Point defect scattering driven low lattice thermal conductivity in p-type Mg3Sb2 for mid-temperature thermoelectric applications

Abstract

Zintl-phase p-type magnesium antimonide (Mg₃Sb₂) is a promising mid-temperature (300- 900 K) thermoelectric (TE) material owing to its intrinsic low thermal conductivity, less toxicity, greater abundance, and compatibility. This present study focuses on enhancing the TE properties of Mg₃Sb₂ via the introduction of heavy elements Ge and Ag at lighter element Mg sites by two-step solid-state techniques. The influence of Ag-Ge modifies the band structure and strengthens the scattering of different wavelength phonons via various types of defects. This investigation indicates that (Ge, Ag) co-doping could significantly enhance the electrical conductivity (5328 S/m), and Seebeck coefficient (171.6 μV/K). The band structure modification leads to improving the overall power factor of 158.5 μW/mK² at 753 K for Mg_2.92Ge_0.05Ag_0.03Sb₂. Simultaneously, the contribution of different types of defects strengthened the phonon transport, which leads to achieve a minimized lattice thermal conductivity of 0.42 W/mK for Mg_2.92Ge_0.05Ag_0.03Sb₂. Importantly, the enhanced power factor and low thermal conductivity resulting in a peak zT of 0.24 at 753 K for Mg_2.92Ge_0.05Ag_0.03Sb₂. Thus, the results highlight the effect of heavy element co-doping strategy modifies the band structure and strengthens the phonon scattering via defect engineering in p-type Mg₃Sb₂.