Intrinsic phase separation in low-temperature quenched arsenic trisulfide glass

The nature of intrinsic phase separation initiated under different homogenization routes is studied in arsenic trisulfide As₂S₃ glass using Raman scattering spectroscopy. It is shown that As₂S₃ glass prepared within conventional melt-quenching route is subjected to essential phase separation dependent on the homogenization of elemental constituents sealed in evacuated ampoules. Under condition of low-temperature homogenization at 450-550 °C, chemical interaction due to limited solubility of liquid S in solid As results in structurally intrinsic As- and S-rich phases with high content of homoatomic As-As and S-S bonds, respectively, which are "wrong" from the point of As₂S₃ stoichiometry This process can be essentially facilitated with more rapid heating and greater amount of initial elemental ingredients taken for synthesis. During prolonged homogenization of this intrinsically-decomposed melt (such as lasting 2 days in a rocking furnace), these products are partially separated giving main glassy phase enriched on As in the form of realgar- and dimorphite-type molecules, isolated As-As bonds in a glassy network and volatilized S-rich phase, which condenses on the walls of ampoules. If such melt is insufficiently homogenized as under 6-h heating at 500 °C with only 2-h rocking, the coordination disordering is maintained in the ultimate glass. This provides that volatilized S-rich phase does not form, and all decomposition products are stabilized in glassy state as quasi-tetrahedral units and compensating homoatomic As-As bonds.