Synthesis and structural investigation of a new ternary transition metal nitride, Co3W3N

Abstract

A new ternary transition metal nitride, Co3W3N, has been synthesized by the ammonolysis of a chemically derived metalloorganic precursor. The compound crystallizes in the η-carbide structure which is cubic in the space group Fd3̄m (227) with Z=16, as determined from powder X-ray diffraction and Rietveld refinement of the resulting diffraction pattern. The refinement converged with Rwp=0.1198, Rp=0.0725, RI=0.0400, and S=1.63. The unit cell of Co3W3N has a lattice parameter of a=11.0995(2) Å. The compound is isostructural with Co3W3C, the ideal structure consisting of eight regular octahedra of tungsten atoms centred on a diamond cubic lattice and eight regular tetrahedra of cobalt atoms centred on a second diamond cubic lattice that interpenetrates the first through a 12, 12, 12 unit cell translation. Sixteen additional cobalt atoms are tetrahedrally coordinated around the cobalt tetrahedra and sixteen nitrogen atoms surround the tungsten octahedra in tetrahedral coordination.