Search for a precursor crystal-to-crystal phase transition to amorphization in &#945;-GeO<SUB>2</SUB> and &#945;-AlPO<SUB>4</SUB> under pressure

Recent X-ray diffraction studies on &#945;-quartz (SiO2) by Kingmaet al [1], have shown the occurrence of a reversible, crystalline-to-crystalline, phase transition just prior to amorphization at &#8776; 21 GPa. This precursor transition has also been confirmed by our recent molecular dynamics simulation study [2]. In order to investigate the possibility of a similar behaviour in other isostructural compounds, which also undergo pressure induced amorphization, &#945;-GeO2 and &#945;-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 reversal is found to be time dependent in GeO2