Electron-diffraction study on ∈-iron nitride powders with various nitrogen contents: Variation of long-range nitrogen ordering

Abstract

Homogeneous ∈-iron nitride powder particles of the compositions Fe3N1.00, Fe3N1.22, Fe3N1.30, and Fe3N1.39were investigated using selected-area electron diffraction. The superstructure reflections, due to N ordering on the octahedral interstitial sites of a hexagonal close-packed (hcp) arrangement of Fe, indicate a hexagonal supercell witha′ = 31/2ahcp,c′ =chcpfor all cases;P6322 space group symmetry for Fe3N1.00, Fe3N1.30, and Fe3N1.39; and lower symmetry (P312) for Fe3N1.22and some of the Fe3N1.30particles. Recognition of the occurrence of double diffraction is essential for correct interpretation of the diffraction patterns. Additionally, diffuse scattering by some of the Fe3N1.39grains was observed.