9622025 Kannewurf This research is concerned with the use of molten polychalcogenide salts as reactive media to explore the synthesis of new chalcogenide materials at low and intermediate temperatures (200-500 C). Various A2QX salts (A=alkali cation, Q=S, Se, Te) will be used in reactions with late transition metals and main-group elements. Emphasis will be given in the stabilization of quaternary phases. Three kinds of quaternary compounds will be explored in this stage. One kind involves the mixed-metal system A/M/M'/Q (M=late transition metal, M'=lanthanide, actinide). The second involves the mixed-chalcogen system A/M/S/Te. The synthetic approach will use binary alloy compounds as starting materials and mixed fluxes such as mixed A2TexSy. The third kind involves the use of the thio- and seleno- phosphate fluxes in materials synthesis. These fluxes are new and are designed to yield novel thiophosphate and selenophosphate solids containing the PxQy n- polyanions (where Q=S, Se). The physical properties of the new compounds, such as spectroscopic, thermal and magnetic will be studied as a function of temperature. In order to probe for unusual electronic phenomena, the charge transport properties of the new compounds will be studied in detail via variable temperature four-probe resistivity and thermoelectric power (Seebeck) measurements on single crystals. %%% This research is concerned with new methodologies to discover new solid state materials having various technologically important properties. Promising materials will be studied further and their potential for applications will be evaluated. The subject of this proposal is performing reactions using molten salts as solvents. Molten salts have been employed for well over 100 years for high temperature single crystal growth. Although many salts are high melting species, eutectic combinations of binary salts and salts of polyatomic species often have melting points well below the temperatures of class ical solid-state synthesis, making possible their use in the exploration of new chemistry at intermediate temperatures. In some cases, such salts act not only as solvents, but also as reactants, providing species which can be incorporated into the final product. Such studies are important because polysulfide ligands have been implicated in the hydrodesulfurization of crude oil, where they are thought to be present at the surface of metal sulfide catalysts. Polychalcogenide glasses also are important as materials for non-linear optics, IR wave guides, optical switching, and optical information storage, but the structure/property relationships have not been well determined due to the amorphous nature of the compounds.
