HIGH-PRESSURE BEHAVIOR OF THE BETA-CRISTOBALITE-TYPE PHASE OF PHOSPHORUS OXYNITRIDE, PON

Phosphorus oxynitride, PON, is isoelectronic with SiO2 and can beused as a model for silica. The crystalline behaviour of the beta-cristobal ite-type phase was determined as a function of pressure by angular dis persive x-ray diffraction in a diamond anvil cell to 48 GPa. No eviden ce for a phase transition or amorphization was observed. The cell para meters were measured as a function of pressure. The macroscopic bulk m odulus is 71(3) Gpa with a first pressure derivative of 3.2(5). The po lyhedral bulk modulus was inferred to be about 800 Gpa, assuming that the tetrahedra remain regular.