Three-dimensional structure of fast ion conducting 0.5Li2S + 0.5[(1 −x)GeS2+xGeO2] glasses from high-energy X-ray diffraction and reverse Monte Carlo simulations

A high-energy X-ray diffraction study has been carried out on a series of 0.5Li ₂S + 0.5[(1 − x)GeS ₂ + xGeO ₂] glasses with x = 0.0, 0.1, 0.2, 0.4, 0.6 and 0.8. Structure factors were measured to wave vectors as high as 30 Å ⁻¹ resulting in atomic pair distribution functions with high real space resolution. The three dimensional atomic-scale structure of the glasses was modeled by reverse Monte Carlo simulations based on the diffraction data. Results from the simulations show that at the atomic-scale 0.5Li ₂S + 0.5[(1 − x)GeS ₂ + xGeO ₂] glasses may be viewed as an assembly of independent chains of (Li ^{+ -}S) ₂GeS _2/2 and (Li ^{+ -}O) ₂GeO _2/2 tetrahedra as repeat units, where the Li ions occupy the open space between the chains. The new structure data may help understand the reasons for the sharp maximum in the Li ⁺ ion conductivity at x ∼ 0.2.