Wire Structure and Morphology Transformation of Niobium Oxide and Niobates by Molten Salt Synthesis

Perovskite alkaline niobates, especially of one-dimensional morphology, have many important industrial applications. Wirelike Nb2O5 and ANbO(3) (A = K, Na, (Na,K)) were fabricated by a topochemical method based on the molten salt synthesis. First, the precursor KNb3O8 with wire structure was prepared under the condition of molten salt KCl environment at 800 degrees C for 3 h. Then, rodlike H3ONb3O8 and Nb2O5 were obtained from the wirelike KNb3O8 precursor. Finally, the rodlike ANbO(3) (A = K, Na, (Na,K)) were achieved with the intermediate oxide Nb2O5. The wirelike structure of the final product can be achieved when using wirelike Nb2O5 precursor only. The structural evolution was investigated among protonic niobate, niobium oxide, and niobates. The mechanism of these shape transitions was elucidated in the view of structure recombining and atomic diffusing. The (Na,K)NbO3 ceramic sintered from the as-prepared rodlike particles under pressureless condition in the air performed with high piezoelectricity (d(33) = 140 pC/N), which is much better than that of ceramics obtained from cubic or spheric particles.