| Phase-change materials are defined here as materials that undergo reversible, thermally-activated glass-to-crystal transformations. These materials are utilized commercially in data storage 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 nonstochiometric alloys of Ag, Sn, Sb, Ge, In, and Te. The next generation of data storage devices calls for faster switching rates, higher storage density, and better cyclability, for which the currently used materials may not be sufficient. This thesis will present several new chalcogenide-based phase-change materials that contain alkali metals and the lighter chalcogenides S and Se. These materials, including K1-xRbxSb5S8, K2Sb8Se13, and K2Bi8S13, can be reversibly, thermally interconverted between glassy and crystalline phases. They are semiconductors and have optical band gaps in the range of 0.9-1.8 eV, which permits encoding by visible or ultraviolet laser irradiation. The 1-xRbxSb5S8 family of solid solutions shows the ability to 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 two distinct amorphous phases as well as a crystalline phase, and each is stable and can be isolated at room temperature. Formed as a thin film on glass and silicon substrates, K2Bi 8S13 was 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 diffraction (XRPD, PDF), and electron microscopy (TEM, SEM). |
