Thermo-structural characterization of (As2Se3)(100-x)-(As2Te3)(x) glasses for infrared optics

Abstract

Differential scanning calorimetry was used to study thermokinetic behavior of (As2Se3)(100-x)(As2Te3)(x) infrared glasses (seven compositions along the pseudo-binary were investigated). Glass-transition kinetics was described in terms of the Tool-Narayanaswamy-Moynihan model and the relaxation motions were interpreted using Raman spectroscopy data. The enthalpy relaxation kinetics was found to be absolutely uninfluenced by changing Se/Te ratio. On the other hand, DSC crystallization behavior changed significantly with increasing As2Te3 content: Te-rich compositions show marked affinity toward crystallization, whereas in case of the compositions with 0-34 mol.% As2Te3 crystal growth is significantly suppressed. X-ray diffraction analysis indicated presence of monoclinic As2Se3, As2Te3, and As2Se(Te)(3) phases. The complex crystallization behavior occurring in case of the Te-rich compositions was described by superposition of two autocatalytic kinetic signals. Based on the information from infrared microscopy the two overlapping crystallization processes can be attributed to the respective formations of spherulitic and needle-shaped crystallites. Best glass stability was identified in case of the (As2Se3)(66)(As2Te3)(34) composition, which appears to be a potential candidate for optic applications in the far-infrared region of the spectrum.