The realization of a high thermoelectric figure of merit in Ge-substituted β-Zn4Sb3 through band structure modification

Abstract

In this study, we demonstrate a realization of a favorable modification of band structures and an apparent increase in the density of state effective mass in β-Zn₄Sb₃ compound by introduction of a slight amount of Ge at the Zn site, in a manner of adding a shape peak below the valence band edge and giving rise to a significant enhancement in the power factor which is similar to the case of Tl-doped PbTe. As a consequence, the high power factor exceeding 1.4 mW m⁻¹ K⁻², coupled with the intrinsic very low thermal conductivity originated from complex crystal structures and a high degree of disorder, results in a maximum figure of merit of ∼1.35 at 680 K for the 0.25 at% Ge-substituted sample, which is ∼20% improvement as compared with that of the unsubstituted sample in this study. What is most important is the average ZT between 300 and 680 K reaches ∼1.0, which is ∼35% enhancement in comparison with the unsubstituted sample and superior to most of p-type materials in this temperature range. Furthermore, the combination of high thermoelectric performance and improvement in the thermodynamic properties makes this natural-abundant, “non-toxic” and cheap Ge-substituted β-Zn₄Sb₃ compound a very promising candidate for thermoelectric energy applications.