Modification of the structural properties of NiTiO3 materials by transition metal dopants: The dopant size effect

Abstract

In this study, we investigated the changes of the structural and optical properties of NiTiO3 materials modified by transition metal doping. Cobalt (Co) or tungsten (W)-doped NiTiO3 materials were successfully prepared by a modified Pechini method via solvothermal treatment. Raman, FTIR, and XRD spectroscopic analyses showed that the Co2+ ions were selectively doped into Ni2+ sites in the NiTiO3 lattice while maintaining an ilmenite structure, resulting in a solid solution of triple transition metal oxides. The size similarity between Co and Ni induced the formation of a solid solution, CoxNi1-xTiO3, in the ilmenite structure. In contrast, W doping into the NiTiO3 ilmenite structure resulted in an irregularity of the materials due to the characteristics of the heavy transition metal dopant. Along with increasing the W content, the crystallite size in the ilmenite structure decreased from 90.2 to 74.5 nm and new Raman bands at 831 and 892 cm−1 for WOx appeared at high W contents. However, the PL emission intensities gradually decreased with increasing doping content, implying that the recombination process was inhibited in the NiTiO3 materials by the dopants.