GeAs thiophosphate glasses: properties and NMR spectroscopy

Stoichiometric GeAsP sulphide glasses containing 50-90 mol% GeS2 and 4-25 mol% P2S5 have been investigated to determine the compositional and structural dependence of physical properties. The latter vary monotonically with increasing P2S5 concentration: at constant GeS2 content, the thermal expansion coefficient increases, whereas refractive index, isokom temperatures and density decrease as P2S5 replaces As2S3. The introduction of P is marked by absorption bands in the 900-1400 cm(-1) range that are absent in P-free glasses. The compositional dependence of optical properties and molar volume indicates that the dominant P species in these glasses is the tetrahedral S=PS3/2 group. This interpretation of the local P environment is confirmed by P-31 MAS NMR spectral data, which further indicate that the latter species tend to have AsS3 groups as next-nearest neighbors. (C) 2000 Elsevier Science B.V. All rights reserved.