Coordination disordering in near-stoichiometric arsenic sulfide glass

Compositionally-dependent deviations in structural metastability of near-stoichiometric glassy arsenic sulfides As38S62, As40S60 and As42S58 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 As42S58 glass. Optical transmission measurements in the bandgap cut-off region demonstrate increased light scattering losses in high-temperature-quenched As38S62 and As40S60 glasses, while no changes are detected in As42S58 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-As40S60 prepared by slow cooling from relatively low temperatures such as 500 °C. Coordination disordering due to double-bond-based quasi-tetrahedral S3/2AsS units, identified in respect to increased Raman-active stretching modes near 530-540 cm− 1, along with extra homopolar AsAs bonds enhances a compositional misbalance in this stoichiometric specimen, tending towards As-rich glass-forming network approaching g-As42S58. 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 AsAs bonds.