Pressure-Driven Chemical Disorder in Glassy As2S3 up to 14.7 GPa, Post-Densification Effects and Applications in Materials Design

A small difference in energy between homopolar vs. heteropolar bonds and the glass-forming ability of pure chalcogens lead to unexpected trends in densification mechanisms of glassy chalcogenides compared to vitreous oxides. Using high-precision compressibility measurements and in situ high-energy X-ray diffraction up to 14.7 GPa, we show a new densification route in a canonical glass As2S3. After the first reversible elastic step with a maximum pressure of 1.3 GPa, characterized by a strong reduction of voids and cavities, a significant chemical disorder is developed under higher pressure, reaching a saturation of 30 % in the population of As-As bonds above 8-9 GPa. The pressure-driven chemical disorder is accompanied by a remarkable structural relaxation and a strongly diminished optical gap, and determines structural, vibrational and optical properties under and after cold compression. The decompressed recovered glass conserves dark color and exhibits two relaxation processes: (a) fast (a few days), an...