SEARCH FOR A PRECURSOR CRYSTAL-TO-CRYSTAL PHASE-TRANSITION TO AMORPHIZATION IN ALPHA-GEO(2) AND ALPHA-ALPO(4) UNDER PRESSURE

Recent X-ray diffraction studies on alpha-quartz (SiO2) by Kingma et a l [1], have shown the occurrence of a reversible, crystalline-to-cryst alline, phase transition just prior to amorphization at almost-equal-t o 21 GPa. This precursor transition has also been confirmed by our rec ent molecular dynamics simulation study [2]. In order to investigate t he possibility of a similar behaviour in other isostructural compounds , which also undergo pressure induced amorphization, alpha-GeO2 and al pha-AlPO4 (berlinite form) were studied using energy dispersive X-ray diffraction. In either of these materials, no such phase transition is detected prior to amorphization. The onset of amorphization and its r eversal is found to be time dependent in GeO2.