A neutron diffraction study of oxygen and nitrogen ordering in a kinetically stable orthorhombic iron doped titanium oxynitride

The synthesis of a polycrystalline powder sample of iron doped orthorhombic titanium oxynitride, Ti2.92Fe0.01O4.02N0.98, on the scale of 0.7 g has been achieved. This was conducted by the unusual route of delamination from a steel substrate of a thin film deposited using atmospheric pressure chemical vapour deposition. The structure of the titanium oxynitride is presented, determined from a combined analysis of X-ray and neutron powder diffraction data. The use of neutron diffraction allows the position of the oxygen and nitrogen ions in the material to be reported unambiguously for the first time. In this study Ti2.92Fe0.01O4.02N0.98 is found to crystallise in the Cmcm space group, iso-structural pseudobrookite, with lattice parameters a=3.81080(6) Å, b=9.6253(2) Å, and c=9.8859(2) Å, and contains partial oxygen–nitrogen ordering. Of the three anion sites in this structure one is exclusively occupied by oxygen, while the remaining two sites are occupied by oxygen and nitrogen in a disordered manner. Testing indicates that this iron doped titanium oxynitride is a metastable phase that decomposes above 700 °C into TiN and TiO2, the thermodynamic products.