SYNCHROTRON X-RAY-DIFFRACTION STUDY OF ALPHA-CRISTOBALITE AT HIGH-PRESSURE AND HIGH-TEMPERATURE

Energy-dispersive x-ray diffraction using synchrotron radiation was ca rried out on alpha-cristobalite to 3 GPa and 350 degrees C in a cubic anvil press. A cascading structural phase transition occurred beyond 0 .61 GPa at room temperature, The transition was accompanied by a split ting of most of the cc-cristobalite reflections: the (111) reflection at 0.61 GPa through the (211) reflections at 2.13 GPa, with many other lines between. The pressure of this transition decreased with increas ing temperature.