Enthalpy relaxation and structure in vitreous Ge15Te85

The structural relaxation of amorphous Ge₁₅Te₈₅ is investigated by calorimetry (DSC). We have evaluated the apparent activation energy, Δh*, the non-exponentiality parameter, β, of the stretched exponential response function and the Narayanaswamy parameter, x, which controls the relative contributions of temperature and of structure to the relaxation time. The values obtained are, x=0.67 with the peak shift method, β=0.6 with the C_p,u^N and CF methods and, Δh*=944 kJ/mol with the Moynihan's method. When these values are compared with those obtained for the Ge–Se system and applied to the structure of Ge₁₅Te₈₅ in the glassy and liquid states, the results suggest that it is the movement of GeTe₄ tetrahedra that bring about the relaxation in Ge₁₅Te₈₅.