Study of thermal and optical parameters of ？？ glass has been undertaken. Crystallization and glass transition kinetics has been investigated under nonisothermal conditions by DSC technique. Phase separation has been observed in the material and is investigated by taking the XRD of annealed bulk samples. The material possesses good glass forming ability, high value of glass transition temperature about 420？K, and glass stability. Optical band gap and other optical constants such as refractive index and extinction coefficient have been determined. The isoelectronic substitution of Ge with Sn in the glassy system reduces the optical band gap and enhances the thermal properties. 1. Introduction In amorphous semiconductors, among inorganic glassy materials, chalcogenide glasses occupy a unique place in material science towards advancement of technology. Generally these materials are weakly bonded materials than oxide glasses. But in comparison with amorphous silicon, halide glasses, and other group IV tetrahedral bonded semiconductors these materials exhibit the superior properties which can be tailored by varying the composition. The physical properties such as optical band gap, dielectric behavior, and conductivity of chalcogenide glasses mark their strong dependency on lone pair electrons and density of defect states in the band tails [1, 2]. The disorder in amorphous semiconductors causes perturbation in density of state functions resulting in band tails at the edges of the bottom of the conduction band and the top of the valence band [3]. The lone pair orbits have higher energy than the bonding states and hence occupy the top of the valence band. Interactions between lone pair electrons with their local environment and different atoms result in localized states in the band tails [4]. These localized states play crucial role in deciding optical properties of the materials. The better optical and thermal properties of these materials make them of potential use in the technological applications such as in photonics and phase change memories because of higher values of refractive index and lower value of phonon energy of these glasses [5, 6]. The present Investigation on phase change memories (PCM) shows the possibility of obtaining multistate behavior, enhanced ability to withstand thermal cycling, and use of lower voltages for achieving desired phase change response by using the bilayers of Ge-chalcogenide and Sn-chalcogenide [7]. Germanium is a good glass former and has good glass forming region with Se but has the disadvantage that the Ge compositions
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