SI-29 AND AL-27 MASS-NMR STUDIES OF LI2S + AL2S3 + SIS2 GLASSES

The first investigation of the preparation, characterization, and local structure of Li2S + Al2S3 + SiS2 glasses is reported. Glass-forming range, T(g), infrared spectra and Al-27 and Si-29 MASS-NMR have been measured. The glass-forming range, although more extensive than that of the Li2S + SiS2 binary, is still quite restricted and limited to compositions containing at least 40 mol% SiS2 and at most 60 mol%. The glass transition temperature shows a monotonic increase with substitution of Al2S3 for SiS2 and Al2S3 for Li2S. Highest T(g)s are measured for glasses with maximum mol% Al2S3. This observation is used to suggest that Al2S3 is reducing the number of non-bridging sulfur ions in the glass. Like the Si-29 MASS-NMR of the binary Li2S + SiS2 glasses, the spectra are insensitive to composition. This observation suggests that the extent of edge-sharing rather than non-bridging sulfurs is the dominant effect on chemical shift. The Si-29 MASS-NMR experiments show that adding aluminum to Li2S + SiS2 glasses decreases edge-sharing SiS4 tetrahedra. Al-27 MASS-NMR experiments show that aluminum goes into tetrahedral coordination in these glasses, and DSC measurements confirm this coordination.