iail t , ABSTRACT ELECTRICAL RESISTIVITY OF ALUMINUM ALLOYS AT LOW TEMPERATURES BY Ronald Leon Carter The electrical resistivities of aluminum and alloys of aluminum with magnesium, copper, zinc, (n: gallium have been measured from 2.5°K to 300°K. The importance of cor- rections for change in volume upon alloying and thermal expansion in determining the magnitude and temperature derivative of deviations from Matthiessen's Rule at high temperatures is stressed. Two hypotheses were found to be consistent with the deviations from Matthiessen's Rule measured at low temperatures. The conclusion that the electron states on the third zone sheet of the Fermi sur- face have an average relaxation time which is considerably different from that for the hole states on the second sheet was drawn from the application of the two—band model. h ph' were shown to be consistent with thermoelectric power data. The relative resistivities of the two bands, 03h > p The data were also found to be consistent with a theory due to Mills, which considers the additional resistivity for a process which involves simultaneous scattering from an impurity ion and the emission or absorption of a phonon. ELECTRICAL RESISTIVITY OF ALUMINUM ALLOYS AT LOW TEMPERATURES BY Ronald Leon Carter A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Physics 1971 PLEASE NOTE: Some Pages have indistinct print. Filmed as received. UNIVERSITY MICROFILMS ACKNOWLEDGMENTS I would like to express my appreciation to Professor Frank J. Blatt, who first suggested this study, and whose advice and assistance on theoretical and experimental matters was invaluable and cheerfully offered. And to Professor Peter A. Schroeder, who heard many tales of woe and experimental failure, thank you for your freely offered help. I also acknowledge Professors Blatt and Schroeder and the National Science Foundation for financial support received during this study. I would like to acknowledge Professor Carl L. Foiles for his work in doing the resistivity at high pressure measurements which were useful in the analysis of this study, and for many helpful discussions on transport meas- urements. Thanks are due also to Professor W.M. Hartmann for providing the results of his phonon dispersion calcula- tions for aluminum before publication. The efforts of Professors B.H. Wildenthal and W.H. Kelly in providing computer time on the XDS Sigma Seven are greatly appreciated for the time their efforts saved for me. I would like to acknowledge the help of Mr. J. Thomas and Miss G. Pucilowski in setting up the computer programs, and to Miss Pucilowski for doing the drawings. ii I am pleased to also acknowledge the help of Mr. B. Shumaker in the manufacture of some of the alloy samples. My deepest appreciation is for my wife, Carole, who accepted many things that were less than they might be, offered encouragement when needed, typed this manuscript, and who worked very hard to make this study possible. iii TABLE OF CONTENTS Chapter INTRODUCTION . . . . . . . . Matthiessen's Rule . . . . . Deviations from Matthiessen's Rule Deviations from Matthiessen's Rule in Aluminum . . . . . . EXPERIMENTAL APPARATUS . . . . Cryostat and Sample Mounting . Current Control . . . . . . Temperature Control . . . . Potentiometric Measurements . . SAMPLE PREPARATION . . . . . . Manufacture of the Alloys . . Forming of Wires . . . . . Resistance Ratios . . . . . Annealing . . . . . . . . Sample Characterization . . . RESISTIVITY DATA . . . . . . Introduction . . . . . . . Room Temperature Resistivity Measurements . . . . . . Temperature Dependence of the Resistance . . . . . . . Calculating the Resistivity from the Data . . . . . . . RESULTS AND CONCLUSIONS . . . . The Phonon Resistivity of Aluminum The Deviations from Matthiessen's in Aluminum Alloys . . . . The Two-Band Model . . . . . The Ehrlich Theory . . . . . The Mills Theory . . . . . iv Page 11 13 15 l9 19 20 21 22 23 25 25 25 28 29 33 33 38 45 66 67 Chapter Page SUMMARY AND IMPLICATIONS FOR FURTHER STUDY . . . . . . . . . . . . . . 73 REFERENCES . . . . . . . . . . . . . . 75 APPENDICES . . . . . . . . . . . . . . 78 APPENDIX A. FORTRAN Listing of Computer Program for Calculating Resistivities . . . 78 B. Typical Data Output . . . . . . . 90 C. Analysis of Errors . . . . . . . . 97 LIST OF TABLES Table Page 1. Lot Assay for HPM 2404 . . . . . . . . 20 2. Coefficients of the T2 and T5 Components of the Resistivity of Aluminum . . . . 35 3. Volume Corrections . . . . . . . . . 44 . Residual Resistivity of Aluminum Alloys . . 45 4 C-1. Standard Deviations for Measurements Using Equation C.l . . . . . . . . 97 C—2. Phonon Resistivity of Aluminum at 273.160K O O O O O O 0 O O O O 100 vi LIST OF FIGURES Figure Page 1. Schematic Representation of the Cryostat . . . . . . . . . . . . 10 2. Constant Current Source . . . . . . . 12 3. Temperature Controller . . . . . . . . 14 4. Schematic Representation of Experimental Apparatus . . . . . . . . . . . l6 5. Spring Loaded Electrical Contacts . . . . l7 6. Temperature Dependent Resistivity of Pure Aluminum . . . . . . . . . . 34 7. Deviations from Matthiessen's Rule in Al—Mg Alloys 0 c o o o o o o o o 39 8. Deviations from Matthiessen's Rule in Al-Cu Alloys 0 O O O O O O O O O 40 9. Deviations from Matthiessen's Rule in Al-Zn Alloys 0 o o o o o o o o o 41 10. Deviations from Matthiessen's Rule in Al-Ga Alloys 0 O O O O O O O O O 42 11. Low Temperature Deviations from Matthiessen's Rule in Aluminum Alloys . . 43 12. Residual Resistivities of Aluminum Alloys . . . . . . . . . . . . 46 13. Fermi Surface of Aluminum . . . . . . . 47 14. Kohler-Sondheimer-Wilson Plot at 30°K . . . 53 15. Kohler-Sondheimer-Wilson Plot at 70°K . . . 54 16. Kohler-Sondheimer-Wilson Plot at 295°K . . 55 vii Figure 17. 18. 19. 20. 21. 22. 23. Page KSW Parameters a and b as a Function of Temperature . . . . . . . . . . 57 Phonon Resistivity of the Hole Band . . . 59 Phonon Resistivity of the Electron Band . . 6O Backscattering Event on Third Zone Extremal Cross-Section . . . . . . . 62 Phonon Dispersion Spectrum for Aluminum . . 63 Fit of the Coefficients a and B to the Ehrlich Theory . . . . . . . . . . 68 Coefficients of the T3 and T2 Terms as a Function of pO . . . . . . . . 71 viii INTRODUCTION Matthiessen's Rule More than a century ago, Matthiessen (1,2) observed that near room temperature the temperature derivative of the resistivity of a dilute metal alloy is the same as for the pure base metal. Thus, the Matthiessen Rule (MR) is, dpp _ dpA 1.1 dT ‘dT where T is the absolute temperature, and DP and CA are the resistivities of the pure metal and alloy respectively. When temperatures near the absolute zero became experimentally attainable, it was observed that the limit- ing behavior of a "perfectly pure" metal was oP(T=0) o, 1.2 and for an alloy Where p0, the residual resistivity, appears in the inte- grated form of the MR: When Bloch (3,4) and later Grfineisen (5), formu- lated early theories of the effect of the thermal motion of the ions (phonons) on the electrical resistivity of a pure metal, was identified as pph’ the resistivity due “P to scattering of the electrons by the phonons. The residual resistivity, po, was then identified as due to scattering of the electrons by imperfections in the lattice. Thus, the MR was given the more general inter- pretation: the partial resistivities arising from the scattering of the conduction electrons by different types of scatterers are additive. Deviations from Matthiessen's Rule In practice, deviations from the MR are usually observed in dilute metal alloys. The temperature dependence of the alloy resistivity is not identical to the temperature dependence of the pure resistivity. Thus, (T) _(T) 0A -0 ph + pO + A(T), 1.5 where A(T), the deviation from the MR, depends on the nature and concentration of defects and impurities in a complex manner. Departures from the MR can arise for a number of reasons. Some of the most important (for nonmagnetic im- purities) are: A1: The addition of impurities may change the phonon spectrum of the metal. 2: The electronic band structure may be altered by the impurity. A3: Scattering from the thermally oscillating impurities may give a temperature dependent impurity resistivity (phonon-assisted impurity scattering). A4: Interference terms between scattering by the vibrating impurities and the host ions. A5: Two (or more) groups of electrons may con- tribute to the conductivity, giving (as will be shown later) an apparent deviation from the MR. A6: The simultaneous presence of thermally induced Umklapp processes and impurity scattering. In this study, dilute alloys were considered; the maximum impurity content being less than two atomic per cent (2 a/o). In this case, de Haas-van Alphen measure- ments (6) support the assumption that changes in the electronic band structure are negligible. Furthermore, the results of Massbauer experiments (7,8) indicate that the phonon spectrum is little changed. Extensive reviews of the theoretical and experi- mental work on departures from the MR have been given by Lengler, Schilling and Wenzl (9), Stewart and Huebener (10). and Seth and Woods (11). A brief discussion of the theo~ retical points important to this study follows. Kagan and Zhernov (12) have developed a theory of the electrical resistivity of a metal with impurities which takes into account deformation of the phonon spectrum due to the presence of the impurity ions and the electron scattering by the thermally oscillating impurity ions. In the low temperature range, scattering by the oscillating impurity ions gives a term proportional to poTz, inter- ference between scattering by the perturbed phonon spectrum and the oscillating impurity ion gives a term proportional to poT4, and scattering by the deformed phonon spectrum gives a term prOportional to poTS. The temperature vari- ation was shown to exhibit an anomaly in the case of heavy impurity atoms when a quasilocal level appears in the phonon spectrum. At high temperatures, the impurity part of the resistivity was shown to vary linearly with temper- ature, the sign of the derivative depending on the relative positions of the impurity (solute) and matrix (solvent) atoms in the periodic table. A theory for the phonon-assisted impurity scatter- ing due to the average strain induced in the lattice by the thermally oscillating impurity atoms has been formu- lated by Klemens (13). Assuming the change in the impurity potential to be prOportional to strain, Klemens showed the additional resistivity to be prOportional to po. The mean-square thermal strain of the lattice, <€2>, is pro- portional to the thermal vibrational energy of the lattice, so A3apoT4(T<<6D), and A3¢poT(T26D). Ehrlich (14) has calculated the low temperature resistivity for the case for which the Fermi surface touches or nearly touches the Brillouin zone boundaries, extending the Klemens-Jackson (15) theory to include the simultaneous presence of impurity and thermally induced umklapp scatter- ing. Assuming an isotropic, temperature independent, im— purity relaxation time, Ehrlich solved the Boltzmann equation in terms of a Legendre series in the scattering angle for current-carrying electrons. For the case in which the phonon resistivity, pph’ in the absence of 5 umklapp processes is proportional to T , the numerical solution for the total resistivity is of the form _ 2 S p(T) - p0 + a(P,€)T + b(P,e)T 1.6 where P = Zoo/pph and e is the angle of contact of the Fermi surface on the Brillouin zone. The combined effect of impurity and umklapp scattering processes introduces a T2 term as well as enhancing the T5 term. Mills (16) has calculated the resistivity for a process which involves simultaneous scattering from an impurity ion and the emission or absorption of a phonon. 3 Breakdown of momentum conservation leads to a T depend- ence for this resistive contribution. Further, as a result of the small energy difference between initial and inter- mediate states for the process, this contribution to A4 is weakly dependent on the impurity concentration. Dugdale and Basinski (l7) interpreted the results of measurements on copper and gold based alloys using a simple two-band model. Originally proposed by Sondheimer and Wilson (18) and Kohler (19) the two-band model approxi- mates anistropies of the relaxation times associated with phonon and impurity scattering with two non-interacting conduction bands with isotropic relaxation times. Deviations from Matthiessen's Rule in Aluminum Aluminum was chosen for this study of deviations from the MR for three reasons. First, there is reason to suspect a priori that the sources for deviations A3, A4, A5, and A6 should be manifest in aluminum alloys. Second, the cubic symmetry of the face-centered cubic aluminum lattice permitted the use of wire resistance samples. Last, deviations from the MR had been previously reported in aluminum systems (11, 20-24). The light aluminum ions should experience rather large amplitude thermal vibrations, so the scattering effects of thermal strain at impurity sites might be ex- pected to be pronounced. The relatively light mass of the aluminum ion should favor creation of in-band local modes or quasilocal levels in the phonon spectrum upon alloying with heavy solutes. This might be expected to give the anomalous impurity resistivity anticipated by Kagan and Zhernov (12). The reversal of the Hall field in pure aluminum reported by Luck (25) and Forsvoll and Holwech (26) from the low field electron-like limit to the high field hole-like limit supports the hypothesis that aluminum may be treated as a two-band metal. With this hypothesis, the Kohler-Sondheimer-Wilson equation (18,19) may be used to fit the deviations, A from the MR, and thus infer the 5: relative relaxation times for scattering by impurities and phonons for electrons in the two bands. Alley and Serin (20) have reported departures from the MR in alloys of aluminum with zinc, magnesium, ger— manium, or silver from 4.2 to 300°K. This work did not include dimensional measurements, so deviations could only be inferred and not quantitatively compared with theory. Van Zytveld and Bass (21) have carefully documented size dependent deviations from the MR in thin foils and fine wires of aluminum from 1.3 to above 40°K. Panova, Zhernov and Kutaisev (22) have reported deviations from the MR in alloys of aluminum with gold or silver solutes from 4.2 to 300°K, interpreting their results on the basis of the Kagan and Zhernov (12) theory. Panova §t_gl, did not, however, study the effects of change in valence or of light solutes. Recently, Seth and Woods (11) have reported deviations from the MR in alloys of aluminum with magnesium or silver from 4.2 to 300°K. Caplin and Rizzuto (23) report devia- tions from the MR in alloys of aluminum with magnesium, iron, silicon, cobalt, manganese, copper, chromium, or vanadium. Campbell, Caplin and Rizzuto (24) later inter- preted these deviations in light of the Mills theory (16). In the following chapters, the deviations from Matthiessen's rule are reported for aluminum with magnesium, zinc, copper, or gallium solutes. EXPERIMENTAL APPARATU S Cryostat and Sample Mounting The cryostat used was of the sample holder-within a cannister-within a vacuum jacket-within an outer cannister- design. A schematic representation of the cryostat is shown in Figure l. The sample holder was made of aluminum to minimize the effects of differential thermal expansion between the samples and the sample holder. The inner diameter of the hollow cylindrical sample holder was designed for a loose fit on the oxygen free high conductivity (OFHC) copper block (to minimize strains due to differential thermal ex— pansion), with firm thermal contact insured by mechanically bolting the sample holder to the OFHC block at a single point. The outside of the sample holder was insulated by cigarette paper attached with GE 7031 Varnish. Samples were annealed in a coil slightly larger than the sample holder diameter, placed on the sample holder, and held in place by spring-loaded clamps. Thus, strains induced in the samples due to mounting or thermal cycling were mini- mized. Platinum and germanium resistance thermometers were mounted in the thermometer well in the interior of the OFHC c0pper block for measurement of the sample temperature. 10 .umumOMHo on“ no coHuMDcmmemmH caumfimnomii.a whamfim /../// /////// f\\\\ \\\\. muzz. . / mun—.5: m4u2 «mt; _ # M 00. \\ x.oo~ .95 05 H .18. . “ 00. ES». . n~:z_ " . 00. 2.0070 v..c....oo_ voonxn ._ .o~m 2m 35 or 3 new s: woo. > 000m 08. V S. 15 average power to be put into the cryostat, causing heating or permitting cooling of the samples. Potentiometric Measurements The sample potentials, sample current, thermometer potentials, and thermometer current were measured in a circuit schematically represented in Figure 4. In practice, up to ten samples were connected in series for a given run. Copper potential and current leads were attached to the samples using the spring loaded system shown in Figure 5. The insulated washers were made by attaching cigarette paper to one side of a brass washer with GE 7031 Varnish. The insulating coating was removed from the end of the current or potential lead and the bared c0pper wire placed between the insulated washer and the sample. The nylon screw was then tightened compressing the spring, which then held the c0pper lead rigidly against the sample wire. Creeping of the lead along the sample was not observed, as inferred by the fact that the resistance of the sample at a specific temperature did not change upon thermal cycling. The distribution switch for the potentiometers was made of three Chicago Dynamics Industries two pole-sixteen position printed circuit switches. This enabled connecting. the digital voltmeter, K-3 potentiometer, or 6-Dia1 poten- tiometer independently to any of the potential measuring _circuits. These switches are of noble-metal construction; 16 .mnumummmm Hopcmfiflummxm mo coflumucmmmnmmu owumfimsomil.v whamam meJOmPZOO . mmakdmwmzwh - Fmo II II.II|I .1.II Tull.ll fl _ _ wFJO mmh o zozbefima to“: «:3 - lzu nx mamthoz 1.2m x3 26 momma 17 .muomucoo amoeuuomam topmoa mcflummiu.m musmflm 322.. o_qu|muv\ \ \ 3.3 29.55 - toouamlv\\\\\\mfillli 5.3.. .233 3.2:»... Iv “ll. .1 3:23. outnmlv ml... , a! Horace .233 :95 III carom 3025 c012 omuo 1» 18 and low thermal solder was used for all connections. Spurious thermal emfs observed upon reversal of the current were less than .02 uV. The Leeds and Northrup K—3 potentiometer was used to measure the thermometer potentials and the potential drops across the standard resistors in the current supply circuits. The precision for this instrument is .015% or 2uV whichever is greater in the range used. The Rubicon 2768 6-Dial potentiometer was used to measure the potential drops across the samples. The precision for this instrument is .01% or .OluV whichever is larger in the range used. SAMPLE PREPARATION Manufacture of the Alloys All of the alloys (except the Mg series) in this investigation were made from 6-9 grade aluminum, lot HPM 2404, purchased from Cominco American. The lot assay is shown in Table l. The total impurity level was less than one part per million (ppm). A piece of lot HPM 2404 was also used for the pure aluminum sample, as well as some Gallard Schlesinger B 3015 zone refined aluminum. The doping level for the alloys ranged from .05 a/o (500 ppm) to 2 a/o. The doping material used was 5-9 or 6-9 grade material. A master alloy (maximum concentration) for each series was made by R.F. induction melting the solute and solvent (pure aluminum) in a vitreous graphite crucible. After about two minutes of mixing by the stirring action of the induction heater, the molten alloy was poured into an aluminum chill-cast mold. A portion of the master alloy was melted and poured into the chill-cast mold a second time, for better mixing, and then used for the maximum con- centration alloy. The remainder of the master alloy was further diluted with pure aluminum and chill-cast for the more dilute alloy samples. In some cases (as described 19 20 TABLE l.--Lot assay for HPM 2404. Impurity Concentration (in ppm) Ca .1 Cn .1 Fe .3 Mg .1 Mn .3 Total .9 below) chill-casting did not yield a homogeneous dopant concentration throughout the casting. These samples were given a homogenization period of one week at a temperature of about 550°C in an argon atmosphere. The magnesium series of alloys was kindly provided in wire form by Dr. R. P. Huebener of the Argonne National Laboratory. Spectrographic analysis on the least concen- trated alloy of the magnesium series revealed <10 ppm copper as the only detectable impurity. Electron micro- probe analysis found copper and carbon present in amounts barely sufficient for detection (much less than 100 ppm). Forming of Wires The castings were removed from the chill-cast mold, a piece of the casting cut out and etched. This piece was then passed through a rolling mill until it formed a wire 21 of 1 mm square cross section. This wire was then drawn through tungsten carbide dies to 0.75 mm diameter. The final drawing operations were performed using diamond dies to a final diameter of 0.5 mm or 0.25 mm. After each pass through the rolling mill or dies the wires were carefully wiped clean using a lint-free tissue and ethyl alcohol. Sufficient time was allowed for the ethyl alcohol to evapo- rate before subsequent milling or drawing operations. The dies and rolling mill were also carefully cleaned with ethyl alcohol prior to use. Triple-distilled water was used if lubrication was needed during the drawing operations. Resistance Ratios For characterization of the samples, the resis- tivity ratio RR = R(295°K)/R(4.2°K), where R is the sample resistance, was found to be quite useful. The procedure was as follows: A piece of wire sample about 7 cm long was fixed with current and potential leads. This sample was placed in the room temperature resistivity apparatus and given time to come into thermal equilibrium with the appa- ratus. The resistance and temperature were then measured. Matthiessen's rule was assumed to calculate the resistance at 295°K. The sample was then placed in liquid helium and the resistance at 4.2°K was measured. The ratio RR, thus calculated, was then used in the characterization pro- cedures. It should be noted that the resistance ratio thus found is not wholly accurate (since this investigation is 22 indeed founded on the experimental fact that Matthiessen's rule is not obeyed for aluminum alloys). This procedure can be prOperly used to infer the effect of annealing on residual resistivity and the homogeneity of alloy concen- tration along a wire, since a decrease or increase in RR, so defined, can be unequivocally used to infer a commen- surate increase or decrease in the residual resistivity. Annealing A study of the effect of annealing on both pure and alloy samples revealed the following: No advantage could be found in annealing in an inert atmosphere as compared to air. All samples were therefore annealed in an aluminum foil "envelope" in air. After one hour of annealing at approximately 500°C, the residual resistivity decreased (as inferred by an increase in the resistance ratio) to within 1% of the minimum observed for a given sample. In the next one to two hours the minimum residual resistivity was observed to be reached. For further annealing no consistent variation was observed, until ten to twenty hours elapsed after which the residual resistivity began to increase. This was probably due to contamination from the air or aluminum foil. All samples were annealed in 10 cm diameter coils for two hours, then the room temperature resistivity was measured. The wire was then coiled to the diameter of the sample holder and given one more hour of annealing time. The resistivity ratio RR was observed to be constant to 23 within experimental error before and after the second anneal for all samples tested. Sample Characterization After formation into wires, and the initial two- hour anneal, the samples were tested by resistance-ratio, electron microprobe and chemical analysis to characterize the usefulness for this study. A wire 90 cm in length was required for the resistivity measurements. Additional 10 cm lengths from each end were used for resistance ratio analysis. The sample was considered satisfactory for this study only if the resistance ratio of the two end pieces matched to within 5%. Furthermore, when installed in the cryostat, the sample from the central piece was required to have a resistance ratio within 3% of the average of the end pieces. This criterion was established to infer that fluctuations in alloy concentration of the samples used were about 3% of the average concentration. It was particularly difficult to achieve a sample with zinc, cadium, or silver as the solute which could pass this test. Even after one week of homogenization, only two zinc and one silver alloy samples were homogeneous enough to pass this test. An Applied Research Laboratories electron micro- probe was used to qualitatively analyze the least concen- trated gallium and most concentrated copper samples for impurities. The electron microprobe is not suitable for 24 quantitative analysis of impurity levels below 300 ppm. However, it is possible to detect the presence of trace impurity levels to below 10 ppm. In addition to aluminum and the desired dopant, carbon, silicon, manganese, and copper were each observed at the threshold detection level. The lot analysis for the pure aluminum used included copper and manganese at below the 1 ppm level. It was assumed that carbon and silicon were picked up from the vitreous carbon crucible and vycor glass sleeve used in the melting operation. Chemical analysis for the quantity of solute mate- rial was performed by Schwarszpf Microanalytical Labora- tories. RES ISTIVITY DATA Introduction The resistivities of pure aluminum and fourteen aluminum alloys were measured from 4.2°K (as low as 2°K in some cases) to 300°K. The specific resistivity of each sample was determined at room temperature. Resistances were measured for each sample as mounted in the cryostat as a function of temperature. These data were then con- verted to resistivities by normalization to the measured specific resistivity at room temperature. Room Temperature Resistivity Measurements The resistivity of a cylindrical wire sample of resistance R, length 2, and cross-sectional area A is given by The resistivity of each wire sample used in this study was carefully determined at room temperature by measurement of the resistance per unit length and the mass, m, of a known length, 2, of wire. The area was calculated from the hand- book value (27) for the density, d, according to the rela- tionship 25 26 _ m A — 35—. 4.2 0 Each wire sample was placed on an Invar scale mounted in a channel milled out of a massive, thermally insulated, aluminum block. Razor blades were used for potential probes. Simultaneous position, potential, and current measurements were used to determine the resistance per unit length of the wire sample. The temperature was measured using a platinum resistance thermometer which was mounted in the aluminum block. Potentiometric measure- ments were made with the circuitry described under Experi- mental Apparatus, and shown in Figure 5. At the greatest length, £0, the razor blade potential probes were pressed down, cutting off £0 of the wire. This amount of wire was weighed for its mass, m, using a Cahn microbalance (if microgram precision was required) or a Mettler model B-6 semi-micro balance. Corrections for the bouyancy of air were made when the Mettler Balance was used, but were not needed with the Cahn microbalance since the mass standards used were aluminum alloys within .3% of the density of the wire samples. This procedure is applicable if the cross-sectional area is uniform along the entire length of the wire. To insure this, R/£ was measured as a function of the position along the wire. The variation in R/£ was assumed to be due to variation in A rather than alloy concentration. This 27 was assumed by the restrictions on the residual resistivity described previously. If any part of the sample had a variation of R/l of more than .03% from the mean, an alternate procedure was used. If the wire is supposed to be composed of segments 1i in length with each segment Ai in cross-sectional area, the mass of the length, 20 = nzi, of wire is Now, since the resistance of each segment, R1 is R. = 0 %E. 4.4 _ ii Ai—pfi-O— 4.5 1 giving n m=d2..zp z i. 4.6 l . R. 1=l 1 28 In practice, then, the wire was divided into n sections such that the values of Ri from adjacent sections varied by less than .03%, then Ri was measured for each 2i and the resistivity calculated using the above expression. Temperature Dependence of the Resistance In practice, up to ten wire samples were connected in series in the cryostat for a given run. One of these samples was always pure aluminum. The data were taken in the sequence: potential for the pure aluminum sample (for- ward current), potential for alloy sample (forward current). thermometer potential, potential for alloy sample (reverse current), potential for pure aluminum sample (reverse current). In this way, the resistances of the alloy and pure aluminum were obtained for the same average tempera- ture, minimizing the effect of uncertainty in temperature measurement. The cryostat was immersed in or above liquid helium when taking data from 2°K to 65°K. The helium was pumped for data points below 4.2°K and temperature control achieved by regulation of the pumping speed. Good thermal contact with the bath was effected by introducing a small amount of helium gas into the inner and outer cannisters. For data points above 4.2°K, the outer cannister was pumped out and the temperature controller used to adjust the sample temperature and hold it constant. 29 The cryostat was immersed in liquid nitrogen when taking data above 65°K. In the range from 65°K to 77°K, the nitrogen was pumped and temperature control was achieved by regulation of the pumping speed. Helium gas was introduced into the inner and outer cannisters. For temperatures above 77°K, the outer cannister was evacuated and the temperature controller used to adjust the sample temperature and hold it constant. Calculating the Resistivity from the Data It is not sufficient over the entire range of tem- perature studied to simply normalize the resistance to the room temperature resistivity by using a temperature inde- pendent shape factor. Corrections must be made for change in volume due to thermal expansion and alloying. Dugdale (17) has pointed out that deviations from Matthiessen's rule can be properly inferred only if the resistivities are all measured at the same atomic volume. The resistivity at a volume V was corrected for volume change to V0 by the relation V -V _ V 8p 0 0(VO) — 0(V)[l+-5—3—\—,(-—V—)]. 4.3 The volume derivative may be calculated from the pressure derivative 30 Y.§E = _ 1.334- l.§X)—l 4.9a pBV paP VBP ’ = - 1.22.1 4.9b 0 BP x' where x is the compressibility of the sample material. The pressure derivative for the resistivity of an alloy may be separated into phonon and impurity resistivity terms. This is suggested by taking the pressure derivative of Matthiessen's rule. = 4.10 0t pph + po 80 30 89 4 11 t _ ph o ' a? ” 3P + 5? Defining 1 439 h 4 12 3"‘3—"5’g" ' ph and 30 _ _ IL._JE 4.13 Y— D 8P! 0 we have 1 apt _ _ 8 92h _ fig 4.14 "‘ 3P ’ Y 31 Bridgman (28) has measured the pressure derivative of aluminum between 90°K and 273°K. This data was extended to 4°K using the relation (29) 114 _ 1 3I3 8P]high T _ [E aPllow T' Bridgman (30) has also reported the pressure derivatives of the resistivity of Al-Mg and Al-Zn alloys at 273°K. Foiles (31) has measured the pressure derivative at 77°K of the Al-Mg alloys used in this investigation. For Al-Mg alloys, Y is 1.5(10_6)cm2/kg, and is independent of temperature. For Al-Zn alloys, 7 is -3.8(10-6)cm2/kg. For pure aluminum at 273°K, e is 4.03(1o'6)cm2/kg. Corrections were made to the resistivities follow- ing the two-step program suggested by Dugdale (17). First, ideal phonon resistivity, pph' has been corrected for volume dilatation on alloying. Thus corr 38(a-ao pph = Ophil + X a )1: 4.16 0 where a0 and a are the lattice parameters of the pure mate- rial and the alloy respectively as reported by Pearson (27). Second, the residual resistivity of the alloy, po, has been corrected for the volume change due to thermal expansion. Thus _ 3Y _ 00(T) — po[1 + 57(00 a)]. 4.17 32 where a and do are the fractional linear expansion at temperature T and 0°K relative to 293°K as tabulated by Corruccini and Gniewek (32). The deviation from Matthiessen's rule at the temperature T is then COI'I' A(T) = ot(T) - 00(T) - oph O 4.18 Since 7 was known for the Al—Mg and Al-Zn systems only, complete corrections have not been made for alloys in the Al-Cu, Al-Ga, and Al-Ag systems. The maximum error thus incurred is at high temperature. If we assume the y value observed for Al-Zn is large, an approximate maximum for the correction is -6 2 2‘90"“)90 = 3(3.8)(10 12m /§g(.00415)po 4.19a X 1.34(1o )cm /kg = .045 p . 4.19b 0 Consequently, for the Al-Cu, Al-Ga, and Al-Ag systems, it has been assumed uncertainties, Spvol’ due to volume cor- rections are dpvol S .05 00. 4.20 A FORTRAN listing of a computer program used to calculate resistivities from the voltage data is shown in Appendix A. A typical data run computer output is in Appendix B. An error analysis is in Appendix C. RESULTS AND CONCLUS IONS The Phonon Resistivity of Aluminum The temperature dependent resistivity, 6(T) = p(T) - po, for three pure aluminum wire samples is shown as 6/T2 vs T3 in Figure 6. Reich (33) measured the resis- tivity of three samples from l4°K to 20°K. The power series fit to 6 = aT2 + bT5 obtained by Reich for p0 = .068 nQ-cm sample is represented by a solid line in the region of data, and extended with a dashed line. On the basis of the data of Aleksandrov and D'yakov (34), Aleksandrov (35) proposed the fit shown as the dash-dot line in Figure 6. The coefficients a and b reported by Garland and Bowers (36), Reich (33), and Aleksandrov (35) and fit to the data of this investigation between 25°K and 40°K are summarized in Table 2. Below 25°K, the data deviates considerably from the straight line fit. This feature will be discussed later in terms of deviation from the MR. Above 45°K, the temperature dependence is weaker than T5; eventually falling to a nearly linear functional behavior for temperatures above 100°K. The Bloch—Grfineisen (3-5) theory for the resis- tivity due to phonon scattering predicts p a T5, T << 9D. 5.1 ph 33 34 .ESGHESHM mafia mo muw>flumwmmu ucmpcmmmp musumummfimaii.m whamflh Anxe me w .v N O a A. 1 d a m 4 \ \ x a. .. \. \ 4 m .. t .\.\\ 0 do .1. 1.0 T .\\\ 4 1 m 2d .\\\\ no ) \ \ o .n T . \\ l mw WU .\\\ 4 «V o. 1. \ . \\ \ o Igwm .. mmO. u «KI In If: (WI \\ 358248.34 __ «mo. u mo .3: \\ 0 82.28 .. 2m. . m. a 1 J. no 82.28 .. 8N u m. o - N. Eon mo 50.6.: NE u Q a D _ rIL 4» l _ x . 8 9. or F on on “Miami 0.0. 3 35 TABLE 2.--Coefficients of the T2 resistivity of aluminum. 5 components of the Wire p 10 . . o axlO bx10 Investigator Diagfiter (nQ-cm) (uQ—cm/°K2) (uflcm/°K Present In— vestigation .50 1.42 1.25 1.56 Present In- vestigation .25 2.03 1.50 1.46 Present In- vestigation .25 .97 1.55 1.61 Garland & Bowers 1.05 1.04 0.44 Reich 1.25 .22 0.64 1.18 Reich 5.22 .068 0.375 1.38 Reich 5.22 .055 0.511 1.22 Aleksandrov m .092 0.535 1.17 Such behavior is not always observed. The simplifying assumptions of the Bloch-Grfineisen model are: 1. Elastic scattering of the electrons by the phonons is assumed. 2. A Debye spectrum is assumed for the phonons. 3. The microscopic scattering cross-section for the electron-phonon interaction is assumed to be independent of the scattering angle. (The relaxation time is assumed isotropic.) 4. Umklapp (U) processes in which a reciprocal lattice vector is included in momentum con- servation are not included. 36 With these approximations, it is surprising that the re- sistivity of a real metal would even approximate the T5 law. Pytte (37), Kaveh and Wiser (38), and Klemens and Jackson (15) have shown that consideration of U processes alters the phonon resistivity considerably. In calcu- 1ating the resistivity of aluminum, Pytte (37) has shown that when U process are included, a T4 term appears, and for temperatures below the cutoff for U processes, the resistivity falls off more rapidly than T4. Kaveh and Wiser (38) calculated the resistivity for sodium, and having taken account of U processes and the momentum de- pendence of the electron-phonon scattering amplitude they accounted for the observed change from T5(T 2> 9°K) to T6(T < 9°K) in the temperature dependence of the resis- tivity. They assert further that the T5 behavior of the resistivity of a metal has nothing to do with the Bloch result, but is merely a fortuitous numerical accident. The theory of Klemens and Jackson (15) predicts the U processes will not affect the temperature dependence, but will enhance the coefficient of the T5 term. In consider- ing the effect of impurity scattering in the Klemens- Jackson model, Ehrlich (14) derived an added term prOpor- tional to T2 as well as an additional enhancement to the coefficient of the TS term. Klemens and Jackson and 5 Ehrlich assumed pph « T in the absence of U processes. 37 Dugdale and Basinski (17) have pointed out that presence of deviations from the MR due to the two-band effect can also enhance the coefficient of the pph power law term in the limit, p0 >> pph' Although there is little agreement among the above authors as to what the power, n, should be for pph « Tn, there is agreement on the premise that n is as large as or larger than the highest power observed in 6(T) = p(T) - p0, and that it is difficult to underesti- mate pph from the experimental data. The resistivity due to phonon scattering in pure aluminum has been assumed to be the smaller of pph = 1.56 x 10-10(u9cm/°K5)T5, 5.2 the low temperature limit, or at high temperatures, pph _ — Q o 5.3 ppure o The cross-over from use of Equation 5.2 to Equation 5.3 usually occurred at ~40°K. The T2 term has been associated with electron-electron scattering (35, 36) but, as will be discussed later is most likely a deviation from the MR. The values for b reported by Reich (33) were rejected since his data were taken in the region pph 3 po, which as will be seen later, is the region where additional de- viations from MR are large, thus affecting the apparent coefficient of the T5 term. Aleksandrov (35) relied on 38 data (34) from the region T > 50°K, the data taken in this study indicates n < 5, so the T5 coefficient reported by Aleksandrov was considered unreliable. The b value for the sample measured in this study which had the lowest residual resistance was not used, since it was relatively small (.25 mm diameter) and size effects have been shown to exhibit temperature dependent deviations from the MR (21). The largest diameter sample (.5 mm) with the lowest residual resistivity (p0 = .0014 uQ—cm) was chosen as the most reliable, thus giving the value for b quoted in Equation 5.2 The Deviations from Matthiessen's Rule in Aluminum Alloys The deviations, A(T), from the MR for thirteen aluminum alloy wire samples are shown as A/pO vs tempera- ture in Figures 7 through 10. The AlfMg system is repre- sented in Figure 7, AlfCu in Figure 8, Alen in Figure 9, and AlfGa in Figure 10. The qualitative behavior of the deviations ob- served was the same in all cases. The temperature depend- ence is characterized by a sharp rise from zero for low temperatures (T < 40°K), a peak or saturation plateau in the region 40°K < T < 100°K followed by a region with dp/dT 1’0 as 300°K is approached. Figure 11 shows the deviations from the MR for the same alloys as log A/pO vs 39 .mmoaam mziam cfi Odom m.cmmmmwnuumz Scum mcowumw>mall.h musmflm CE mmzkmoll.m mnsmfim gov mmak o 4 0 >> < p» q 0 ED D D D g Q o 3» >>>B>>>>>>>>>Kyos a 1.0 .. o a %% a co Sq <<<<<<<<<<<woli.m musmwm AxovmmDH’umma—zwk oom 0mm OON on. 00_ On 00 . _ . . . Edwin 4 Q 0 d «cc 0 <<<<<<<<<<<mali.oa whomam .xcmm=h>>> >>>>>>> puppppptb 4x0 ‘ X 4 Se eeaaegi: x o t 4 . a 444 <4 xxxxxxxxxxxxx 00 1V 4 a a x a“ 00008088003. 0 d a a I! “O O as r ””0“ 00 I”. 0 fl 0 a u o so-a1~v_..oHHm ESCHEDHM mo mmHuH>HpmHmmu Hospflmmmil.ma musmflm Czwommm oiohds o N . o 46 A d o6 No ad _. ton mo nu w d lmoo ( 26...: «o -._< > 964.: zN-._ 0 for all no # 0. Consequently, a non-zero deviation from the MR is implicit in the phonon resistivity calculation of Equation 5.3. 53 I l I I 1 T l l aoI- AL-MG ALLOYS 0.. AL‘CU ALLOYS 7o- AL-ZN ALLOYS AL-GA ALLOYS 60 " P .2 5 d A 2 30 °K .1 Io- '/ - 0 .I . , . B (pH-cm) Figure 14.—-Koh1er-Sondheimer-Wilson plot at 30°K. 54 2() I l l GAL-MG alloys AAL-CU “ VAL -GA '5r xAL-ZN " O. I 1 1 O .2 £1 .6 p,(/.LQ-cm.I Figure 15.--Kohler-Sondheimer-Wilson plot at 70°K. 55 .xommm um “Cam COmHABIHmEflmspcomlumanomii.oH mnsmwm 28-0.3 ml IMII r 3.44 1 m Q 4 30.44 w§3a§$ E I 62...; EC- 0 G O @234 m’gbowmmoo “Moo Waco 2‘39, oz o. 365% 6.34 Am. _ b b _ P 56 In the temperature regions for which Equation 5.3 was the appropriate definition for pph’ corrections were made to pph to insure the inferred deviation from the MR in the pure sample was consistent with that observed in the alloy samples. A KSW plot was generated using the uncorrected p . The average intercept ph lim Do """"'I pd+0 A b: was used to calculate a pph from the pure data consistent with the alloy data, pph(T) = pP(T) - po(l + 1/b), which was then used to generate another KSW plot. Usually one more iteration yielded self—consistency to within the ac- curacy of the dimensional measurements. The parameters a and B are shown in Figure 17. The parameter a is strongly temperature dependent varying from ~104 at 8°K to ~2 at 100°K, while B is relatively in- sensitive to change in temperature in this range. Two in- consistencies with the two-band model are apparent in Figure 17. The variation in B with temperature is not anticipated since p: and pg are assumed to be temperature independent. The two band approximation may not fully repre- sent the relaxation time anisotropies, or additional mechan- isms may give a temperature dependent 90 for one or both of the bands. The KSW scheme for extracting a and 8, however, rely heavily on a constant impurity resistivity. Below 20°K the value for B is quite sensitive to the choice of 57 20000 I I IInIII I ITIIIHI T I IIII IOOOO:- ! -—__1 500g: 5 a .8 ALLOY j _ O 0 AL MG .. 2000- A A AL CU _ I D AL ZN V V IOOO__— ' AL GA _— E 2 : 500'- q I m 200“ _. ICK):- ‘x _— .. :- . : c3 50- _. . v —1 20" g : —-I A 9 V _. I .—_ IO: 6 5A 1 I- . : 5: g o “I : g g§°o‘: .. 2+ 6AA! - 38", I 1 1111111L 1 1111111I 1 1111111 | 2 5 I0 20 50 I00 200 500 T (°K) Figure l7.--KSW parameters a and B as a function of tempera- ture. ' 58 intercept in the KSW plot, which in turn is quite sensi- tive to deviations in the MR implicit in Equation 5.2. If the T5 coefficient were about 20% smaller, 8 = 4 :_2 would fit to within the precision of the experiment. A flaw of an even more serious nature is evident at about 90°K, where Figure 17 shows a = B. This would be consis- tent with the two-band model only if deviations from Matthiessen's rule were zero at the temperature for which a = B. This is the region where thermal expansion begins to be important, and the error bars implicit make a choice of a > 8 possible up to 300°K. Figure 18 shows p; = (a+l)pph/a as a function of 5 T, showing that for T : 60°K, is of the form bT . The 3' Dph total phonon resistivity pph follows the same power law for T < 40°K, but follows a weaker temperature dependence at higher temperatures. The error bars shown indicate the magnitude of the uncertainties for the points representing 3' . j . _ pph and pph. Below 30 K, a >> 1 and pph cannot be dlS . . j i = tinguished from pph' In contrast to pph’ pph(T) (a+l)pph is linear in T as shown in Figure 19. Below 20K the in- determinant nature of a makes the calculated values for pgh quite uncertain. Using the evidence summarized in Figures 18 and 19, it is proposed that the bands i and j represent the states on the third zone electron and second zone hole surfaces of the aluminum Fermi surface, respec- tively. 59 '04:; j I IIIIIII I II III' I I TIITT-‘IOZ I '0 AL-MG Alloys : r blaAtcu : 1 -13 lPh DIALTIZDI ' '0 F LVAL-GA " q l0 C T5 «T : ”' I. Z 1 b 1 '01? . —. IO° E - a h : 4+. 1 h Pph ,Pph _ ‘ " Pph 0P” (II-$7.1m)r :1 #97ch '01? 1 I0”. IO-Sp ' P"= 9%! @55le E + Pph E -6 L 1 L1 0'3 '0 |.O IO .0 l. . . T (’K) Figure 18.--Phonon resistivity of the hole band. 60 .pcmn couuomam man no wuw>flumflmmn coconmll.mH munmflm 35 .r OON OO— Om ON 0. m N _ I—. 114 q q _ d —« 51 0% - a A _O. .m>01_l_4 4011.4 4 . NO. um>0.._l_4 ZNll_4 o 1 rm>0134 3011.4 4 - .810 @634 3.-.: o w\ H no.1. n m .n n. l. _0 U 4.. . .3 W T 1 n “no 1 .r. . p —P__ . p . . .lL 4 Ava 61 Phonon resistivity linear in temperature is usu- ally associated with segments of the Fermi surface with dimensions such that the phonon wave vector, Eb, necessary for large electron wave vector scattering angles has a population density, n(qb) 3 1. Where -1 éhw/kt-l) . 5.17 + n(qb) = ( The characteristic temperature for which n(qb) = l is de- fined by + hm T(qb) = k , 5.18 where mg is the frequency of the phonon ab. Figure 20 shows such an event scattering an electron from the state ki to kf on the external cross-section of an arm of the third zone of the Ashcroft model of the aluminum Fermi surface. Hartmann (41) has fit neutron diffraction data to a dynamical model of the aluminum lattice giving the phonon dispersion shown in Figure 21. The phonons 3b 7 cm-l), which are appropriate for the scattering event shown in Figure 20 have mg 2 40 x 1011 sec-1. Thus (2 10 11 —1 sec I 5.19a -1 I (10-27)erg-sec(40x10 ~16 T(qb) = 1.4 x 10 erg °K giving T(qb) 2 3o °K. 5.19b 62 BRAGG PLANEx (' 'I\ l J 1 ' 01 ALU. Figure 20.-—Backscattering event on third zone extremal cross-section. 63 f Janu‘w 600 ”x'0 500 400 r it ___- -e __t 1‘”, (3/4 3/4 O)(ll0)(|00)(l'/4 V4) 1‘”, Figure 21.~-Phonon dispersion spectrum for aluminum. 64 Since the phonon wave vector ab crosses a Bragg plane, a reciprocal lattice vector also enters into the momentum conservation for this event. Phonons such that q :_qb can also participate in similar backscattering events. If T(qb) = 30°K then T(q < qb) < 30°K and the population of phonons capable of resistive backscattering is large enough to expect a linear temperature dependent resistivity even below 30°K. Thus, it is reasonable to interpret the linear temperature dependence of the resistivity, pgh, in- ferred from the KSW equations as associated with the third zone electron states. We set i _ e pph " pph 0 This leaves the interpretation of the resistivity p; as being associated with the second zone hole states. Ehrlich (14) has calculated the low temperature resistivity of monovalent metals whose Fermi surface touches or nearly touches the Brillouin zone boundaries, extending the Klemens-Jackson (15) theory to include the simultaneous presence of impurity and thermally-induced Umklapp scatter- ing. The second zone hole sheet of the trivalent aluminum Fermi surface when considered alone and in the extended zone scheme, is analogous to the case considered by Ehrlich. The application of the Ehrlich theory to devia- tions from the MR in pure aluminum will be treated later. In this case, however, the resistivity, does 3' pph. 65 not exhibit the T2 component which Ehrlich predicts for the case of U processes in the presence of impurity scat- tering. The T5 component is compatible with the Ehrlich theory, assuming, as does the Ehrlich-Klemens-Jackson approach, that pph s T5 for no U scattering processes. In presenting the Bloch-Grfineisen pph a T5 formal- ism, Ziman (42) asserts that the fifth power of T, or as has been pointed out (14, 15,37, and 38) some other high power of T, is a characteristic quantum effect in the limit of phonon momentum too small for effective large- angle resistive backscattering. Phonons capable of direct resistive backscatter on the hole surface must extend to the region of the {100} and {110} planes in reciprocal space (see Figure 21), so 350 x 1011 < mg < 600 x 1011 rad./sec. giving 250 < T: < 430 °K. This band then, is considerably removed, in terms of available phonon momen- tum, from the region where single event, large-angle scattering is anticipated. We thus set pph = pph. 5.21 Since a > 1 at low temperatures, the phonon resis- tivities of the hole and electron bands are in the order pgh > pgh. Huebener (43) has applied a two-band model to the low temperature phonon drag thermopower he has ob- served in aluminum alloys, and concluded that 02h > 02h is consistent with the data. 66 Although the data fit the KSW equations, applica- tion of the two-band model to the deviations from the MR in these aluminum alloy systems cannot be carried out without the ambiguities previously discussed. The phonon resistivities inferred for the two bands are consistent in temperature dependence with the dimensions of the third zone sheet of electron states and second zone sheet of hole states in momentum space. The Ehrlich Theory The parameters a and b, of the Ehrlich (14) Theory, in Equation 1.6 are related by for 8 (angle of contact of the Fermi surface with the Brillouin zone boundary) held constant. This Can be shown by dimensional analysis. The quantity a/b must have di- mensions (temperature)3. Now the only variable parameter 0 5.23 5 must be fixed in terms of po and b0, where boT is the phonon resistivity in the absence of U processes. Thus 3 2" _ 0 3/5 T _ (B—O'fi’)’ 5024 67 so a a 3/5 B (00) . 5.25 Figure 22 shows log(a/b) vs log p0 for the data in Table 2 and one Al-Ga alloy. SlOpes corresponding to po3/5, the 2/5 have been drawn. Al— theoretical relationship, and po though the Ehrlich theory predicts the correct temperature behavior for deviations from the MR for relatively pure aluminum or very dilute aluminum alloys, the coefficients 3/5 2 do not follow the predicted po law. Further, the T term could not be detected in the low temperature resis- tivity of the more concentrated alloys even though the T2 3 term which was term should be about as strong as the T observed for T < lO°K. Although the processes which the Ehrlich Theory considers are certainly appropriate to aluminum and aluminum alloys, the data do not support the predictions of the theory. The Mills Theory Mills (16) has calculated the additional resis- tivity A(T) for the second order process involving scat- tering from an impurity and the .Subsequent, emission or absorption of a phonon. The result is the form A(T) o: 0 5.26 O 68 .suomaa noaausm map on a cam m mpcmfiofimmooo man no unmnu.mm museum .80..ch m. i O. Om ON 3 m. N. . _ Jj-_ _E-u fidJl _. 00. N0 _0. 1... .. . MO— l J IIIIITI T 111111 1 o o D\NQ O. o ..o. amhm. 12mm n. . >omozz_ .rzmmmmm 0 >041? <05... 9 __.k... _ ___. __L I. __....r. r 00— l l TlllllT llLl l l 69 where y(T) is proportional to the electron-phonon inter- action relaxation rate, and y(T) ~ 0 In the limit ph' 90 >> Y(T) I A(T) = cT3, 5.27 which is consistent with the data below 20°K as shown in Figure 11. The form of Equation 5.26 is also consistent with the situation that T3 behavior is followed to higher temperatures for the more concentrated alloys. For larger p higher temperatures must be reached before the y(T) 0! term becomes important, thus altering the T3 temperature dependence. In order to determine the dependence of A(T) on the residual resistivity, y(T) must be included to first order. In the limit pO >> pph ~ y(T): 3 T A(T) “ 5.28a 1 + ——YzT) ' O a T3 (1 - 1131), 5.28b Do a - T3 1n(11319. 5.28c p0 Thus, for the T3 region of the data, A(T) = cT3 « T3 ln pO-T3 ln T 5.29 70 so, c a 1n p0. 5.30 Figure 23 shows the value obtained for c from a fit of A(T) to Equation 5.27 as a function of log 00. The dashed straight line was taken from data reported by Caplin and Rizzuto (23) for 14°K. The points for Ekin and Maxfield (44) were taken from their published data from 1.2°K to 7°K for a mono- crystalline wire (p0 = .85 nQ-cm), a polycrystalline ribbon (p0 = .42 nQ—cm) and a polycrystalline wire (00 = .40 nQ-cm). At temperatures above 20°K the pure samples have a T2 deviation from the MR. Yet, as shown in Figure 6, the T2 deviation is replaced by some higher power of T below 20°K. Figure 11 suggests that the deviations follow a T3 law below 15°K. The T3 at low temperatures--T2 at high temperatures behavior is not consistent with a simple power law composition but may be understood as the effect of the coefficient of the T3 term modulating the tempera- ture dependence from the T3 low temperature limit to T2 at higher temperatures. This is consistent with the re- sult in Equation 5.26 if pph ~ p0 and 00 + Y(T) or T. 5.31 71 C (pfl- cm/°K3) .oQ mo :OHvOCSM m mm mEHmu B can a man no muqmnoammmouuu.mm musmHE m m .Eo-d1. m. 00_ _.0_ NF? m..O_ .70. 0.9 0’114.. « . ~..q.m. . J —qdq+.u . . :...«1. q 1... 11W. O .2252 .. 5.5 o . . .. . 9.3. 5.80--- . xx .. 4012. D xxx ”032.: .. ZN-_< D xxx libs: D 2 DUI—q 4 C \\\m 1m, . :22 22.... o m .. xx 6 _< 8525 x .xxx .. r . .4 2.5 + p xxx 0 m D \ O_xN.| I \\ / s- kzmoiumoo ._._..o x 1 o n u xxx 65:09.24 9 w.o_xN M2 . o D xxgxx 5:... u ( p a xxvx mtosom w 23:00 4 . xxx 6:4 40:3 D #9me a xx 5:03.32: 2.39... o 4 D O\\ 10'0—Xm xxx HszEum—oo uh u D V\O\ KNO—xv :P.-h . » —:.P-rr _ rP-er. r » P:p..b - r _pppp.~ . p 72 If this were the situation, one would expect the coefficients a, of the T2 term, and b, of the T3 term, to be proportional, and thus a m lnpo. 5.32 The coefficientsxaslisted in Table 2 and for the least dilute Al-Ga alloy are also plotted as a function of lnpo in Figure 22. The change in scale was calculated from the average experimental ratio, c/a = 0.105°K-l, for 3 and T2 terms observed in the three pure samples the T measured in this study. The agreement in functional de- pendence upon po indicates that it is consistent to con- sider the T2 and T3 terms to be the intermediate and low temperature manifestations of the same effect. As pointed out in Equation 5.31, the relaxation rate must have a nearly linear temperature dependence for such a modulation effect to take place. In the pure matrix, one expects (45) that. the relaxation rate y(T) « T3 for T << 6D. Conse- quently the assumption of Equation 5.31 is not consistent with theoretical anticipation. The Mills Theory is successful in predicting the concentration and temperature dependence of the deviations from the MR in aluminum alloys at low temperatures. The theory is not successful at higher temperatures, since the observed temperature dependence is not consistent with that theoretically anticipated for y(T). SUMMARY AND IMPLICATIONS FOR FURTHER STUDY At low temperatures, the two-band model and the Mills Theory are both consistent with the deviations from the MR observed in the resistivity of aluminum and dilute aluminum alloys. Both theories (Equations 5.12 and 5.26) predict deviations from the MR of the form oof('1‘) + g (T) A(T) 6.1 Do so it is necessary to weigh the relative merits of the two theories on the basis of the functions f(T) and g(T). The a and 8 parameters of the two-band model and the y(T) and T3 terms of the Mills Theory have all shown inconsistencies between the experimentally-determined and theoretically- anticipated values. Two-band effects have been used in considering Hall field reversals (46) in aluminum and phonon drag thermopowers of aluminum alloys (43). A coordinated effort of resistivity (and associated pressure measurements), thermopower, Hall effect, magneto resistance and thermal conductivity measurements on the same high purity aluminum and well-characterized dilute aluminum alloy samples could 73 74 provide evidence as to the relative importance of the Mills or two-band theories. There is a further, more specific test. The Mills Theory may be construed as implying (see Figure 22) that for p0 ~ 10-5uQ-cm, the T2 and T3 terms in the resistivity of aluminum should be negligible. The two-band model (Equation 5.12) predicts that for all pure samples in the region, po >> pph’ the deviation from the MR is proportional to the phonon reSistivity. An experimental measurement of the resistivity of pure aluminum (RR > 105) would be par- ticularly useful in weighing the relative merits of the two theories. REFERENCES 10. 11. 12. l3. 14. 15. l6. 17. REFERENCES A. Matthiessen, Ann. Physik. Chem. 110, 190(1860). A. Matthiessen and C. 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B, chum; 15, 1971). J.M. Ziman, Electrons and Phonons (Clarendon Press, London, 1960), p. 365. R.P. Huebener, Phys. Rev. 171, 634(1968). J.W. Ekin and B.W. Maxfield, Phys. Rev. B 3, 4805(1970). A.A. Abrikosov, L.P. Gorkov and I.E. Dzyaloshinski, Methods of Quantum Field Theory in Statistical Physics, translated and edited by R. Silverman (Prentice-Hall, Englewood Cliffs, N.J., 1963), p. 182 f. N.W. Ashcroft, Phys. kondens. Materie 3, 45(1969). APPENDICES APPENDIX A FORTRAN LISTING OF COMPUTER PROGRAM FOR CALCULATING RESISTIVITIES ll“! 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