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

Mg₃Sb₂-based n-type Zintl compound has attracted intensive attention for its superior thermoelectric performance, which makes it a potential candidate for medium-temperature (< 900 K) application. 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 κL 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 highest 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 via the strengthening of multiscale phonon scattering. In addition, optimized carrier density and thermal conductivity resulting in a maximum 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 defect engineering leads to simultaneous improvement in thermoelectric transport properties of p-type Mg_1.8Zn_1.2Sb₂-based Zintl compounds.