High-pressure x-ray-diffraction study of α-AlPO4

Our high-pressure x-ray diffraction experiments on berlinite AlPO4, (alpha-AlPO4,) show that it transforms to a crystalline Cmcm phase beyond 13 GPa. The persistence of diffraction pattern up to 40 GPa does not confirm the previous conclusions of high-pressure amorphization of AlPO4 around 12-18 GPa. Our experimental results, in agreement with earlier Raman scattering results, suggest that the so called memory glass effect observed earlier may in fact be due to the reversibility of alpha-phase double left right arrow Cmcm phase transformation. These new experimental observations raise serious doubts about the theoretical understanding of the high-pressure behavior of alpha-AlPO4.