The structure of permanently densified CaAl2O4 glass

High-energy X-ray diffraction experiments have been performed on CaAl2O4 glass pressure cycled to 12 GPa. A comparison of the radial distribution functions of ambient pressure glass and material that has been pressure cycled shows little change in the local Al–O and Ca–O correlations or nearest-neighbour Al–Al interactions. It is found that the main structural changes occur through a breakup of the chemical ordering of the Ca polyhedra. By comparison with the known crystal structure, this is interpreted as a consequence of the distortion and shrinking of holes in the Al network under pressure, in which the Ca ions reside. The Al framework up to ∼15 Å appears to largely recover upon decompression, leaving the local Ca–Ca and Ca–Al interactions significantly altered.