Band engineering and phonon softening enable the achievement of significant enhancement in the thermoelectric performance of EuMg2Sb2 by Zn doping

Abstract

The Zintl compound EuMg₂Sb₂ is a promising thermoelectric material due to its inherently low lattice thermal conductivity and tunable electronic and thermal properties related to its multi-component nature. However, the large difference in electronegativity between Mg and Sb results in poor electronic transport properties, reducing its thermoelectric conversion efficiency and limiting its practical application. Thus, this study investigates a doping modification strategy for enhancing the thermoelectric performance of EuMg₂Sb₂ and the microscopic mechanism using the first-principle calculations combined with the Boltzmann transport theory. Indeed, the larger energy separation at the valence band maximum is the key factor affecting the electronic transport properties of EuMg₂Sb₂. The results demonstrate that Zn doping at the Mg site effectively increases the thermoelectric performance by promoting the valence band convergence owing to the close electronegativity to Sb and softening the phonon thus largely suppressing the lattice thermal conductivity. By optimizing the Zn doping concentration, the highest figure of merit (zT) value is significantly increased to 2.24 (2.66) in the x (z) direction at 800 K. The results suggest that the proposed modulation strategy and effect are of great significance for improving the thermoelectric performance of Zintl materials.