Intrinsic vacancy suppression and band convergence to enhance thermoelectric performance of (Ge, Bi, Sb)Te crystals

Abstract

GeTe-based alloys have drawn increasing attention because of the excellent thermoelectric (TE) performance and potential applications in mid-temperature range. Although reducing carrier concentration by aliovalent doping plays an important role in maximizing the TE performance of GeTe alloys, modulating the intrinsic Ge vacancies is also indispensable. In this work, the intrinsic Ge vacancies of GeTe crystals were suppressed by the synthesis process of temperature gradient cooling technique (TGCT) and Bi-Sb co-doping. The later aliovalent doping also derives a facilitated band convergence, enhanced density-of-state effective mass, and maintained carrier mobility with optimized carrier concentration, along with enhanced phonon scattering from the fluctuations of mass and strain. Benefiting from enhanced electrical properties and reduced thermal conductivity, Ge0.91Bi0.06Sb0.03Te achieved a maximum ZT of 1.9 at 753 K, together with a comparable average ZT of 1.14 at 300–773 K. The results reveal the potential of the TGCT fabrication and Bi-Sb co-doping on enhancing TE performance of GeTe-based alloys with a strengthened suppression of Ge vacancies.