Dense Structure of Yttrium Nitride as a Post-Rock-Salt Phase: High-Pressure Experiments and Computations.

The post-rock-salt (1) phase in yttrium nitride was investigated under pressures above 100 GPa. The starting 1 phase was prepared by a direct elemental reaction between yttrium metal and supercritical nitrogen in a laser-heated diamond anvil cell. Compression of the resulting compound under nitrogen pressure revealed that the experimental bulk modulus was significantly lower than that reported for previous compression experiments but consistent with values predicted by theoretical calculations. The post-1 phase transition started at 116 GPa and was almost completed at 170 GPa, with slow kinetics of conversion. In contrast to the likely transformation to 2 from 1, the phase was determined to be 10, which is identical to a high-pressure BaO structure. Theoretical enthalpy calculation demonstrated that a transition from 1 to 10 takes place at 108 GPa prior to the 2 transition. The present YN is the first non-4-nitride compound reported to crystallize with a 10 structure.