RAMAN AND INFRARED SPECTROSCOPIC STUDIES OF GE-GA-AG SULFIDE GLASSES

Gallium sulphide forms stable glasses with GeS2 over a wide range of composition, and in the same system complex materials are obtained by dissolving silver sulphide. In such glasses Ga2S3 acts as a co-former with GeS2 whereas Ag2S plays the role of modifier. Raman scattering and infrared absorption measurements have been carried out on the Ge2S4-Ga2S3-Ag2S glass system. The structural arrangement of these glasses is studied as a function of the composition in the ternary glass-forming region. The vibrational assignment is made mainly in terms of bridging and non-bridging sulphur in the vitreous network. The tendency of gallium atoms to form GaS4 tetrahedra forces germanium atoms to induce the formation of S3Ge-Ge-3, structural groups due to the shortage of sulphur atoms. When Ag2S is associated with Ge2S4-Ga2S3 glasses, its defavors the edge-shared GeS4 tetrahedra and contributes to the cohesion of corner-shared tetrahedra. When Ag2S content increases, we observe a band located at low frequency that we have attributed to charge-coupled silver cation motion. A slight distortion of the tetrahedral groups is also seen from the vibrational features.