Revealing Phosphorus Nitrides up to the Megabar Regime: Synthesis of alpha-P3N5, delta-P3N5 and PN2

TL;DR

This study synthesizes and characterizes three novel phosphorus nitride phases under high pressure, revealing their structures, properties, and stability, and demonstrates how high-pressure conditions enable exploration of otherwise inaccessible phases.

Contribution

It reports the discovery and detailed characterization of three new phosphorus nitride phases synthesized at megabar pressures, expanding knowledge of their structures and properties.

Findings

Delta-P3N5 forms at 72 GPa with a dense PN6 network.

PN2 forms at 134 GPa with a dense PN6 network.

Delta-P3N5 transforms into alpha'-P3N5 below 7 GPa, which is stable at ambient conditions.

Abstract

Non-metal nitrides are an exciting field of chemistry, featuring a significant number of compounds that can possess outstanding material properties. This characteristic relies on maximizing the number of strong covalent bonds, with crosslinked XN6 octahedra frameworks being particularly intriguing. In this study, the phosphorus-nitrogen system was studied up to 137 GPa in laser-heated diamond anvil cells and three previously unobserved phases were synthesized and characterized by single-crystal X-ray diffraction, Raman spectroscopy measurements and density functional theory calculations. Delta-P3N5 and PN2 were found to form at 72 and 134 GPa, respectively, and both feature dense 3D networks of the so far elusive PN6 units. The two are ultra-incompressible, having a bulk modulus of K0 = 322 GPa for delta-P3N5 and K0 = 339 GPa for PN2. Upon decompression below 7 GPa, delta-P3N5 undergoes a transformation into a novel alpha'-P3N5 solid, stable at ambient conditions, that has a unique structure type based on PN4 tetrahedra. The formation of alpha'-P3N5 underlines that a phase space otherwise inaccessible can be explored through high-pressure formed phases.