Influence of particle size on crystallization and relaxation behavior of Ge20Se4Te76 glass for infrared optics

Influence of particle size on relaxation and crystallization behavior of the Ge20Se4Te76 chalcogenide glass was studied by differential scanning calorimetry (DSC). The structural relaxation kinetics was described by means of the Tool-Narayaswamy-Moynihan (TNM) model; it was found that the structural relaxation processes are not influenced by powder particle size or by the mechanically induced defects and heterogeneities originating from the grinding procedures the evaluated TNM parameters were constant for all tested powders. On the other hand, the crystallization kinetics of the Ge20Se4Te76 glass was found to be significantly influenced by the powder size. While the coarser powders exhibited a single-peak behavior corresponding to the nucleation growth Johnson-Mehl-Avrami (JMA) kinetics, the crystallization of finest powders proceeded in two distinct steps. XRD analysis identified the two DSC signals as crystallization of hexagonal Te and rhombohedral GeTe, indicating that large amounts of mechanically induced defects accelerate the Te precipitation. Regarding the overall thermal characterization, the evaluated glass-stability criteria have shown that although the studied chalcogenide glass is a very good glass-former, its stability largely depends on the sample form. (C) 2015 Elsevier B.V. All rights reserved.