Synthesis and characterization of ilmenite NiTiO3 and CoTiO3 prepared by a modified Pechini method

Powders of ilmenite structure NiTiO₃ and CoTiO₃ were prepared by a simple method based on the modified Pechini process. The raw compounds and citric acid (CA) were mixed in ethanol (EA) with the molar ratio Ni(Co)/Ti/CA/EA = 1/1/1/7.5. The DTA curve shows exothermic peaks only around 300-350 °C and 600 °C, which correspond to the decomposition of the organic compound and direct crystallization of the ilmenite phase. X-ray diffraction patterns indicated that the ilmenite phase was successfully synthesized as the Ni(Co)-Ti precursor calcined above 600-900 °C for 3 h, and the activation energies of NiTiO₃ and CoTiO₃ were calculated to be about 8.84 and 13.23 kJ/mol. TEM bright field images showed that the grain sizes of powders of NiTiO₃ and CoTiO₃ at 600-900 °C were estimated to be about 10-250 and 20-200 nm depending on the nature of the aggregate. The samples of NiTiO₃ calcined at 600-800 °C have the larger specific surface area of 31.51, 18.78, and 6.01 m²/g, respectively. The UV-Vis diffuse reflectance spectra show the optical band gaps of NiTiO₃ and CoTiO₃ as 3.02 and 2.43 eV.