Realizing high thermoelectric performance in p-type CaZn2Sb2-alloyed Mg3Sb2-based materials via band and point defect engineering

Abstract

Layered Zintl-phase compound Mg3Sb2, possessing the advantages of high abundance, environmental friendliness, and low lattice thermal conductivity, are emerging materials for thermoelectric applications. However, p-type Mg3Sb2-based materials perform unfavorably than their n-type counterparts in terms of thermoelectric performance, which is mainly ascribed to undesirable valence band structure. Herein, we implement the strategy of alloying CaZn2Sb2 to achieve simultaneously improved electrical and thermal performance in p-type Mg3Sb2: (i) alloying CaZn2Sb2 not only optimizes the Seebeck coefficient, but also leads to improved carrier mobility; (ii) the mass and strain field fluctuations caused by alloying CaZn2Sb2 enhance phonon scattering, which significantly reduces the lattice thermal conductivity of the samples. By doping Ag in (Mg3.2Sb2)0.7(CaZn2Sb2)0.3 to realize higher electrical conductivity, the Mg2.22Ag0.02Ca0.3Zn0.6Sb2 sample reaches an excellent peak zT value of 0.90 at 823 K, which compares favorably to those of reported p-type Mg3Sb2-based materials. This study develops an effective pathway to advance thermoelectric performance of p-type Mg3Sb2-based materials.