High-pressure behavior of As2 O3: Amorphous-amorphous and crystalline-amorphous transitions

The room temperature compression of As2 O3 has been studied by in situ diamond anvil cell Raman and x-ray diffraction up to a pressure of 35 GPa. Upon compression, we discovered a crystal-to-amorphous transition in arsenolite, while claudetite, which is another crystalline polymorph of As2 O3, remains crystalline up to at least 40 GPa. We have also observed an amorphous-amorphous transition in As2 O3 glass at 25 GPa. This transition is characterized by a dramatic change in the Raman spectrum, which is reversible upon decompression. In situ diamond anvil cell x-ray diffraction of As2 O3 glass reveals that the amorphous-amorphous transition is associated with an increase in the arsenic coordination. The amorphous-amorphous transition is reversible with little hysteresis.