Enthalpy relaxation kinetics of Ge₂₀Te_(80-y)Se_y far-infrared glasses in the glass transition range

Abstract

Differential scanning calorimetry was used to study enthalpy relaxation kinetics of the Ge₂₀Te_(80-y)Se_y infrared chalcogenide glasses for the compositional range y = 0–8. The relaxation behaviour was described in terms of the phenomenological Tool–Narayanaswamy–Moynihan (TNM) model. The direct curve-fitting procedure was used to determine the values of TNM parameters. Compositional evolution of the TNM parameters was interpreted with respect to the involved structural entities and their motions. Based on the joint Raman scattering study, the addition of Se leads to increased amount of edge-shared GeTe_4-xSe_x tetrahedra. While the primary structural basis for the relaxation movements appears not to be affected by addition of Se (constant value of non-linearity), changes of the non-exponentiality parameter indicate increased structural variability occurring within the groups of directly interlinked tetrahedra, which were found to carry the main portion of relaxation movements. Increased activation energy was explained by the presence of significantly stronger Ge–Se bonds and increased amount of edge-shared tetrahedra.

Keywords:

• Enthalpy relaxation
• TNM model
• DSC
• Ge–Te–Se glasses
• Raman scattering