Sulfide glasses: Glass forming region, structure and ionic conduction of glasses in Na 2SXS 2 (XSi; Ge), Na 2SP 2S 5 and Li 2SGeS 2 systems

Abstract

Na 2S forms with GeS 2, SiS 2 and P 2S 5 stable glasses with a large range of composition as well as a Li 2SGeS 2 system. A vibrational assignment in terms of terminal (GeS) and bridge (GeSGe) stretching has been made (Na 2SGeS 2 system). The ionic transport number obtained by e.m.f. measurements (glasses 0.5 Na 2S0.5 XS 2 (XGe, Si)) was found to be equal to 1. The electrical conductivity of these glasses has been measured over a range of temperature (−20°C, 150°C) and composition by the complex impedance diagram method. The glass 0.5 Li 2S0.5 GeS 2 exhibits good conductivity 4 × 10 −5 ω −1cm −1 (20°C) higher than the best conductive glasses currently known. Replacement of the oxygen atom by a sulphur atom (comparison with oxide glasses at the same composition) is found to noticeably improve the ionic conductivity. This may be due to a great polarisability of the sulphur. For the glasses with the same molar ratio in sodium sulfide, the ionic conductivity increases when the electronegativity of the network forming sulfide decreases.