High-pressure X-ray investigation of the moganite- and quartz-type phases of phosphorus oxynitride Original Research Article

The high-pressure behavior of the moganite-type polymorph of phosphorus oxynitride PON (monoclinic, I2/a, Z=12) has been determined by angle dispersive X-ray powder diffraction in a diamond anvil cell to 50 GPa. The pressure variations of the three cell parameters display a distinct slope change: the axial compressibilities are about three times larger below 9 GPa than above this pressure. This behavior is completely reversible. The molar volume of the moganite-type phase under pressure remained larger than that of the quartz-type phase determined under similar conditions. The pressure-induced amorphization of the quartz- and moganite-type phases is compared: while it was reversible upon decompression for moganite it was not for the quartz-phase. This difference in behavior is attributed to local configurations in the structures of the two phases.