We have investigated the high-pressure behavior of low-cristobalite form of AlPO4 (c-AlPO4) using a combination of Raman scattering, synchrotron powder X-ray diffraction, and classical molecular dynamics simulations. Our experiments indicate that under non-hydrostatic conditions c-AlPO4 initially transforms to a monoclinic phase, which then transforms to the Cmcm phase via an intermediate, disordered structure. In contrast, X-ray diffraction measurements made under hydrostatic conditions show that the ambient structure transforms directly to the Cmcm phase. Our classical molecular dynamics simulations, carried out under hydrostatic conditions, also show that c-AlPO4 directly transforms to the Cmcm phase at ~13 GPa.

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