Enhancing thermoelectric performance of AB2Sb2-type Zintl phase through band shaping and lattice distortion

Abstract

AB2Sb2-type Zintl phases, especially Mg3Sb2, have garnered widespread attention in virtue of their nontoxic constituent elements and outstanding thermoelectric performance in n-type materials. However, the p-type counterpart of AB2Sb2 still struggles with a low figure of merit zT, primarily because of the limited valence band degeneracy, large band effective mass, and relatively high thermal conductivity. Here we simultaneously optimize the electrical and thermal transports of p-type AB2Sb2-based materials through shaping the band edge and distorting the crystal lattice. By alloying Zn at Mg2 site and Ca at Mg1 site, we successfully decorate the crystal lattice of Mg3Sb2 in real space and thereby modify the band structure in reciprocal space. Zn alloying promotes the band degeneracy while Ca alloying reduce the single band effective mass, which largely promotes the transport of charge carriers. Moreover, the distorted crystal lattice effectively blocks the heat-carry phonons to reduce the lattice thermal conductivity κL. A high zT of 0.81 is finally realized at 750 K in our Zn/Ca co-alloyed samples, which is three times larger than that of Mg3Sb2 matrix. Our work opens new possibilities for the synthetic optimization of both electrical and thermal transports in Zintl phase and other thermoelectric systems.