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

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 beta-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 similar to 1.35 at 680 K for the 0.25 at% Ge-substituted sample, which is similar to 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 similar to 1.0, which is similar to 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 beta-Zn4Sb3 compound a very promising candidate for thermoelectric energy applications.