A p-type thermoelectric material BaCu4S3 with high electronic band degeneracy

Abstract

Thermoelectric materials have been considered as an alternative clean energy technology that can realize direct conversion between heat and electricity. However, few studies have focused on the underlying relationship between the bonding orbitals and physical properties, which has severely impeded the development of new thermoelectric materials with outstanding electrical properties. α-BaCu4S3 is a thermoelectric material that has a high density of states at the upper end of the valence band due to triply-degenerate Cu 3d orbitals in the CuS4 tetrahedral structure. Thus, it has a high Seebeck coefficient at the same carrier density among thermoelectric materials. α-BaCu4S3 shows a zT value of 0.22 at 750 K. A higher zT of 0.32 at 750 K was realized in BaCu3.96S3 by introducing copper vacancies. The current study provides a strategy to identify high-performance thermoelectric materials through high degeneracy of orbitals that comprise the electronic bands.