Abstract
Raman spectra were collected on Ni1-xCoxTiO3 (0 ≤ x ≤ 1) ilmenite samples as a function of temperature between 4 and 1200 K. An evident symmetry lowering from the prototype R3 ̅ symmetry is observed. The distortion was largest for x = 0.40 and 0.50 samples, and significantly diminished for a small and large value of x. The distortion was preserved in the whole temperature range and, except for the x = 0.50 sample, did not show significant changes. The direct cation-cation interactions and oxygen mediated indirect interactions are discussed as mechanisms behind the distortion and magnetic order. A reversible order-disorder phase transformation, assigned to occur between ilmenite and corundum phases, took place at 973 K in x = 0.50 sample. Completion of the transformation took over one hour. The role of the overlap of Co/Ni and Ti 3d orbitals through oxygen octahedral faces for charge transfer is discussed.
