Atomistic origin of glass-like Zn4Sb3 thermal conductivity

Zinc antimony stands out among thermoelectrics because of its very low lattice thermal conductivity, close to the amorphous limit. Understanding the physical reason behind such an unusual crystal property is of fundamental interest for the design of new thermoelectric materials. In this work we report the results of atomistic computer simulations on experimentally determined beta-Zn4Sb3 structures. We find a remarkably anharmonic behavior of Zn atoms that could be responsible for the low thermal conductivity of Zn4Sb3: their movement, better explained as diffusive, does not contribute to thermal conduction. Moreover, phonon transport is impeded by a lack of coupling between Zn and Sb atoms in crystalline positions.