The crystal structures of the superionic conductors Li9.81Sn0.81P2.19S12 and Li10.35Si1.35P1.65S12, both having a Li10GeP2S12 (LGPS)-type structure, were determined by neutron diffraction analysis over the temperature range 12-800 K. The maximum entropy method was also employed to clarify the lithium distribution in these materials. The Sn system showed one-dimensional diffusion in the c direction over a wide temperature range, even though the Ge-based system typically exhibits three-dimensional conduction at higher temperatures. The ionic conduction mechanisms of analogous Si, Ge and Sn phases with LGPS-type structures are discussed on the basis of the observed structural parameter changes.
Keywords: MEM analysis; lithium battery; solid state battery; superionic conductor.