Origin of Fast Ion Conduction in Li10GeP2S12, a Superionic Conductor

Abstract

The discovery of additional sites has revealed important insights into the possibility of cross-channel ionic diffusion in Li10GeP2S12 (LGPS). Here, we present an ab initio study of a Li diffusion mechanism in LGPS. The presence of fractional occupancy for Li sites leads to different c channel population of Li and different local environment for Li hop both along the c-directional channels and in the ab plane. We perform a rigorous computation of the energy barriers with different population of Li and different environment of Li surrounding the c channels. It is found that the diffusion energy barrier in LGPS depends significantly on channel population, local environment, and the type of hop which leads to a range of relative diffusivity along different directions. A novel mechanism of correlated diffusion between the c channel and the ab plane is found with significantly low energy barrier. The relative frequency of occurrence of the novel hop mechanism critically controls the degree of anisotropy in LGP...