Thermal analysis and Raman scattering study on crystallization and structure of Agx(As0.4Se0.6)100-x glasses

DSC, XRD, and Raman scattering measurements for Agx(As0.4Se0.6)100-x glasses with x=0-35 at.% were carried out to investigate the crystallization kinetics and the local structure. The DSC curves were obtained at various heating rates for different Ag contents and two or three exothermic peaks for the crystallization were found depending on the Ag content. The XRD phase analysis has shown that the cubic AgAsSe2 is formed in the first crystallization process and it is then transformed into the tetragonal AgAsSe2 phase. Small Ag3AsSe3, Ag2Se, and Ag7AsSe6 phases were additionally found in the crystallization of the samples with x=30 and 35 at.%. In order to determine the dimension of crystal growth of sample particles and activation energy, the DSC data were analyzed using Matusita's equation. Surface and bulk crystallization take place depending on the Ag content and peak crystallization temperatures. The Raman spectra of the glasses with high Ag content (x=15-35 at.%) are different from those for low Ag content. The latter spectrum is attributed to the symmetrical stretching mode of a pyramidal AsSe3 molecule consisting of the As2Se3 glass and the former spectrum is attributed to the molecular vibration of a threefold As3Se6 ring consisting of the AgAsSe2 glass. 21 refs.