Hydrothermal synthesis of morphology-controlled KNbO 3 , NaNbO 3 , and (K,Na)NbO 3 powders

Abstract NaNbO 3 , (K,Na)NbO 3 and KNbO 3 powders were synthesized using (1− y) NaOH–y KOH solutions ([OH − ] =7.5–15 M) with y=0, 0.78, and 1 at 200 °C by the hydrothermal method, respectively. Their compositions, structures, and morphologies were analysed. Both of the synthesized NaNbO 3 and KNbO 3 powders had sub-micron- or micron-sized grains. The [OH − ] drastically influenced the size and morphology of the KNbO 3 particles but did not influence those of the NaNbO 3 particles. In contrast, the morphology of the (K,Na)NbO 3 particles, which were aggregates of nano-grains, was influenced by the hydrothermal-treatment time rather than [OH − ]. Moreover, their composition and phase were influenced by both annealing and the hydrothermal-treatment time, and their formation mechanism was discussed by comparison with those of KNbO 3 and NaNbO 3 particles. The present synthetic strategy enables tailoring the compositions, morphologies, and structures of the niobate products to different applications by controlling the process parameters.