Zinc antimony stands out among thermoelectrics because of its very low lattice thermal conductivity and thermal stability at moderate temperature.Recent experiments have shown that zinc antimony becomes metastable by heating and can recover its structure stability after 565K [1].Here we study the atomistic origin of this phenomenon using molecular dynamics simulations on experimentally determined crystal structures.Our results show that the diffusion of Zn atoms to interstitial sites gradually leads to a subtle phase transition above 500K.Their movement,better explained as diffusive,is proven not to contribute to phonon conduction [2].We find that this structural change makes Zn atoms confined at interstitial sites impeding their diffusion mobility,resulting in a more stable crystal structure of beta-Zn4Sb3 at high temperature [3].