Stability, electronic structures and thermoelectric properties of binary Zn-Sb materials

We report first principles studies of the binary Zn-Sb phases in relation to thermoelectric properties and chemical stability. We identify the unknown structure of the Zn3Sb2 phase using particle swarm optimization, finding a tetragonal structure different from the hexagonal Mg3Sb2 and the hexagonal or cubic Ca3Sb2 phases. All the phases are found to be semiconducting with bandgaps in the range of 0.06-0.77 eV. This semiconducting behavior is understood in Zintl terms as a balance between the Zn: Sb and Sb3- :1/2(Sb-2)(4-) ratios in the stable crystal structures. With the exception of Zn3Sb2, which has a small gap, all the compounds have electronic properties favorable for thermoelectric performance.