Heat Treatment and Crystallization of Glasses in the System As-Se

Abstract

Glasses in the system As-Se were heat-treated at temperatures higher than Tg (glass transition temperature) for 20-340 hours in order to study the relation between the crystalline phase formed in a glass and the structure of the glass.The crystalline phases formed during the thermal treatment were identified by X-ray diffraction technique as hexagonal Se in the case of Se glass and As2Se3 in the case of As2Se3 and AsSe glasses.The crystallization of Se glass, which was initiated by homogeneous nucleation, was determined by density change, but heterogeneous crystallization was observed in As2Se3 glass and the crystal growth was measured by means of metallurgical microscopy as functions of temperature and time.The activation energies for nucleation (EN) and for crystal growth (EG) calculated from the Arrhenius plots of the induction periods of crystallization and the growth rate G are as follows; EN=29.4±0.8kcal/mole and EG=12.6±2.2kcal/mole for Se glass, and EN=41.2kcal/mole and EG=26.7kcal/mole for As2Se3 glass. They turned out to be much smaller than the activation energy for viscous flow at constant pressure or than the cleavage energy of a single bond such as Se-Se bond (44kcal/mole) or As-Se bond (42kcal/mole.).