UCLA

The thermoelectric figures of merit of bulk materials up to date have not overcome zT = 3, and only in rare occasions have they surpassed zT = 2. Bulk thermoelectrics with zT > 3 have been desired but have not yet been theoretically predicted let alone experimentally realized. In this doctoral work, high-performance thermoelectric materials theoretically capable of zT > 4 are identified and characterized using state-of-the-art first-principles com- putational methods based on density-functional theory. Ba2BiAu and Sr2BiAu full-Heusler compounds in particular are predicted to deliver ultrahigh thermoelectric performances – the latter across all temperature domain from cryogenic to high: 0.3 ≤ zT ≤ 5 at 100 K ≤ T ≤ 800 K. While unfortunately the compounds look not n-dopable and their predicted zT values inaccessible, they constitute a theoretical proof of concept that zT > 4 is within reach for bulk compounds. With the lessons learned from these compounds and others, the optimal electronic structures for intrinsic thermoelectric performance are generally determined for both semiconductors and metals. Highly dispersive bands at off-symmetry points that min- imize electron-phonon scattering is optimal for semiconductors, while a flat-and-linear band crossing that leads to electron filtering and high Seebeck coefficients is optimal for metals. May these generalizations help propel discoveries of more high-performance thermoelectrics.