Solid State Chemistry of Crystalline and Glassy Chalcogenides

Northwestern University, Evanston IL

Investigators

Abstract

The present research program aims to expand the boundaries of what is possible in the solid state by pursuing and developing new synthetic methodologies for metal chalcogenides. The project deals with the effectiveness of salt fluxes to discover new materials in the broad chalcogenide class of compounds as well as with the in-depth studies of these materials. The need to control chemical reaction systems and to discover new materials through developing general synthetic methodologies defines one of the main challenges to our understanding of the relationships between chemistry, crystal structures, and properties in complex solids. Many of the relationships are subtle and poorly understood. In particular, the project focuses on complex ternary and quaternary metal chalcophosphate and chalcoarsenate materials. This class continues to present marvelous scientific challenges and it is broadly relevant to many technological applications. An extensive and diverse set of characterization tools will be applied. Exciting new materials are anticipated with interesting and potentially useful physical properties such as semiconducting behavior, non-linear optical activity, glass formation, and reversible phase-change crystal to glass transitions. The project will explore (a) lithium polythiophosphate and poly-selenophosphate fluxes to discover new alkali metal-free phases and also lithium-containing phases; (b) the synthesis of low valent selenophosphates and tellurophosphates (i.e. compounds with phosphorous atoms in a low valent state); (c) alkali metal polythioarsenate and polyselenoarsenate fluxes to further develop this chemistry and discover new materials; (d) investigation and study of the properties of glass forming systems occurring in certain chalcogenide stoichiometries.. These are called phase-change materials and are relevant in non-volatile data storage and computer memory applications. The results obtained from this research will enhance our understanding of chalcogenide phase stability, structure, bonding and properties. This project will educate and expose students in a worthwhile intellectual discourse. The students working on the project will receive outstanding training in synthetic solid state chemistry and materials research. They will acquire a direct awareness of the relevance of their materials to science and technology. The proposed activity will strive to furnish a meaningful, coherent research and education program for students so they, as future independent scientists, are able to synthesize, handle and manipulate novel classes of solid-state materials. Relatively few laboratories in the US provide this type of synthesis training. Undergraduate students also participate in this type of research, which has a lasting impact on their college laboratory experience and future career choices. Non-Technical Abstract New materials are at the core of many advanced technologies and products. This project seeks to discover new materials using novel synthesis techniques and to train students in the discourse of this type of research. The materials belong to the broader class of semiconductors and are expected to possess potentially useful physical properties and economic value. These include controllable electrical conductivity, photoactivity, glass forming properties and phase-change properties. In this project will investigate new phase-change materials which are relevant in non-volatile data storage and computer memory applications and in the sensing of chemicals in the environment. The methodology developed and the insights gained during this work, about the formation, chemistry and properties of unusual solids, could enable or facilitate useful technologies and thus could make an important contribution to science and could have a significant impact in a number of technologies and by extension on the US economy. Graduates and undergraduate students participate in this type of research, which is expected to have a lasting impact on their college laboratory experience and future career choices. The results of this research will be open to the public and will undergo peer-review before being published. The broad dissemination of scientific results and knowledge through the communications media, the web and journal publications will help enhance the public's awareness in the new knowledge being generated as well as its scientific understanding and appreciation of science.