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The possibility of a post-stishovite phase transition of SiO₂ occurring at very high pressures has long been of interest. Recently, a transition from rutile to CaCl₂ structure was suggested from the results of high-pressure Raman spectroscopy and X-ray diffraction studies. However because of experimental difficulties at extremely high pressures, the exact structure of this new phase has not yet been confirmed.

GeO₂ in an analogue material for SiO₂ in which the rutile to CaCl₂ transition is expected to occur at considerably lower pressures. We are investigating the possible occurrence of this phase transition in GeO₂ by performing a precise X-ray diffraction structural analysis on quenched samples synthesized in the multianvil apparatus. Recent preliminary molecular dynamic calculations have predicted that the rutile to CaCl₂ transition occurs in GeO₂ at around 30 Gpa. We have therefore attempted synthesis experiments in the 25-30 Gpa pressure range at 600° to 800° using a 6/2.5 (octahedron edge length/truncation edge length, in mm) multianvil assembly. The transition observed in SiO₂ is reversible and therefore difficult to quench. We have attempted to quench the high-pressure GeO₂ phase by using very fine powder as a starting material. Using such a starting material, we were previously able to quenched a high-pressure phase of ZrO₂ which also shows the characteristics of a displacive phase transition.