Mechanical relaxation in amorphous selenium

Literature mechanical relaxation data of amorphous selenium are interpreted in terms of the soft potential model and its extension to higher temperatures, the Gilroy-Phillips model. At the crossover temperature from tunneling states to thermally activated relaxation, one finds a stronger decrease of the barrier density f(V) with increasing barrier height V than in silica. On the high barrier side, f(V) is determined by the Kohlrausch tβ-tail of the viscous flow, with β = 0.31. In longitudinal ultrasound absorption data, one finds weak oscillations of the Kohlrausch barrier density, similar to those found recently in metallic glasses, consistent with an increase of the barrier by V1 = S1Tg/β for the addition of one selenium atom to the rearranging domain, where S1 is the structural entropy per atom at the glass temperature Tg.