Phase-change materials are defined here as materials that undergo reversible, thermally activatedglass-to-crystal transformations. These materials are utilized commercially in datastorage media such as rewriteable CDs and DVDs as a way to reversibly encode binary data.The current industry standards for these materials are Ge2Sb2Te5 and several nonstochiometricalloys of Ag, Sn, Sb, Ge, In, and Te. The next generation of data storage devices callsfor faster switching rates, higher storage density, and better cyclability, for which the currentlyused materials may not be sufficient. This thesis will present several new chalcogenide-basedphase-change materials that contain alkali metals and the lighter chalcogenides S andSe. These materials, including K1-xRbxSb5S8, K2Sb8Se13, and K2Bi8S13, can be reversibly,thermally interconverted between glassy and crystalline phases. They are semiconductorsand have optical band gaps in the range of 0.9-1.8 eV, which permits encoding by visibleor ultraviolet laser irradiation. The 1-xRbxSb5S8 family of solid solutions shows the abilityto tune the thermal and optical properties of these materials by changing the value of x.K2Sb8Se13 shows the extremely rare behavior of polyamorphism wherein there exists twodistinct amorphous phases as well as a crystalline phase, and each is stable and can be isolatedat room temperature. Formed as a thin film on glass and silicon substrates, K2Bi8S13was shown by kinetic measurements to have the potential to switch faster than existing materials.These compounds were characterized by thermal and optical analysis (DTA, DSC,UV-Vis), X-ray diraction (XRPD, PDF), and electron microscopy (TEM, SEM).
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