Effect of solvent and temperature on the preparation of potassium niobate by hydrothermal-assisted sol-gel processing

In this study the preparation of potassium niobate powder, a material with high electro-optic and nonlinear optical coefficients, by hydrothermal-assisted sol-gel processing from potassium-niobium ethoxide [KNb(OC2H5)(6)] have been performed. The development of potassium niobate phases by hydrothermal hydrolysis of potassium niobium, ethoxide at 100 and 200 degrees C in ethanol, toluene, and a mixture of benzene and ethanol was pursued by X-ray diffraction. Selected powders obtained from hydrothermal-assisted sol-gel processing were characterized by X-ray powder diffraction, thermal analysis (TGA/DSC), and scanning electron microscopy (SEM). X-ray diffraction results showed that the hydrothermal hydrolysis of potassium-niobium ethoxide in ethanol at 100 and 200 degrees C results in the formation of cubic phase KNbO3. Hydrolysis in a mixture of benzene/ethanol and toluene at 200 degrees C produces an orthorhombic phase KNbO3, which is a mixture of the potassium deficient phase, K4Nb6O17, and cubic and orthorhombic KNbO3 phases. The potassium niobate powder prepared by the hydrothermal method had the advantage of low weight loss during calcination. SEM micrographs showed that the shape of particles prepared by hydrothermal-assisted sol-gel processing is more uniform when compared with the sample prepared by conventional sol-gel processing. (C) 2009 Published by Elsevier Ltd and Techna Group S.r.l.