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

Modulated differential scanning calorimetry (MDSC) has been performed on Ge xSe1=x glasses prepared over close-by compositions using conventional melt- quenching technique. From the non-reversing heat flow we determine a time s cale tau (T) characterising the relaxation of the time derivative of config urational enthalpy above the kinetic glass transition temperature T-k. A Vo pel-Fulcher type divergence of this relaxation time [tau similar to exp{A/( T- T-k)(Y)}] is studied as a function of composition. We find an overall an alytical dependence the "divergence exponent" gamma with the mean atomic co ordination number (r) = 2x + 2. A 'pulse function' fit [gamma (0) + Delta ( 1 - exp{(r - r(p))/delta (r)})(w) exp{(r - rp)/delta (f)}] to gamma (r) pro vides a precise rigidity percolation threshold r(p) and the scales delta (r ) and delta (f) governing the growth (decay) of rigid (soft) regions, with compositional variation. Our findings do not conform with the results of co nventional non-linear relaxation models that constrain the gamma -exponent to only a few discrete values. (C) 2001 Elsevier Science B.V. Ail lights re served.