Chemical design of highly water-soluble Ti, Nb and Ta precursors for multi-component oxides

Novel citric acid based Ti, Nb and Ta precursors that are highly stable in the presence of water were developed. No alkoxides of Ti, Nb and Ta were utilized in the preparation, instead much less moisture-sensitive metallic Ti, NbCl₅ and TaCl₅ were chosen as starting chemicals for Ti, Nb and Ta, respectively. The feasibility of these chemicals as precursors is demonstrated in the powder synthesis of BaTi₄O₉, Y₃NBO₇ and LiTaO₃. The water-resistant Ti precursor was employed as a new source of water-soluble Ti in the amorphous citrate method, and phase pure BaTi₄O₉ in powdered form was successfully synthesized at 800 °C. The Pechini-type polymerizable complex method using the water-resistant Nb and Ta precursors was applied to the synthesis of Y₃NbO₇ and LiTaO₃, and both the powder materials in their pure form were successfully synthesized at reduced temperatures, viz. 500-700 °C. The remarkable retardation of hydrolysis of these water-resistant precursors is explained in terms of the partial charge model theory.