Composition dependence of the energy gap and thermal diffusivity in bulk As-Se glasses

We have measured the composition dependence of the optical energy gap and thermal diffusivity in bulk As _x Se_1−x (0.10⩽x⩽0.50) glasses using photoacoustic technique. The energy gap shows a threshold minimum value and thermal diffusivity has a threshold maximum value at the stoichiometric composition As₂Se₃ corresponding tox=0.40. The decrease in energy gap is explained on the basis of chemical bonding. It is argued that the threshold percolation of rigidity in the random network is responsible for the peaking of the thermal diffusivity at the stoichiometric composition.