Reverse Monte Carlo study of structural relaxation in vitreous selenium

Abstract

Vitreous selenium is used extensively for light detection. Its photoconducting properties are altered by structural relaxation near room temperature. X-ray diffraction, densiometry, and calorimetry are used to determine the change of the glass state during relaxation. Annealing for 24 h at 300 K increases the density by 0.14% and lowers the enthalpy by 105 J/mol. The structure factor of cast samples was measured before and after annealing, and reverse Monte Carlo models of the structure of selenium glass were generated to match the data for the quenched and annealed states. Atoms in amorphous selenium are arranged in randomly oriented chains. In the model clusters annealing effects are found by analyzing inter- and intrachain distances, bond angle distributions, and dihedral angle distributions. The average bond length remains unchanged upon annealing, while the distribution of bond lengths becomes narrower by 1.2%. Distances between atoms in adjacent chains decrease by about 0.03%, i.e., the selenium chains move closer together, and the distribution of interchain distances becomes narrower. Bond angles within the chains are affected slightly. The mean bond angle decreases by 0.016°, which indicates a greater folding of the selenium chains and represents an evolution towards the angles found in crystalline selenium phases. The bond angle distribution for the annealed state is 0.006° narrower.

Influence of the quench rate and the pressure on the glass transition temperature in selenium

“…Brüning et al 24 investigated the change of enthalpy upon aging a glass for 14 h at Tϭ300 K and find an increase in density by 0.14% and a lowering of enthalpy by 1 meV/ atom. We would expect to find similar values upon changing the quench rate from the experimental value of 10 K/min to something like 1 K/h.…”

Mechanisms of photoinduced fluidity in chalcogenide glasses: Molecular orbital analyses

“…the dihedral angle φ and the inter-chain distance R [18,19]. A single chain may be longer than 10 5 in the atom number [12,18].…”

Volume and enthalpy relaxation of a-Se in the glass transition region

“…4, 5, 7, and 8 were calculated by a curve fitting technique by using Eqs. (12), (13), and (15) for the set of AGS parameters corresponding to volume relaxation ( Table 2).…”

“…They found that the times to reach equilibrium appear to be the same in the vicinity of the glass transition temperature, but seem to diverge at lower temperatures with enthalpy coming to equilibrium before volume and creep. Enthalpy relaxation of vitreous Se, the contributing microscopic processes and their entropic relation has been discussed by Bruning et al [12].…”