Structural Study of Superionic Conductors by Neutron Scattering

Abstract

  Electrical conductivity, synchrotron X-ray diffraction, and time-of-flight neutron diffraction measurements were carried out for ⁷Li₇P₃S₁₁ metastable crystal and (⁷Li₂S)₇₀(P₂S₅)₃₀ glass. Reverse Monte Carlo modeling based on the neutron and X-ray data showed three-dimensional structures of ⁷Li₇P₃S₁₁ metastable crystal and (⁷Li₂S)₇₀(P₂S₅)₃₀ glass. A detailed polyhedral analysis of the three-dimensional atomic configuration yielded the spatial distribution of LiS₄ tetrahedra ([LiS₄] units) and S₄ tetrahedra (without Li⁺ ion; [S₄] units) in ⁷Li₇P₃S₁₁ metastable crystal and (⁷Li₂S)₇₀(P₂S₅)₃₀ glass. When an ac-[S₄] unit is recognized as a fully acceptable unit of the Li⁺ ion, the coordination number of ac-[S₄] units around a [LiS₄] unit for ⁷Li₇P₃S₁₁ metastable crystal was estimated to be twice as large as that for (⁷Li₂S)₇₀(P₂S₅)₃₀ glass on average. Such structural characteristics in ⁷Li₇P₃S₁₁ metastable crystal and (⁷Li₂S)₇₀(P₂S₅)₃₀ glass are intimately related to electrochemical properties.