New Materials From Reactions in Intermediate Temperature Molten Salts. Synthetic Methodologies for Multinary Solid State Chalcogenides

Abstract

The critical role solid state chemistry and physics play in modern technology is in little doubt. Solid state compounds have been the foundation of the entire electronics industry for many years, and many emerging technologies such as nonlinear optics, high-T_c superconductors, high energy density storage batteries, and photovoltaics, to name just a few, will hinge on developments in the economical processing of existing solid state materials and the discovery of new materials with new or enhanced properties. In this context, the importance of exploratory solid state synthesis is obvious. The bulk of exploratory synthesis in solid state chemistry traditionally has relied on high temperatures (>600 °C) to defeat the problem of solid state diffusion. These high temperatures give rise to two important synthetic limitations. First, the reactions almost always proceed to the most thermodynamically stable products; the high energies involved often leave little room for kinetic control. These thermodynamically stable products are typically the simplest of binary or ternary compounds, and because of their high lattice stability, they become synthetic road blocks which often take a considerable investment of effort to circumvent, if they can be circumvented at all. Second, the high reaction temperatures also dictate that only the simplest chemical building blocks can be used; that is, elements on the atomic level. Attempts to synthesize using molecules of known structure are doomed because the high temperatures used disrupt most bonds and reduce the system to atoms rushing to a thermodynamic minimum. Hence, multinary compounds are more difficult to form, the preference lying with the more stable binary and ternary compounds.