Amorphization of quartz-type structures and a new high-pressure phase of AlAsO4

X-ray powder diffraction measurements and investigations on single crystals of AlAsO4 and GaPO4 were performed near the pressure at which the quartz- type structures become unstable using precession technique and polarizing light microscopy. AlAsO4 transformed into a new high-pressure phase before amorphization took place. On release of pressure the compound showed a ''memory effect''. Non-reversible amorphization of GaPO, occurred under non-hydrostatic conditions.