Synthesis of a New Ternary Nitride, Fe4W2N, with a Uniqueη-Carbide Structure

Abstract

The structure of a new ternary nitride, Fe4W2N, prepared using a metal-organic precursor synthesis route, has been determined by Rietveld refinement of the monochromatic X-ray powder diffraction data. The compound crystallizes in a cubic,η-carbide structure, space groupFd3m(227), withZ=16 and a lattice parameter ofa=11.0810(9) Å. The refinement converged withRwp=0.1273,Rp=0.0709,RI=0.0478, andS=1.72. The compound is isostructural with Fe4W2C, the ideal structure consisting of eight octahedra of metal atoms, a random mixture of which one-third are iron and two-thirds are tungsten, centered on a diamond cubic lattice and eight regular tetrahedra of iron atoms centered on a second diamond cubic lattice that interpenetrates the first through a 12,12,12 unit cell translation. Sixteen additional iron atoms are tetrahedrally coordinated around the iron tetrahedra and sixteen nitrogen atoms surround the metal octahedra in tetrahedral coordination.