Synthesis and properties of oxygen-bearing c-Zr3N4 and c-Hf3N4

This paper presents our recent results on synthesis and properties of high-pressure cubic zirconium(IV)- and hafnium(IV) nitrides having Th3P4-type structure, c-M3N4 (M = Zr or Hf). c-M3N4 were first synthesized in microscopic amounts in a laser-heated diamond anvil cell (LH-DAC) at pressures above 15 GPa and temperatures above 2500 K. Further, macroscopic amounts of c-Hf3N4 and of a new oxygen-bearing zirconium nitride, c-Zr2.86(N0.88O0.12)4, were synthesized at 12 GPa and about 1900 K using a multi-anvil apparatus. The lattice parameter of c-Hf3N4 was determined to be a0 = 670.2(1) pm. The a0 of c-Zr2.86(N0.88O0.12)4 of 675.49(1) pm was found to be slightly larger than that of c-Zr3N4 (674.0(6) pm). The bulk moduli, B0, of 219 GPa for c-Zr2.86(N0.88O0.12)4 and of 227 GPa for c-Hf3N4 were obtained from compression measurements. Combining the compression and indentation data we determined for c-Zr2.86(N0.88O0.12)4 its isotropic shear modulus G0 = 96 GPa. Finally, Vickers microhardness, indentation fracture toughness and thermal expansion of c-Zr2.86(N0.88O0.12)4 were measured.