High-pressure polymorphism in phosphorus nitrides

Based on first-principles density functional calculations, we have investigated the high-pressure polymorphism of phosphorus nitrides (P(3)N(5)). In addition to the recently-determined alpha and gamma phases, our study predicts three new meta-stable high pressure phases existing in the 5 to 35 GPa range, with structures related to the Al(2)SiO(5) mineral polymorphs sillimanite, andalusite, and kyanite, and a new thermodynamically stable phase with a structure related to V(3)O(5), that should form above 35.5 GPa. All these phases contain octahedrally coordinated phosphorus. By providing new insights on the different P-N bonding coordination within different pressure ranges and on the structural connection between isoelectronic oxides and nitrides, our predictive theoretical study will serve as a guideline for future experiments to explore synthesis of novel dense main group nitrides under high-pressure conditions. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.