Nitride Spinel: An Ultraincompressible High-Pressure Form of BeP$_2$N$_4$

Owing to its outstanding elastic properties, the nitride spinel γ‐Si$_3$N$_4$ is of considered interest for materials scientists and chemists. DFT calculations suggest that Si$_3$N$_4$‐analog beryllium phosphorus nitride BeP$_2$N$_4$ adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite‐type BeP$_2$N$_4$ by single‐crystal synchrotron X‐ray diffraction and report the phase transition into the spinel‐type phase at 47 GPa and 1800 K in a laser‐heated diamond anvil cell. The structure of spinel‐type BeP$_2$N$_4$ was refined from pressure‐dependent in situ synchrotron powder X‐ray diffraction measurements down to ambient pressure, which proves spinel‐type BeP$_2$N$_4$ a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel‐type BeP$_2$N$_4$ is an ultraincompressible material