Band convergence and defect engineering synergistically revamping the carrier-phonon dynamics in Mg_3-xZn_xSb₂ solid solutions: an experimental and theoretical insights

Abstract

Mg₃Sb₂-based n-type Zintl compounds have attracted greater attention for their superior thermoelectric performance, making them a potential candidate for medium-temperature (< 900 K) applications. Herein, this work verifies the p-type Mg_1.8Zn_1.2Sb₂ solid-solution and defect engineering could be the key mechanism to reduce the lattice thermal conductivity (κ_L) for improving the thermoelectric performance. The carrier and phonon transport properties were studied by adding heavy element Ag at Mg-sites of Mg_1.8Zn_1.2Sb₂ solid-solution. As a result, the Ag_0.03Mg_1.77Zn_1.2Sb₂ sample simultaneously obtained the maximum power factor of 456 μW/mK² via band convergence and defect engineering, which led to reduced thermal conductivity of 0.56 W/mK at 753 K by the strengthening of multiscale phonon scattering. In addition, optimized carrier density and thermal conductivity resulting in a maximum figure of merit (zT) of 0.5 at 753 K has been obtained for Ag_0.03Mg_1.77Zn_1.2Sb₂, which is 285% higher than undoped Mg_1.8Zn_1.2Sb₂. This work demonstrates that heavy element substitution induces band convergence and that defect engineering leads to simultaneous improvement in thermoelectric transport properties of p-type Mg_1.8Zn_1.2Sb₂.

Keywords

Mg_1.8Zn_1.2Sb₂ / defect engineering / solid solution / band convergence / thermal conductivity

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