STRUCTURAL TRANSFORMATION OF NONOXIDE CHALCOGENIDE GLASSES - THE SHORT-RANGE ORDER OF LI2S-P2S5 GLASSES STUDIED BY QUANTITATIVE P-31 AND LI-6,7 HIGH-RESOLUTION SOLID-STATE NMR

The local structure of crystalline and glassy compositions in the (Li2S)x(P2S5)1–x system is investigated by solid-state high-resolution 31P, 6Li, and 7Li MAS NMR. Four stable crystalline pseudobinary compounds, LiPS3, Li4P2S6, Li3PS4, and Li7PS6, are identified. The 31P NMR spectra obtained on amorphous samples within the region of glass formation (0.4 < x < 0.7) show successive formation of sulfide analogues of metaphosphate (Q(2), pyrophosphate (Q(1)), and orthophosphate (Q(0)) species with increasing concentration of lithium sulfide. The NMR studies show unusually large chemical shift changes upon the crystallization of the glasses. For x = 0.5 this is believed to be due to a different type of interlinking of the Q(2) units. For x = 0.67, the P2S74− units, which are present in the glassy phase, are quantitatively destroyed upon crystallization, leading to the formation of a P2S64− species containing a phosphorus-phosphorus bond. The NMR results illustrate the role of the glassy state in trapping metastable local environments that have no analogues in crystalline compounds. © 1990, American Chemical Society. All rights reserved.