Synergy of grain size and texture effect for high-performance Mg3Sb2-based thermoelectric materials

Abstract

High-performance n-type Mg3Sb2-based thermoelectric materials have attracted much attention due to the six-fold degenerate carrier pockets in the conduction band. This study uncovers the electrical and thermal transport behaviors in different directions with respect to the spark plasma sintering (SPS) pressure that is rarely investigated. Results indicate that the grain size in the ⊥P direction (perpendicular to the SPS pressure direction) is slightly larger than that in the ∥P direction. In addition, a moderate texture is observed, reflecting a preferential orientation of the (001)-plane in the ⊥P direction. The synergy of both grain size and the texture leads to an improved electrical conductivity for Mg3.24Sb1.5Bi0.49Te0.01 compounds with lamellar crystal structures. Consequently, the highest thermoelectric figure of merit ZTpeak ∼1.71 and ZTavg ∼1.12 (almost the best ZT values ever reported for Te-doped Mg3Sb2-based materials) are achieved in the ⊥P direction compared to the ∥P direction.