Shear strength and optical bandgap in As₂Se₃ glasses permanently compacted under GPa pressures

The application of GPa pressures on glassy As₂Se₃, at temperatures just below and above its glass transition, leads to permanently compacted glasses that exhibit increased densification. Also, melt-quenching of the same glass under a pressure of 7 GPa gives rise to the formation of its crystalline β-phase. The structure of these As₂Se₃ compacted solids have been explored by X-ray diffraction. Measurements of 10 MHz ultrasound velocities reveal that the density increase is associated with a substantial hardening of the elastic continuum as well as a growing shear strength of glassy solids: the shear modulus G increases by more than 35 % and the Poisson's ratio ν decreases by more than 13 %. The optical properties have been investigated by UV–VIS diffuse reflectance spectroscopy, which shows a well defined linear reduction of the optical bandgap E_g with increased density. All of these observations have been explained by considering a disordered layered structure of glassy As₂Se₃, where densification produced by compaction under GPa pressures gives rise to a progressive strengthening of the interlayer interactions.