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 similar to 15 angstrom appears to largely recover upon decompression, leaving the local Ca-Ca and Ca-Al interactions significantly altered. (c) 2006 Elsevier Ltd. All rights reserved.