Study of As―Se―Te glasses by neutron-, X-ray diffraction and optical spectroscopic methods

The atomic structures of amorphous As ₄₀Se _(60−x)Te _x (x = 10 and 15) and As ₄₀Se ₆₀ glasses have been investigated by neutron and high energy X-ray diffraction methods. The two datasets were modeled simultaneously by reverse Monte Carlo (RMC) simulation technique. The RMC simulations revealed a glassy network built-up from As(Se, Te) ₃ pyramids in which Te atoms substitute Se atoms. The As―Se correlation function shows a strong and sharp first peak at 2.4 Å and two broad and much less intense peaks at 3.7 and 5.6 Å, related to 1st, 2nd and 3rd neighbor distances of the As―Se bonds, respectively. They are an evidence for existence of short and medium ordering in the studied glasses. The similarity of Θ _Te―As―Te and Θ _Se―As―Se bond distributions suggests that Te atoms have a similar role in the structure formation as Se atoms. The FTIR spectra analysis revealed impurity bonds of Se―H, As―O, Se―O, and Te―O in the glasses which contributed to enhanced absorption in visible spectral range. From the ellipsometric data analysis the optical constants and the energetic parameters of the studied glasses were established. The compositional variation of these parameters is explained in terms of chemical bonds formation and change in the density of charged defects.