedlatticerelaxation.Theeffectresults
fromthetrappingofaspatiallydiffuseelectronasshowninFigure
4.6Self-activatedInSAdrivenscintillatorstheluminescentspeciesisaconstituent
ofthecrystal.Thismechanismtypicallyhasreduceddecaytime
andluminosityatRT.
Activatorions
Figure
4:Self-trappedexciton.
ThisextrinsicmechanismisdrivenbydopantionssuchasTl
+,Ce3+,andEu
2+.Theionizationelectron-holesandelectronsare
trappedonthesameluminescentionthatfallswithintheenergy
gap.ThespeciÞcactivatorionexploredinthisstudyistheCe
3+5d#4ftransitionfortheCedopedCe:LuAGsinglecrystal.AtRT,
the5d#4ftransitionofCe
3+centercanbeexploitedforfastand
efÞcientscintillationinbothyttriumaluminumgarnet(YAG)and
lutetiumaluminumgarnet(LuAG)matrices.
RareearthionsarecharacterizedbyanincompletelyÞlled
4fshell.TheCe
3+iondealsspeciÞcallywithanelectronthatreturns
fromthe
5dorbitaltothe
4forbital.Ofthetrivalentions,Ce
3+isthesimplestcasewithitssingleelectronwiththeexcited
5dconÞguration.1111G.BlasseandB.C.Grabmaier.
Lu-minescentMaterials
.Springer-Berlin
Heidelberg,Þrstedition,
1994The5d#4ftransitionshowninCe
3+dopedscintillatorspro-
ducesahighLYinthevisibleregionwithtimeresponsesinthe
nanosecondrange.
1212C.W.E.vanEijk,J.Andriessen,
P.Dorenbos,andR.Visser.Ce
3+dopedinorganicscintillators.
NuclearInstrumentsandMethodsinPhysics
ResearchSectionA:Accelerators,Spectrom-
eters,DetectorsandAssociatedEquipment
,348(2-3):546Ð550,1994IonssuchasCe
3+andPr
3+areimportantdopantsinscintilla-
torsbecausetheyoccurinmorethanonevalencestateandcan
inducephotoionization.Theenergygapmustbelargeenoughto
accommodatetheseadditionalenergytrapsforutilization.Itis
importanttonotethattheenergygapcannotbetoolargebecause
thisreducesthelightyieldofthescintillator.
1313M.Nikl,J.A.Mares,N.Solovieva,
J.Hybler,A.Voloshinovskii,K.Nejezch-
leb,andK.Blazek.Energytransferto
theCe
3+centersinLu
3Al5O12:Cescin-
tillator.
Physicastatussolidi
,201(7):R41ÐR44,May
2004Animportantconsiderationinthesecrystalsisinhomogeneous
distributionsofthedopant.Inhomogeneousdistributionsare
associatedwiththedependenceofthesegregationcoefÞcient
ofdopantonthecrystallizationrate.Asaresult,theactivator
distributionisnotuniformthroughtheÞber.Thecoreofacrystal
willhavealowerscintillationefÞciencyrelativetoitsperimeter.
1414A.V.Gektin.
TrendsinScintillation
Crystals,chapter
17,pages
299Ð312.Wiley-VCHVerlagGmbHandCo.
KGaA,2010ThisefÞciencycanbeexpressedas,
keff
=k!k+(1"k)exp""V%D#$"1(4)where
k=CS/CLinwhich
CSandCLaretheactivatorconcen-
trationincrystalsandmelt,
DisthediffusioncoefÞcient,
Visthe
growthrate,and
%isthedistanceofthesolidiÞcationinterface.
7Core-valenceluminescence
TheCVmechanismoccurswhentheenergygapbetweentheVB
andthetopcorebandislessthanthefundamentalenergygap.
ThisCVtransitionisresponsibleforafastsub-nanosecondlumi-
nescence,characteristicofCVluminescence.
15Thismechanismis
15P.Lecoq,A.Annenkov,A.Gektin,
M.Korzhik,andC.Pedrini.
Inorganic
ScintillatorsforDetectorSystems:Physical
PrinciplesandCrystalEngineering
.Springer-Verlag,Þrstedition,
2006alsodepictedinFigure
1.Charge-transfer
Lastly,theCXmechanismischaracterizedbytheexcitationof
radiativecentersresultingfromanenergytransferfromexcited
states.InorganicScintillator:Applications&Requirements
Scintillatorshaveavarietyofapplicationsandconsequentlydiffer-
entmaterialrequirements.Abroadercategoryofscintillatorsused
withincountingtechniquedevicescanbegeneralized.Theseap-
plicationsincludeHEPcalorimeterforSSC/LHC,nuclearphysics,
astrophysics,PET,gammacameras,neutrons,andindustrialappli-
cations.Theseapplicationsdemandhighlightyieldsbutvaryin
requirementsforshortdecaytimes.Decaytimesforastrophysics
andgammacamerasaretypicallylessimportant.
Densitiesacrosstheseapplicationsarepreferredhighwiththe
exceptionofneutroncounting.Ruggednessisalsoacriticalfactor
fornon-laboratoryapplicationsinindustryanduseintheÞeld.
Integratingtechniqueapplicationsincludex-raycomputed
tomography(CT)andx-rayimaging.Bothoftheseapplications
requirehighlightyields.Additionally,CThasstrictrequirements
fordecaytimeandnoafterglowisideal.Decaytimeisconsidered
lessimportantinx-rayimaging.
1616C.W.E.vanEijk,J.Andriessen,
P.Dorenbos,andR.Visser.Ce
3+dopedinorganicscintillators.
NuclearInstrumentsandMethodsinPhysics
ResearchSectionA:Accelerators,Spectrom-
eters,DetectorsandAssociatedEquipment
,348(2-3):546Ð550,1994HistoricalDevelopment
Inorganicscintillatorshavebeenstudiedforwelloveracentury
withthelastseventy-Þveyearshavingshownthemostproductive
developmentandreÞnementofscintillatorsforbothmedicaland
industrialapplication.Alistofinßuentialscintillatorsisshownin
Table
1.1896-1939Theearliestscintillatorswerehighlightedbythediscoveryofcal-
ciumtungstate(CaWO
4)andzincsulÞde(ZnS).Notableachieve-
mentsincludedthediscoveryofx-raysbyWilhelmRıntgen,
radioactivitybyHenriBecquerel,and
&-particlescatteringby
8ErnestRutherford.Theobservationof
&-particlesiswidelycon-
sideringthestartingpointofmodernnuclearphysics.William
CrookesthenusedZnStocountradioactiveparticles,markingthe
beginningofscintillatorcommercialization.
1940-1980ApushofexplorationfueledbyWorldWarIIandtheColdWar
yieldedscintillationpropertiesofmostpureandactivatedal-
kalihalidecrystals.Thisperiodofscintillatordevelopmentwas
highlightedwiththedevelopmentofthePMTandexperimental
physicswherescintillatorsfoundacriticalroleinthedetectionof
elementaryparticlesandtomeasuretheirfrequency.
1980-Present
Moderndevelopmentofscintillatorshasfocusedonprecisionap-
plicationsinHEPandhighlightoutputsdemandedfrommedical
imagingapplications.
9CompoundMechanism
Density%g/cm3&LightYield
(phot
/MeV
)DecayTime
(ns)Emissionmax
(nm)EnergyResolution
(%fwhm@662
keV
)Reference
BaF
2SX4.883
,900-11,000340
-92031011
.4[29,37,44,66]BaF
2CV4.881
,300-2,0000
.6-0.8220
[13,37,44,72]BiGe
3O12(BGO
)Bi3+7.137
,100-10,600300460
-5109
.05[8,63,66]CaF2:EuEu
2+3.1824
,000[29]CaWO
4CX6.115
,000-25,0008
,0004256
.3-6.6[47,51,81]CdS
:InIn
3+4.80.2520
[10]CdWO
4CX7.97,800-15,8005
,000-20,0004808
-8.8[32,44,66]CeF
3Ce3+6.164
,0002734020
[48]CsF
CV4.1-4.641
,900-2,0002
-4390
[50]CsI
:NaNa
+4.5138
,000-49,0004257
.4[8,29,66]CsI
:TlTl
+4.5155
,000-61,000980530
-5605
.7[8,24,29,53,66]Gd2SiO
5:Ce(GSO
)Ce3+6.712
,800-21,50056
-6004307
-9.2[2,45,66]LaBr
3:CeCe
3+5.161
,00030356
;3872
.9[74]LaCl
3:CeCe
3+3.849
,00025330
;3523
.1[75]LiL
:EuEu
2+4.0815
,0001
,2004757
.5[54,69]Lu2SiO
5:Ce(LSO
)Ce3+7.422
,200-33,00040420
[45]Lu3Al5O12:Ce(LuAG
)Ce3+6.75,606-12,50010
-70500
-510[41,43]Lu3Al5O12:PrPr
3+6.716
,000-17,00021
-26308
;3104
.6-5[16,17,57,60,68]LuAlO
3:Ce(LuAP
)Ce3+8.349
,600-20,50011
-835365
;390[41,49]LuI
3:CeCe
3+5.676
,000complex474;522;5403
.3[6,23,67]LuPO
4:CeCe
3+6.5317
,20025360
[40]NaI
:TlTl
+3.6743
,000-45,0004155
.6-7.1[29,61,66]PbWO
4CX8.23002
.5-98490
[11]Y3Al5O12:Ce(YAG
)Ce3+4.5516
,70085
-119300
;550[46,53]YAlO
3:Ce(YAP
)Ce3+5.3515
,900-21,60024
.2-27347
;365[3,9,41,43]ZnO
:GaGa
3+5.70.36-0.82385
[13,39]Table
1:Historicallyinßuentialscintillators.
101010Background:SelectedCompoundsandMethods
ScintillatorCandidate:Ce:LuAG
TheÞrstscintillatorcandidatecompoundinvestigatediscerium
dopedlutetiumaluminumgarnet(Ce:LuAG),molecularformula
Ce:LuAG.TheundopedlatticeisshowninFigure
5.Lutetiumbelongstothelanthanidechemicalelementseries
whichalongwithscandiumandyttriumformwhatisreferredto
astherareearthelements.Thelanthanideserieshasfourdiffer-
enttypesofelectronictransitionswithfourteenofthesehaving
theabilitytoadoptthe
2+and
3+chargestates.Thesecanbein-
tegratedintonumerouscompoundswheresmalldiscrepancies
inthelocationofthelanthanideimpuritystatecandramatically
effectscintillatorperformance.
1717P.Dorenbos.Electronicstructure
engineeringoflanthanideactivated
materials.JournalofMaterialsChemistry
,22(42):22344Ð22349,2012Whileseveralotherscintillatorsalsouseceriumasadopant,
includingceriumdopedyttriumaluminumgarnet(Ce:YAG),and
ceriumdopedyttriumaluminiumperovskite(Ce:YAP),Ce:LuAG
hasbeenusedpreferablybecauseofitshigherdensity.
18This18Y.Zorenko,V.Gorbenko,I.Kon-
stankevych,B.Grinev,andM.Globus.
ScintillationpropertiesofLu
3Al5O12:Cesingle-crystallineÞlms.
NuclearInstru-
mentsandMethodsinPhysicsResearch
SectionA:Accelerators,Spectrometers,
DetectorsandAssociatedEquipment
,486(1-2):309Ð314,2002increaseddensityresultsinmorestoppingpowerforlikesized
scintillators.Thisalsoallowsthescintillatortobemaderelatively
thinner,increasingspatialresolution.Forthisreasonitsapplica-
tionasathinÞlmhasalsobeeninvestigated.Foramoredetailed
comparisonoftheirpropertiesreferenceTable
1.TheseceriumdopedscintillatorsbeneÞtfromthefastdecay
timeofthe
5d#4fradiativetransitionoftheCe
3+luminescentcenterandhighquantumefÞciencyatRT.
1919S.Liu,X.Feng,M.Nikl,L.Wu,
Z.Zhou,J.Li,H.Kou,Y.Zeng,Y.Shi,
Y.Pan,andA.Setlur.Fabrication
andScintillationPerformanceof
NonstoichiometricLuAG:CeCeramics.
JournaloftheAmericanCeramicSociety
,98(2):510Ð514,February
2015Ce:LuAGisamechanicallyandchemicallystablescintillation
materialthatalsohashighhardness,higheffectiveZ(
62.9),short
decaytime,andhighlightyield.Forthesereasonsithasfound
applicationsinHEphysicsandmedicalapplicationswhereits
abilitytodetectx-rayand
!-rayemissionsisutilized.
20Withan
20E.Auffray,D.Abler,S.Brunner,
B.Frisch,A.Knapitsch,P.Lecoq,
G.Mavromanolakis,O.Poppe,and
A.Petrosyan.LuAGmaterialfordual
readoutcalorimetryatfuturehigh
energyphysicsaccelerators.
IEEENuclearScienceSymposiumConference
Record,pages
2245Ð2249,2009emissionintherangeof
500-550nmitcanbecoupledwithpho-
todetectors.ForthisreasonmanyfutureHEparticleaccelerators
plantoemploythesecrystalsasscintillators.
Severalmethodsofcrystalgrowthhaveusedtocreatesingle
crystalsofthiscompoundfromameltofoxidepowdersincluding
theCzochralski(CZ),Bridgman(BD)andmicro-pulling-down
(µ-PD)method.
11AnalysisoftheLu
2O3-Al2O3PhaseDiagram
Figure
5:AcubicCe:LuAGlattice
structurewithatomicpositionsof
lutetium(green),aluminum(brown),
andoxygen(red)takenfromICDDÕs
PDF-4+database,CrystalStructure
Source:LPF.
TheCe:LuAGcompoundbelongstotheLu
2O3-Al2O3phasediagramshowninFigure
6.Itisalsothemoststablecompound
ofthosedevelopedfromthephasediagramandcanbeobtained
fromsolid-statereaction.Thisiscriticallyimportantandallows
ustopreparethedopedversionofthismaterialfromsynthesizing
highpuritypowderedoxideswherewecanexpectcongruent
meltingatapproximately
2060¡C.Thisphasediagramcanbereferencemoregenerallyasthe
Al2O3-RE2O3systemforrareearthelements.Eachcontainsup
tofourintermediatecompoundsofaluminatypethatarestable
onlyforthelargerRE
3+,agarnettype(suchastheCe:LuAG
investigatedhere),orthorhombicdistortedperovskitetypeand
monoclinictypethatareofrecentdiscovery.
2121D.Klimm.Themeltingbehaviorof
lutetiumaluminumperovskiteLuAlO
3.JournalofCrystalGrowth
,312:730Ð733,2010SinglecrystalscanbemadefrommanyoftheseREcompounds
Þndingapplicationsaslasersandscintillators.Thesecrystalsalso
beneÞtfromrelativelyeasydopingwithotheractivatorsofsimilar
radiiastheRE
3+.Figure
6:TheLu
2O3-Al2O3phasediagram.[62]12ScintillatorCandidate:MgTa
2O6Figure
7:AtetragonalMgTa
2O6latticestructurewithatomicpositionsof
magnesium(green),tantalum(blue),
andoxygen(red)takenfromICDDÕs
PDF-4+database.
Whileseveralmagnesiumtantalatesexist,thefocusofthisstudy
willbeonthealkalineearthtantalateMgTa
2O6.Thelatticestruc-
tureofthiscompoundisshowninFigure
7.Thismagnesium
tantalatewasselectedbecauseithadbeenprovenstableinprevi-
ousstudies.
2222G.HalleandH.Mueller-Buschbaum.
InvestigationsofZn(
1-x)M(x)Ta
2O6(M=Mg,andNi)withareÞnementofthe
crystalstructureofMgTa
2O6.JournalofTheLess-CommonMetals
,142:263Ð268,September
1988ThegrowingofMgTa
2O6crystalsforscintillatorsisanex-
ploratorystudyatthispointwithfewexamplesofgrowthbyany
growthmethodwithnoknownexamplesof
µ-PDmethodgrowths.
Thistantalatehas,however,beensuccessfullygrownusingthe
ßoatingzone(FZ)method.
2323M.Higuchi,K.Ando,J.Takahashi,
andK.Kodaira.GrowthofMgTa
2O6singlecrystalsbyßoatingzonemethod
andtheiropticalproperties.
Journalofthe
CeramicSocietyofJapan
,101(1):118Ð120,1993Otherapplicationsforthistantalatehavebeendiscoveredfor
useasadielectricresonatorwhichhasledtoadditionalatomistic
computersimulationresearchinanefforttobetterquantifyits
defectandpossibledopantproperties.
2424C.Tealdi,M.S.Islam,L.Malavasi,and
G.Flor.Defectanddopantpropertiesof
MgTa2O6.JournalofSolidStateChemistry
,177(11):4359Ð4367,2004Magnesiumoxide(MgO),aconstitutivecompoundofMgTa
2O6hasfoundapplicationasaneasilypreparedscintillator.Here,
theirrelativeinsensitivitycanbeabeneÞtinsomeapplication
becausethelightoutputdoesnotsaturateevenunderintense
radiation.ThisscintillatorhasfoundapplicationattheMichigan
StateUniversityCyclotronforbeamfocusing.Theyhavealso
foundadditionalapplicationsindirectviewingofnarrowbeam
imagesinthefocalplaneinmagneticspectrography,andasa
phasemeasuringprobe.
2525J.A.Nolen.Aneasilyprepared
scintillatorforviewingacceleratorbeam
spots.NuclearInstrumentsandMethods
,156(3):595Ð596,November
1978AnalysisoftheMgO-Ta
2O5PhaseDiagram
TheMgTa
2O6compoundbelongstotheMgO-Ta
2O5phasedi-
agramshowninFigure
8.Fromthephasediagramshownwe
canidentifythreestablecompoundsformedbytheMgO-Ta
2O5system:Mg
4Ta2O9,Mg
3Ta2O8,andMgTa
2O6.BothMg
4Ta2O9andMgTa
2O6havebeenstudiedandappeartobestableupto
theirmeltingpoints.ThestabilityofMg
3Ta2O8islimitedtothe
1475-1675¡Crange.Pertinentmeltingtemperaturesarelistedin
Table
2.Thesetemperatureswillprovideausefulreferencewhen
performingour
µ-PDmethodexperiments.
CompoundMeltingPoint(C)
Ta2O51872MgO2852MgTa
2O61775Table
2:Constitutivecompoundmelting
temperaturesinMgTa
2O6.13Figure
8:Preliminaryphasediagramof
thesystemMgO-Ta
2O5.[4]14PowderSynthesis
Powderpreparationandprocessingiscriticallyimportanttothe
qualityofthecrystalgrowth.Constituentpowderoxideswere
combinedalongmolarratiostoproducepowdersamplesofthe
desiredcompound.
Figure
9:Mortarandpestlemade
fromagatestoneusedtomixpowder
compounds.Itiscriticalthatthepowdercomponentsarehighpurity
($99.99%),approximately
100%phasepurity,havehigh-speciÞc
surfacearea
$5m2g"1,andpossessamedianparticle(agglomer-
ate)sizelessthan3
µm,withnoparticlesgreaterthan7
µm.2626C.GreskovichandS.Duclos.Ceramic
scintillators.AnnualReviewofMaterials
Science,27(1):69Ð88,August
1997Thecompoundstestedinthisstudyarelimitedtoasingle
dopantorassumedtobeself-activated.Additionalprecautions
aretypicallyneededwhenmixingdopantsduetotheirsmall
quantityrelativetotheotheroxides,requiringmolecularcontrol
ofscintillationpropertieswheredopantsareessentiallysmall
percentageimpurities.Nosinteringorhot-pressingwasconducted
onsamples,however,theseareoptionsforfurtherreÞningthese
powdercompoundsinfuturetrailsastheycanfurtherreduce
samplecontaminationandimprovedensiÞcation.
Figure
10:DensiÞcationwasaccom-
plishedwitha
12-tonforcemanual
press.
Theconstitutivecompoundsmustbemixedthoroughlyin
ordertoensurethatthecombinedsamplewillmeltcongruently
inthecrucible.Constituentswerecarefullyweighedandinsome
instancesmixedwithhighpurityethanol
($99.5%)anddried
afterthoroughmixingwithamortarandpestle.Othersamples
weremerelymixedthoroughlywithamortarandpestle.Samples
wereweighedonananalyticalbalancefromMettlerToledo.
Insomeinstancessamplesweremademoredensewitha
12-tonforcemanualbriquettingpressfromChemplex.Betweenuses,
thecomponentsofthepresswerecleanedinaVWRModel
50Dultrasoniccleanertoremovecompactedpowderfromthehousing
andcompressionrod.
Inotherinstancesahydraulicpresswasusedtocompress
powdersamples.Theseapproachesareexplicitlystatedforeach
experimentconducted.
15Micro-Pulling-DownMethod
Themicro-pulling-down(
µ-PD)methodwasusedtoconductthin
ÞbercrystalgrowthsandisillustratedinFigure
11.Theexperi-
mentalsetuputilizesinductionheatingfromanelectromagnetic
coiltoheatsamplespasttheirmeltingpoint.Thiscoilencircles
acruciblecontainingthecompoundtobeformedintoacrystal.
Thiscrucibleissupportedonanafter-heaterandsurroundedby
thermalinsulation.Theinsulationisconstructedfromceramics,
typicallyhighpurityAl
2O3.Thisisusedtobettercontrolthetem-
peraturedistributionsurroundingthecrucible.Additionally,the
insulationsavesRFpoweroverthecoarseofanexperiment.
Figure
11:Schematicdiagramof
µ-PDsystemwithexternalinductiveRF
heating.Theµ-PDmethodworksbyphasetransformationfromtheliq-
uidmelttoasolidcrystal.Thecompositionofthemeltisdirectly
relatedtothecompositionoftheproducedcrystal.Itisassumed
thatwhenthemeltiskeptabovetheliquidustemperature,itho-
mogenizesandfurtherchangesinitspropertiesareprevented.The
stabilityandhomogenizationofmeltareinßuencedbythephase
interfaceswiththecrucible,atmosphere,andcrystal.
2727T.FukudaandV.I.Chani.
ShapedCrystals:GrowthbyMicro-Pulling-Down
Technique
.Springer-Verlag,Þrstedition,
2007Themajorityofgrowthtechniquesproducecrystalsbycontin-
uouslytransportingtheseedandtheas-growncrystalupwards
awayfromthemelt.ThisistheprocessusedinCzochralski(CZ)
andedge-deÞned-Þlm-fed(EFG)amongotherapplicationsthatare
16typicallyemployedtogrowcommerciallyproducedcrystals.Ben-
eÞtsoftheseprocessesincludebettercontrolofsystemvibrations
andtemperatureßuctuationswhencomparedtothe
µ-PDmethod,
makingtheseprocessesinherentlymorestablethanpulling-down.
Amajoradvantageofthe
µ-PDmethodoverpulling-upappli-
cations,however,isthatitdramaticallyreducestheprobability
ofincorporatingbubblesintothegrowncrystalwhichimproves
thequalityofthegrow.Thesebubblesaredrawntothesurface
ofthemeltbyconvection,awayfromtheformingcrystal.Con-
sequentlyheaviersolidparticlesarealsomoreeasilyincluded
intheas-growncrystal,suchasdopants.ThiscanbebeneÞcial
ifthemeltincludestheseparticlesbutcanalsoincreasetheodd
ofcontaminationfromthecrucibleasanyprecipitatedcrucible
materialmaybegrownintothecrystalbecauseitsrelativelyhigher
densitywhencomparedtothemelt.Anotheradvantageofthe
µ-PDmethodisthatithasahigherutilizationrate,decreasing
productioncosts.
2828X.Xu,K.Lebbou,F.Moretti,
K.Pauwels,P.Lecoq,E.Auffray,and
C.Dujardin.Ce-dopedLuAGsingle-
crystalÞbersgrownfromthemeltfor
high-energyphysics.
ActaMaterialia
,67:232Ð238,April
2014InductiveHeating
Theinductivecoilheatstheconductivecrucibleandafter-heater
viaeddycurrents.Theafter-heaterheatsthemelt/crystalinterface
andalsosupportstherimofthecrucible,holdingitupright.While
systemheatingmayremainconstant,itseffectonthesystemisnot.
Thisvariationisbasedofftheamountofmeltwithinthecrucible
comparedtotheamountsolidiÞedinthepulledcrystal.
Whileseveralmethodsofheatingareavailablefor
µ-PDcham-
bersthisstudywillfocusoninternalinductiveRFheating.Other
heatingmethodologiessuchasinternalorexternalresistiveheat-
inghavealsobeenused.Boththecrucibleandafter-heaterare
heatedfromaninductioncoilsurroundingthem.Thiscoilissup-
pliedwithanACcurrentwhichgeneratesamagneticÞeldthat
subsequentlyformseddycurrents(alsocalledFoucaultcurrents)
inboththecrucibleandafter-heater.Theseeddycurrentsacton
theseconductingcomponentsandtransferheattothemeltand
growthinterface.
Thetemperaturegradientiscriticalforestablishingthemenis-
cus,acrosswhichthemeltsolidiÞesintoasinglecrystal.This
meniscusisthecriticalregionofcrystalgrowthandin-situob-
servationofthemeniscusaredonethroughaviewingwindow
inthechamberwhichisalignedwithholesdrilledinboththe
insulationandafter-heater.Crystalprogresscanalsobemeasured
byasensitiveloadcellthatweighstheformingcrystal.
2929T.FukudaandV.I.Chani.
ShapedCrystals:GrowthbyMicro-Pulling-Down
Technique
.Springer-Verlag,Þrstedition,
2007Inductiveheatingcanalsobeimplementedexternallywhereby
thesurroundingcylindricalinsulationisconstructedofconductive
materials,inducingsecondaryeddycurrentsseparatefromthe
primaryeddycurrentsproducedbythecrucibleandafter-heater
17toheatthemelt.TheseeddycurrentsarelessefÞcientduetotheir
greaterdistancefromthemeltandincreasethecostofproduction.
CrucibleandAfter-Heater
Forthepurposesofthisanalysiswewillassumethatthecrucible
andafter-heaterarecomprisedofthesamematerials,whichis
beneÞcialforhightemperaturethermalexpansion.Theselection
ofthismaterialiscriticallyimportanttothesuccessoftheexper-
imentanditsrepeatability.Thecrucibletypicallyhasaconical
bottomandgrowcrystalsinthe
µ-PDmethodindiametersofa
fewmillimeters.
TheÞrstrequirementofacrucible/after-heatermaterialisthat
itmusthaveanappreciablylargermeltingtemperaturethanthe
meltcontainedwithin.Decompositionofthecrucibleintothemelt
eveninsmallamountshasextremelydetrimentaleffectsoncrystal
qualityandseedingcharacteristics.
Additionallythemechanicalperformanceofthecrucible/after-
heaterpairisimportantastheymustretaintheirgeometrybe-
tweenRTandhightemperatures.Mechanicalpropertiesare
importantatRTwhereitisfabricatedintothedesiredgeometry.
Chemicalcompatibilitymustalsobeestablishedbetweenthe
crucible,themeltandthesurroundingatmosphere.Compatibility
alsoextendstothesolventsusedtocleanthemofremainingmelt
aftertheexperimentsarecomplete.Thewettingpropertiesofthe
meltalongtheexteriorandinteriorsurfacesofthecruciblemust
alsobeconsidered.
Ifthewettingpropertiesaretoostrong,themeltwilladhere
aggressivelytotheexteriorofthecrucibleafterithasexitedthe
cruciblenozzleratherthanseedingcorrectly.Ifthewettingproper-
tiesaretooweakthemeltwillhavedifÞcultytravelingdownthe
capillarychannel.
Crucibleandafter-heatermaterialsareoftenmadeofpure
metalsduetodiffusionconcernsbutsomecompoundshave
alsobeenimplemented.Table
3showsalistofcommonlyused
cruciblematerialsalongwithmeltingtemperaturesandgrowth
atmospheres.
Thecruciblenozzlealsodeterminestheshapeofthesubsequent
crystalgrowth.Currentlythe
µ-PDmethodisprimarilylimited
tocylindricalorrectangularcrystalgrowthsasmorecomplex
geometriesaredifÞculttomachinegiventhematerialconstraints
ofthecrucible.
MeltConvectionplaysanimportantroleatthemelt/crystalinterface.
Themaincruciblereservoircontainingthemeltisstirredeffec-
18MaterialMeltingPoint
(¡C)GrowthAtmosphereReference
C(densegraphite)
3500Ar,Ar+CF[
80]Re3180Ar+H2(3-4%)[
52]Mo2617Ar,Ar+H
2(2%)[
36]Ir2410Ar,N
2,N2+O2(1%)[
59]Al2O32054Air[
20]Rh1966[20]Pt1772Air,Ar+CF,[
20]SiO21600[20]Au1064[20]Al660[34]Ir+2%ReAr[
30]Table
3:Common
µ-PDcrucibleand
after-heatermaterials,meltingtempera-
tures,andgrowthatmospheres.
tivelybythermo-capillaryconvection.Thecapillarychannelis
governedbydiffusivePoiseuilleßowandthemeniscusissub-
jectedtoMarangoniconvection.
3030B.M.Epelbaum,G.Schierning,
andA.Winnacker.ModiÞcationof
themicro-pulling-downmethodfor
high-temperaturesolutiongrowthof
miniaturebulkcrystals.
JournalofCrystal
Growth
,275(1):867Ð870,December
2005MeltßowinthemoltenzoneislargelytheresultofMarangoni
convection.Thisconvectioneffectshowthesteadystateofthe
systemisevaluatedastheMarangonivelocityislargerthanthe
growthrates,playinganinßuentialrolewhenmodelingthe
µ-PDmethodcomputationally.
3131T.Fukuda,P.Rudolph,andS.Uda.
FiberCrystalGrowthfromtheMelt
,volume
6.SpringerBerlinHeidelberg,
2004Themeltisfurtherinßuencedbytemperaturegradientspro-
ducedbytheinductioncoil.Numericalstudieshavebeencon-
ductedtomodelthesegradientsinordertobetterunderstand
systemresponse.
3232H.S.Fang,Z.W.Yan,andE.D.Bourret-
Courchesne.Numericalstudyof
themicro-pulling-downprocessfor
sapphireÞbercrystalgrowth.
CrystalGrowth&Design
,11(1):121Ð129,2011Anotherconsiderationwhenevaluatingthemeltßowissegrega-
tionattheendofthecapillarychannel.Singlecrystalsareformed
byshortdistancedisplacementofparticlesintheliquidphase
andre-orderinginthesolidcrystal.Thisorderingprocesstakes
placewithinthemeniscusregionthatoccursbetweentheliquidus
meltandthesolidcrystal.Thisre-orderingprocessismadeeasier
whenthecompositionofthemeltandcrystalarethesame.Since
thisisgenerallythecaseinthe
µ-PDmethod,relativelyfastpull-
downratescanbeusedwhencomparedagainstotherpulling-up
methods.DiameterControl
Diametercontrolcontinuestobeanareaofimprovementforthe
relativelynew
µ-PDmethod.Thisisstillprimarilydonethrough
directvisualexaminationofthegrowthprocess.Thegrowthpa-
rameterssuchaspulling-downrateandchambertemperatureare
adjustedmanuallybasedontheseobservations.Someautoma-
tiondoesexistthatusesvisionsoftwaretorelaytheappropriate
adjustmentbutthesesystemresponsesaredeterminedÞrstby
observationsofmeniscusstability.
Inaddition,sensitiveloadcellscanbeusedtoadjustgrowth
parametersbasedonthecurrentweightandpull-downdistanceof
19thegrowncrystal.Thissecondmethodislesspracticalasthesmall
diametersofthecrystalimplyanextremelylightweight,requiring
averypreciseloadcellthatincreasesproductioncosts.
3333T.FukudaandV.I.Chani.
ShapedCrystals:GrowthbyMicro-Pulling-Down
Technique
.Springer-Verlag,Þrstedition,
2007GrowthChamber
Thegrowthchamberusedfor
µ-PDisimportantinestablishing
theappropriateenvironmentandallowingtheoperatortoevaluate
theprocess.Thisisespeciallycriticalwhentemperaturesneed
tobeadjusteddynamicallytocompensateforreductioninmelt
volume.TheviewingwindowistraditionallycomprisedofCaF
2whichistransparentandcantoleratehightemperatures.
X-rayPowderDiffraction
X-raypowderdiffraction(XRPD)isatechniqueemployedto
analyzeÞnepowdersamples.Thistechniqueisbasedoffthere-
peatingstructureofatomsinasolidmaterial.Itisalsodependent
onthewavelengthofx-raysusedandthespacingbetweenlayers
ofatomsintherepeatingstructuretobesimilar.Theserepeating
structuresofatomsarecapableofscatteringtheincomingx-rays.
Fromthesex-rays,energypeaksdevelopinmagnitudepropor-
tionaltothefrequencyofeachlatticeplaneofthecrystal.The
sizeandpositionofthesetofpeaksischaracteristicofthecrystal
structureandchemicalcomposition.
X-raysareusedbecausetheyhavehighenergiesandshort
wavelengthsontheorderoftheatomicspacingofthesolidsbeing
investigated.
Thediffractedx-raybeamiscomposedofalargenumberof
scatteredwavesthatconstructivelyanddestructivelyinterferewith
eachother.Otherphaserelationshipsareacombinationofthese
effects.Togethertheseeffectsformanx-raydiffractionpattern.
ThedistancebetweentheseparallellatticeplanesisdeÞned
as,d.BraggÕsLawdevelopsarelationshipbetweenx-raywave-
lengthandthe
d-spacingbetweenlatticeplanes.Thislawcanbe
expressedas,
n'=2dsin((5)where
nisawholenumber,typicallyone,
'isthewavelengthof
x-ray,whichisoperatordeÞnedand
(istheanglebetweenthe
directionofincomingx-raysandthelatticeplane.
XRPDessentiallysolvesthisequationfortheunknownvalueof
d.Diffractionenergiesarelowwhentheangleisdifferentforeach
adjacentcrystalplaneandisnotawholelength.Thisisdueto
theemittedwavebeingoutofphase.Consequentlyiftheemitted
wavesareawholewavelengththenthewaveswillreinforceeach
otherandproduceanenergypeak.
20Arecorderplotsthediffractedbeamintensityasafunction
of2(.Thisiscalledthediffractionangle.Thisconstructedplot
displayshigh-intensitypeaksthatsatisfytheBraggdiffraction
condition.X-rayLuminescence
X-rayluminescence(XRL)testingisusedtodeterminetheemis-
sionspectraofscintillationcrystals.Theemissionspectraistypi-
callyanoutputofrelativeintensitiesoverarangeofwavelengths.
Themaximumofthisemissioncurveisconsideredthepeakofthe
emissionband.
3434G.BlasseandB.C.Grabmaier.
Lu-minescentMaterials
.Springer-Berlin
Heidelberg,Þrstedition,
1994Eachscintillatorhasacharacteristicemissionspectrumthatis
correlatedtothetypescintillatormechanismdominantinthema-
terial.Knowingtheemissionspectrumofaparticularmaterialis
importantbecauseitcandetermineiftheemissionisinthevisible
ornear-visiblerange.AlsobyknowingthespeciÞcwavelengths
ofemissionfromthescintillatoritcanthenbecoupledwithan
appropriatePMT.
ScanningElectronMicroscopy
Scanningelectronmicroscopy(SEM)utilizesascanningelectron
microscopethatproducesimagesofasamplebyscanningina
rasteringpatternwithafocusedbeamofelectrons.Inorderto
preventaninsulatorsamplefromcharging,athinmetalcoating
isoftenapplied.Amorecomplicatedmorphologywouldrequire
thickercoatinginordertomaintainitscontinuity.
Anothermethodtopreventcharginginasampleistoobserve
thesampleunderlowaccelerating-voltage.Fundamentally,charg-
ingoccursinasamplewhentheelectronsenteringthesample
aredifferentfromthoseexiting.Thesamplecanalsobeviewed
atatilt,wheretheelectronbeamentersasampleobliquely.This
methodologyisemployedwhenaspecimenhaslesssurfaceirreg-
ularities.Anon-conductivesamplecanalsobeobservedunder
lowvacuum.Low-vacuumscanningelectronmicroscopy(LVSEM)
ionizestheresidualgasmolecules,however,thisprocesstypically
involvespressurizingthechamber.
Energy-DispersiveX-raySpectroscopy
Energy-dispersivex-rayspectroscopy(EDS)testingutilizesthe
photoelectriceffecttoproduceaspectrumofcountsthatcan
identifyelementswithinacompound.Thephotoelectriceffectis
showninFigure
12.Thebasicphysicalprocesscanbedescribed
21withintheEinsteinequation,
EB=hv"EK(6)where
EBisthebindingenergy,
hvistheenergyofthex-ray
source,whichisoperatordeÞned,and
EKisthekineticenergy
oftheemittedelectronthatisthenmeasuredbytheEDSdetector.
Thisanalysisdetectselementsthatarepresentintheouter
10nmofthesample.Inthecaseofcoatedsamplesthecoatingmay
contributeadisproportionatelylargepercentageofthematerialÕs
identity.Theimpactofthiscanbereducedbycoatingthesam-
pleswithanelementthatisnotexpectedtobefoundwiththe
compoundofinterest.
Figure
12:Sequentialimagesofphoto-
electriceffectwithphotonabsorption
andphotoelectronejection(top)fol-
lowedbyßuorescentx-rayemission
(bottom).Fordataoutput,theareaunderneaththedetectedpeaksis
relatedtotheamountofeachelementpresent.Percentagesofeach
elementpresentaretypicallycalculatedwiththeexpression,
Iij=KáT(EK)Lij(!))ij'ni(z)e"z/'(EK)cos(dz(7)where
Iijistheareaofpeak
jfromelement
i,Kisaninstrument
constant,T(EK)isthetransmissionfunctionoftheanalyzer,
Lij(!)istheangularasymmetryfactorfororbital
jofelement
i,)ijisthe
photoionizationcross-sectionofpeak
jfromelement
i,ni(z)isthe
concentrationofelement
iatadistance
zbelowthesurface,
'(EK)istheinelasticmeanfreepathlength,and
(isthetake-offangleof
thephotoelectronsmeasuredwithrespecttothesurfacenormal.
X-rayßux,areaoftheirradiatedsampleandthesolidangleofthe
photoelectronsacceptedbytheapparatusarecontainedwiththe
instrumentconstant
K.Fromthisequationitisalsoimportanttonotethatifasample
isasinglecrystal,theoutgoingelectronscanhavepeakintensities
thatdeviatefromthepredictedvalues.Thisiscriticallyimportant
inourevaluationsasitisassumedthatweareevaluatingsingle
crystals.
3535B.D.RatnerandD.G.Castner.
Electron
SpectroscopyforChemicalAnalysis
,pages
47Ð112.JohnWileyandSons,Ltd,
200922ExperimentalProcedures
PowderSynthesis:Ce:LuAG
LutetiumOxide(Lu
2O3),aluminumoxide(Al
2O3),andcerium
(IV)oxide(CeO
2)weresynthesizedtoproduceLu
3Al5O12:Ce(Ce:LuAG)asdetailedinTable
4.36Powderedoxideswerepur-
36N.G.Nause.Powderx-raydiffraction
dataforrareearthgarnets.MasterÕsthe-
sis,StephenF.AustinStateUniversity,
2003chasedfromSigma-Aldrich.
CompoundMoleratioDensity
(gcm3)Mass(mg)%Purity
Lu2O30.3659
.42689499
.99Al2O30.6253
.95302599
.997CeO20.0107
.658299
.995Lu3Al5O12:Ce16.68110000
Table
4:Compoundmixtureforten
gramsampleofCe:LuAG.
HydraulicallyPressed:Sample
1TheÞrstsamplepreparedwasahydraulically-pressed(HP)
10grampowdersynthesis.Thissamplewaspreparedpriortothe
beginningofstudy.
ManuallyPressed:Sample
2Thesecondsamplepreparedwasamanually-pressed(MP)
5grampowdersynthesis.Thepowdersynthesisprocedureisdetailed
below,
1.Thethreeconstitutivecompoundswereweighedonananalyti-
calbalanceandmixedwithamortarandpestle.
2.Ethanol(
$99.5%)wasaddedandthecompoundsweremixed
untiltheethanolhadevaporatedfromthoroughuseofmortar
andpestle.
3.Thesamplewaspressedat
6000psifor
5minutes.Oncere-
movedthesamplewasinspectedforanysignsofcontamination
priortoloadingintothecruciblefor
µ-PDexperiments.
23PowderSynthesis:MgTa
2O6Magnesiumoxide(MgO)andtantalumpentoxide(Ta
2O5)were
mixedat
50/50mol%toproduceMgTa
2O6asdetailedinTable
5.PowderedoxideswerepurchasedfromSigma-Aldrich.
CompoundMoleratioDensity
(gcm3)Mass(mg)%Purity
Ta2O50.5008
.2458299
.99MgO0.5003
.5841899
.999MgTa
2O617.575000
Table
5:CompoundmixtureforÞve
gramsampleofMgTa
2O6.LoosePowder:Sample
1TheÞrstsamplepreparedwassimplymixedtogetherwitha
mortarandpestleandnotdensiÞedinanymanner.Powder
compoundsweremeasuredonananalyticalbalanceandloaded
intothecrucibleinpreparationfor
µ-PDexperiments.
ManuallyPressed:Sample
2AÞvegramsampleofMgTa
2O6waspreparedfromTa
2O5andMgOcompoundsasoutlinedabove.Thepowdersynthesisproce-
dureisdetailedbelow,
1.Bothpowdercompoundswereweighedoutonananalytical
balanceandmixedtogetherwithamortarandpestle.
2.Bothpowdercompoundswereverysimilarinappearance,both
chalkywhite,becauseofthisitwasmoredifÞculttodetermine
whenthetwocompoundshadbeenthoroughlymixed.
3.Tobetterensurepropermixing,thetwocompoundswere
mixedwithethanol(
$99.5%).Thewettedsamplewasthen
mixedthoroughlyuntiltheethanolhadevaporatedout.
Figure
13:PressedsampleofMgTa
2O6,singlepressattemptwithsigniÞcant
lossinprocess.
4.Thesamplewasthencompressedinthe
12tonmanualpressat
4000PSIfor
3minutes.Underpressure,aportionofthesample
spilledfromthetopofthepress.Itwasdiscoveredthatthe
ethanolhadnotcompletelydriedandsamplewaslostasit
bubbledout.
5.Theapparatuswascleanedandthesamplewasrepackedand
pressedagainat
5000PSIfor
5minutes.6.Thesamplewasweighedaftercompressing,measuring
3982mgdownfromtheoriginal
5000mg(
20.36%loss).
Itwasdeterminedthatthesamplemustberemadeovercon-
cernsthatwemayhavelostthetantalatestoichiometry.Thesam-
plepreparedisshowninFigure
13.24ManuallyPressed:Sample
3AsecondÞvegramsamplewasprepared.Thepowdersynthesis
procedureisdetailedbelow,
1.Bothpowdercompoundswereweighedoutonananalytical
balanceandmixedwithamortarandpestle.
2.Ethanol(
$99.5%)wasaddedandthecompoundsweremixed
untiltheethanolhadevaporated.Thewaittimeforthisprocess
wasincreasedandtheamountofethanoluseddecreased.This
wasinanefforttopreventanotherspillofcompoundatthe
press.
Figure
14:PressedsampleofMgTa
2O6,twodifferentpresseswereusedto
breakthesampleintoamoremanage-
ablesize.
3.Thesamplewasdividedinhalfandpressedat
8000PSIfor
5minutes.Thesamplewasmadeslightlylargerat
5250mgandcameout
to4977mg(
5.19%loss).ThesamplepreparedisshowninFigure
14.ManuallyPressed:Sample
4Atengramsamplewaspreparedfortesting.Samplewascold-
pressedintofourseparatesamples.Thepowdersynthesisproce-
dureisdetailedbelow,
1.Bothpowdercompoundswereweighedonananalyticalbal-
anceandmixedwithamortarandpestle.
2.Ethanol(
$99.5%)wasaddedandthecompoundsweremixed
untiltheethanolhadevaporated.Thewaittimeforthisprocess
wasincreasedandtheamountofethanoluseddecreased.This
wasanefforttopreventanotherspillofcompoundatthepress.
3.Thesamplewasdividedintofourthsandpressedat
8000psifor5minutes.Oncethesamplewasremoved,contamination
fromthepresswasobservedontheperimeterofthesample.
4.AttemptsweremadetoremovethiscontaminationwithMgO
powderbutwereunsuccessful.
5.Arazorbladewasusedtoremovethecontaminationfromthe
pelletsurface.Thisdramaticallyimprovedthequalityofthe
samplebutsacriÞcedasmallportionofthesample.
Thesamplewasweighedafterpressingwithlossesofapproxi-
mately5%.25Micro-Pulling-DownMethod
Theµ-PDtestchamberusedwasconstructedbyCyberstarandis
showninFigure
17.Thechamberiscooledcontinuouslywitha
waterchillerloopthroughthechamberwalls.In-situadjustments
canbemadetotheseedrodinthexandydirections.Mitutoyo
micrometerheadsareusedtotranslatetheseedrodwith
0.01mmaccuracymarkings.Verticaltravelcouldbeadjustedmanuallyor
couldbeprogrammedataconstantrateasshowninFigure
15.Thechamberpossessesaninecoilinductionheaterthatcanheat
samplesuptoapproximately
2300¡C.Figure
15:Translationspeedcontrols
withlocal(programmed)andremote
(user)adjustment.
ThechambercouldalsobeevacuatedandÞlledwithareducing
atmosphere.Forourexperiments,thereducingatmospherewas
argon.Thispreventedcomponents,speciÞcallythecrucibleand
after-heater,fromoxidizingatourultra-highexperimentaltemper-
atures.Thechamberwasconnectedtoareservoirofargonthat
wascirculatedcontinuouslybeforeandduringourexperiments.
ThiscirculationwasadjustedwithapairofKeyInstrumentsglass
tubeßowmetersthatregulateinputandoutputßow.
ASylvacindicatorisusedtomeasuretheverticaltranslation
distancesothecrystalcanbemeasuredinprocess.Thetestcham-
beralsopossessedfourviewingwindows,oneofwhichwas
equippedwithaSonyXCD-SX
90FireWirecamerathatstreamed
imagestoanearbyPCformonitoringatarateofupto
30FPS.Thiscamerawasalignedtoviewthecruciblenozzlethroughsmall
holesdrilledintotheinsulatorsandafter-heater.
Figure
16:Fracturedceramicinsulator
capremovedfromchamberafterhigh
temperaturecycling.
Doubleceramicinsulation,madeofhighpurityAl
2O3,was
usedfortheCe:LuAGsamplesduetoitshighermeltingpoint.A
singlelayerofinsulationwasusedfortheMgTa
2O6experiments.Thecylindricalceramicspacersandlidneededtobecutinhalf
duetothermalexpansionduringtesting.Ifnotseparatedthecom-
ponentswerepronetofracturingundertheintenseexperimental
temperatures.Anexampleofthesefracturesfromthermalexpan-
sionisshowninFigure
16.Viewingportsweredrilledintothe
ceramicinsulatorwithadiamondtippedbit.Thisoperationwas
performedataDremelworkstationthatactedasadrillpressfor
thispurpose.
ChamberTemperatureCurve
Apryometerwasusedtoapproximatethetemperatureatthe
cruciblenozzle.Thechambertemperatureisadjustedbyset-point
(SP)ontheconnectedPC.Argonwascirculatedforanhourprior
tothetemperaturecurvebeingconstructed.
26Figure
17:Thewater-cooled
µ-PDtest
chamberfromCyberstar.
27Figure
18:MarathonMM
2MHpyrome-
ter.
TemperaturesweremeasuredwithaMarathonMM
2MHpry-
ometerfromRaytekwithatemperaturerangeof
450-2250¡C,spectralresponseof
1.6µmandaresponsetime(
95%response)
of2ms.Thisnon-contactIRreal-timetemperaturemonitorwas
usedinconjunctionwiththeRaytekDataTempMultidropsoftware
toevaluatetemperaturestabilityforagivenSP.Thetemperature
curvecollectedisshowninFigure
19.OffsettingforRT,weareabletoapproximatethiscurveaccu-
ratelyforhightemperaturereadings.Wecanalsooffsetthiscurve
withknowledgethattheCe:LuAGcompoundhasameltingtem-
peratureof
2000¡C.Meltingwasachievedataset-pointof
47.The
governingSPtotemperaturerelationcanbeapproximatedwith
theexpression,
temperature
=f(SP)=1742(SP)0.1287"859(
8)whichhasanR-squaredvalueof
0.9999.Figure
19:Set-pointtotemperature
calibrationcurvefordoubleinsulated
µ-PDexperimentsatthecrucible
nozzle.28SoftwareDevelopment
Figure
20:Applicationsplashscreen.
Thecamerasoftwarewascapableofsavingscreenshotsandvideos
foraspeciÞcnumberofframes,howeversavingtheseformats
duringanexperimentwasfoundtobeprohibitivelytimecon-
suming.Thisfunctionalitywasgreatlyimprovedwithsoftware
improvementsIimplementedoverthecourseoftheexperiments
performed.
AMicrosoftWindowsapplicationwaswritteninVBthat
streamlinedimagecapturestoasinglebuttonclick.Thesource
codewaswritteninVisualStudiowhichisanIDEfromMicrosoft.
SecondaryscriptswerewritteninPythontocropandappend
texttoeachimage,detailingtheexperimentalparameters.The
sourcecodewaswritteninIDLEforPython.Asampleoutput
fromthesescriptsisshowninFigure
22.Figure
21:Imagecaptureapplication
writtenforWindows.
Lastlytheseimagesweresequencedandconvertedintoavideo
Þleforbetterpresentation.ThesevideoÞlesareselfcontained
aseachincludesthecrystaltype,timestamp(HH:MM:SS),spe-
ciÞcimageoftotalimagesequence,productionsite,dateand
temperature.
CrystalSynthesis:Ce:LuAG
Doubleceramicinsulationwasusedbecauseofthehighmelting
temperature.TheCe:LuAGhasacubicstructureandgoodirid-
iumcompatibilitywithameltingtemperatureofapproximately
2060¡C,whichisapproachingthemeltingtemperatureofiridium
at2447¡C.Pullratesforthiscompoundhavebeensuccessfulbe-
tween
0.32-0.75forCZgrowthand
0.25-0.75mm/minfor
µ-PD.3737X.Xu,K.Lebbou,F.Moretti,
K.Pauwels,P.Lecoq,E.Auffray,and
C.Dujardin.Ce-dopedLuAGsingle-
crystalÞbersgrownfromthemeltfor
high-energyphysics.
ActaMaterialia
,67:232Ð238,April
2014HydraulicallyPressedSample
1,Trial
1Aµ-PDtechniquecrystalgrowthattemptwasconducted.The
crucibleusedhada
1mmODcapillarynozzle.The
µ-PDexperi-
mentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
2044¡C(SP:45)over
2.75hours.Figure
22:Sampleoutputofaformat-
tedsingleframe.
Noappreciablechangeobserved.
3.Temperaturewasincreasedto
2060¡C(SP:47)andtheseedwas
leftincontact.
Crystalseededandwaspulleddownatarateof
0.60mmmin.294.Afteraperiodofgrowthitwasnotedthatthemeltwasslanted
andwasmovingbackandforthside-to-sidemorethanex-
pected.TheCe:LuAGcrystalnolongerseemedtobegrowing
downwardsataconstantrateanditwasdeterminedthatthe
Ce:LuAGcrystalhadbrokensomewhereoutofview.
5.ChamberwascooledtoRTin
1hour.
HydraulicallyPressedSample
1,Trial
2ItwasdeterminedthattheCe:LuAGcrystalgrownpreviously
wastoosmallasampletoperformOEtesting.Inordertoincrease
thisquantityanothergrowthattemptwasscheduled.The
µ-PDexperimentalprocedureisdescribedbelow,
Figure
23:Continuousbutuneven
Ce:LuAGcrystalgrowth(Sample
1,Trial
2).1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
2044¡C(SP:45)over
2hours.Noappreciablechangeobserved.
3.Temperaturewasincreasedincrementallyto
2068¡C(SP:48)andtheseedwasleftincontactafterthemeltwasobserved
emergingfromthecruciblenozzle.
Crystalseededandwaspulleddownatarateof
0.50mmmin.4.ChamberwascooledtoRTin
1hour.
Figure
24:Ce:LuAGcrystalgrowth
withlargemoltenregionbetweenthe
crucibleandorderedcrystal(Sample
1,Trial
2).HydraulicallyPressedSample
1,Trial
3Thefocusofthisgrowthwastoproducealargerandmoreconsis-
tentCe:LuAGcrystal.Whilethepreviousattemptwasrelatively
long,ithadasigniÞcantamountofdiametervariabilityandwas
overallslightlyundersizedforthe
1mmdiametercapillaryopen-
ing.The
µ-PDexperimentalprocedureisdescribedbelow,
Figure
25:SmoothandstableCe:LuAG
crystalgrowth(Sample
1,Trail
3).1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
2044¡C(SP:45)over
2hours.Noappreciablechangeobserved.
3.Temperaturewasincreasedincrementallyto
2068¡C(SP:48)andtheseedwasleftincontactafterthemeltwasobserved
emergingfromthecruciblenozzle.
304.Crystalseedingfailedshortlyafterstart.
5.Seedleftincontactwiththemeltfor
30minutes.6.Crystalseedingfailedshortlyafterstart.
Figure
26:Ce:LuAGcrystalgrowth
withhorizontallinedefectsvisible
(Sample1,Trail
3).7.Temperaturewasincreasedto
2076¡C(SP:49)andtheseedwas
leftincontactfor
30minutes.8.Crystalseedingfailedshortlyafterstart.
9.Temperaturewasincreasedincrementallyto
2083¡C(SP:50)andseedwasleftincontactfor
30minutes.10.Pulling-downratewasdecreasedto
0.10mmmin.11.Crystalseededandwaspulleddownatreducedspeedand
increasedtemperaturecomparedtolastgrowthattemptfrom
thissamemelt.
12.ChamberwascooledtoRTin
1hour.
HydraulicallyPressedSample
1,Trial
4Thefocusofthisgrowthwastoproduceacrystalwithasimilar
diameterandconsistencyofthecrystalgrowninTrial
3.Thistest
isexpectedtogrowovernightduetotheslowanticipatedgrowth
rateof
0.1mmmin.The
µ-PDexperimentalprocedureisdescribed
below,
Figure
27:Ce:LuAGgrowthfailure
shortlyaftersuccessfulseeding.With
anabrupttemperatureincreasethemelt
pulledbackintothecapillarychannel
(Sample1,Trial
4).Figure
28:Stable
Ce:LuAG
crystal
growth(Sample
1,Trial
4).1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
2044¡C(SP:45)over
2hours.Noappreciablechangeobserved.
3.Temperaturewasincreasedincrementallyto
2083¡C(SP:50)andtheseedwasleftincontactafterthemeltwasobserved
emergingfromthecruciblenozzle.
4.Crystalseedingfailedshortlyafterstart.
5.Seedleftincontactwiththemeltfor
30minutes.6.Crystalseedingwassuccessfulbutdetachedfromtheseedafter
approximately
1mmasshowninFigure
27.7.Temperaturewasincreasedto
2098¡C(SP:52)andthemelt
pulledbackintothecapillary.
8.Seedleftincontactwiththemeltfor
90minutesat
2090¡C(SP:51).319.Temperaturereducedto
2083¡C(SP:50)andcrystalwassuc-
cessfullyseededasshowninFigure
??.10.Chamberwasprogrammedfor
14.5hoursatapull-downrate
of0.1mmmin.11.ChamberwascooledtoRTin
1hour.
ManuallyPressedSample
2,Trial
1Thefocusofthisgrowthwastoproduceacrystalusingawider
capillarychannelinanefforttogrowalargerdiameterCe:LuAG
crystal.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
2044¡C(SP:45)over
2hours.Noappreciablechangeobserved.
3.Temperaturewasincreasedincrementallyto
2083¡C(SP:50)ata
rateof
1SPevery
3minutes.Figure
29:TheCe:LuAGmeltattached
totheseed,pullingitfromtheseedrod
holderbelow(Sample
2,Trial
1).Noappreciablechangeobserved.
4.Temperaturewasleftat
2083¡C(SP:50)for
30minutes.5.Crystalseedingfailedandtemperatureincreasedincrementally
to2098¡C(SP:52)whereitwasthenheldfor
60minutes.Slight
meltshowwasvisiblefromtheendofthecapillarychannel.
6.Seedwasleftincontactfor
10minutesthenpulleddownafter
themeltwasobservedspreadingacrossseedinterface.
7.Crystalseedingwassuccessfulandwaspulledataslower
rateof
4mmhr.Afterapproximately
20minutestherewasno
discernibleretractionoftheseed.Retractionwasswitchedover
tomanualanditwasdiscoveredthattheseedrodwasnot
sufÞcientlyclampedandnowstucktothemeltasshownin
Figure
29.Effortsweremadetotryandreleasethemeltbutwereunsuc-
cessful.Theverticalmotionoftheseedholdercouldbeob-
servedfromtheviewingwindowalongwiththenowstationary
rod.
8.ChamberwascooledtoRTin
2hours.32ManuallyPressedSample
2,Trial
2Thefocusofthisgrowthwastoproduceacrystalusingawider
capillarychannelinanefforttogrowalargerdiameterCe:LuAG
crystal.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
2044¡C(SP:45)over
2hours.Noappreciablechangeobserved.
3.Temperaturewasincreasedto
2060¡C(SP:47)in
6minutes.Noappreciablechangeobserved.
4.Temperaturewasincreasedto
2083¡C(SP:50)in
9minutes.5.Seedwasleftincontactwiththemeltfor
30minutes,after
whichtherewasnoobservablechangeinthemelt.
6.Temperaturewasincreasedto
2098¡C(SP:52)in
6minutes.Noappreciablechangeobserved.
7.Temperaturewasincreasedto
2105¡C(SP:53)in
3minutes.8.Seedingattemptfailedafterlessthanamillimeteratarateof
0.1mmmin.Seedwasleftincontactfor
30minutes.9.Crystalseedingfailed.
10.Temperatureincreasedto
2112¡C(SP:54)instantly,seeding
failed.11.Temperatureincreasedto
2119¡C(SP:55)instantly,seeding
failed.12.ItwasdeterminedthatthebottomofthemelthadsolidiÞed
andwaspreventingcrystalseeding.ChamberwascooledtoRT
in1hour.
ManuallyPressedSample
2,Trial
3Thefocusofthisgrowthwastoproduceacrystalusingawider
capillarychannelinanefforttogrowalargerdiameterCe:LuAG
crystal.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
332.TemperaturewasincreasedfromRTto
2068¡C(SP:48)over
2hours.Noappreciablechangeobserved.
3.Temperaturewasincreasedto
2083¡C(SP:50)in
6minutesand
heldfor
10minutes.Noappreciablechangeobserved.
4.Temperaturewasincreasedto
2098¡C(SP:52)in
6minutesand
heldfor
10minutes.Figure
30:StableCe:LuAGcrystal
growthwithlargercruciblenozzle
(Sample2,Trial
3).Noappreciablechangeobserved.
5.Temperaturewasincreasedto
2112¡C(SP:54)in
6minutesand
heldfor
30minutes.Noappreciablechangeobserved.
6.Temperaturewasincreasedto
2119¡C(SP:55)in
3minutesand
heldfor
30minutes.7.Seedingattemptfailed,withnodiscerniblemotionfromthe
melt.8.Temperaturewasincreasedto
2132¡C(SP:57)in
6minutesand
heldfor
10minutes.9.Seedingsuccessfulatapull-downrateof
0.1mmmin,temperature
wasincreasedto
2142¡C(SP:57.5)towidendiameter.
10.Growthattemptwasallowedtorunovernightandcooledto
RTin
1hour.
CrystalSynthesis:MgTa
2O6Iridiumwasusedasthecrucibleandafter-heatermaterialbecause
ofitshighresistancetohigh-temperatureoxidemelts,thislimits
thechemicalinteractionbetweentheliquidandthecrucible.
ThegrowthatmospherewasmodiÞedandÞlledwithapositive
argonpressureof
5PSIsothatthecruciblewouldnotoxidize.A
singlelayerofceramicinsulationwasusedtomaintainexperimen-
taltemperaturesaroundthecrucibleandafter-heater.
LoosePowderSample
1,MeltCheck
Duetothelimitedamountofliteraturepresentforthismagnesium
tantalate,ameltcheckwasusedtoanswersomeinitialquestions
ofcompatibility.AmeltcheckwasperformedtoconÞrmcrucible
compatibilityandgetanideaofthemeltbehaviorforagiven
temperaturerange.ThistestwascompletedusingaÞvegram
sample.ThissamplewasnotdensiÞedandÞlledthecruciblewith
34apowdermixture.Asampleofthemixedoxidepowderwastaken
forXRPDtoconÞrmthatitwasformingthecorrectmagnesium
tantalate,MgTa
2O6.Figure
31:MeltcheckforMgTa
2O6.Additionalprecautionsweretakenbecausetheviscosityofthe
liquidmeltwasunknown.Ifthesurfacetensionofthemeltwas
notsufÞcientitwouldsimplyfree-ßowfromthecrucibleonceit
liqueÞed,movingundertheforceofgravity.Theexperimental
procedureislistedbelow,
1.Chamberwasevacuatedtoavacuumof-
25psithenargonwas
pumpedintoapressureof+
7psiandleftcirculatingfor
1hourpriortothestartoftheheatingproÞle.
2.Inductionheaterwasprogrammedtoincreasefrom
0to27set-point.Figure
32:MgTa
2O6seedattempt
(Sample1,Trial
1).3.HeatingproÞlewasstoppedat
26.5set-pointwhenthemelt
wasseenemergingfromthecruciblenozzleasshowninFigure
31.4.Chamberwascooledfrom
26.5set-pointtoRTin
1hour.
AsecondXRPDsamplewastakenfromthecrucibleafterthe
melttestwascompletedtoconÞrmthatthecompoundwasstill
presentandthataprinciplecompoundhadevaporated.
LoosePowderSample
1,Trial
1Figure
33:SecondMgTa
2O6seedattemptwithmoreemergingmelt
(Sample1,Trail
1).WithcompatibilityconÞrmedweinstalledourseedrod,shownin
Figure
34.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1876¡C(SP:28)over
2hours.Oncecomplete,themeltwasseenemergingfromtheendofthe
cruciblenozzle.
Figure
34:SeedusedforMgTa
2O6growthattempt,gluedtoceramicpost
withthermaladhesive.
3.Attemptstocontactthemeltwereunsuccessfulevenwithad-
justmentstotheseedlocationinthey-direction.Theamountof
misalignmentexceededthelengthoftravelforthisadjustment
4.Temperaturewasincreasedincrementallyto
1888¡C(SP:29)in
10minutes.Despitethemeltprotrudingmorefromthecruciblenozzle,seed
attemptscontinuedtofailduetothismisalignment.
5.ChamberwascooledtoRTin
1hour.
35LoosePowderSample
1,Trial
2Werealignedtheseedwiththecrucibleandmadesurethatwe
hadadjustabilityinx/ydirections.Oncethiswascompletewe
assembledandalignedtheÞxtureandpreparedthechamber
forourgrowthattempt.The
µ-PDexperimentalprocedureis
describedbelow,
Figure
35:MgTa
2O6seedattempt
(Sample1,Trial
2).1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1863¡C(SP:27)over
2hours.Noappreciablechangeobserved.
3.Temperaturewasincreasedto
1974¡C(SP:37)over
50minutes.Severalseedattemptsweretriedbuteachtimethedroplet
appearedlargeritwouldshrinkawayfromtheseed.
4.WeconÞrmedthattheseedwasalignedwiththecapillary
channelbutdespitecorrectalignmenttheseedwouldnotcatch.
Figure
36:SecondMgTa
2O6seedattemptafterseedtranslation(Sample
1,Trial
2).5.Aftermakingseveralmoreattemptsat
1974¡C(SP:37)we
determinedthattheapparatusneededtobecleanedandthe
experimentretried.
6.ChamberwascooledtoRTin
1hour.
LoosePowderSample
1,Trial
3Wewereabletoachievegrowthduringthistrial.The
µ-PDexperi-
mentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1863¡C(SP:27)over
30minutes.3.Temperaturewasincreasedto
1900¡C(SP:30)in
9minutes.Figure
37:MgTa
2O6growthinitializa-
tion(Sample
1,Trail
3).Atthistimeitappearedthatasmallpartofthemeltwasat-
tachedtotheseed.Webeganacontrolledpulldownatarateof
0.7mmmin.Afterasmalldistancethegrowthfailed.
4.Temperaturewasincreasedto
1922¡C(SP:32)in
6minutes.Weattemptedanotherseedingoncethetemperaturestabilized
buttheattemptfailedsometimeshortlyafter.Thisgrowth,
whilebrief,waslongerthantheÞrstseeding.
36ThemeltbecametransparentanddifÞculttoseeinanyfocus.
Atsomepoint,contactwaslostandtheseedwasmovedback
uptoestablishcontactagain.
5.Temperaturewasincreasedto
1933¡C(SP:33)in
3minutes.Noappreciablechangeinmeltshapedetected.
6.Temperaturewasincreasedto
1944¡C(SP:34)in
3minutes.Webeganacontrolledpulldownatarateof
0.7mmminandfailed
quickly.
7.Temperaturewasincreasedto
1954¡C(SP:35)in
3minutes.Noappreciablechangeinmeltshapedetected.
Figure
38:Increasingdiameterof
MgTa
2O6growth(Sample
1,Trial
3).8.Temperaturewasincreasedto
1974¡C(SP:37)in
6minutes.Westoppedthetemperatureincreaseat
1972¡C(SP:36.8)aftera
largechangewasobservedintheviscosityofthemelt.
9.Temperaturewasdecreasedto
1954¡C(SP:35)inlessthana
minute.Weimmediatelybegantopullatarateof
0.7mmminwhichwe
foundtobetoofastandtheseedseparatedfromthemelt.The
meltbegantoßowrapidly,coveringtheseedandseedholder.
10.Temperaturewasincreasedto1964¡
C(SP:36).Themeltwasre-seededontopoftheßowthathadstucktothe
seedandseedholder.
11.Crystalseededsuccessfullyandwaspulledatarateof
0.6mmmin.12.Crystalwasgrownatthisrateuntilseparationoccurredwhen
themeltinthecruciblewasexhausted.
13.ChamberwascooledtoRTin
1hour.
ManuallyPressedSample
3,Trial
1Thisattemptwasdonewiththepressedsample.Thisgrowth
attemptwasconductedwithanewceramicinsulatorastheprevi-
ousonewascontaminatedontheinside.The
µ-PDexperimental
procedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1933¡C(SP:33)in
1hour.
HeatingproÞlewasstoppedat
1917¡C(SP:31.5)whenitwas
observedthatthemeltwasvisiblefromtheendofthecrucible
nozzle.Aseedattemptwasattemptedbutfailed.
373.Temperaturewasincreasedto
1922¡C(SP:32)Figure
39:TheMgTa
2O6meltwould
notadheretotheseedduetopoor
materialcompatibility(Sample
3,Trial
1).Noappreciablechangeobserved.
4.Temperaturewasincreasedto
1964¡C(SP:36)over
12minutes.Seedingattemptsoccurredwitheachset-pointincreaseat
1933¡C,1944¡C,1954¡Cand1964¡C.Eachattemptfailed.
5.Seedwasleftincontactwiththeexposedmeltfor
30minutes.Seedattemptfailed.
6.Temperaturewasincreasedto
1969¡C(SP:36.5)over
15min-utes.Seedattemptfailed.
7.Temperaturewasincreasedto
1988¡C(SP:38.5)over
15min-utes.Seedattemptfailed.Itwasobservedthatthemeltwasretreat-
ingbackintothecapillarychannelastheseedwasplacedin
contact.8.ChamberwascooledtoRTin
1hour.
ManuallyPressedSample
3,Trial
2Thisattemptwasdonewiththepressedsample.The
µ-PDexperi-
mentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1900¡C(SP:30)in
1hour.
Noappreciablechangeobserved.
3.Temperaturewasincreasedto
1911¡C(SP:31)in
3minutes.Noappreciablechangeobserved.
Figure
40:Theseedrodpressedagainst
theMgTa
2O6meltwithsufÞcientforce
torotatetheafter-heaterandobstruct
viewing(Sample
3,Trial
2).4.Temperaturewasincreasedto
1933¡C(SP:33)in
6minutes.Seedattemptfailed,meltobservedthinlyacrossthebottomof
thecruciblenozzle.
5.Temperaturewasincreasedto
1944¡C(SP:34)in
3minutes.Noappreciablechangeobserved.
6.Temperaturewasincreasedto
1954¡C(SP:35)in
6minutes.Noappreciablechangeobserved.
7.Temperaturewasincreasedto
1959¡C(SP:35.5)in
3minutes.Noappreciablechangeobserved.
388.Temperaturewasincreasedto
1969¡C(SP:36.5)in
6minutes.Noappreciablechangeobserved.
9.Temperaturewasincreasedto
1974¡C(SP:37)in
3minutes.10.Seedwasleftincontactwiththemeltfor
30minutes.Seedingattemptfailed.
11.Seedwasleftincontactwithmeltforanother
30minutes.Seedingattemptfailed.
12.Temperaturewasincreasedto
1983¡C(SP:38)over
30minuteswithseedincontact.
Seedingattemptfailed.
13.Seedwasleftincontactwithmeltfor
30minutes.Seedingattemptfailed.
Figure
41:TheMgTa
2O6meltdidnot
attachtotheseedbutcontinuedto
discharge(Sample
3,Trial
3).14.Temperaturewasincreasedto
1992¡C(SP:39)in
6minutes.15.Seedleftincontactfor
30minutes.Seedingattemptfailed.
16.ChamberwascooledtoRTin
1hour.
ManuallyPressedSample
3,Trial
3Thisattemptwasdonewiththepressedsample.The
µ-PDexperi-
mentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1922¡C(SP:32)overan
hour.
Seedwasraised,makingcontactwiththecrucible.Nomelt
detected.3.Temperaturewasincreasedincrementallyto1954¡
C(SP:35).4.Seedwasleftincontactfor
30minutes.Figure
42:TheMgTa
2O6discharge
coveredtheentireviewingwindow
(Sample3,Trial
3).Seedwasdrawndownwardsandthemeltfolloweddownwards
butfailedtoseed.
5.Temperaturewasincreasedto1969¡
C(SP:36.5).Seedwasmovedtotherightinordertocenteradefectonthe
seedwiththelowestpointinthemelt.Theseedwasleftin
contactwiththemeltfor
15minutes.Itwashypothesizedthat
themeltwouldhavebettersuccessseedingonaroughsurface.
Thishoweverwasunsuccessfulaswell.Theseedwasmoved
backtoitsoriginalposition.
396.Temperaturewasincreasedincrementallyto1992¡
C(SP:39).Figure
43:TheendoftheMgTa
2O6dischargeemptiedthecrucible(Sample
3,Trial
3).7.Seedwasleftincontactfor
15minutes.Itwasobservedthattheseedwasphysicallysupportingthe
melt.Adjustingtheseedinthex/ydirectionsmovedtheseed
anddownwardsmotionletthemeltmovedownwards.Despite
thisphysicalsupport,themeltfailedtoattachtotheseed.
Meltwetseverelyalongtheentireoutsideofthenozzle,ßowing
upwardsawayfromtheseedwhilestillincontact.
8.Seedwasdeceasedatarateof
0.50mmminandalargemassof
materialßoweddownwardsafteritbutfailedtoseed.
9.Seedratewasadjustedto
0.10mmmin.10.Themassofmaterialdescended,takingwithitmeltthathad
wetontheexteriorsurfaceofthecrucible.
11.AÞnalseedattemptoccurredafterthetopofthematerial
masswasobservedbutthisfailed.
12.Temperaturewasincreasedto
2001¡C(SP:40)in
3minutes.Seedingwasattemptedagainbutwasonlyminimallysuccessful
asthemeltseemedtobeexhausted.
13.ChamberwascooledtoRTin
1hour.
Aseedwaspreparedfromthepreviousgrowth.Asevidenced
fromthepastgrowthattemptstheMgTa
2O6melthadadifÞcult
timeseedingagainsttheiridiumseed.Byproducingaseedofthe
samematerialweeliminatethismaterialcompatibilityissue.Fur-
therexperimentswiththiscompatibleseedwillneedtoproceed
cautiouslyasthemeltingtemperatureoftheseedandthemelt
isnowthesame.Theprocedureusedtoconstructanewseedis
describedbelow,
1.Previousgrowthwasbrokeninhalf.Onehalfwaspulverized
forXRPDtestingandtheotherhalfwouldbeusedasanew
seedforfuturegrowthattempts.
Figure
44:TheMgTa
2O6dischargefrom
thelasttestmadeforacompatibleseed.
2.TheseedportionselectedwassandeddownsothatifwouldÞt
withinthehollowceramicseedrodmadeofhighpurityAl
2O3.Thiswasaccomplishedusing
600/P1200gritgrindingpaper.
3.OncethegrowthwasabletoÞtinsidethehollowceramicseed
rodthetwowereadheredtogetherwithaZirconiaadhesive
producedbyCotronics.
4.Theseedandseedrodwereplacedinafurnaceat
60¡Covernighttoallowtimetosolidify.
40Duetogravitytheexcessadhesivecollectedontheonesideof
theseedwhilesolidifyingandrequiredadditionalsandingso
thatitcouldmovewithoutobstructionwheninstalledwithin
theµ-PDchamber.Thelimitationwasthediameterofthe
ceramicsupportatopthequartztube.Oncethisexcessadhesive
wasremovedthenewseedwasreadytouseinsubsequent
µ-PDexperiments.
Figure
45:ThedriedMgTa
2O6seedneededtobesandeddownslightly
priortouse.
ManuallyPressedSample
4,Trial
1Thisattemptwasdonewiththenewtengrampressedsample.
Theµ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1900¡C(SP:30)over
2hours.Themeltemergedreadilyfromthecruciblenozzle.
3.Temperaturewasdecreasedto
1876¡C(SP:28).Withthisdecreaseintemperaturethemeltstabilizedandno
longerthreatenedtofree-ßowfromthecruciblenozzle.
4.Temperaturewasincreasedbackto
1900¡C(SP:30)in
6min-utes.Meltbegantodescendfromcruciblenozzleandseedingwas
initiatedatapulldownrateof
0.10mmmin.Crystalseparated
shortlyafterwiththediameterofthecrystaldecreasinguntil
termination.
Figure
46:VariablediameterMgTa
2O6growthseededonnewconstructed
MgTa
2O6seed(Sample
4,Trial
1).5.Temperaturewasincreasedto
1906¡C(SP:30.5)in
6minutes.6.Seedwasleftincontactfor
30minutes.Seedingwasre-initialized.Pull-downratewasthesameat
0.10mmmin.Temperaturewasincreasedincrementallytocombat
thedecreasingcrystaldiameterupto
1910¡C(SP:30.9)where
separationÞnallyoccurred.
7.Seedwasleftincontactwiththemeltfor
15minutes.Seedattemptfailed.
8.Temperaturewasincreasedto
1911¡C(SP:31).9.Temperaturewasincreasedto
1917¡C(SP:31.5)in
6minutes.Seedingattemptwassuccessfulbutfailedafterashortdistance
10.ChamberwascooledtoRTin
1hour.
41ManuallyPressedSample
4,Trial
2Thisattemptwasdonewiththetengrampressedsample.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1876¡C(SP:28)in
2hours.Thistemperaturewasthenmaintainedfor
2hoursinanattempt
tobetteracclimatethemelt.
Figure
47:MgTa
2O6growthinitiatedat
asmalldiameterbeforegrowinglarger
andcoolingquickly(Sample
4,Trial
2).3.Temperaturewasincreasedto
1900¡C(SP:30)in
30minutes.Noappreciablechangeobserved.
4.Temperaturewasincreasedto
1911¡C(SP:31)in
6minutes.Seedinginitializedatapulldownrateof
0.10mmmin.Crystal
seededandgrewlargerindiameterbeforeseparatingfromthe
melt.Contactwasreestablishedbuttheexistingcrystalwaspulled
intothemelt.Thebottomsideofthiswastoocoldtoreseed,
preventingfurthercrystalgrowth.
5.ChamberwascooledtoRTin
1hour.
Figure
48:ThesmallinitialMgTa
2O6growthdiameterbrokeoncethemass
aboveitwasseededagain,pluggingthe
capillarychannelwithrelativelycool
MgTa
2O6(Sample4,Trial
2).ManuallyPressedSample
4,Trial
3Thisattemptwasdonewiththetengrampressedsample.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
Figure
49:VariablediameterMgTa
2O6growth(Sample
4,Trial
3).2.TemperaturewasincreasedfromRTto
1900¡C(SP:30)in
2hours.3.Seedwasbroughtintocontactwithmelt.
4.Temperaturewasincreasedto
1906¡C(SP:30.5)in
6minutes.Seedingwasinitializedwithapull-downrateof
0.10mmmin.Diam-
eterdecreasedonformingcrystal.
5.Temperaturewasincreasedto
1910¡C(SP:30.9).Uncontrollableßowoccurred.
6.Temperaturewasimmediatelyreducedto
1906¡C(SP:30.5)as
crystalformationcontinued.
427.Temperaturewasincreasedincrementallyto
1911¡C(SP:31).Thecrystalgrowthterminatedseveraltimesandwasre-seeded
aftereachfailure.
8.ChamberwascooledtoRTin
1hour.
Thecrystalfromtheprevious
µ-PDexperimentwasextracted
fromthechamberbutwhenanattempttoremovethegrowthfrom
theseedwasmade,theseedbroke,withagoodportionofthe
seedstillstucktothesamplegrowthasshowninFigure
50.The
samplerequiredremovalfromtheseedusingawiresawshownin
Figure
53.Theseparationprocedureisdescribedbelow,
1.RubberÞxturewasplacedonahotplatewithsolidglue.The
gluewasallowedtomeltattherubberÞxturesurface.
2.Sampleandseedportiontobeseparatedwerethenplacedon
therubberÞxtureoncethegluehadbeguntomelt.
Figure
50:MgTa
2O6sampletobe
separatedafÞxedonrubberÞxture.
3.RubberÞxturewascooledwiththesampleadheredtoits
surface.4.Sampletobeseparatedwasthencutbythewiresaw.
5.RubberÞxturewasagainheatedonthehotplateuntiltheseed
portionandsamplewereremovedfromthemeltedglue.
Figure
51:VariablediameterMgTa
2O6growth(Sample
4,Trial
4).Figure
52:VariablediameterMgTa
2O6growthafterseedingrestart(Sample
4,Trial
4).Theportionoftheseedseparatedfromthesamplewasdiscarded
andtheremainingseedwasusedforfuturetestingdespitebeing
smaller.Thesmallerseedwasstillpreferabletousingtheiridium
seed.Thetemperaturegradientacrosstheseedandthecrucible
nozzleisnowmoresensitiveduetothesmallerseed.Sincethe
meltandtheseedarebothmadeofthesamematerialitiscritical
tokeepthemeltliqueÞedwithoutliquefyingtheseedbelowit.
ManuallyPressedSample
4,Trial
4Thisattemptwasdonewiththetengrampressedsample.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
2.TemperaturewasincreasedfromRTto
1888¡C(SP:29)set-point
in2hours.3.Seedwasbroughtintocontactwiththeemergingmelt.
4.Temperaturewasincreasedto
1911¡C(SP:31)in
30minutes.43Figure
53:Wiresawusedtoseparate
samplegrowthfrombrokenseed.
Seedingwasinitializedwithapull-downrateof
0.50mmmin.Soonafterthecrystalseparatedfromthemelt.Thecrystal
wasbroughtbackintocontact.
5.Temperaturewasincreasedto
1954¡C(SP:35).Seedingwassuccessfullyrestartedatthesamepull-downrate.
Experimentwaslefttorunovernight.
6.ChamberwascooledtoRTin
1hour.
ManuallyPressedSample
4,Trial
5Thisattemptwasdonewiththetengrampressedsample.The
µ-PDexperimentalprocedureisdescribedbelow,
1.Chamberwasevacuatedtoavacuumof-
25PSI.Argonwas
thenpumpedin,toapressureof+
7PSI,andleftcirculatingfor
1hourpriortoinitializingtheheatingproÞle.
Figure
54:VariablediameterMgTa
2O6growth(Sample
4,Trial
5).2.TemperaturewasincreasedfromRTto
1944¡C(SP:34)in
2hours.3.Seedwasbroughtintocontactwiththeemergingmelt.
4.Temperaturewasincreasedincrementallyto
1954¡C(SP:35).Meltßowwasobstructedbyseedbutwettheoutsideofthe
cruciblenozzle.Seedingwasinitializedwithapull-downrate
44of0.50mmmin,removingthewettedmeltfromtheexteriorofthe
crucible.5.Temperaturewasmaintainedandpull-downcontinuedbut
withseveralrequiredrestarts.
6.ChamberwascooledtoRTin
1hour.
X-rayPowderDiffraction
X-raypowderdiffraction(XRPD)testingwasperformedat
LawrenceBerkeleyNationalLaboratory(LBNL)usingaSiemens
SMART-CCDdiffractometerequippedwithanormalfocus,
2.4kWsealedtubex-raysource(MoK
&,'=0.71073†)operatingat
50kWand
40mA.SamplesweregroundintoÞnepowderswithamortarand
pestleandmountedatthecenterofplasticringswithmasking
tape.ApreparedsampleisshowninFigure
55.Figure
55:PreparedsampleforXRPD
analysis.AndiffractionpatternexampleisshowninFigure
56.These
ringsneedtobeconvertedintoanoutputspectrum,whichis
accomplishedbyin-housesoftwareatLBNL.Theprocedurefor
thisconversionisdescribedbelow,
Figure
56:RawXRPDoutput,priorto
post-processing.
1.Thesampleoutputiscalibratedagainstthesodiumchloride
(NaCl)samplethatthatwasrunthatsameday.
2.Theuserselects
5-10pointsalongtheinnermostoftheNaCl
sample.Thisringrepresentsthe
2(=32peakthatcorrespondsto
thehighestpeakofthesample,registeringthe
200planes.3.Whenthiscalibrationisprocessedthesampleofinterestring
patternisloaded.Fromthisaplotisproduced.
4.ThisplotisthensavedoffandloadedinMatch!,aphaseidenti-
ÞcationprogramcreatedbyCrystalImpact.
5.Heretheplotisanalyzedandcomparedagainstadatabase
ofcompoundsthatcorrectlyidentifypeaksinthesampleand
giveÞgureofmeritvaluesthatdisplaytherelativeconÞdence
ofitsselectionswithavalueofonebeingaperfectmatchtoa
standardonrecord.
X-rayLuminescence
X-rayluminescence(XRL)testingwasperformedatLawrence
BerkeleyNationalLaboratory(LBNL)usingaSpectraPro-
2150ispectrometermadebyPrincetonInstrumentscoupledtoathermo-
electricallycooledPIXIS:
100Bchargecoupleddetector(CCD)also
fromPrincetonInstruments.Thismeasuredtherelativeintensity
ofthex-rayemissionspectra.
45CrystalMounting
SamplemountswerepreparedinaBuehlerPneumetImounting
press,showninFigure
57withBuehlerKonductometinprepa-
rationforSEMtesting.BuehlerKonductometisagraphiteand
silicondioxide(SiO
2)ÞlledphenolicthermosetusedspeciÞcally
fornon-carbonbasedsamplesinSEManalysis.Thisallowsthe
samplemounttobeconductiveduringtesting,however,thesam-
plemuststillbecoated.Sampleswerepositionedverticallyinthe
mountwiththeaidofplasticclipsfromMetLabCorporation.The
procedureforproducingthesemountsislistedbelow,
Figure
57:BuehlerPneumetImounting
press.
1.Airsupplywasturnedonandtheplatformraisedonthepress.
2.Sampleswereplacedverticallyonthepressplatformwiththe
assistanceofplasticclips.Thesectiontobepolishedwasplaced
facingdownagainstthebase.Forpolishing,thiswillactasour
topsurface.
3.Theplatformwasloweredintothecavityandthecavitywas
ÞlledwithBuehlerKonductometthermoset.
4.Theplatformwasloweredfurtherandthesamplewascon-
Þrmedtobeverticalbeforecoveringitwithmorethermoset.
5.Thetopwasscrewedintoplaceandtheheatingelementwas
appliedaroundthecavityÕsexternalcircumference.
6.Oncesecuredandsealedthepresswasbroughttoapressureof
55-60PSIandmaintainedfortenminutes.
Figure
58:Bottomsurfaceofthemount
thatwillactasthetopofthesampleto
bepolished.
7.Theheaterwasthenremovedandpressurewasdecreasedto
ATM.Thesamplewasthenremovedandallowedtocool.
8.Betweeneachmountproduced,theapparatuswasthoroughly
cleanedsothattheplatformwouldactuatesmoothly.
9.Oncesampleswerecompletedtheapparatuswascleanedand
theairsupplywasturnedoff.Acompletedsampleisshownin
Figure
58.CrystalPolishing
Figure
59:BuehlerEcometIVPolisher/-
Grinder.
Aqualitypolishedsurfacemustbepresentinordertoeffectively
conductSEMimaging.PolishingwasperformedwithaBuehler
EcometIVPolisher/GrindershowninFigure
59.Standardgrit
grindingpaperswereusedalongwithdiamondcompoundfrom
Metlabin
10gramdispensingtubes.
Thegrindingpapersusedasourabrasivedisksarelistedin
Table
6.Eachpolishedsamplerequiredauniqueregimentbecause
46ofcrystalfractures.Thesefracturescreatedportionsofloose
crystalthatneededtoberemoved.Onceremovedamorestable
surfacefurtherintothesamplecouldbeusedforpolishing.
Thediamondpastesarecharacterizedbythesizeofthepoly-
crystallinediamondwithinthecompound.Thesepasteswere
appliedtoaStruersMD-Nappolishingclothmadeofshortsyn-
theticnap.Thediamondpastesusedwere
6,3,1,and
1/4micron.
StandardANSIGritEuropean(P-Grade)Diameter(
µm)320P36040
.5600P120015
.3800P24006
.51200P40002
.5Table
6:Grindingpapersusedfor
polishingceramicsamples.
Withthegrindingpapersinstalled,waterwasusedtolubricate
andhelpmoveremovedmaterialawayfromthesamplesurface.
Betweeneachiterationofpolishingthesamplewasdriedalong
withthegrindingpaperandapparatus.Thisadditionalwork
extendedthelifeofseveraloftheÞnergritgrindingpapers.If
neglected,thepaperswouldabsorbtheadditionalwaterand
wrinkleseverely,reducingtheireffectiveness.
Thevariousdiamondpastesemployedwereusedonsinglenap
polishingcloth.Duringprocessthiswaslubricatedwithethanol
andafterwards,cleanedextensivelywithabrushandwatersothat
theremainingdiamondpastewasremoved.Thepolishingcloth
wasthendriedandthenextdiamondpastewasapplied.
Inadditiontodiamondpastesanoxidepolishingsuspension
(OP-S)wasused.OP-Susesacolloidalsilicasuspensionforabra-
sion.Thetypeusedforthistestinghadanaveragegrainsizeof
0.05µ.Figure
60:ZeissStemiSV-
6stereomi-
croscopeusedforobservingpolished
samples.Alow-magniÞcationZeissStemiSV-
6stereomicroscope,shown
inFigure
60,wasusedtoobservesamplesperiodicallybetween
polishestoevaluatesurfacequality.Imageswerestreamedfroma
NikonDS-Fi
2,5.0-megapixelcolorCCDcameraheadandstored
withNISElements,imagingsoftwarefromNikon.
AllimagesandobservationsweredoneatamagniÞcation
(MAG)of
5.0x.Lightingconditionswerechangedduringtestingto
improveimageclaritybyadjustingautoexposure(AE)andanalog
gain(AG).Theseareseenmostnotablyasadjustingtheamountof
lightperceivedintheimages.
AReichertJungmicroscopelightfromCambridgeInstruments
wasusedasanexternallightsourcetofurtherilluminatethe
polishedsurfaceofthesamples.Thiswaskeptrelativelystaticin
positionatitsfulloutputof150
W.47LBNLSample
1468.7MAnewCe:LuAGsamplewithreducedceriumcontent(
<0.5mol%Ce)wassentfromLBNLforanalysis.Whiletheinitialcrystalwas
smoothanduncracked,therewasperimeterdamagetothecrystal
afterthemountingprocesswheretheclipmadecontactwiththe
crystal.Itappearsthatthepressureusedtocreatethemountswas
toohighforthesample.
Speedwasvariedinanefforttogetabetterfeelofwhatwas
appropriateforthismaterial.Thepolishingprocedureisdetailed
below,
1.800/P2400for2minutesat
200RPM.Microscope:crackswerevisiblealongthecircumferenceof
thecrystalwithscratchesacrossthetopsurfaceparalleltothe
directionofpolishasshowninFigure
61.Figure
61:Ce:LuAG(<
0.5mol%Ce)-
10mmlengthcrystalafterÞrstpolish.
MAG:5.0x,AE:
1.5ms,AG:
4.0x.2.800/P2400for2minutesat
300RPM.Microscope:crackswererelativelylargeandunaffectedby
thepolishingprocess.Thesurfacescratcheswerereducedand
paralleltothedirectionofpolish.
3.1200/P4000for2minutesat
100RPM.Microscope:scratcheswerereducedwiththeÞnerpolish,
changesmoresubtle.
Figure
62:Ce:LuAG(<
0.5mol%Ce)-
10mmlengthcrystalpriortodiamond
pastepolishing.MAG:
5.0x,AE:
1s,AG:3.9x.4.1200/P4000for2minutesat
100RPM.Microscope:furtherreducedscratches,portionsofthecrystal
haveacompletelysmoothsurfaceatthislow-magniÞcationas
showninFigure
62.Withanacceptablesurface,diamondpastes
ofdecreasingdiameterwereused.
5.6µfor12minutesat
200RPM.6.1µfor5minutesat
200RPM.7.0.05µOP-Sfor
5minutesat
200RPM.Microscope:OP-Swasnotcompletelyremovedandworked
intothecracksofthecrystal,thisshouldnotbedetrimentalto
studyingthepolishedsurfacebutitwillnotbeusedinfurther
polishingforthisreason.
Ce:LuAGSample
2,Trial
3Theprocedureforpolishingwasseparatedintotwophases:(
1)removematerialuntilaßat,relativelyunfracturedsurfaceis
reached;(
2)polishtheßatsurface.Themountingprocesscreated
fracturesinthecrystalduetotheclipthatwasholdingthesample
verticalasshowninFigure
63.Thefracturedcrystalneededtobe
48removedpriortopolishinganacceptablesurface.Thepolishing
procedureisdetailedbelow,
Figure
63:Ce:LuAG(
1mol%Ce)from
3mmODcruciblenozzle.Initialcrystal
stateaftermounting.MAG:
5.0x,AE:
300ms,AG:
2.8x1.1200/P4000for5minutesat
200RPM.Microscope:crystalfracturesincreasedinspread.Itisapparent
thattheyareseparatedfromthemaincrystalbelowandneedto
beremovedtoestablishasolidsurfaceforSEM.
2.800/P2400for5minutesat
200RPM.Microscope:noticeableimprovementinpolish,howeverthe
crystalremainsfracturedasshowninFigure
64.3.600/P1200for2minutesat
200RPM.Microscope:piecesofcrystalhavebeenremoved,howevermore
crystaldebrisispresent.
4.600/P1200for5minutesat
200RPM.Microscope:slightimprovementbutasigniÞcantaboutof
debrisremains.
5.800/P2400for5minutesat
200RPM.Microscope:littletonoimprovementobserved.
Figure
64:Ce:LuAG(
1mol%Ce)from
3mmODcruciblenozzle.Crystalstate
afterpolishwith
2400gritsandpaper
for5minutesat
200rpm.MAG:
5.0x,AE:150ms,AG:
4.0x6.320/P360for1minuteat
200RPM.Microscope:someremovalofloosecrystal.
7.800/P2400for2minutesat
200RPM.Figure
65:Ce:LuAG(
1mol%Ce)from
3mmODcruciblenozzle.Crystalafter
diamondpastepolishing.MAG:
5.0x,AE:300ms,AG:
4.8xMicroscope:nosigniÞcantchange,coarsergritswillbeused
untilthesurfaceimproves.
8.320/P360for1minuteat
200RPM.9.320/P360for1additionalminuteat
200RPM.10.320/P360for2minutesat
200RPM.Microscope:signiÞcantimprovement,ßatsolidsurfaceemerged
andaccountedforhalfofthecrystaldiameter.Proceededmore
cautiously,withmorevisualchecksduringpolishing.
11.600/P1200for2minutesat
200RPM.12.800/P2400for2minutesat
200RPM.Anewsandpaperwasusedastheotherwaswrinkledfrom
waterabsorption.
13.1200/P4000for2minutesat
200RPM.Microscope:solidsurfaceshowedimprovedpolish.
4914.1200/P4000for2minutesat
200RPM.Polishwasperpendiculartothepreviouspolishtoensurethat
thescratchesinthepreviousdirectionwereremovedfromthe
sample.Withthemajorityofthesurfacescratchesremovedthe
diamondpolishingprocesscouldbegin.
Figure
66:Ce:LuAG(
1mol%Ce)from
1mmODcruciblenozzle.Crystalprior
topolishing.MAG:
5.0x,AE:
30ms,AG:4.0x.15.6µfor12minutesat
200RPM.16.3µfor5minutesat
200RPM.17.1µfor5minutesat
200RPM.Microscope:Surfaceisnoticeablymoretransparentasshownin
Figure
65.Ce:LuAGSample
1,Trial
2Thesampletestedwasextremelysmallwithadiameterof<
0.5mmandviewingunderamicroscoperevealedsurfacefractures
andthermosetalongthetopsurfacethatneededtoberemovedas
showninFigure
66.Thepolishingprocedureisdetailedbelow,
1.320/P360for20secondsat
200RPM.Figure
67:Ce:LuAG(
1mol%Ce)from
1mmODcruciblenozzle.Crystalafter
320gritsandpaper.MAG:
5.0x,AE:
200ms,AG:
5.6x.Microscope:surfacehadbeenpartiallyconcealedbythether-
moset,afterthispolishafracturedsurfaceemerged.
2.320/P360for1minuteat
200RPM.Microscope:somefracturedcrystalremovedasshowninFigure
67.3.600/P1200for1minuteat
200RPM.Figure
68:Ce:LuAG(
1mol%Ce)from
1mmODcruciblenozzle.Crystalafter
diamondpastepolishing.MAG:
5.0x,AE:200ms,AG:
5.6xMicroscope:incrementalimprovementinsurfacequalityspeciÞ-
callyatthecenterofthecrystal.
4.600/P1200for2minuteat
200RPM.Microscope:furtherprogressonthecrystalisdifÞculttoob-
serveduetothesmalldiameter.AsigniÞcantreductionof
scratcheswasobservedonthemountitself.Itisassumedthat
thecrystalsurfaceisnowlevelwiththesurfaceofthesurround-
ingmountandclip.
5.800/P2400for2minutesat
200RPM.6.1200/P4000for2minutesat
200RPM.Microscope:littleobservablechangeatlow-MAG.
7.6µfor12minutesat
200RPM.8.3µfor5minutesat
200RPM.509.1/4µfor5minutesat
200RPM.Microscope:solidsurfacenearcenterofcrystalisnoticeably
improvedwithrespecttoitstransparencyasshowninFigure
68.MgTa
2O6Sample4,Trial
5Thiscrystalpresentedafewchallengesbecauseofitsirregular
geometryandthefracturescreatedinthemountingprocess.The
Þrsttaskwastocreateanacceptablesurfaceasmuchofthecrystal
wassubmergedinthermosetasshowninFigure
69.Figure
69:MgTa
2O6from
1mmOD
cruciblenozzle.Initialcrystalcondition
aftermounting.MAG:
5.0x,AE:
30ms,AG:4.0x.Figure
70:MgTa
2O6from
1mmOD
cruciblenozzle.Crystalaftersecond
perpendicularpolishwith
4000gritpaper.MAG:
5.0x,AE:
200ms,AG:
5.6x.1.320/P360for31/2minutesat
200RPM.Microscope:ßatsurfaceemerged,thecenteroftheirregularly
shapedsurfaceisÞlledwiththermoset.Morematerialwas
removedafterthisinanticipationofthesurfacecomingtogether
underneaththethermoset.
2.320/P360for6minutesat
200RPM.Microscope:ßatsurfaceÞlledinatitscenter,thetopofthe
crystalwasbrokenoffwiththermosetinthegap,implyingthat
thecrackoccurredduringthemountingprocess.
3.800/P2400for2minutesat
200RPM.4.1200/P4000for2minutesat
200RPM.5.1200/P4000for2minutesat
200RPM.Polishwasperformedperpendiculartothepreviouspolishso
thatscratchescouldberemoved.Scratchesremainedasshown
inFigure
70.Figure
71:MgTa
2O6from
1mmOD
cruciblenozzle.Crystalafterrepeated
perpendicularpolishes.MAG:
5.0x,AE:
200ms,AG:
5.6x.6.800/P2400for5minutesat
200RPM.Despitethesepolishesbeingperpendiculartotheotherpolishes,
theywereunabletoremovemanyofthescratches.Atthistime
acoarsergritwasusedtoßattenthesurface.
7.800/P2400for6minutesat
200RPM.PolishhadÞnallyremovedthemajorscratchesobservedat
low-MAGasshowninFigure
71.8.1200/P4000for2minutesat
200RPM.9.6µfor12minutesat
200RPM.10.3µfor5minutesat
200RPM.11.1/4µfor5minutesat
200RPM.51CrystalCoating
Thepolishedsampleswerethencoatedwithathinlayeroftung-
sten(W).ThiswasaccomplishedwithaLeicaEMMED
020modu-larhighvacuumcoatershowninFigure
73.Theprocedureusedto
coatthesesamplesisoutlinedbelow,
1.Theargontankvalvewasopenedandfullspeedvacuumwas
activatedontheLeicacontrolpanel.Pumpdowncontinuedto<
10"4bar.
2.Coaterwasprogrammedtodepositathin
1nmlayeroftung-
stenonthesurfaceofthesamples.Thechamberwaslarge
enoughtoaccommodateallfourofthesamplesinthesame
cycle.
3.OnceatvacuumSPthecoaterwasplacedinstandbyandthe
shutteropened.
Figure
72:Ce:LuAG(<
0.5mol%Ce)-
10mmlengthcrystalaftercoating,
1nmthicknesstungstencoating.MAG:
5.0x,AE:200ms,AG:
5.6x.4.ArgonwasactivatedandthevacuumwasconÞrmedtobe
stable.5.Coaterprocesswasactivatedandthesputterratewassetto
0.1nm/s.6.Oncecoatedtothedesiredthickness,argonwasstoppedand
theshutterclosed.ThechamberwasthenbroughtbacktoATM
andthecoatedsampleswereremoved.
ScanningElectronMicroscopy
PerformingSEMoninsulatorspresentsuniquechallengesasthe
electron-beamradiationproducedinducesastrongelectricÞeld.
ThiselectricÞeldisduetothetrappingofelectronswithinthe
specimen.ThisÞeldaltersthetrajectoriesofthebeamofelec-
tronsenteringthespecimenwhichseverelylimitsthepenetration
depth.Additionally,thistrappingleadstosecondaryelectrons(SE)
contrastdependenceonthechargedsample.
3838M.Belhaj,O.Jbara,S.Odof,K.Msel-
lak,E.I.Rau,andM.V.Andrianov.An
anomalouscontrastinscanningelectron
microscopyofinsulators:Thepseudo-
mirroreffect.
Scanning,22(6):352Ð356,200052Figure
73:LeicaEMMED
020modularhighvacuumcoater(ImagefromLeica).
Figure
74:MiraXMHelectronmicro-
scope(ImagefromTescan).
Duetotheseeffectstheceramiccrystalsampleswerecoated
inaconductortoproperlygroundthem.Thisconductivelayer
requiredaconductivemountandamirror-Þnishpolishedsample.
SEMmeasurementswereperformedonaMira
3XMHelectron
microscope,whichisahighvacuummodel(<
9%10"3Pa)for
largerconductivesamples.ItisequippedwithaSchottkyField
Emissionelectrongun.
Theprocedureforacquiringimagesisdescribedbelow,
1.Samplesareloadedontothefullymotorizedstageandmoved
intothechamber.
2.Chamberissealedandpumpeddowntovacuum.Theelectron
gunisturnedonandthesampleislocatedbyadjustingthe
stagepositionandviewingthroughwideÞeld.
3.Oncethedesiredpositionisnavigatedtotheelectrongunis
changedtoresolutionmode.
4.ThesampleisbroughtintofocusbymakingÞneadjustmentsto
theworkingdistance.
5.ImagesarecapturedatvariousmagniÞcationsafterfocusis
achieved.
536.Oncecomplete,thechamberisbroughtbacktoATMandthe
samplesremoved.
Energy-dispersiveX-raySpectroscopy
Energy-dispersivex-rayspectroscopy(EDS)testingwasperformed
withintheMira
3XMHmicroscopefromanApolloXmodulewith
anactiveareaof
10mm2.Imageswerecollectedandprocessed
throughtheTextureandElementalAnalyticalMicroscopy(TEAM)
softwarepackage.Samplesweremeasuredinthreedifferent
locationstoreducetheoddsofafalsereading.
Surfacechargingisalsoaconcernforinsulators.Forthisrea-
sonsthesamplestestedwerecoatedintungstenandsetinconduc-
tivemounts.Thesurfacepotentialcanrisequicklyonun-coated
samplesduetotheinputofpositivechangeandtheemissionof
secondaryelectrons.
ThecharacteristicK,L,andMx-raylineenergiesarelistedin
Table
7fortheelementsofinterestinourCe:LuAGandMgTa
2O6samples.3939J.B.KortrightandA.C.Thompson.
X-raydatabooklet
,chapter
1,pages
8Ð13.LawrenceBerkeleyNationalLaboratory,
2009Thevalueslistedareonlythestrongestlines.Thewavelength,
',oftheemissioncanbeobtainedfromtheexpression,
'=12398E(9)where
EistheenergyoftheemissionineV.Thebindingenergies
fortheselectedelementsareshowninTable
8.Abriefdescription
oftheprocedureislisted,
1.SamplesareloadedintotheMira
3XMHmicroscope,pumped
tovacuumandthemicroscopefocusedontheregionofinterest.
2.TheApolloXmodulewasactivatedandtheviewscanned
withtheTEAMsoftware.Theremaininganalysiswasalso
performedthroughthisapplication.
3.Fromthisscannedimage,areaswerehighlightedtoperform
EDStesting.
4.Energy-dispersivex-rayspectroscopywasperformedonthe
areaofinterestandtheoutputcountswerecomparedagainst
theeZAFstandardlessmodelalgorithmforpeakidentiÞcation
intheTEAMsoftware.
5.Testingwasrepeatedthreetimesondifferentregionsofthe
samesampletoensurearepresentativeresult.
54ElementK
&1K&2K"1L&1L&2L"1L"2L!1M&18O0.524912Mg1.253601.253601.3022
13Al1.486701.486271.55745
58Ce34.719734.278939.2573
4.84024.82305.26225.61346.0520.883
71Lu54.069852.965061.283
7.65557.60498.70909.048910.1434
1.581373Ta57.53256.27765.22381.461
8.08799.34319.651810.89521.710
74W59.3182457.981767.2443
8.39768.33529.672359.961511.28591.7754
77Ir64.895663.286773.56089.17519.099510.708310.920312.51261.9799
Table
7:Photonenergies(keV),ofprincipalK-,L-,andM-shellemissionlines.Boldvaluesarewithinourdetectorrange.[
35]ElementK1sL
12sL
22p1/2
L32p3/2
M23sM
23p1/2
M33p3/2
M43d3/2
M53d5/2
N14sN
24p1/2
N34p3/2
8O543.141.6
12Mg1303.088.749.7849.50
13Al1559.6117.872.9572.55
58Ce40443654961645723143612741187902.4883.8291.0223.2206.5
71Lu633141087010349924424912264202416391589506.8412.4359.2
73Ta674161168211136988127082469219417931735563.4463.4359.2
74W6952512100115441020728202575228118721809594.1490.4423.6
77Ir7611113419128241121531742909255121162040691.1577.8495.8
ElementN
44d3/2
N54d5/2
N64f5/2
N74f7/2
O15sO
25p1/2
O35p3/2
O45d3/2
O55d5/2
P16sP
26p1/2
P36p3/2
58Ce109Ð0.10.137.819.817.0
71Lu206.1196.38.97.557.333.626.7
73Ta237.9226.423.521.669.742.232.7
74W255.9243.533.631.475.645.336.8
77Ir311.9296.363.860.895.263.048.0
Table
8:Electronbindingenergies,inelectronvolts,ofselectedelements.[
35]555555ResultsandDiscussion
ThissectionoutlinesthegrowthresultsofboththeCe:LuAGand
MgTa
2O6compounds.TheMgTa
2O6growthcompositionwas
conÞrmedthroughmultiplex-raypowderdiffractiontests.Both
compoundsweretestedusingx-rayluminescencetodetermine
theiremissionspectraandpotentialasascintillator.Samples
ofbothcompoundswerethenmounted,polishedandcoated
inpreparationforscanningelectronmicroscopyandenergy-
dispersivex-rayspectroscopyanalysis.Theseresultsareshown
anddiscussed.
CrystalResults:Ce:LuAG
GroupSampleLength(mm)
11460.3B51460.7M51460.10E521468.3B51468.7M531482.3E51482.10B51482.7M10
Table
9:AdditionalCe:LuAGsamples
sentfromLBNLfortesting.
ThegrowthresultsoftheCe:LuAGcrystalsaresummarized
individuallyinthissectionalongwithdetailsandadditional
observations.ResultsaresummarizedinTable
10.Experiments
1-4werecompletedonasamplethatwasinitially
10gramswhile
experiments5-7werecompletedonasamplethatwas
5grams.Experimentsproceededsequentiallywiththelastexperiment
havingthesmalleststartingmelt.Thissteadyreductioninhead
pressurerequiredslightlydifferentadjustmentsfromexperiment
toexperiment.
ExperimentSampleTypeSample/TrialResultLength(mm)
1HP1/1+252HP1/2+1003HP1/3+134HP1/4+1025MP2/1-Ð6MP2/2-Ð7MP2/3+23Table
10:Resultssummaryfor
Ce:LuAGµ-PDgrowths.Sample
typeisthemethodofpreparation
whichwaseitherhydraulically-pressed
(HP)ormanually-pressed(MP).
AdditionalsampleswerealsoreceivedfromLBNLforfurther
testing.ThesesamplesarelistedinTable
9.Theamountofdopant
inthesesampleswaslessthan
0.5mol%,whichislessthanhalf
oftheceriumcontentastheexperimentallygrownsamples.The
mostobviousdiscrepancy,outsideofthequality,istherelatively
palercoloryellowcomparedtotheintenseyellowoftheexperi-
mentallygrowncrystals.Allofthe
5mmcrystalssentfromLBNL
areshowninFigure
75alongwiththeirinternallydesignated
samplenumbers.
56Figure
75:Compositeimageofthe
5mmCe:LuAGsamplessentfromLBNL
forfurthertesting.
PressedPowder:Sample
1,Trial
1A25mmlongCe:LuAGcrystalwassuccessfullygrownand
pulled-downatarateof
0.60mmmin.Duringthiscrystalgrowththe
crystalseparatedatapositionoutsideoftheviewingarea,ending
theexperiment.Oncethesystemwasventeditwasdiscovered
thatthecrystalhadseparatedapproximately
2-3mmfromthe
bottomofthecrucibleasshowninFigure
76withthemajorityof
thecrystalstillattachedtotheLu
3Al5O12seed.Figure
76:PositionofCe:LuAGcrystal
separationthatoccurredjustoutofthe
viewingwindowofthe
µ-PDchamber
(Sample1,Trial
1).Thecrystalwasremovedbyhandfromtheseedandisshown
inFigure
77.Asmallportionofthecrystalattachedtothecrucible
wasrecoveredwiththeremainingcrystalremovedwithgrinding
paper.
Thecrystalremovedfromtheseedmeasuresapproximately
25mm.Smallvariationsindiameterwereobservedalongthegrowth
axis.Thepulsesofmaterialcouldbearesultofsystemvibration
orinconsistencyinthemeltitselfthateffectedtheßowofthe
compoundthroughthethincapillarychannelofthecrucible.
Figure
77:A25mmlongCe:LuAG
crystalwithanapproximatediameterof
1mm(Sample
1,Trial
1).Vibrationsarehypothesizedtobetheprimarysourcebecause
theycouldbefeltsubtlyalongtheweldmentofthe
µ-PDchamber
baseandtherewasaslightvibrationofthecamerapositionwhich
wasmountedtothechamberlid.
Themeltstillcontainedwithinthecruciblewasalsoinspected
andisshowninFigure
78.Alargecrystalhadformedinthe
crucibleandshowsevidenceofhomogeneousmixing.Fromthis
weareabletoconcludethatourexperimentaltemperaturewas
appropriateforthecompound.Theyellow/greenappearancewas
57dramaticallydifferentfromthewhitepowderstheexperiment
startedwith.Asmallportionofiridiumalsoappearedtohave
precipitatedontothesurfaceofthemelt.
PressedPowder:Sample
1,Trial
2A100mmlongCe:LuAGcrystalwasgrownatarateof
0.5mmminandisshownstillattachedtotheseedinFigure
80.Discrepancies
ofthecrystaldiametercanbeobserved,similartothoseobserved
inTrial
1.Theseundulationsappeartocomeinatnearlyregular
intervals,smoothingoutbetweeneachpulseofcrystal.
Figure
78:RemainingCe:LuAGmelt
containedinthecrucible(Sample
1,Trial
1).Figure
79:SmoothmoltenCe:LuAG
withincrucibleremainingaftercrystal
growth(Sample
1,Trial
2).TheCe:LuAGcrystalwasinitiatedonthesameportionofthe
Lu3Al5O12seedasTrial
1.ThetopportionoftheCe:LuAGcrystal
separatedfromthecrucibleduringcool-down,makingremoval
easier.
Temperaturewasheldsteadyfortheentiretyofthegrowthwith
theexceptionoftheveryendsoanyvariabilityalongitslengthis
mostlikelynotduetodifferencesintemperature.
TheleftovermeltisshowninFigure
79.TheCe:LuAGcrystal
formedwithinthecrucibleissmootherthanafterTrail
1andappearstobehomogeneouslymixed.
Figure
80:A100mmlongCe:LuAG
crystalwithanapproximatediameterof
1mm(Sample
1,Trial
2).58PressedPowder:Sample
1,Trial
3A13mmlongCe:LuAGcrystalwasgrownatarateof
0.1mmminandisshownstillattachedtotheseedinFigure
81.Themost
signiÞcantprocesschangewasareductioninpull-downratefrom
0.5-0.6mmminofpreviousgrowths.
Itisimmediatelyapparentthatthediameteroftheslower
drawncrystalislargerandmoreconsistent.Anotherfactorthat
mayhaveattributedtothisdiscrepancyingrowthwasaslight
increaseintemperaturefrom
2068¡C(SP:48)to
2083¡C(SP:50).Figure
81:A13mmlongCe:LuAG
crystalwithanapproximatediameterof
1mm(Sample
1,Trial
3).Vibrationsintheapparatuswerealsoobserved.Thiswasevi-
dentintheslightmovementoftheseedandseedrodduringthe
µ-PDexperiment.Oncetheexperimentwascompletedtheseed
holdercollarthatclampstheseedrodintoplacewascleanedthor-
oughly.Thiscleaning,however,wasonlyslightlybeneÞcialasthe
clampingresistancewasstillinsufÞcientatpreventingrotationof
therodintheholder.
PressedPowder:Sample
1,Trial
4Figure
82:TheCe:LuAGcruciblemelt
aftercrystalgrowth,contaminationis
observedonthetopsurfacefromthe
iridiumcrucible(Sample
1,Trial
4).A102mmlongCe:LuAGcrystalwasgrownatarateof
0.1mmmin.Wewerenotabletoexhaustthemeltsupply.Itwasalsoobserved
thatthemeltwascontaminatedwithwhatappearstobeiridium
thatprecipitatedfromthecruciblewalls.Themeltheightonly
decreasedbyapproximately
1mmsoitisassumedthatthemelt
withinthecruciblecontainsbubbleorispossiblyhollow.Theleft
overmeltisshownin
82.Itwasalsoobservedthatthepreviouslystainedquartzholder
wasnowcleanafterapproximately
16.5hoursattemperatures
greaterthan
2000¡C.Thisprolongedexperimentalongwiththe
previousonesconductedwiththismeltandcruciblecausedthe
iridiumtocontaminatethemeltinsigniÞcantquantities.Forthis
reasonthiscruciblewasabandonedforfuturegrowths.Itwas
cycledagainathighertemperaturesupside-downinaneffortto
removethecrystalpriortochemicalcleaning.
PressedPowder:Sample
2,Trial
1Figure
83:CrystallizedCe:LuAGmelt
withinthecrucibleaftergrowthattempt
(Sample2,Trial
1).Thiscrystalattemptwasconductedonanewcruciblewithalarger
capillarychannel,measuring
3mmODatthenozzlewiththe
capillarychannelmeasuring
1.5mm.Thiscrystalhadamuch
moredifÞculttimeseedingwiththelargernozzle,likelydueto
thetemperaturegradientacrosstheincreaseddiameterofthe
attemptedgrowth.Thecrystalwasmomentarilygrownataslower
pull-downrateof
4mmhrbeforetheliquidmeltpulledtheseedrod
outoftheholder.
OncecooledbacktoRTtheseedwassuccessfullyseparated
fromthecrucible.Theseedhadinitiatedatamuchlargerdiameter
59thanthepreviousgrowths.Themelthadcrystallizedwithinthe
crucibleasshowninFigure
83.Thenewiridiumcruciblewasalso
slightlydeformedaftertheexperiment.
PressedPowder:Sample
2,Trial
3A23mmCe:LuAGcrystalwassuccessfullygrownatarateof
0.1mmminandisshowninFigure
85.Thesecondexperimentconducted
onthissamplewasunsuccessfulduetothebottomofthemelt
solidifyingpriortoinitiatingtheseed.Thisthirdattemptwasthe
ÞrstsuccessfulCe:LuAGcrystalgrowthwiththelargerdiameter
capillarychannel.Thelargersizehadpresentedchallengesbe-
causethetemperaturegradientacrossthethicksamplewasmore
difÞculttocontrol,leavinglesstimetoseedandagreaterriskto
separatefromthemeltprematurely.
Figure
84:InitializationoftheCe:LuAG
crystalattherightwithcontamination
appearingasdarkdiscolorationalong
thecrystalexterior(Sample
2,Trial
3).Crystaldiscolorationwasobservedinallbutneartheinitial
seedingsurface.Thisdiscolorationisnotpresentintheothersam-
plesandisconsideredtobecontaminationintroducedsomewhere
inprocess.ThiscontaminationishighlightedinFigure
84.Itis
hypothesizedthatthecontaminationoccurredduringthemanual
pressingofthesampleandthatthedarkdiscolorationisdueto
carboninclusionthatwascompactedintothesampleunderthe
highpressureofthepress.
Duetothehightemperaturesandtherepeatedcyclingon
theafter-heaterandcrucible,thetwocomponentsweredifÞcult
toseparateaftertheexperiment.Thiswaslargelyduetothe
deformationinducedbythehightemperatureswheretheiridium
wasnotabletoproperlymaintainitsgeometry.Thecrucibleand
after-heaterwereseparatedbutbrokesuddenlyapartwiththe
after-heaterstrikingthecrystalstillattachedtothebottomofthe
crucible.Thecrystalbrokebuttheotherportionofcrystalwas
recoveredandisshowninFigure
85.Futurecrystalgrowthswiththislargerdiametercapillary
channelwillneedtobecontrolledcarefully.Thetemperatureof
thechamberwasalsohigherforthiscrystalwhencomparedtothe
smallerdiametercrystalsgrown.
Thetemperaturehadtobeincreasedfurtheroncethecrystal
begantogrowbecausethediameterwassteadilydecreasing.The
compensationseemedtostabilizethegrowthasobservationsfrom
theÞnishedcrystalshowaveryconsistentdiameterthereafter.
WhiledifÞculttogrow,thesecrystalsmaybeaboveacriticaldi-
ameterwheretheyareabletoremainunaffectedbythevibrations
duetotheiradditionalmass.
60Figure
85:Ce:LuAGcrystalgrowthwas
approximately
23mminlengthand
wasbrokenduringafter-heaterremoval
(Sample2,Trial
3).61Ce:LuAGCrystalDiscussion
ThelengthsandweightsofeachCe:LuAGcrystalgrowthfrom
Sample1arecomparedinTable
11.CrystalPull-downRate(
mmmin)Length(mm)Weight(mg)Ratio
Trial
10.602531
.40.80Trial
20.50100114
.10.88Trial
30.101337
.70.34Trial
40.10102330
.00.31Table
11:Ce:LuAGSample
1crystal
comparisonwithlength-to-weightratio.
Figure
86:The
100mmlongCe:LuAG
crystalpulledatarateof
0.5mmmin(Sample1,Trial
2)comparedtothe
shorterCe:LuAGcrystalgrownatarate
of0.1mmmin(Sample1,Trial
3).Allfourofthesesamplesweredrawnfromthesamemeltand
crucible/after-heaterpair.Whileheadpressureofremainingmelt
undoubtedlyplayedaroleinhoweasilythemeltisseeded,the
pull-downratewasfoundtobethemostinßuentialparameter
toadjusttoimprovecrystalquality.Whilethesamplehadbeen
hydraulicallypressedpriortothegrowthsthesamplecouldhave
beneÞtedfrompossiblesinteringathighertemperaturebelowthe
meltingtemperature.Thistypeofsinteringhasbeenoutlinedin
previousstudies.
4040B.C.Grabmaier,W.Rossner,and
J.Leppert.Ceramicscintillatorsforx-ray
computedtomography.
PhysicaStatus
Solidi(a)
,130(2):K183ÐK187,April
1992ThediscrepancyinrelativethicknessisevidentinFigure
86.ThetwoCe:LuAGcrystalsintheimageweregrownback-to-back
undersimilartemperatures.TheshorterCe:LuAGcrystalhas
asigniÞcantlylargerdiameterandismoreconsistentwithits
diameterthanthelonger,thinnerCe:LuAGcrystal.
ThelongestCe:LuAGcrystalsgrownatfastandslowpull-
downratesarecomparedinFigure
87.Theslowerpull-downrate
grewalargerdiametercrystalthatwasrelativelyconsistentwhen
comparedtothefastergrowncrystal.Theslowpull-downrate
crystalfromTrial
4displayedwhatappearedtobeabubbleafter
approximately
75mmofgrowth.Bubblesaretypicallyrarein
µ-PDexperimentsbecausetheytendtorisetothetopofthemelt.
ThiswastheÞrstexampleofabubbleinanyofourgrowthsand
theywerenotseeninourlargerdiametergrowswithSample
2usingthelargercruciblenozzlediameter.
62Figure
87:A103mmlongCe:LuAG
crystalgrownat
0.1mmmin(Sample1,Trial
4)comparedtoa
100mmlong
Ce:LuAGcrystalgrownat
0.5mmmin(Sample1,Trial
2).CrystalResults:MgTa
2O6ThegrowthresultsoftheMgTa
2O6crystalsaresummarized
individuallyinthissectionalongwithdetailsandadditional
observations.ResultsaresummarizedinTable
12.ExperimentSampleTypeSample/TrialInitialSizeLength(mm)
1NP1/Ð5gÐ2NP1/1Ð3NP1/2Ð4NP1/315
ÐMP
2/Ð&5gÐ5MP3/15gÐ6MP3/2Ð7MP3/3328MP4/110g89MP4/2Ð10MP4/31211MP4/413612MP4/547Table
12:Resultssummaryfor
MgTa
2O6µ-PDgrowths.Sample
typeisthemethodofpreparation
whichwaseithernon-pressed(NP)or
manually-pressed(MP).
NoexperimentswereconductedwithSample
2becauseof
concernsoverexcessivesamplelosswhilemanuallypressingthe
sample.Sample
3wasmadeshortlyafterandthepowderproce-
durewasadjustedtopreventexcessivesamplelossagain.This
sampleretainedmuchofitsmassandwasusedinsubsequent
µ-PDexperiments.Trial
LoosePowder:MeltCheck
AmeltcheckwasperformedontheMgTa
2O6compoundbefore
attemptingany
µ-PDexperiments.Thischeckwastoensurethat
thecompoundwasrelativelycompatiblewiththeiridiumcrucible.
Figure
88:Topofcrucible,melttestfor
MgTa
2O6(Sample1).Thiscompatibilityiscriticalatthecapillarychannelleading
downtothecruciblenozzle.IfthemeltresiststheiridiumsufÞ-
cientlyitwillnottraveldownthechannel,ifthechannelistoo
wideweriskedfreeßowofthemeltfromthecrucibleonceit
liqueÞes.63FromthemeltcheckwewereabletoconÞrmthatthemelt
ßoweddownthecapillarychannelandemergedfromthenozzle
whereitwasheldinplaceforaperiodoftimewithoutinteraction
fromtheseed.OncethemeltcompoundwasconÞrmedtobesta-
bleinthispositionthechamberwascooledtoRT.Afterthecheck
wascompletetheremainingmeltinthecruciblewasinspected
andisshowninFigure
88.Thepowdersampleusedwasuncom-
pressedandthetopofthemeltwithinthecrucibleappearedto
benotcompletelymeltedandappearedorange-brownincolor.
Themeltthathademergedfromthecruciblenozzleslightlywas
whiteandsmoothinappearance.Thischangeincolorimpliesa
signiÞcanttemperaturegradientacrossthesampleandwillbe
monitoredinfuturegrowthattempts.
LoosePowder:Sample
1,Trial
1Figure
89:Semi-smoothmolten
MgTa
2O6withincrucibleafterthe
µ-PDexperiment(Sample
1,Trial
1).ThisÞrst
µ-PDexperimentfailedduetoamisalignmentbetween
theseedandthecruciblenozzle.Despitethelackofgrowthat-
temptseveralobservationsweremadepost-experiment.
Afterthe
µ-PDexperimentwasperformeditwasobservedthat
thequartzpedestalhadabluediscoloration.Thiswasbelievedto
befromthenotcompletelydriedaluminaadhesivethatwasused
toconstructtheseedrod.ThisdiscolorationisshowninFigure
90.Anotherpossiblesourceofthisdiscolorationcouldhavebeen
fromtheMgOevaporatingoffofthemeltandfallingasprecipitate
ontothequartztube.Thisphenomenahasbeenobservedin
similarµ-PDexperimentswhenmagnesiaceramicsareused
insteadofalumina.
41Thealuminapasteseemsmorelikelyas
41T.FukudaandV.I.Chani.
ShapedCrystals:GrowthbyMicro-Pulling-Down
Technique
.Springer-Verlag,Þrstedition,
2007themeltingtemperatureofMgOissigniÞcantlyhigherthanour
desiredcompoundandtheconstitutivecompound.
Themeltleftinsidethecrucibleafterthe
µ-PDexperimentwas
inspected.Nosinglecrystalsformedinthemeltandthemelt
appearedtotaketwodifferentcolors,itschalkywhiteappearance
wassimilartothatofthepowderenteringthechamberandthe
orangeportionsofthesampleseemedtohavechangedcolordue
toexcessiveheat.itdidshowimprovementsoverthestillpowdery
surfaceofthemeltafterthemeltcheck.
Figure
90:Bluediscolorationonquartz
pedestalafterseedattempt(Sample
1,Trial
1).LoosePowder:Sample
1,Trial
2Thissecond
µ-PDexperimentwasproperlyalignedbutdidnot
produceanygrowth.ThemelthaddifÞcultyinteractingwiththe
seedandwouldnotattachtoinitiategrowth.
Aftertheexperimentitwasobservedthattheentiretyofthe
compoundhadbeenmoreuniformlyheatedandappearedmolten
asshowninFigure
91.Theseedwasremovedandsandedwith
600/P1200gritgrind-
64ingpapertocreateamoreuniformtip,howeverthegrooveinthe
middleoftheseedwasdeepandwasonlypartiallycompensated.
Thiswasdoneinanefforttoimprovetheinteractionsbetweenthe
emergingmeltandseedsurface.
Figure
91:SmoothmoltenMgTa
2O6meltwithincrucible(Sample
1,Trial
2).Thecruciblewasalsosandedwith
600/P1200gritgrinding
papersothatallexcesscompounddirectlyoutsideofthecapillary
channelwasremoved.Thecruciblenozzlewassandedsuchthat
theiridiumcircumferencewasvisible.Someofthemeltwasalso
removedfromtheoutsideofthecapillarychannel.
LoosePowder:Sample
1,Trial
3Figure
92:LoweredMgTa
2O6crystal
withintestchamber,belowinduction
coil(Sample
1,Trial
3).ThisattemptmarkedtheÞrstsuccessfulgrowthofMgTa
2O6.The
MgTa
2O6crystalwithinthe
µ-PDchamberisshowninFigure
92.Thetemperaturegradientislargelyresponsibleforthecolor
gradient.Acriticalscintillatorpropertyistransparencyandwhile
themajorityofthisgrowthrangedincolorfromdarkbrownto
lightorangetheveryendofthegrowthwaswhiteandslightly
transparent.Itwasthegoalofsubsequent
µ-PDexperimentsto
reproducethetransparentwhiteportionofthecrystal.
ThisgrowthmarkedthethirdandÞnaltestfromtheÞvegram,
powdersample.Thissamplewasnotpressedandwasplaced
withinthecrucibleinitspowderedform.Thepreviousgrowth
attemptswiththissamplefailedtoseed.
Thecrystalwassuccessfullyremovedfromtheapparatusand
isshowninFigure
94.Thisportionofthegrowthwasthefocusof
furthertestingasitpossessedamoreuniformandorderedgrowth
whencomparedtootherexperimentstofollow.
Theinitialdischargeofthemeltfreeßowedfromthecapillary
channelandwasofadarkercolorwhichcorrelatedtothehigher
experimentaltemperatures.Thislargemassfreeßowedfromthe
crucibleatatemperatureof
1972¡C(SP:36.8).Thetemperatureof
thechamberwasreducedandthecolorlightenedtowhite.This
yellow-browncolorwasalsoobservedonthemeltsurfacethatwas
stillwithinthecrucibleaftertheexperiment.
Figure
93:TheMgTa
2O6meltwithin
crucibleafterthe
µ-PDexperiment
(Sample1,Trial
3).Whilesomesampleremainedwithinthecruciblenofurther
testingwascompletedusingthissample.Intheinterestoftime
anothersamplewaspreparedthatwaspelletpressedwiththe
thoughtthatthiswouldimprovethebondsinthepowderpriorto
µ-PD,leadingtoamoreorganizedandimprovedgrowthwhen
comparedtothesetrialsofsimplyexperimentingwithloose
powder.
65Figure
94:MgTa
2O6crystalgrowth
(Sample1,Trial
3).PressedPowder:Sample
3,Trial
3Sample2wasnotusedfor
µ-PDexperimentsduetoasigniÞcant
lossofcompoundduringthemanuallypressprocess.Forthis
reason
µ-PDbeganagainwithSample
3.Trial
1and2withthis
samplecontinuedtohavethecompatibilityissueswehaveseen
previouslybetweentheseedandtheemergingmelt.Trial
3withthissampledidproduceagrowththatwaslargelyuncontrolled
butcouldbeusedasaseedinsubsequent
µ-PDexperiments.
Figure
95:MgTa
2O6dischargeattached
totheseedrod,avoidingcontactwith
theseed(Sample
3,Trial
3).TheMgTa
2O6growthisshowninFigure
95.Thisdischargewas
largelyunorganizedandfreeßowedfromthecapillarychannel.
Thisgrowth,aswiththelast,didnotseedeasilywiththeiridium
seed.Instead,themeltavoidedcontactandgrewarounditafter
solidiÞcationinitiatedontheceramicseedrodbelow.BothTrial
1and2withthissamplefailedtoseedandthiswastheÞrst
actionablegrowthachievedfromthissample.
Figure
96:Compounddepositon
surroundingceramicinsulatorandlid
(Sample3,Trial
3).Thisfreeßowalsoexhaustedthemeltandwasthereforethe
lasttrialwiththissample.Sincethegrowthwasnotorderlyand
arrangedstoichiometricallyitisnotbeingcharacterizedasa
singlecrystal,alsolackingtheanticipatedtransparencythatwas
visibleslightlyattheendofour
µ-PDexperimentonSample
1,Trail
3.Itwasalsoobservedthattheceramicinsulatorandlid
weredarkenedaftertheexperiment,implyingthatoneofthe
66compoundsmayhaveevaporatedoffduringthegrowthattempt.
Withthesampleexhaustedthereisnoconcernofthiseffectingthe
qualityofsubsequentcrystalgrowths.
Thecrucibleandafter-heaterweresubjectedto
2hoursatexper-
imentaltemperaturesinanefforttocleanthepairofanyresidual
compound.Theseblackenedceramicswerealsoaddedwith
thelidslightlyaskewwiththehopethatthecompoundwould
burnoffsimilartowhatwesawwiththebluediscolorationof
thequartztube.Thiseffortdidnotyieldanappreciableimprove-
mentandnewceramicinsulatorswereusedinsubsequent
µ-PDexperimentsasaprecaution.
PressedPowder:Sample
4,Trial
1Anewtengrampressedpowdersamplewaspreparedandused
fortheÞrsttimeinthis
µ-PDexperiment.Anewseedhadbeen
constructedfromthepreviousgrowthanddramaticallyimproved
compatibilityoveritsiridiumcounterpartusedpreviously.
Figure
97:TheMgTa
2O6meltwithin
crucibleafterthe
µ-PDexperiment
(Sample4,Trial
1).ThelargersampleandthefactthatitwasdensiÞedpriortothe
experimentseemedtomakegrowtheasierthanpreviousattempts.
Theremainingmeltinthecruciblewaswhiteatthecenterand
discoloredyellowalongtheperimeterasshowninFigure
97.This
appearancewasdifferentfromthedarkerdiscolorationwehad
observedwiththeloosepowdersample.
AnotherimprovementwasusingMgTa
2O6astheseedmaterial
ratherthanpureiridium.Theonlygrowththatwascompleted
withtheiridiumseedwasfreeßowthatfortunatelyenoughat-
tacheditselftotheseedrodandZirconiaadhesive.Thisgrowth
markedtheÞrstthatseededcorrectlytotheseedandproceeded
toformonthatsurfacelargelyduetothisimprovedcompatibility.
ThegrowthisshowninFigure
98.The8mmlonggrowthdidnotappeartobeoverheatedand
wasevenlywhitethroughout,however,thegrowthformationwas
ratherunorganizedandrequiredrestartatseveralpointswhere
thediameterofthecrystalreduceduntilseparationoccurred.The
temperaturehadbeenincreasedtocompensatebutthisriskedfree
ßowofthecompoundfromthecapillarychannel.
Toavoidthis,webegantoholdtheseedagainstthecrucible
nozzleandletthetwoacclimateforanextendedperiodoftime
beforetheseedwasbroughtdown.Thisallowedustoincrease
thetemperaturefurtherandensurethatthecapillarychannelwas
Þlledwithcompoundpriortopull-down.Adrawbackofthiswas
thatthesurfaceoftheseedwasvisiblymeltingattimes,beingthe
samematerial,itwassubjecttothesametemperatures.
Anothersourceofthediameterßuctuationswasthevibrations
fromthesystem.Thiscompoundwasmuchmoreßuidthanthe
Ce:LuAGcrystalstestedsotheimpactonthesolidifyingcrystal
67wasmostlikelymoresigniÞcant.Thiscoupledwithtemperature
adjustmentswhilethecrystalwasgrowingcompoundedmore
diametervariability.
Figure
98:The
8mmMgTa
2O6growth
attachedtothenewlyconstructed
MgTa
2O6seed(Sample
4,Trial
1).PressedPowder:Sample
4,Trial
3Thisattemptmarkedthethird
µ-PDexperimentonthissample.
Trial
1,hadproducedasmallgrowthmeasuringapproximately
8mmandTrial
2hadseededataverysmalldiameterandquickly
expanded.Whenthegrowthrequiredreseedingthemeltpulled
thesmallalreadyformedgrowthfromtheseed.Duetothelow
temperatureoftheundersideofthisgrowthreseedingfailed.
Onthisattemptaslightlylargergrowthwasachievedandis
showninFigure
100.Thisgrowthmeasuredapproximately
12mm,slightlylongerthantheÞrstgrowth.Thisgrowthexperienced
momentsoffreeßowfromthecruciblenozzlethatcoatedthe
seedandseedrod.Thesefreeßoweventswerecorrectedwith
reductionintemperatures.
Figure
99:TheMgTa
2O6meltinsidethe
crucible(Sample
4,Trial
3).Temperatureadjustmentwerealsoneededwhilegrowthwasin
progressandtheresultinggrowthshowsthesamevariablediam-
eterthatTrial
1displayed.Thetemperatureswerenearlyidentical
withmanyofthesameproblemscontributingtovariabilityinboth
experiments.Pull-downrateswerekeptrelativelyslowat
0.10mmmin,adjust-
mentfromthisvalueineitherdirectionwasmetwithdifÞculty.
Iftherateofpull-downwasslowedfurtherthegrowthwould
solidifyafterashorterandshorterdistancebelowthecrucible
nozzleresultingineventualterminationofthegrowth.Iftherate
wasincreased,theseedwouldoutpacetheemergingmelt,the
meniscuswouldbeextendedandwouldeventuallyseparate.Due
toprocesssensitivityanyadjustmentinpull-downrateneeded
tobecoupledwithanadjustmentintemperaturetomaintainan
appropriatelylargemeniscus.
Figure
100:The
12mmMgTa
2O6growthattachedtothenewlycon-
structedMgTa
2O6seed(Sample
4,Trial
3).ThemeltremaininginthecrucibleisshowninFigure
99.The
appearanceissimilartothatofTrial
1withtheinteriorthewhite
coloroftheoriginalpowdersandtheperimeterdiscoloredyellow.
Twospotsinthemeltwereadarkerorangeandmayhavebeen
precipitatedcontaminationfromtheexperimentalapparatus.
PressedPowder:Sample
4,Trial
4Thisµ-PDexperimentproducedthelongestsinglegrowthofany
experiment,measuring
136mm.Thegrowthinitsentiretyis
showninFigure
101priortoremoval.Thisgrowthhadbeenleftto
runovernightatapull-downrateof
0.50mmmin.Severalpointsalongthegrowthlengthwereextremelysmall
andthegrowthwasbrokenuppriortoremovingitfromthe
68chamberasitwasunlikelythegrowthcouldtolerateanyhandling
initsfullform.Despitethiscontrolledbreakup,anotherportion
ofthegrowthbrokefreeandfracturedintoseveralpieces.These
pieceswerecollectedandareshowninFigure
102.Figure
101:The
136mmMgTa
2O6growthattachedtotheseedstillinthe
µ-PDchamber(Sample
4,Trial
4).Thisexperimentmarkedanimportantstepforwardinthe
process.Amajorityofthegrowthgrewunsupervisedandcon-
sequentlygrewwithoutparameteradjustment.This
µ-PDexper-
imentdifferedfrompreviousattemptsbyrunningatahigher
temperatureandahigherpulldownrate.Themajorityofthis
growthexperimentwasrunatatemperatureof
1954¡C(SP:35)wheretheotherexperimentswererunatamaximumtemperature
of1911¡C(SP:31).Thisincreaseintemperatureneededtobecou-
pledwithanincreaseinpull-downrate.Thepull-downratewas
increasedto
0.50mmminwhilepreviousattemptsusedarateof
0.10mmmin.Thegrowthexperienceddiameterßuctuationssimilartopre-
viousgrowthattemptsdespitetheparameteradjustments.This
lendsmoreevidencetothe
µ-PDchamberexperiencingvibra-
tionissuesthathavebeenseeninbothMgTa
2O6andCe:LuAG
experiments.Priorgrowthshadrequiredseveraltemperatureadjustments
duringthegrowingprocessmakingitdifÞculttodeterminewhat
eventswerecausingthechangesindiameterandincolor.For
thisgrowththetemperaturewaskeptconstantandthisisevident
bythemoreuniformcolorofthegrowth.Therewasagradient
acrossthediameterofthegrowthwherepartsofthegrowthhad
brokethecolorappearedwhiterontheinterior.Thisimpliesa
temperaturegradientacrossthediameterofthegrowthwherethe
exteriortemperaturesofthegrowthwerehotterthantheinterior.
Whilethismakesintuitivesenseitisaconcernattheapparent
severityofthisgradient,implyingthatgrowthofthiscompound
couldremaindifÞcultwiththecurrentcapillarychanneldiameter,
whichisalreadysmall(>
1mm).69Figure
102:BrokenupMgTa
2O6growth,measuring
136mmtotal
(Sample4,Trial
4).70PressedPowder:Sample
4,Trial
5Thisµ-PDexperimentproducedagrowthof
47mm.Thegrowth
initsentiretyisshowninFigure
105.Likethepreviousattempt
thechambertemperaturewasincreasedto
1954¡C(SP:35)andthe
pull-downratewassetto
0.50mmmin.Oneimportantexperimental
differencewasthatthesetwoexperimentswereconductedfrom
thesamesample.Thisgrowthhadtheleastamountofhead
pressureofanyoftheexperimentsonthissampleforthatreason.
ThegrowthismeasuredandshowningreaterdetailinFigure
105.Figure
103:MgTa
2O6meltwithinthe
crucible,suspectedcontaminationfrom
theiridiumcrucible(Sample
4,Trial
5).Figure
104:Theexteriorofthecrucible
afterthe
µ-PDexperiment,grain
boundariesprominentafterhigh
temperaturecycling(Sample
4,Trial
5).Asimilargrowthstrategyofobstructingthecruciblenozzle
withtheseedwasemployedforthisexperiment.SomedifÞculty
wasencounteredwhenthemeltbegantowetseverelyonthe
exteriorofthecruciblenozzle,thiswasfollowedbyaperiodof
freeßowthatremovedthemeltfromtheexteriorofthenozzle
completelyandresultedinalargemassdepositingaroundand
overtheMgTa
2O6seed.Itwasonthisnewsurfacethatthegrowth
beganwhichprovidedalargesmoothsurfaceinwhichtoinitiate
growth.Aswiththepreviousgrowththebeginningwasnoticeably
largerindiameterbeforetaperingoff.Uponremovalthesample
appearednoticeablywhiterthanourpreviousgrowthatthis
temperatureandpull-downratewhichmaybeaproductofthe
slightlyundersizedaveragediameter.
ThemeltremaininginthecrucibleisshowninFigure
103.Here
itisobservedwhatappearstobeiridiumcontaminationfromthe
crucibleitselfwhichappearsassilverspotsonthetopsurfaceof
themelt.Thisalongwiththegenerallychangedappearanceofthe
crucibleexteriorimpliesthatthecruciblemayhavecontaminated
thecrystalformation.
Duetothenumerousexperimentalcyclesandextendedtimeat
elevatedtemperaturesthegrainstructureoftheiridiumcrucible
becamemorepronouncedandisshowninFigure
104.Inaddition
tothegrainstructureobservationsonecanalsoobservethewet-
tingpropertiesoftheMgTa
2O6compoundontheexteriorofthe
crucible,wherethemelthastraveledupwardsalongthecrucible
exterior.Thisremainedevenafterthemajorityofthiswettedcom-
poundhadjoinedthegrowthoncethepull-downprogramwas
initiated.71Figure
105:BrokenupMgTa
2O6growth
(Sample4,Trial
5).72X-rayPowderDiffraction
MultipleMgTa
2O6sampleswerepreparedperiodicallyduring
testingtoensurethatwewereworkingwiththecorrectphase
ofthecompound.NoCe:LuAGsamplesweretestedusingthis
method,insteadXRLwasusedtocharacterizeandcomparethe
crystalstopublishedvalues.XRPDtestingwasperformedonthe
looseMgTa
2O6powder,afterthemeltcheck,andonsubsequent
growths.Theseresultsareoutlinedbelowandcomparedagainst
theMgTa
2O6standardpeaksprovidedbytheMatch!,aphase
identiÞcationprogramcreatedbyCrystalImpact.
MgTa
2O6:Sample
1,Powder
Inorderensurethatwewerestartingwiththecorrectcompound
asampleoftheloosepowderwastakentoperformXRPD.This
testwasdonepriortorunningthemeltcheckwiththesynthesized
compound.TheresultsofthistestareshowninFigure
106,against
thestandardMgTa
2O6samplepeaks.
Figure
106:Diffractionpatterntaken
fromtheMgTa
2O6powdersampleprior
torunningthemeltcheckcompared
againstthepeakstandard(Sample
1).Thesamplepeaksshowgoodcorrelationtothestandardand
wecanconcludethatourpowdersynthesiswassuccessful.The
resultsdidhaveasigniÞcantamountofnoiseforthelowervalues.
Aftersomeinvestigationitwasdeterminedthatthesamplesimply
usedadifferenttypeoftapetoadherethepowdertowhencom-
paredagainsttheNaClstandardusedtocalibratetheresulting
diffractionpattern.ThiswascorrectedinsubsequentXRPDtests.
MgTa
2O6:Sample
1,MeltCheck
Ameltcheckwasperformedtoensurethattheiridiumcrucible
andtheMgTa
2O6compoundwerecompatibleenoughtoproduce
conditionsinwhichacrystalcouldbeformed.Fromin-situobser-
vationswewereabletoconÞrmthiscapabilityasmeltemerged
fromtheendofthecruciblenozzle.Afterthetest,asampleofthe
73powderwastakenfromthecrucibleandtested.Theresultsofthis
testareshowninFigure
107.Figure
107:Diffractionpatterntaken
fromtheMgTa
2O6meltaftercomplet-
ingthemeltcheck,comparedagainst
thepeakstandard(Sample
1).Thecompoundhasgoodcorrelationtothestandardpeaksand
thenoisefromthelowervalueshasbeenreducedbyrunninga
moreappropriatecalibration.
MgTa
2O6:Sample
1,Trial
3TwosamplesweretakenandpulverizedforXRPDtestingonSam-
ple1,Trial
3.TheseregionsarehighlightedinFigure
108.Two
samplesweretakebecausethecolorofthemeltchangedsigniÞ-
cantlyasitsolidiÞedandthetemperaturegradientstabilizedtoa
lowertemperature.Thedarkbrownmass,labeledtheheadregion
becauseitwasÞrsttoexitthecrucible,wasofinterestbecause
ofitscolor.Weneededtoensurethatmultiplephasesdidnot
existinthesampleandthatwewerenotloosingaconstitutive
compoundathightemperature.Thesecondregion,labeledthetail
waslighterinappearanceandtransparentattheend.Thissample
wasnottakenfromtheorderedgrowthatthefarleftofFigure
108becausethiswouldbetestedlaterwithXRL.
TheseoutputproÞlesareshowninFigure
109andFigure
110.Oncephotographedthetwocomponentswereseparatedand
groundforx-raydiffractiontesting.
Figure
108:Highlightedregionsof
MgTa
2O6growthwhereXRPDsamples
weretaken(Sample
1,Trial
3).Eachofthesampleddiffractionmatchcloselywiththatofthe
standardsamplepattern.
MgTa
2O6:Sample
3,Trial
3AfterSample
3,Trial
3afreeßowgrowthofconsistwhiteappear-
ancewasformed.Thisdischargewaslargeenoughtoproducea
newseedoutofandaXRPDwastakenfromtheunusedportion
toconÞrmthattheseedusedinsubsequentexperimentswasin
factidenticaltothecompoundwewerewishingtogrow.This
wouldensurecompatibilitywiththemeltinfuturegrowths.
74Figure
109:Diffractionpatterntaken
fromtheMgTa
2O6headregioncom-
paredagainstthepeakstandard
(Sample1,Trial
3).Figure
110:Diffractionpatterntaken
fromtheMgTa
2O6tailregioncompared
againstthepeakstandard(Sample
1,Trial
3).Figure
111:Diffractionpatternstaken
fromtheMgTa
2O6growthusedfor
asaseedcomparedagainstthepeak
standard.(Sample
3,Trial
3).75TheseedshowedgoodcorrelationwiththestandardMgTa
2O6peaksandweconcludedthatwehadaseedmadeofthedesired
compound.WiththisconÞrmationwemovedforwardwithother
µ-PDexperiments.
X-rayLuminescence
X-rayluminescence(XRL)testingwasperformedonboththe
Ce:LuAGandMgTa
2O6growths.Thistestrequiredlargersample
sizestobebrokenupandstackedinglassvialssolikegrowths
werecombinedfortestingtheCe:LuAGsamples.TheMgTa
2O6growthswerealsocombinedinonecaseandthetailgrowth
highlightedinSample
1,Trial
3wastestedbyitself.
Ce:LuAG:Sample
1,Trial
1+2Figure
112:Ce:LuAGcrystalsprepared
forXRLtesting,Sample
1,Trial
3+4(top)andSample
1,Trial
1+2(bottom).ThesamplespreparedforXRLtestingareshowninFigure
112.Trial
1and2werecombinedbecausetheyweregrownatsim-
ilarpull-downratesof
0.6mmminand0.5mmminrespectively.These
twocrystalgrowthsweresigniÞcantlydifferentlengths,there
generalstructureanddiameterswerenearlyidentical.Forthis
reasonthesesampleswerecombinedtoperformx-raylumines-
cencetesting.Theresultingoutputspectrumisshownforthese
smallerdiametergrowthsinFigure
113.Thesevaluesforthepeak
emissionspectramatchpublishedvaluesforthiscompound.
4242T.Yanagida,Y.Fujimoto,Y.Yokota,
K.Kamada,S.Yanagida,A.Yoshikawa,
H.Yagi,andT.Yanagitani.Comparative
studyoftransparentceramicandsingle
crystalCedopedLuAGscintillators.
RadiationMeasurements
,46(12):1503Ð1505,2011Thepeakemissionofthiscombinedsamplewasat
547nm,well
intothevisiblerangeandwouldbegreen-yellowinappearance.
Thesegrowthswerealsocharacterizedbyrelativelyfastpull-down
ratesintherangeof
0.5-0.7mmmin.Itwasdeterminedthatthiswas
themostinßuentialfactorthatdeterminedoverallcrystalgrowth
diameter.Therelativelyfasterpull-downrateresultedinsmaller
diametercrystalswhencomparedtoaslowerpull-downrate.
Ce:LuAG:Sample
1,Trial
3+4DuetotherelativelysmallsizesandsimilarappearanceofTrial
3and4,thesesampleswerecombinedtoperformXRLtesting.
ThesetwocrystalsweregrowtosigniÞcantlydifferentlengthsbut
sharedsimilardiametersandappearanceduetotheiridentically
slowerpull-downratesof
0.1mmmin.Theresultingoutputspectrum
isshowninFigure
114.Thepeakemissionofthiscombinedsamplewasat
547nm,well
intothevisiblerangeandwouldbegreen-yellowinappearance.
Therelativeintensitiestakenfromeachtestgrouparecomparedin
Figure
115.76Figure
113:XRLintensityforthe
combinationofCe:LuAGcrystal
growthsfromSample
1,Trial
1+2.77Figure
114:XRLintensityforthe
combinationofCe:LuAGcrystal
growthsfromSample
1,Trial
3+4.78SourcePeakEmission(nm)
[38]520[56]500-550[65]520[71]510[73]530Trial
1+2547
Trial
3+4550
Table
13:Peakemissionvaluesfrom
publicationscomparedtotheexperi-
mentallygrownCe:LuAGcrystals.
Asexpectedtherelativeintensitypeaksaroundthesamewave-
length.Thethickerdiametersampleshadastrongerintensity
whencomparedtothethinnerdiameterssamples.Thismost
likelyhasmoretoduewiththelargercrystalvolumeusedinthe
testratherthanthedensityoftheindividualcrystalsbeingsig-
niÞcantlydifferent.Thepeakemissionvaluesfrombothsample
groupsarethencomparedtopublishedvaluesinTable
13.Publicationvalueseitherexplicitlystatedthedopant,Ce,con-
centrationat
1mol%oromittedtheconcentrationentirely.The
measuredvaluesareonthehighendofthespectrumforCe:LuAG
buttheyarewithintheexpectedvisiblerange.
Figure
115:XRLintensitycomparison
forthecombinationofCe:LuAGcrystal
growthsfromSample
1,Trial
1+2andSample1,Trial
3+4.79MgTa
2O6:Sample
1,Trial
3ThetailportionoftheMgTa
2O6growthfromSample
1,Trial
3was
analyzedbecauseofitsorderedappearanceandwasnotmixed
withanyotherXRLsamples.TheXRLresultsareshowninFigure
116.Figure
116:XRLintensityforthetail
portionoftheMgTa
2O6growth(Sample
1,Trial
3).Therelativeintensityvaluesfromthissampleareextremelylow.
Whilethereappearstobeanemissionpeakaround
850nmand
980nm,bothintheinfraredspectrum,theintensitycountsarenot
abovethelevelofbackgroundnoiseoftheapparatus.
MgTa
2O6:Sample
4,Trail
1+3FromSample
4,twotrialswerecombinedtotestinXRLbecause
oftheirsimilardisorderedappearance,pull-downrateand
µ-PDexperimentaltemperature.TheXRLresultsfromthistestare
showninFigure
117.Againtherelativeintensityvaluesfromthissampleareex-
tremelylow.Whilethereappearstobeanemissionpeakaround
850nmand
980nm,bothintheinfraredspectrum,theintensity
80Figure
117:XRLintensityforthe
combinationofMgTa
2O6growthsfrom
Sample1,Trial
1+3.81countsarenotabovethelevelofbackgroundnoiseoftheappara-
tus.WhiletheMgTa
2O6emissionresultsmaylookencouraging
withthererepeatableemissionpeakstheyarenothingabove
backgroundnoisewhencomparedtotherelativeintensityofthe
Ce:LuAGsamples.ThiscomparisonisshowninFigure
118.Figure
118:Four-waycomparisonof
XRLresults.TheMgTa
2O6testresults
arebarelydiscerniblealongthex-axis
whiletheCe:LuAGrelativeintensities
dominate.82ScanningElectronMicroscopy
Scanningelectronmicroscopy(SEM)wasperformedonfour
Ce:LuAGandasingleMgTa
2O6growth.Allofthesampleswith
theexceptionofLBNLSample
1468.7Mwerecoatedwithtung-
stenpriortoanalysisbecauseoftheinsulatingpropertiesofthe
growths.Thiscoatedgroundedthesamplesproperlyandallowed
imagingtooccuratgreatermagniÞcation.LBNLSample
1468.7MwasleftuncoatedtodeterminetherelativeeffectivenessofSEMon
aninsulatingsample.
Ce:LuAG:LBNLSample
1482.7MFigure
119:Ce:LuAGcrystal(LBNL
Sample1482.7M).AnewCe:LuAGsamplewithreducedceriumcontent(<
0.5mol%Ce)wassentfromLBNLforanalysis,measuring
10mminlength.
ThissamplewascoatedintungstenpriortoSEMtesting.
Figure
120:Ce:LuAGcrystal,MAG:
100x(Sample
1,Trial
2).Thiscrystal,priortocoating,wasnoticeablymoretransparent
thanthehigherceriumcontentcrystalsgrownexperimentallyin
thisstudy.Itsuniformtransparencyimpliedthatitwasasingle
crystal,SEManalysiswasconductedtoconÞrmthis.Imageswere
takenat
200,400,800,1600and2000xmagniÞcationat
20kVacceleratingvoltage.
Thecrystaldidnotpossessanygrainstructureatanyofthe
magniÞcationsorlocationsinvestigatedatthesamplesurface.
Thesurfacewascrackedseverelyinsomeregionsduetothe
highpressuremountingprocedure.AthighermagniÞcationsthe
surfaceremainedfeaturelessfromagrainboundaryperspective
asshowninFigure
121.AdditionalSEMimagesofthisCe:LuAG
crystalcanbefoundintheAppendix.
Ce:LuAG:Sample
1,Trial
2ThisCe:LuAGcrystalwasproducedfromthe
1mmODcrucible
nozzle.Itwasthesmallestsampleinvestigatedastherewere
concernsaboutperimeterdamagefromthemountingprocess.
Thisdamagewasevidentwhenthesamplewasexaminedunder
lowmagniÞcationasshowninFigure.Imagesweretakenat
100,200,400,600,800and1000xmagniÞcationat
20kVaccelerating
voltage.
Asmallßatsurfaceexistedontheleftsideofthecrystal.This
areawasinvestigatedforgrainboundariesbutnonewerefound.
AdditionalSEMimagesofthisCe:LuAGcrystalcanbefoundin
theAppendix.
83Figure
121:Ce:LuAGcrystalunder
secondaryelectrons(left)andback-
scatterdetection(right),MAG:
2000x(LBNLSample
1482.7M).Bothimages
arefeaturelessoutsideofsomedust
particles.84Ce:LuAG:Sample
2,Trial
3Figure
122:Ce:LuAGcrystal,MAG:
100x(Sample
2,Trial
3).ThisCe:LuAGcrystalwasproducedfromthe
3mmODcrucible
nozzle.ItwasalargerdiametersamplethantheCe:LuAGcrystal
analyzedinSample
1,Trial
2.Duetothelargerdiameterandmass
thiscrystalwasnotdamagedasseverelyinthemountingprocess
asshowninFigure
122.Imagesweretakenat
100,200,400,800,1600and2000xmagni-
Þcationat
20kVacceleratingvoltage.AdditionalSEMimagesof
thisCe:LuAGcrystalcanbefoundintheAppendix.
Ce:LuAG:LBNLSample
1468.7MThisCe:LuAGsamplewasleftuncoatedandtapedtotheplatform
withcarbontapesoitwouldnotbemovedwhenvacuumwas
appliedtothechamber.Thiswasdonetodetermineifdetailedim-
agescouldbeacquiredonaninsulatingmaterialwhenprovided
withasufÞcientlylowacceleratingvoltage.
LowermagniÞcationsoflessthan
200xappearedtobedisplay-
ingproperlywithacceleratingvoltagesloweredtobetween
3-5kV.
AthighermagniÞcationstheimagesbecameseverelydistorted,
changingappearanceinwavesevenatlowervoltages,anexample
ofthisdistortionisshowninFigure
123.Figure
123:UncoatedCe:LuAGcrystal
(LBNLSample
1468.7M).Astheinvestigationofthesamplecontinuedtheresultssteadily
decreasedinquality.Itwasdiscoveredthatthemicroscopewas
notcapableofacceleratingvoltageslowerthan
3kV,laterin-
creasingto
3.5kV.Belowthesevaluesthedetectorwouldsimply
returnstaticthatcouldnotbefocusedoradjustedmeaningfully.
Athigheracceleratingvoltageschargescouldbeseencoursing
throughthesample,distortingtheimagewhenfocusedon.Ad-
justingtheworkingdistanceresultedinseverelocaldistortion.For
thesereasonsitwasdeterminedthatfuturesampleswillneedto
becoatedforhighmagniÞcationworkbutlowmagniÞcationwork
coupledwithaloweracceleratingvoltagemayprovidesufÞcient
results.AdditionalSEMimagesofthisCe:LuAGcrystalcanbe
foundintheAppendix.
MgTa
2O6:Sample
4,Trial
5Figure
124:MgTa
2O6two-phasegrowth
(Sample4,Trial
5).ThisMgTa
2O6crystalwasproducedfromthe
3mmODcrucible
nozzleandlikeallofthegrowthsproducedontopoftheMgTa
2O6seeditpossessedpoordiametercontrolandnotransparency.
WhiletheCe:LuAGcrystalgrownexperimentallyandthose
analyzedfromLBNLhadbeenfeaturelesswithrespecttograin
boundariestheMgTa
2O6showedclearevidenceofatleasttwo
phasespresent.ThesephasesareshownindetailinFigure
124.AdditionalSEMimagesofthisMgTa
2O6crystalcanbefoundin
theAppendix.
85Energy-dispersiveX-raySpectroscopy
TheEDSspectrumoutputsforthetestedsamplesarelistedbelow.
EachplotdisplaysthenumberofcountsagainstthespeciÞed
energyrange.Thesecountsareshowninred.Thetestingautomat-
icallyappliesbackgrounddeterminationandpeakdeconvolution
beforedeterminingtheelements.Elementsarecomparedagainst
databaseentriesandlabeledwiththeirelementandK,LorM
energylinesbythesoftware.
Thespectrumbackgroundnoiseisoutlinedinblue,conse-
quentlythepeakdeconvolutioncalculationisplotincyan,follow-
ingtheproÞleofthecollectedspectrum.
Ce:LuAG:Sample
2,Trial
3TheinvestigatedsampleofCe:LuAGgrowthhadbeenpreviously
coatedwithathinlayeroftungstenandhadalreadyundergone
SEMtesting.TheEDStestingwasconductedonthreedifferent
locationsalongthesamplesurfaceinregionsdevoidofvisible
surfacedefectsordebrisatamagniÞcationof
4000x.TheÞrst
locationanalyzedisshowninFigure
125wherethehighlighted
regionwastheareaanalyzed.
Figure
125:HighlightedareaofEDS
analysis.Area
1ofCe:LuAGSample
2,Trial
3growth.
Thethreespectrumoutputsshowedgoodcorrelation,theÞrst
isdisplayedinFigure
128.Iridiumcontaminationwasdetected
withthecruciblebeingthelikelysource.Thisiridiumprecipitation
inthemeltwasobservedinpost-experimentimageryandwith
ahigherdensitythanthemeltitwouldreasonthatitwouldfall
downintothecrystalÕsformation.Themagnesiumpeakdetected
mayhavebeenfromthechamberorceramicsupportsusedinthe
MgTa
2O6growthattempts.Thesecondandthirdlocationand
spectrumoutputsareshownintheAppendix.
Spectrumanalysisoccurredatanacceleratingvoltageof
20kV,
MAG:2000,livetimeof
30s,amptimeof
0.8µsandaresolution
of133.7eV.SummarystatisticsforthisanalysisareshowninTable
15.ElementWeight%Atomic%NetIntensityNetIntensityError
OK20.4357.971440.240.01
MgK0.250.4767.110.16
AlL14.9225.114788.830.00
CeL0.240.0816.220.53
LuL50.6913.151976.040.01
WL3.090.7681.20.26
IrL10.382.45212.960.14
Table
14:eZAFSmartQuantitative
ResultsfromTEAMsoftware.Area
1ofCe:LuAGSample
2,Trial
3growth.
86Figure
126:EDSoutputspectrumof
Area
1ofCe:LuAGSample
2,Trial
3growth.
87Ce:LuAG:LBNLSample
1482.7MFigure
127:HighlightedareaofEDS
analysis.Area
1ofLBNLCe:LuAG
Sample1482.7Mgrowth.
TheinvestigatedsampleofCe:LuAGgrowthhadbeenpreviously
coatedwithathinlayeroftungstenandhadalreadyundergone
SEMtesting.TheEDStestingwasconductedonthreedifferent
locationsalongthesamplesurfaceinregionsdevoidofvisible
surfacedefectsordebrisatamagniÞcationof
4000x.TheÞrst
locationanalyzedisshowninFigure
127wherethehighlighted
regionwastheareaanalyzed.
Thethreespectrumoutputsshowedgoodcorrelation,theÞrst
isdisplayedinFigure
128.Iridiumcontaminationwasdetected
withthecruciblebeingthelikelysource.Thisiridiumprecipitation
inthemeltwasobservedinpost-experimentimageryandwith
ahigherdensitythanthemeltitwouldreasonthatitwouldfall
downintothecrystalÕsformation.Themagnesiumpeakdetected
mayhavebeenfromthechamberorceramicsupportsusedinthe
MgTa
2O6growthattempts.Thesecondandthirdlocationand
spectrumoutputsareshownintheappendix.
Figure
128:EDSanalysisofArea
1ofLBNLCe:LuAGSample
1482.7Mgrowth.
ElementWeight%Atomic%NetIntensityNetIntensityError
OK18.7455.341553.580.01
MgK0.521.02170.360.06
AlL14.9426.175740.850.00
CeL0.140.0511.000.53
LuL51.0413.782389.970.01
WL3.590.92113.270.22
IrL11.032.71271.970.12
Table
15:eZAFSmartQuantitative
ResultsfromTEAMsoftware.Area
1ofLBNLCe:LuAGSample
1482.7M.88MgTa
2O6:Sample
4,Trial
5Figure
129:HighlightedareaofEDS
analysis.Area
1ofMgTa
2O6Sample4,Trial
5Growth.
TheinvestigatedsampleofMgTa
2O6growthhadbeenpreviously
coatedwithathinlayeroftungsten.Thetwophaseswereinves-
tigatedandcompared.Duetotheirregularshapeofthephases
formedafreedrawregionwascreatedforanalysisasshownin
Figure
129.EachphasewasthenanalyzedusingEDS.Theresultsforthe
darkandlightphasesareshowninFigure
130.Whenthedark
phasesareanalyzedacrossthesampletheyshowasigniÞcant
increaseinMgcontent.Toensurethatthesereadingswereaccu-
rate,threedifferentregionsofthecrystalwereselectedatrandom
wherethesetwophasesexistednexttoeachother.Eachdark
phasemeasuredsigniÞcantlyhighermagnesiumcontent.The
secondandthirdlocationandspectrumoutputsareshowninthe
appendix.Figure
130:EDSanalysisoflightphase
(top)anddarkphase(bottom),notethe
discrepancyintheMgKpeaks.
89ElementWeight%Atomic%NetIntensityNetIntensityError
OK19.0065.28964.980.01
MgK5.2411.84979.280.01
TaL51.1515.531244.690.02
WL24.377.28491.610.05
IrL0.240.073.760.53
Table
16:DarkphaseeZAFSmart
QuantitativeResultsfromTEAM
software.Area
1ofMgTa
2O6Sample4,Trial
5growth.
ElementWeight%Atomic%NetIntensityNetIntensityError
OK18.8072.02928.260.01
MgK0.280.7050.960.16
TaL55.5318.811364.130.02
WL25.318.44515.860.05
IrL0.080.031.330.55
Table
17:LightphaseeZAFSmart
QuantitativeResultsfromTEAM
software.Area
1ofMgTa
2O6Sample4,Trial
5growth.
90ConclusionsSinglecrystalCe:LuAGandmulti-phaseMgTa
2O6growthswere
synthesizedusingthe
µ-PDmethodandwerepreparedfrom
powderoxides.Samplepreparationtechniquesand
µ-PDmethods
wereoutlinedandreÞned.
ThesinglecrystalCe:LuAGmatchedpublicationimageryand
wasconÞrmedtobecorrectlysynthesizedwhenx-raylumines-
cencewasperformedwheretheemissionpeakwaswithinthe
publishedemissionrange.Scanningelectronmicroscopyimagery
alsoconÞrmedtheabsenceofgrainboundarieswithinthegrown
crystalsaswellasthosesentlaterfromLBNL.Energy-dispersive
x-rayspectroscopywasperformed,conÞrmingtheappropriate
compoundsofthecrystalbutalsocontaminationfrombothmag-
nesiumandiridium.Itwashypothesizedthatthemagnesiumwas
fromsomeoftheceramicinsulationbutthequantityinwhichit
wasdetectedwassurprisinghigh.Iridiuminclusionwastheresult
ofthebreakdownoftheiridiumcruciblecontainingthemolten
melt.Thiswassupportedwithpost-experimentalimageryof
iridiumprecipitatedonthetopsurfaceofthemelt,withahigher
densitythanthemeltitundoubtedlymoveddownwardsandinto
thecrystal.
Afteranextensiveliteraturesearchtherewasnoevidenceof
MgTa
2O6growthsfrom
µ-PD.X-raypowderdiffractionanalysis
showedsuccessfulformationoftheMgTa
2O6compoundfrom
theµ-PDexperiments.X-rayluminescencetestingshowedno
emissionsabovebackgroundnoise,fromthisitwasconcluded
thatthecompoundcouldnotbeusedasascintillatorinitspresent
formation.Scanningelectronmicroscopyrevealedadetailed
two-phasestructurethatwasundoubtedlyafactorinitspoor
scintillationproperties.Thesetwophaseswerecomparedusing
EDS.HereitwasdiscoveredthatthedarkerphasefromtheSEM
imageryhadastatisticallysigniÞcanthighermagnesiumcontent.
Thiswastrueacrossallsampleareas.
91APPENDIX92SEMResults:LBNLCe:LuAGSample
1482.7MFigure
131:Ce:LuAGcrystal,under
variousmagniÞcations(LBNLSample
1482.7M).93SEMResults:Ce:LuAGSample
1,Trial
2Figure
132:Ce:LuAGcrystal,under
variousmagniÞcations(Sample
1,Trial
2).94SEMResults:Ce:LuAGSample
2,Trial
3Figure
133:Ce:LuAGcrystal,under
variousmagniÞcations(Sample
2,Trial
3).95SEMResults:UncoatedLBNLCe:LuAGSample
1468.7MFigure
134:Ce:LuAGcrystal,under
variousmagniÞcations(Sample
1,Trial
2).96SEMResults:MgTa
2O6Sample4,Trial
5Figure
135:MgTa
2O6crystal,under
variousmagniÞcations(Sample
4,Trial
5).97EDSResults:Ce:LuAGSample
2,Trial
3Area2Figure
136:HighlightedregionofEDS
analysis.Area
2ofCe:LuAGSample
2,Trial
3growth.
Figure
137:EDSoutputspectrumof
Area
2Ce:LuAGSample
2,Trial
3growth.
98ElementWeight%Atomic%NetIntensityNetIntensityError
OK20.4557.951442.180.01
MgK0.330.6290.210.10
AlK14.9125.054795.170.00
PbM0.110.027.810.31
CeL0.070.024.780.54
LuL50.2113.011961.960.01
WL3.420.8490.030.26
IrL10.502.48216.000.13
Table
18:eZAFSmartQuantitative
ResultsfromTEAMsoftware.Area
2ofCe:LuAGSample
2,Trial
3growth.
99Area3Figure
138:HighlightedregionofEDS
analysis.Area
3ofCe:LuAGSample
2,Trial
3growth.
Figure
139:EDSoutputspectrumof
Area
3Ce:LuAGSample
2,Trial
3growth.
100ElementWeight%Atomic%NetIntensityNetIntensityError
OK20.8858.381476.980.01
MgK0.300.5579.890.11
AlK15.0825.014791.000.00
CeL0.620.2041.240.41
LuL49.5012.661920.990.01
WL3.180.7883.240.26
IrL10.442.43213.210.14
Table
19:eZAFSmartQuantitative
ResultsfromTEAMsoftware.Area
3ofCe:LuAGSample
2,Trial
3growth.
101EDSResults:LBNLCe:LuAGSample
1482.7Area2Figure
140:HighlightedregionofEDS
analysis.Area
2ofLBNLCe:LuAG
Sample1468.7Mgrowth.
Figure
141:EDSoutputspectrumof
Area
2ofLBNLCe:LuAGSample
1468.7Mgrowth.
102ElementWeight%Atomic%NetIntensityNetIntensityError
OK18.7555.201577.220.01
MgK0.611.18200.70.05
AlK15.0526.275857.560.00
CeL0.130.0510.950.53
LuL50.8213.682411.790.01
WL3.710.95118.690.22
IrL10.922.68272.830.13
Table
20:eZAFSmartQuantitative
ResultsfromTEAMsoftware.Area
2ofLBNLCe:LuAGSample
1468.7Mgrowth.
103Area3Figure
142:HighlightedregionofEDS
analysis.Area
3ofLBNLCe:LuAG
Sample1468.7MGrowth.
Figure
143:EDSoutputspectrumof
Area
3ofLBNLCe:LuAGSample
1468.7Mgrowth.
104ElementWeight%Atomic%NetIntensityNetIntensityError
OK18.7455.231572.990.01
MgK0.601.17198.30.05
AlK15.0026.215824.040.00
CeL0.160.0613.300.54
LuL50.6713.662402.550.01
WL3.560.91113.530.23
IrL11.272.77281.450.13
Table
21:eZAFSmartQuantitative
ResultsfromTEAMsoftware.Area
3ofLBNLCe:LuAGSample
1468.7Mgrowth.
105MgTa
2O6:Sample
4,Trial
5Area2Figure
144:HighlightedregionsofEDS
analysis.Area
2ofMgTa
2O6Sample4,Trial
5growth.
ElementWeight%Atomic%NetIntensityNetIntensityError
OK19.0365.27981.580.01
MgK5.2711.901000.870.01
TaL51.1615.511263.790.02
WL24.137.20494.260.05
IrL0.400.116.390.52
Table
22:DarkphaseeZAFSmart
QuantitativeResultsfromTEAM
software.Area
2ofMgTa
2O6Sample4,Trial
5growth.
ElementWeight%Atomic%NetIntensityNetIntensityError
OK18.9272.01940.030.01
MgK0.390.9770.570.10
TaL55.4118.651366.90.02
WL25.208.35515.630.05
IrL0.090.031.390.53
Table
23:LightphaseeZAFSmart
QuantitativeResultsfromTEAM
software.Area
2ofMgTa
2O6Sample4,Trial
5growth.
106Figure
145:EDSoutputspectrum
oflightphase(top)anddarkphase
(bottom),notethediscrepancyin
theMgKpeaks.Area
2ofMgTa
2O6Sample4,Trial
5growth.
107Area3Figure
146:HighlightedareaofEDS
analysis.Area
3ofMgTa
2O6Sample4,Trial
5growth.
ElementWeight%Atomic%NetIntensityNetIntensityError
OK19.1165.36981.280.01
MgK5.2911.90998.40.01
TaL50.8115.361248.370.02
WL24.527.30499.450.05
IrL0.270.084.280.53
Table
24:DarkphaseeZAFSmart
QuantitativeResultsfromTEAM
software.Area
2ofMgTa
2O6Sample4,Trial
5growth.
ElementWeight%Atomic%NetIntensityNetIntensityError
OK18.7771.83919.700.01
MgK0.370.9366.970.12
TaL55.7818.881359.150.02
WL25.048.34506.160.05
IrL0.040.010.640.58
Table
25:LightphaseeZAFSmart
QuantitativeResultsfromTEAM
software.Area
3ofMgTa
2O6Sample4,Trial
5growth.
108Figure
147:EDSoutputspectrum
oflightphase(top)anddarkphase
(bottom),notethediscrepancyin
theMgKpeaks.Area
3ofMgTa
2O6Sample4,Trial
5growth.
109Softwaresourcecode
Sourcecodeforprogramsandscriptsareshown.TheWindows
applicationthattheuserusedtocaptureimageswaswritteninVB
whilethepost-processingscriptswerewritteninPython.
110Figure
148:Pythonprogramming
language.import
osimport
math
from
PIL
import
Image
from
PIL
import
ImageFont
from
PIL
import
ImageDraw
def
Cropper
(directory
):for
filename
inos.listdir
(directory
):print
(filename
)img
=Image
.open
(directory
+filename
)#Define
the
crop
region
inpixels
left
=300
top
=125
right
=left
+375
bottom
=top
+360
box
=(left
,top,right
,bottom
)area
=img
.crop
(box
)#Save
off
cropped
image
area
.save
(directory
+filename
,Õpng
Õ)def
TextAdder
(directory
):#Write
crystal
being
grown
oneach
images
crystal
=ÕMgTa2O6
Õ#ÕLuAG
:CeÕ#Write
date
ofexperiment
oneach
image
date
=Õ2015.08.11
Õ#Write
the
location
ofthe
experiment
oneach
image
site
=ÕLBNL
Õ#Define
font
used
onappended
image
text
font
_used
=Õ/usr
/share
/fonts
/truetype
/ttf
-dejavu
/DejaVuSans
.ttf
Õpath
,dirs
,files
=os.walk
(directory
).next
()file
_count
=len(files
)i=1for
filename
insorted
(os.listdir
(directory
)):setpoint
=filename
[20:]
setpoint
=setpoint
[:-4]
temperature
=1742
*(math
.pow
(float
(setpoint
),0.1287))-859
print
(filename
)img
=Image
.open
(directory
+Õ/Õ+filename
)draw
=ImageDraw
.Draw
(img
)font
=ImageFont
.truetype
(font
_used
,16)
draw
.text
((20,15),
crystal
+""+filename
[11]+
filename
[12]
\+":"+filename
[14]+
filename
[15]+
filename
[16]+
filename
[17]+\
filename
[18]+
""+str(i)+\"/"+str
(file
_count
),(255,255,255),
font
=font
)draw
.text
((20,315),
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Class
112GlossaryActivatorSmallamountofimpuritiesintroducedtothelatticeto
enhancephotonemission.
1Afterglow
Fractionofscintillatinglightpresentforagivenperiod
oftimeoncetheionizingradiationhasstopped.
6BraggÕsLaw
DiffractionrelationshipthatdeÞnestheconditions
presentedbyasetofcrystallographicplanes.
20Comptonscattering
Scatteringofaphotonbyachargedparticle,
typicallyanelectron.
5Conductionband
ConsistsofelectronsthathavesufÞcientenergyto
travelthroughoutamaterial.Thisbandisgenerallyempty.
1ConvectionHeattransferbymassmotionofaßuidsuchasairor
waterwhentheheatedßuidiscausedtomoveawayfromthe
sourceofheat,carryingenergywithit.
18Eddycurrents
Thealternatingcurrentinducedinaconductor
whenitissubjectedtoatime-varyingmagneticÞeldinaccor-
dancewithLenzÕslaw.
17Energygap
Alsoreferredtoasthebandgap,thisregionisthe
forbiddengapwherenoelectronstatesexist.Thisgapislocated
betweenthetopofthevalencebandandthebottomofthe
conductionband.
1Energy-dispersivex-rayspectroscopy
Utilizesthephotoelectriceffect
toproduceaspectrumofcountsthatcanidentifyelements
withinacompound.
21ExcitonAnelectricallyneutralquasiparticlethatoccurswhere
anelectronandanelectron-holeareattractedtoeachotherby
electrostaticCoulombforces.
6Fullwidthathalfmaximum
Describesthewidthofafunctionwhere
thedistancebetweenextremepointsonthecurvereacheshalf
itsmaximumvalue.
5Lightyield
Ameasureoflightoutputfromascintillator,typically
measuredinphotons/MeV,thatisanimportantcharacteristicin
determininganappropriatescintillatorforanapplication.
4113Marangoniconvection
Thiseffect(alsocalledtheGibbs-Marangoni
effect)isthemasstransferalonganinterfacebetweentwoßuids
duetosurfacetensiongradient.Inthecaseoftemperature
dependence,thisphenomenonmaybecalledthermo-capillary
convection(orBenard-Marangoniconvection).
19Poiseuilleßow
Steadyviscousßuidßowdrivenbyaneffective
pressuregradientestablishedbetweenthetwoendsofalong
straightpipeofuniformcircularcross-section.Firststudied
experimentallybyJ.L.M.Poiseuillein
1838.19Pyrometer
Apyrometerisatypeofremote-sensingthermometer
usedtomeasurethetemperatureofasurface.
26,28Scanningelectronmicroscope
Amicroscopethatusesafocused
electronbeamtoimagesamples..
21ScintillatorAmaterialpossessingluminescentcentersthatabsorbs
high-energyphotonsandemitslightinthevisibleornear-
visiblespectrum.
1Valenceband
Highestrangeofelectronenergiesinwhichelectrons
aretypicallypresentandareboundtothelatticestructure.
1X-rayluminescence
Techniqueusedtoanalyzeemissionspectraof
scintillatorcrystalsanddeterminethepeakofitsemissionband.
21X-raypowderdiffraction
TechniqueusedtoanalyzeÞnepowder
samplesbasedofftherepeatinglatticestructureofasoliditcan
accuratelydeterminecompositionsofcompounds.
20114BIBLIOGRAPHY115BIBLIOGRAPHY[1]E.Auffray,D.Abler,S.Brunner,B.Frisch,A.Knapitsch,
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CrystalGrowth
,285(4):445Ð449,2005.[81]Y.G.Zdesenko,F.T.Avignone,V.B.Brudanin,F.A.Danevich,
S.S.Nagorny,I.M.Solsky,andV.I.Tretyak.Scintillation
propertiesandradioactivecontaminationofCaWO
4crystal
scintillators.NuclearInstrumentsandMethodsinPhysicsResearch
SectionA:AcceleratorsSpectrometersDetectorsandAssociated
Equipment,538(1):657Ð667,2005.[82]Y.Zorenko,V.Gorbenko,I.Konstankevych,B.Grinev,and
M.Globus.ScintillationpropertiesofLu
3Al5O12:Cesingle-
crystallineÞlms.
NuclearInstrumentsandMethodsinPhysics
ResearchSectionA:Accelerators,Spectrometers,Detectorsand
AssociatedEquipment
,486(1-2):309Ð314,2002.123Indexµ-PDmethod,
16after-heater,
18crucible,18growthchamber,
20,26inductionheating,
17insulation,26melt,18softwaredevelopment,
29temperaturecurve,
26Ce:LuAG,
11EDSresults
sample1482.7M,88sample2,trial
3,86SEMresults
sample1,trial
2,83sample1468.7M,85sample1482.7M,83sample2,trial
3,85XRLresults
sample1,trial
1+2,76sample1,trial
3+4,76crystalresults
sample1,trial
1,57sample1,trial
2,58sample1,trial
3,59sample1,trial
4,59sample2,trial
1,59sample2,trial
3,60crystalsynthesis
sample1,trial
1,29sample1,trial
2,30sample1,trial
3,30sample1,trial
4,31sample2,trial
1,32sample2,trial
2,33sample2,trial
3,33experimentalprocedure,
29phasediagram,
12polishLBNLsample
1468.7M,48sample1,trial
2,50sample2,trial
3,48powderpreparation,
23processing
sample1(HP),23sample2(MP),23MgTa
2O6,13EDSresults
sample4,trial
5,89SEMresults
sample4,trial
5,85XRLresults
sample1,trial
3,80sample4,trial
1+3,80XRPDresults,
73sample1,meltcheck,
73sample1,powder,
73sample1,trial
3,74sample3,trial
3,74crystalresults
sample1,meltcheck,
63sample1,trial
1,64sample1,trial
2,64sample1,trial
3,65sample3,trial
3,66sample4,trial
1,67sample4,trial
3,68sample4,trial
4,68sample4,trial
5,71crystalsynthesis
sample1,meltcheck,
34sample1,trial
1,35sample1,trial
2,36sample1,trial
3,36sample3,trial
1,37sample3,trial
2,38sample3,trial
3,39sample4,trial
1,41sample4,trial
2,42sample4,trial
3,42sample4,trial
4,43sample4,trial
5,44experimentalprocedure,
34phasediagram,
13polishSample4,Trial
5,51powderpreparation,
24processing
sample1(NP),24sample2(MP),24sample3(MP),25sample4(MP),25sample/seedseparation,
43seedconstruction,
40Activator,
1,7Appendix,92Background,
11Bibliography,
115Charge-transfer,
8Coating,52Conclusions,91Convection,
18Core-valenceluminescence,
7Diamondpaste,
47Discussion,56Energy-DispersiveX-raySpec-
troscopy,
21Exciton,6free,
6impurity-bound,6self-trapped,6ExperimentalProcedure,
23Energy-dispersivex-rayspec-
troscopy,
54Scanningelectronmicroscopy,
52x-rayluminescence,
45x-raypowderdiffraction,
45Grindingpapers,
46InorganicScintillators,
3afterglow,
6applications,8decaytime,
5extrinsic,6historicaldevelopment,
8intrinsic,6lightyield,
4linearityoflightoutput,
5machinability,
4mechanisms,6physicaldensity,
3production,
4124requirements,
8self-activated,
6transparency,
4Introduction,
1Microscope,
47Microscopelight,
47Mountingclips,
46Mountingpress,
46OP-S,47Polishing,46Powdersynthesis,
15Pyrometer,
26Rareearthions,
7Results,56Scanningelectronmicroscopy,
21insulators,52samplepreparation,
46Scintillator,
1Software,
110Python,111VisualBasic,
112Tungsten,
52Wiresaw,
43X-rayluminescence,
21X-raypowderdiffraction,
20125