High-pressure synthesis, crystal growth, and compression behavior of hexagonal CrN2 having one-dimensionally aligned nitrogen dimer

A hexagonal chromium pernitride, CrN2, has been successfully synthesized via a direct chemical reaction between chromium and molecular nitrogen at a pressure of approximately 70 GPa. The advanced synchrotron x-ray diffraction (XRD) measurements after recovery and structural refinement at 0.1 MPa demonstrated that CrN2 crystallizes in the anti-NiAs-type structure with lattice parameters of a = 2.7465(3) angstrom and c = 7.3670(4) angstrom. Micron-sized hexagonal habit compounds were found in the synthesized products, which indicated that the single crystal of hexagonal CrN2 was grown in the supercritical nitrogen at high pressure. High-pressure in situ XRD measurements were performed to determine the zero-pressure bulk modulus, K-0, value of 286(6) GPa [K'(0) = 2.5(7)] and remarkable incompressibility of the c axis. CrN2 is a unique example of the recoverable transition-metal pernitride which presents one-dimensionally aligned N-N dimers in the structure. The onedimensionally aligned N-N dimers play an important role in controlling the mechanical and electronic properties of CrN2 as predicted by theoretical calculations.