Synthesis of Zintl Phases for Thermoelectric Applications

University Of California-Davis, Davis CA

Investigators

Abstract

TECHNICAL SUMMARY: This project, supported by the Solid State and Materials Chemistry program focuses on the synthesis of new Zintl phases, incorporating transition metals in order to target a high density of states (DOS) at the Fermi level (through partially filled d orbitals) to obtain high Seebeck coefficient (Power factor) and therefore high zT. Nanostructuring will be employed to further reduce the thermal conductivity. Phases will be synthesized via flux and metallurgical routes. Utilizing a suite of physical characterization techniques including single crystal and powder X-ray diffraction, SEM and TEM, elemental wave dispersive microprobe and ICP-MS analysis, parallel electrical and magnetic measurements, the structure and phase composition will be correlated with electronic and thermal transport properties. The ultimate goal of the project is to discover new materials with high zT for the direct conversion of waste heat into electricity. Building upon recent results of demonstrated high zT in Zintl phases, this proposal closely links synthetic strategies with characterization of physical and chemical properties, thus providing efficient feedback to guide improvement of these thermoelectric systems. NON-TECHNICAL SUMMARY: Thermoelectric devices for power generation convert thermal energy directly into electrical energy, require minimal maintenance, and can be operated over a large temperature range (room temperature to 1000 degrees C). Thermoelectric materials are described by a figure of merit, zT, which relates to how well a material converts heat flow to electricity - the higher the value, the greater the efficiency. Recent discoveries of Zintl phases with zT of 1.0 or greater highlight the importance of continued exploration of new materials. A Zintl phase is a compound which contains both cations such as alkali, alkaline earth, and rare earth elements which donate electrons to polyanionic units composed of main group elements such as those from groups 13, 14, and 15 of the periodic table. These types of compounds naturally provide low thermal conductivity which is a requirement for thermoelectric devices. With higher zT, the potential for solid-state power generation from waste heat recovery provides a framework for investigating new Zintl phase materials with stability and optimal properties at high temperatures (>300 degrees C). This project supports minorities and women at the initial stages (high school to college and college to graduate school), along with training graduate student for scientific careers. Students develop scientific, social, and professional skills through hands-on training, exploration, and dissemination of research to the broader scientific community. The topics under study include materials synthesis and property measurements, fundamental training in materials synthesis and structure-property correlations, providing an important foundation for the development of thermal to electrical energy conversion and the advancement of multidisciplinary research aligned with technology. The research will be presented at national and international meetings and the findings published in peer-review journals. Additionally, the PI supports students through the ACS SEED program (high school), MURPPS (undergraduate), and AGEP (graduate) programs focused on increasing underrepresented groups in science on campus. The ChemWiki will be employed to enhance student learning through writing and critical evaluation.