Combined dilatometric and calorimetric study of kinetic processes occurring in Ge20Te76Se4 infrared bulk glass

• Relaxation and crystallization kinetics of Ge20Te76Se4 glass were studied by TMA and DSC.
• Relaxation behaviour was described in terms of TNM phenomenological models.
• Relaxation parameters were interpreted with respect to involved molecular structures.
• Crystallization behaviour was described in terms of JMA and AC models.
• Activation energies determined by the two techniques (TMA and DSC) are similar.

Kinetic processes (cold crystallization and structural relaxation) occurring in the Ge20Te76Se4 infrared bulk glass were studied by means of differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The crystallization behaviour was described in terms of the Autocatalytic and Johnson–Mehl–Avrami kinetic models. The crystallization activation energies evaluated by the two techniques were: 164 ± 7 kJ mol− 1 (DSC) and 153 ± 8 kJ mol− 1 (TMA). The agreement between the two values was explained in terms of the marked glass stability and glass-forming ability of the Ge20Te76Se4 glass, where the crystal growth proceeds at rather low viscosities. Regarding the process complexity, increasing heating rate led to a decrease of the dimensionality of the formed crystallites (3D → 2D). Structural relaxation kinetics was described in terms of the Tool–Narayanaswamy–Moynihan model. Values of the parameters of the TNM model were interpreted with respect to the molecular structures determined by Raman spectroscopy. The Se ↔ Te substitution appears to lead to larger interconnection between the GeTe4 tetrahedral chains rather than to significant changes in the intra-chain bonding. Good agreement between the activation energies of the relaxation process determined by the two experimental techniques was again obtained: 501 ± 10 kJ mol− 1 (DSC) and 490 ± 34 kJ mol− 1 (TMA).