Effect of vacancy disorder in phase-change materials

Ge-Sb-Te-based phase-change materials (PCMs) exhibit contrasting electrical and optical properties upon change in atomic structures, which contain the octahedral p -orbital bonding and also substantial disordered vacancies. While extensive studies have been carried out, there is little detailed analysis of how the vacancy distribution and bonding nature are inter-correlated to affect the physical properties. We studied the effect of vacancy distribution on the octahedral p -bonding network in PCMs using a simple tight-binding model and ab initio calculations. We showed that the octahedral p -bonding network can be described as a collection of independent linear chains and that the vacancy disorders are rephrased as a distribution of atomic chain pieces. This finding enables to link the vacancy distribution to various aspects of materials properties such as total energy, structural distortions, and charge localization.