Abstract
In general, the ionic conductivity of sulfide glasses decreases with their crystallization, although it increases for a few sulphide glasses owing to the crystallization of a highly conductive new phase (e.g., Li7P3S11: 70Li2S-30P2S5). We found that the ionic conductivity of 75Li2S-25P2S5 sulfide glass, which consists of glassy and crystalline phases, is improved by optimizing the conditions of the heat treatment, i.e., annealing. A different mechanism of high ionic conductivity from the conventional mechanism is expected in the glassy phase. Here, we report the glassy structure of 75Li2S-25P2S5 immediately before the crystallization by using the differential pair distribution function (d-PDF) analysis of high-energy X-ray diffraction. Even though the ionic conductivity increases during the optimum annealing, the d-PDF analysis indicated that the glassy structure undergoes no structural change in the sulfide glass-ceramic electrolyte at a crystallinity of 33.1%. We observed the formation of a nanocrystalline phase in the X-ray and electron diffraction patterns before the crystallization, which means that Bragg peaks were deformed. Thus, the ionic conductivity in the mixture of glassy and crystalline phases is improved by the coexistence of the nanocrystalline phase.
Highlights
The ionic conductivity of sulfide glasses decreases with their crystallization, it increases for a few sulphide glasses owing to the crystallization of a highly conductive new phase (e.g., Li7P3S11: 70Li2S-30P2S5)
The differential pair distribution function was utilized as a methodology for the mixed materials in this study to extract the glassy structure in the 75Li2S-25P2S5 sulfide glass ceramic
This method quantitatively reproduced the fraction of mixed phases, which was in agreement with the result of NMR
Summary
The ionic conductivity of sulfide glasses decreases with their crystallization, it increases for a few sulphide glasses owing to the crystallization of a highly conductive new phase (e.g., Li7P3S11: 70Li2S-30P2S5). We report the glassy structure of 75Li2S-25P2S5 immediately before the crystallization by using the differential pair distribution function (d-PDF) analysis of high-energy X-ray diffraction. Even though the ionic conductivity increases during the optimum annealing, the d-PDF analysis indicated that the glassy structure undergoes no structural change in the sulfide glass-ceramic electrolyte at a crystallinity of 33.1%. Significant progress has been made so far with the discovery of numerous sulfide compounds with high ionic conductivities such as Li7P3S112, 3, Li10GeP2S124, 5, Li7P2S8I6, Li10SnP2S127, and 90Li7P3S11 -10LiBr8 Their conductivities are higher than those of the corresponding sulfide glasses. We report the local glassy structure with a mixture of glass and crystalline phases by using pair distribution function (PDF) analysis
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