Template compositional behaviour of relaxation-time divergence in GexSe1−x

Modulated differential scanning calorimetry (MDSC) has been performed on GexSe1−x glasses prepared over close-by compositions using conventional melt-quenching technique. From the non-reversing heat flow we determine a time scale τ(T) characterising the relaxation of the time derivative of configurational enthalpy above the kinetic glass transition temperature Tk. A Vogel–Fulcher type divergence of this relaxation time [τ∼exp{A/(T−Tk)γ}] is studied as a function of composition. We find an overall analytical dependence of the “divergence exponent” γ with the mean atomic coordination number 〈r〉=2x+2. A ‘pulse function’ fit [γ0+Δ(1−exp{(r−rp)/δr})w exp{(r−rp)/δf}] to γ(r) provides a precise rigidity percolation threshold rp and the scales δr and δf governing the growth (decay) of rigid (soft) regions, with compositional variation. Our findings do not conform with the results of conventional non-linear relaxation models that constrain the γ-exponent to only a few discrete values.