The structure of densified As₂O₃ glasses

In situ high energy X-ray diffraction and Raman experiments have been carried out to probe the structure changes of vitreous As₂O₃ under pressure. The first sharp diffraction peak reduces in intensity up to 10 GPa, indicating a breakdown of intermediate range order with pressure. All features in the Raman spectra broaden with increasing pressure up to 11.6 GPa. The mode at 378 cm^-1 associated with As₄O₆ molecule-like vibrations increases in intensity up to 6.2 GPa and decreases at higher pressures. In addition, X-ray and neutron structure factors have been measured for normal density and permanently densified As₂O₃ glasses recovered from 10 and 23 GPa. The results show the local AsO₃ pyramids and 3-membered rings essentially remain intact after compression. The increase in density is mainly associated with an inward shift of the third nearest neighbor peak in the X-ray radial distribution function, which indicates an increased packing of 3-membered AsO₃ rings.