RINGS, INTERMEDIATE-RANGE ORDER AND VIBRATIONAL-SPECTRA OF CHALCOGENIDE GLASSES

Short-range order, intermediate-range order and vibrational density of states of vitreous GeSe2 were investigated using the molecular dynamics method. The static structure factor exhibits the first sharp diffraction peak (FSDP), a characteristic of intermediate-range order in chalcogenide glasses as well as the other peaks observed in structural measurements. The anomalous dependence of the FSDP, i.e., the decrease in its height on cooling is due to frustration enhanced by the increased density. The calculated phonon density of states shows peaks at 8.0, 10.8, 26.4, 34.4, and 37.2 mev which are in good agreement with neutron experiments. In addition a companion line, A1c, to the symmetric breathing mode A, (26.4 mev) is identified with a feature at 27.8 mev. Raman studies also find A1c to be 1.5 mev higher than the A1. Calculations show that the A1c mode arises due to vibrations of tetrahedra belonging to 5- and 7-fold rings.