Triclinic Ni0.6Co0.4TiO3 Ilmenite Oxide

Abstract

Forming a solid-solution of NiTiO3 and CoTiO3, two isostructural (ilmenite) and isosymmetrical (space group R-3) compounds, result in a single-phase compound with a remarkably low crystal symmetry. By neutron and X-ray synchrotron powder diffraction techniques, the space group symmetry of the Ni0.6Co0.4TiO3 sample was found to be triclinic P-1 at room temperature, far above the magnetic transition temperature. Ni and Co ions were found to prefer positions close to the octahedron center, whereas Ti ions took off-center positions. This structural distortion is the first known case in ilmenites and opens up ways to modify functional properties of magnetic oxides. Origin of the symmetry lowering is discussed.