Glass formation in and structural investigation of Li2S + GeS2 + GeO2 composition using Raman and IR spectroscopy

Li2S + GeS2 + GeO2 ternary glasses have been prepared and a wide glass-forming range was obtained. The glass transition temperatures increase with the GeO2 concentration in the glasses. The vibrational modes of both bridging (Ge–S–Ge) and non-bridging (Ge–S−) sulfurs are observed in Raman and IR spectra of binary Li2S + GeS2 glasses. Additions of GeO2 to this binary glass increase the bridging oxygen band (Ge–O–Ge) at the expense of decreasing the bridging sulfur band (Ge–S–Ge), whereas the bands associated with the non-bridging sulfurs (Ge–S−) remain constant in intensity up to high GeO2 concentrations. At higher concentrations of GeO2 (⩾60%), the non-bridging oxygen band, which is not observed at low and intermediate GeO2 concentrations, appears and grows stronger. From these observations, it is suggested that the added lithium ions favor the non-bridging sulfur sites over the oxygen sites to form non-bridging sulfurs, whereas the added oxygen prefers the higher field strength Ge4+ cation to form bridging Ge–O–Ge bonds. The structural groups in the Li2S + GeS2 + GeO2 glasses that are consistent with results of Raman and IR spectra are described and are used to develop a structural model of these glasses.