Structural analysis of xCsCl(1-x)Ga2S3 glasses by means of DFT calculations and Raman spectroscopy

The alkali metal halide doping of gallium-sulfide glasses yields improvements in the optical, thermal and glass forming properties. To understand these improvements, the short-range order of xCsCl(1 - x)Ga2S3\ glasses was probed by Raman spectroscopy. Raman spectra have been interpreted using density functional theory (DFT) harmonic frequency calculations on specific clusters of GaS4H4 and/or GaS3H3Cl tetrahedral subunits. The assignment of the observed vibrational bands confirms the main structural conclusions obtained with X-ray and neutron diffraction experiments and gives some new insights into the gallium-network present in the xCsCl(1 - x)Ga2S3 glasses. At the lowest concentration, the observed spectrum may be interpreted with small clusters such as dimers and trimers connected by corner-sharing (CS) GaS4H4 tetrahedral subunits. The vibrational fingerprints of tri-clusters with three-fold coordinated sulfur atoms have also been identified; however, no Raman signature of chlorine-doped subunits has been found to be caused by their insufficient intensity. For higher CsCl concentrations, distinct spectral features corresponding to chlorine-doped clusters appear and are increasing in intensity with x. In other words, undoped and Cl-doped tetrahedra coexist in the xCsCl(1 - x) Ga2S3 glasses. The added chlorine atoms induce a fragmentation of the glass network and replace the sulfur atoms in the CS tetrahedral environment. The comparison of the observed spectra with theoretical predictions and diffraction data favoured one-fold coordinated chlorine atoms in the glass network. Copyright (C) 2009 John Wiley & Sons, Ltd.