Stoichiometric deviations in bond distances in the mixed As2S3-As2Se3 system: Raman spectroscopy and EXAFS studies

Raman spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy have been applied to find evidence for isostructural substitution of chalcogen atoms in pyramidal structural units of network glasses from stoichiometric/pseudo-binary As2S3-As2Se3 system. The obtained values of the nearest neighbours atomic distance (r(As-Se) = 2.37 +/- 0.01 angstrom; r(As-S), = 2.33 +/- 0.01 angstrom for As40Se30S30) suggest the existence of mixed AsS2Se and AsSe2S pyramids in which each of As atoms is bonded with S and/or Se atoms in relation to S/Se ratio in composition, while Se atoms are bonded only with As ones with the same bond distance in the form of = As-Se As = bridges that connect the main pyramidal structural units. No evidence for existence of heteroatomic or heteronuclear Se-S bonding is found for the examined glasses.