HIGH-PRESSURE AMORPHIZATION OF THE ALPHA- QUARTZ PHASE OF PHOSPHORUS OXYNITRIDE PON

The alpha-quartz phase of phosphorus oxynitride PON was prepared from the cristobalite phase submitted to 4.5 GPa and 750 degrees C. The hig h-pressure behaviour of this alpha-quartz phase was investigated by an gle-dispersive X-ray powder diffraction in a diamond anvil cell up to 48 GPa. The cia ratio of cell parameters increased under pressure, but at a slower rare than in silica. At about 20 GPa, the ratio increased suddenly by 2% indicating a first-order phase transformation. Progres sive amorphisation was observed, particularly above 30 GPa. Amorphisat ion was complete above 42 GPa, and remained irreversible upon decompre ssion. The high-pressure behaviour of the alpha-quartz phase of PON pa rallels that of silica. (C) Academie des Sciences/Elsevier, Paris.