Microstructure and Thermophysical Characterization of Tetra-Arsenic Biselenide As4Se2 Alloy Nanostructured by Mechanical Milling

Nanomilling-driven effects on polyamorphic transitions are examined in tetra-arsenic biselenide As₄Se₂ alloy, which is at the boundary of the glass-forming region in the As-Se system, using multifrequency temperature-modulated DSC-TOPEM^® technique, supported by X-ray powder diffraction (XRPD) and micro-Raman spectroscopy analysis. As shown by XRPD analysis, this alloy reveals a glassy-crystalline nature due to rhombohedral As and cubic As₂O₃ (arsenolite) inclusions, which especially grew after milling in a PVP (polyvinylpyrrolidone) water solution. At the medium-range structure level, nanomilling-driven changes are revealed as the disruption of intermediate-range ordering and enhancement of extended-range ordering. The generalized molecular-to-network amorphization trend in this alloy is confirmed by the microstructure response revealed in the broadened and obscured features in micro-Raman scattering spectra collected for nanomilled specimens. Thermophysical heat-transfer phenomena are defined by molecular-to-network polyamorphic transformations activated under nanomilling. The domination of thioarsenide-type As₄Se_n entities in this alloy results in an abnormous nanomilling-driven network-enhanced glass transition temperature increase. The nanomilled alloys become notably stressed owing to the destruction of molecular thioarsenide and incorporation of their remnants into the newly polymerized arsenoselenide network. This effect is more pronounced in As₄Se₂ alloy subjected to dry nanomilling, while it is partly counterbalanced when this alloy is additionally subjected to wet milling in a PVP water solution, accompanied by the stabilization of the As₄Se₂/PVP nanocomposite.