Structural studies on xLi2S–(1 − x)P2S5 glasses by X-ray diffraction and molecular dynamics simulation

Short range order in xLi2S–(1 − x)P2S5 glasses with x = 0.50 and 0.60 was studied by X-ray diffraction and molecular dynamics simulation. The glasses were prepared in evacuated quartz ampoules by the melt quenching method. Results from an RDF analysis of the X-ray data show the presence of a direct P–P bond at 2.30 Å and the presence of PS4 and PS3 units. A very small fraction of S–S neighbors at distances less than 2.00 Å is also suggested. Equilibrium configurations at 300 K from molecular dynamics simulations (constant volume) were analyzed using the novel technique of graph theory for various connectivities among basic units of PSn and LiSn. Chain and ring structures were identified. Branching in chains was estimated by calculating P–P and Li–Li neighbors in various shells. Molecular dynamics results do not show the presence of short S–S and direct P–P bonds. However, they confirm the occurrence of PS3 and PS4 units in the glass network. An increase in Li concentration brings about a decrease in P–S–P bridges, as in phosphate glasses. Edge-connected LiSn polyhedra increase with x, though corner sharing LiSn units predominate in the network.