Nuclear Spin Relaxation in Nanocrystalline β-Li3PS4 Reveals Low-Dimensional Li Diffusion in an Isotropic Matrix

Abstract

Lithium-containing thiophosphates represent promising ceramic electrolytes for all-solid-state batteries. The underlying principles that cause high Li+ diffusivity are, however, still incompletely understood. Here, β-Li3PS4 served as a model compound to test the recently presented hypothesis that a channel-like Li+ diffusion pathway influences ionic transport in its 3D network of the LiS4, LiS6, and PS4 polyhedra. We looked at the temperature dependence of diffusion-induced 7Li nuclear spin-lattice relaxation rates to check whether they reveal any diagnostic differences as compared to the nuclear spin response frequently found for isotropic (3D) diffusion. Indeed, distinct anomalies show up that can be understood if we consider the influence of low-dimensional diffusion. Hence, even for isotropic materials without clearly recognizable 1D or 2D diffusion pathways, such as layered or channel-structured materials, structurally hidden dimensionality effects might help explain high ionic conductivities and refine the design principles currently discussed. In the present case, such rapid pathways assist the ions to move through the crystal structure.