Local structure of interstitial Zn in β-Zn₄Sb₃

Graphical Abstract

Observations of exceptionally low lattice thermal conductivity and high Zn diffusion rates in the state-of-the-art thermoelectric material β-Zn₄Sb₃ have been attributed to high levels of interstitial Zn atoms. Here, density functional theory (DFT) calculations of interstitial energies in a relaxed lattice reveal a multitude of low energy positions which correspond to either vacancy–interstitial couplings or a concerted distortion of nearest neighbours. Such a flat energy landscape is in agreement with the observed properties.

Abstract

The low thermal conductivity of the thermoelectric material β-Zn₄Sb₃ 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. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)