Multianvil synthesis, X-ray powder diffraction analysis, 31P-MAS-NMR, and FTIR spektroscopy as well as material properties of γ-P3N5, a high-pressure polymorph of binary phosphorus(V) nitride, built up from distorted PN5 square pyramids and PN4 tetrahedra

The high-pressure phase gamma-P3N5 was synthesized at a pressure of I I GPa and a temperature of 1500 degreesC in a multianvil apparatus. Partially crystalline P3N5 has been used as a starting material. The crystal structure was solved by direct methods on the basis of X-ray powder diffraction data and it was refined by the Rietveld method (Imm2, a = 1287.21(4), b = 261.312(6), c 440.03(2) pm, Z = 2, R-p = 0.073, wR(p) = 0.094, R-F = 0.048). gamma-phosphorus nitride crystallizes in a three-dimensional network structure built up from corner sharing PN4 tetrahedra and trans-edge sharing distorted PN5 square pyramids. In the P-31-MAS-NMR spectrum two sharp isotropic resonances with an intensity ratio of I : 2.02(5) are observed at -11.95(3) and -101.72(7) ppm, respectively The IR-spectroscopic and thermal properties of gamma-P3N5 are described. Measurement of the Vickers hardness resulted in a value of 9.7(21) GPa for sintered polycrystalline gamma-P3N5, which is significantly higher than that for the partially crystalline normal pressure modification Of P3N5 (5.1(7) GPa).