Local structure of interstitial Zn in β-Zn₄Sb₃

The low thermal conductivity of the thermoelectric material β-Zn ₄Sb₃ has been linked to disorder arising from multiple interstitial Zn sites. Here we investigate the energetics and local distortions associated with these interstitial sites via DFT calculations. Our results show the β-Zn₄Sb₃ structure is able to distort into many inequivalent geometries of similar energies, suggesting a topology rich with transport pathways through energetically accessible metastable states. The occurrence of such a shallow energy landscape may explain the recently discovered liquid-like diffusivity of Zn in β-Zn₄Sb₃ - comparable to that found in superionic conductors.