****NON-TECHNICAL ABSTRACT**** The thermoelectric effect is the conversion of a voltage difference to a temperature difference and vice versa. A material that exhibits a large thermoelectric effect is called a thermoelectric material. A measure of how big an effect a material exhibits is called the material's 'figure of merit' and is designated ZT. Developing new thermoelectric materials with a high value of ZT is an important national goal for both energy and cooling applications and requires an understanding of the behavior of new materials at both atomic and macroscopic scales. This individual investigator award supports a project that will carry out local structure investigations for a series of thermoelectric materials to better understand the local (atomic-level) physics that controls important parameters that determine ZT, such as a very low thermal conductivity and a high power factor. These measurements will determine local distortions, distributions of atoms in the crystals, and changes in the electronic structure; such results provide constraints for theoretical models and important feedback to the project's collaborators who are developing new materials. This project will provide educational and research opportunities for both undergraduate (Senior theses) and graduate students (PhD theses); the students will also gain important experience working as a team at national synchrotron facilities.
Developing new thermoelectric materials with a high figure of merit, ZT, is an important national goal and will require detailed characterizations of new materials at both the local and macroscopic levels. This individual investigator project will use X-ray absorption spectroscopy (XAS) to investigate the local structure of a series of new materials to elucidate the local (atomic-level) physics, which determines the unusual low thermal conductivity and the recently observed enhancement of the power factor when a few specific dilute impurities are added to some systems. The low thermal conductivity is attributed to various types of local disorder within each material which is easily determined using XAS. Changes in the electronic structure about defect atoms will be probed via changes in the shape of the absorption edges. These results will provide important constraints for theoretical models and crucial feedback to the project's collaborators who are developing new materials. This project will provide educational and research opportunities for both undergraduate (Senior theses) and graduate students (PhD theses); these students will also gain significant experience working as a team at national synchrotron facilities.
