Physical properties of thermoelectric zinc antimonide using first-principles calculations

Abstract

We report first-principles calculations of the structural, electronic, elastic, and vibrational properties of the semiconducting orthorhombic ZnSb compound. We study also the intrinsic point defects in order to eventually improve the thermoelectric properties of this already very promising thermoelectric material. Concerning the electronic properties, in addition to the band structure, we show that the Zn (Sb) crystallographically equivalent atoms are not exactly equivalent from the electronic point of view. Lattice dynamics, elastic, and thermodynamic properties are found to be in good agreement with the experiments and they confirm the nonequivalency of the zinc and antimony atoms from the vibrational point of view. The calculated elastic properties show a relatively weak anisotropy and the hardest direction is the $y$ direction. We observe the presence of low energy modes involving both Zn and Sb atoms at about 5--6 meV, similar to what has been found in Zn${}_{4}$Sb${}_{3}$, and we suggest that the interactions of these modes with acoustic phonons could explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the most stable defects, and this explains the intrinsic $p$-type conductivity of ZnSb.