The direct chemical reactivity between phosphorus and
nitrogen
was induced under high-pressure and high-temperature conditions (9.1
GPa and 2000–2500 K), generated by a laser-heated diamond anvil
cell and studied by synchrotron X-ray diffraction, Raman spectroscopy,
and DFT calculations. α-P3N5 and γ-P3N5 were identified as reaction products. The structural
parameters and vibrational frequencies of γ-P3N5 were characterized as a function of pressure during room-temperature
compression and decompression to ambient conditions, determining the
equation of state of the material up to 32.6 GPa and providing insight
about the lattice dynamics of the unit cell during compression, which
essentially proceeds through the rotation of the PN5 square
pyramids and the distortion of the PN4 tetrahedra. Although
the identification of α-P3N5 demonstrates
for the first time the direct synthesis of this compound from the
elements, its detection in the outer regions of the laser-heated area
suggests α-P3N5 as an intermediate step
in the progressive nitridation of phosphorus toward the formation
of γ-P3N5 with increasing coordination
number of P by N from 4 to 5. No evidence of a higher-pressure phase
transition was observed, excluding the existence of predicted structures
containing octahedrally hexacoordinated P atoms in the investigated
pressure range.