Phase Stability and Compressibility of 3R-MoN2 at High Pressure

Abstract

We report phase stability and compressibility of rhombohedral 3R-MoN2, a newly discovered layer-structured dinitride, using in-situ synchrotron high-pressure x-ray diffraction measurements. The obtained bulk modulus for 3R-MoN2 is 77 (6) GPa, comparable with that of typical transition-metal disulfides (such as MoS2). The axial compressibility along a axis is more than five times stiffer than that along c axis. Such strong elastic anisotropy is mainly attributed to its layered structure with loosely bonded N-Mo-N sandwich interlayers held by weak Van der Waals force. Upon compression up to ~15\u2009GPa, a new hexagonal phase of 2H-MoN2 occurs, which is irreversible at ambient conditions. The structural transition mechanism between 3R and 2H phases is tentatively proposed to be associated with the rotation and translation of sandwich interlayers, giving rise to different layer stacking sequences in both phases. At high temperature, the decomposition of 3R-MoN2 leads to the formation of hexagonal δ-MoN and the onset degassing temperature increases as the pressure increases. In addition, the low-temperature electrical resistivity measurement indicates that 3R-MoN2 behaves as a semiconductor with an estimated band gap of Eg ≈ 0.5\u2009eV. 3R-MoN2 also shows weak antiferromagnetic properties, which probably originates from the occurrence of magnetic zigzag edges in the structure.