Enhanced average thermoelectric properties of n‑type Mg3Sb2 based materials by mixed-valence Ni doping

Abstract

Due to their high band degeneracy and intrinsic low lattice thermal conductivity, n-type Mg3Sb2-based thermoelectric materials have drawn a lot of attention in thermoelectric applications in recent years. By using simple and efficient fast induction melting and hot pressing, the n-type Mg3.5−xNixSbBi0.96Te0.04 (x = 0, 0.015, 0.02, 0.03, 0.04, 0.05, and 0.06) samples have been successfully synthesized. The structure of Mg3.5−xNixSbBi0.96Te0.04 samples is examined, as well as their thermoelectric properties. The findings demonstrate that the mixed valence of Ni2+ and Ni3+ that occupied distinct Mg sites occurred as the Ni doping level grew in the Mg3.5−xNixSbBi0.96Te0.04 samples. The trivalent Ni3+ increases carrier concentrations dramatically, while the divalent Ni2+ increases the effective mass. The mixed valence of Ni causes lattice disorder, which enhances phonon scattering and reduces lattice thermal conductivity. As a result, the Mg3.485Ni0.015SbBi0.96Te0.04 sample has a high ZT value of 1.58 at 743 K and an average ZT value of 1.22 from 323 to 743 K. This work suggests that the mixed valence of cationic dopant effectively improve the thermoelectric performance of n-type Mg3Sb2-based compounds.