Coordination disordering in near-stoichiometric arsenic sulfide glass

Abstract Compositionally-dependent deviations in structural metastability of near-stoichiometric glassy arsenic sulfides As 38 S 62 , As 40 S 60 and As 42 S 58 associated with interbalanced chemical, medium-range and coordination disordering are studied with optical spectrophotometry, micro-Raman scattering and X-ray diffraction measurements related to. The glasses quenched from high enough temperatures above boiling point reveal characteristic chemical disordering with additional amount of molecular products having “wrong” homopolar bonds, this effect being inhibited in over-stoichiometric As 42 S 58 glass. Optical transmission measurements in the bandgap cut-off region demonstrate increased light scattering losses in high-temperature-quenched As 38 S 62 and As 40 S 60 glasses, while no changes are detected in As 42 S 58 glass. The most essential influence expressed in obvious increase in the effective periodicity and correlation length of the first sharp diffraction peak is registered in g-As 40 S 60 prepared by slow cooling from relatively low temperatures such as 500 °C. Coordination disordering due to double-bond-based quasi-tetrahedral S 3/2 As S units, identified in respect to increased Raman-active stretching modes near 530–540 cm − 1 , along with extra homopolar As As bonds enhances a compositional misbalance in this stoichiometric specimen, tending towards As-rich glass-forming network approaching g-As 42 S 58 . Possible topological configurations of these structural anomalies are examined using ab-initio quantum chemical calculations with RHF/6-311G ⁎ basis set, testifying in a favor of more distinct spacing arrangement of quasi-tetrahedral units and S-compensating homopolar As As bonds.