Hydrothermal synthesis of morphology-controlled KNbO3, NaNbO3, and (K,Na)NbO3 powders

NaNbO3, (K,Na)NbO3 and KNbO3 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 NaNbO3 and KNbO3 powders had sub-micron- or micron-sized grains. The [OH−] drastically influenced the size and morphology of the KNbO3 particles but did not influence those of the NaNbO3 particles. In contrast, the morphology of the (K,Na)NbO3 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 KNbO3 and NaNbO3 particles. The present synthetic strategy enables tailoring the compositions, morphologies, and structures of the niobate products to different applications by controlling the process parameters.