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

## TL;DR

This paper studies how mechanical milling affects the structure and thermal properties of a specific arsenic-selenium alloy, revealing changes in its crystalline and amorphous states.

## Contribution

The study introduces new insights into nanomilling-driven polyamorphic transitions in As4Se2 alloy using advanced analytical techniques.

## Key findings

- Nanomilling disrupts intermediate-range ordering and enhances extended-range ordering in As4Se2.
- Thermophysical changes are linked to molecular-to-network polyamorphic transformations.
- Wet milling with PVP stabilizes the alloy and reduces stress from nanomilling.

## Abstract

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 As4Sen 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.