Boron Phosphorus Nitride at Extremes: PN Octahedra in the High-Pressure Polymorph β-BP N.

The high-pressure behavior of non-metal nitrides is of special interest for inorganic and theoretical chemistry as well as materials science, as these compounds feature intriguing elastic properties. The double nitride α-BP N was investigated by in situ single-crystal X-ray diffraction (XRD) upon cold compression to a maximum pressure of about 42 GPa, and its isothermal bulk modulus at ambient conditions was determined to be 146(6) GPa. At maximum pressure the sample was laser-heated, which resulted in the formation of an unprecedented high-pressure polymorph, β-BP N . Its structure was elucidated by single-crystal XRD, and can be described as a decoration of a distorted hexagonal close packing of N with B in tetrahedral and P in octahedral voids. Hence, β-BP N is the first nitride to contain PN octahedra, representing the much sought-after proof of principle for sixfold N-coordinated P that has been predicted for numerous high-pressure phases of nitrides.