Structural Insights and 3D Diffusion Pathways within the Lithium Superionic Conductor Li₁₀GeP₂S₁₂

Abstract

Inspired by the ongoing debate about the ion dynamics in the lithium superionic conductor Li10GeP2S12 (LGPS), we present neutron powder diffraction data in combination with analyses of differential bond valence and nuclear density maps to elucidate the underlying diffusion pathways in Li10GeP2S12. LGPS exhibits quasi-isotropic three-dimensional lithium diffusion pathways, which is a combination of one-dimensional diffusion channels crossing two diffusion planes. Furthermore, ultrasonic speeds of sound measurements are used to understand the lattice dynamics and obtain the Debye temperature of LGPS. Temperature dependent X-ray diffraction is performed in order to understand the local temperature-dependent behavior of the prevalent structural backbone, as well as the thermal stability of the material. At elevated temperatures, the superionic conducting Li10GeP2S12 phase partially decomposes into Li4P2S6, explaining the deterioration of the ionic conductivity upon heating.