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

Highlights: • Co (W)-doped NiTiO₃ materials were successfully prepared by a modified Pechini method. • Selective Co²⁺ ion doping into Ni²⁺ sites in the NiTiO₃ lattice formed a solid solution. • W doping into the NiTiO₃ lattice resulted in an irregularity in the lattice structure. • The PL emission intensities gradually decreased with increasing dopant concentration. • The recombination process in the NiTiO₃ materials was inhibited by the metal dopants. 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, Co_xNi_1-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 WO_x 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.