Enhancing Thermoelectric Performance of NaCdSb-Based Materials Through Isovalent Substitution

Abstract

Thermoelectric materials, which enable the direct conversion of heat into electricity and vice versa, are critical for sustainable energy solutions. Recently, the Zintl-phase compound NaCdSb was discovered to have a zT value of 1.3 at 673 K in its pristine form. Subsequently, its zT value was increased to 1.41 through carrier concentration tuning, but optimization remains limited due to experimental constraints. In this study, we employ first-principles calculations to systematically investigate the thermoelectric properties of NaCdSb-based materials. By optimizing carrier concentration, the predicted power factor of NaCdSb can be significantly enhanced. Furthermore, isovalent substitution with Li and K decouples the interdependence of thermoelectric parameters. K alloying improves band convergence, boosting the Seebeck coefficient and enhancing the power factor across a large carrier concentration range. Considering the impact of heavy-element alloying on lattice thermal conductivity and given that the electronic thermal conductivity of KNCS remains almost unchanged, the zT of KNCS is also expected to increase. Our work demonstrates that K alloying can be an effective strategy to enhance the thermoelectric performance of NaCdSb-based materials, making them potential candidates for high-efficiency TE applications.