Structural interpretation of the enthalpy relaxation kinetics of (GeTe4)y(GaTe3)1 − y far-infrared glasses

Abstract

Differential scanning calorimetry was used to study enthalpy relaxation kinetics of the (GeTe4)y(GaTe3)1−y infrared chalcogenide glasses for the compositional range y=0.4−1.0. The relaxation behavior was described in terms of the Tool-Narayanaswamy-Moynihan (TNM) model. Direct curve-fitting procedure was used to determine the values of TNM parameters; these results were successfully correlated with data provided by the non-fitting methodology based on the evaluation from constant-ratio (CR) cycles. The addition of GaTe3 into the GeTe4 matrix led to a moderate decrease of activation energy of the relaxation process and to a large increase of the relaxation linearity – the structural relaxation became driven solely by temperature. Interpretation of the compositional evolution of the TNM parameters was used to verify structural information provided by Raman spectroscopy and molecular dynamics simulations: the initial GaTe3 addition causes dilution of the GeTe4 tetrahedral network, which carries the main portion of the relaxation motions; further increase of GaTe3 content then leads to an increase of connectivity outside the GeTe4 sub-networks due to the threefold coordinated Ga atoms bonding with the lone-pair electrons of Te dimers and short chains.