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

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 Mg(3.5-x)NixSbBi(0.96)Te(0.04) (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 de-monstrate 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 dra-matically, while the divalent Ni2+ increases the effective mass. The mixed valence of Ni causes lattice dis-order, 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 ther-moelectric performance of n-type Mg3Sb2-based compounds. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study successfully synthesized n-type Mg3Sb2-based thermoelectric materials using a novel method and investigated their structure and properties. It was found that the mixed valence of Ni effectively improved the thermoelectric performance, especially by increasing carrier concentrations and reducing lattice thermal conductivity.