MEMORY EFFECTS IN PRESSURE-INDUCED AMORPHOUS ALPO4

A Brillouin scattering study of the pressure dependence of the elastic properties of AlPO4 single crystals is presented. On increasing the pressure there is clear evidence of a phase transformation at 15 GPa; this is consistent with previous Raman and x-ray measurements which report an amorphous phase at high pressures. On decreasing the pressure the sample not only recrystallizes at almost-equal-to 7 GPa but it reverts to a single crystal with the initial crystallographic orientation. This surprising behavior confirms the claims, based on birefringence measurements, of Kruger and Jeanloz [Science 249, 647 (1990)]. Our results also indicate that, even in the amorphous phase, AlPO4 remains elastically anisotropic.