High-pressure high-temperature synthesis of novel binary and ternary nitride phases of group 4 and 14 elements

Our recent experiments on high-pressure high-temperature synthesis of novel ternary nitrides of group 4 and 14 elements are presented. Dense carbon nitride imide, C₂N₂(NH), was synthesized for the first time in a laser heated diamond anvil cell (LH-DAC) at pressures above 27 GPa and temperatures around 2000 K. Based on results of the electron diffraction-, EELS-and SIMS-measurements combined with theoretical calculations the structure of this new C-N-H phase was suggested to be of the defect-wurtzite type. Farther, macroscopic amounts of a new oxynitride of zirconium having cubic Th₃P₄-type structure, c-Zr_2.86(N_0.88O_0.12)₄, were synthesized at high pressures and temperatures using a multi-anvil apparatus. Earlier this structure was observed for binary nitrides of zirconium(IV) and hafnium(IV) synthesized in microscopic amounts in a LH-DAC. The lattice parameter of c-Zr_2.86(N_0.88O_0.12)₄ was found to be a₀ = 6.7549(1) Å which is slightly larger than that of c-Zr₃N₄. Isotropic bulk and shear moduli of c-Zr_2.86(N_0.88O_0.12)₄ of B₀ = 219 GPa and G₀ = 96 GPa, respectively, were determined from the compression and nanoindentation measurements. The Vickers microhardness, H_V(1), of the porous (about 30 vol. %) sample of c-Zr_2.86(N_0.88O_0.12)₄ was measured to be 12 GPa, similar to that of single crystal δ-ZrN.