Theoretical study of P2O5 polymorphs at high pressure: hexacoordinated phosphorus.

Binary oxides of elements belonging to groups 13-15 are of special relevance from a fundamental point of view as well as because of their technological applications as a basis in zeotypes, glasses, or semiconductors. Aluminum oxide, Al2O3, crystallizes in the corundum structure, which is stable at low and high pressures, with the Al showing octahedral coordination. Silicon oxide, SiO2, crystallizes in phases with tetrahedral Si coordination at low pressures as alpha-quartz, but at high pressures, octahedral coordination is stable in the stishovite polymorph. The only known binary phosphorus(V) oxides have tetrahedral P coordination. We have studied the stability of different phases of P2O5 at high pressure, applying density functional theory methodology within the local density and generalized gradient approximations and a plane-wave basis set. Our results indicate that the most stable form of P2O5 at high pressure could be one with hexacoordinated phosphorus. All of the high-pressure phases of Al, Si, and P can be described as a different linking of the same rutile-type blocks.