Molecular origin of the 7-folds narrowing of the Tg transition upon aging in Se-rich multicomponent glasses*

The nature of the glass transition temperature in Se-rich (x < 4%) ternary Ge_xAs_xSe_100-2x [1] glasses is examined as a function of room temperature aging in Modulated DSC experiments. Our experiments show Tg(x) to increase by 6°C with x displaying a trapezoidal variation in the 0% < x < 4% range, with the enthalpy of relaxation, ΔHnr increasing 4-folds and the width (W) of the glass transition decreasing 7-folds upon RT aging for 8 months. The molecular origin of these changes can be connected with the polymeric Se_n chains in the fresh glass steadily correlating with each other to become quasi-helical provided n > 8. These features are due to the undercoordinated nature of Se glass rendering compositions x < x_c to be super-flexible when the length of chains exceeds 10 atoms. Parallel results were obtained in the Ge_xSe_100-x [1] binary, underscoring that these effects are strictly controlled by the topology or network connectedness.

[1] R. Chbeir, M. Bauchy, M. Micoulaut, and P. Boolchand, “Evidence for a correlation of melt fragility index with topological phases of ternary Ge_xAs_xSe_100-2x glasses,” Frontiers in Materials, Jul. 2019.

[2] S. Dash, P. Chen, and P. Boolchand, The Journal of Chemical Physics, vol. 146, no. 22, p. 224506, Jun. 2017.