Hydrothermal synthesis of NaNbO3 with low NaOH concentration

NaNbO3 fine powders were prepared by reacting niobium pentoxide with low NaOH concentration solution under hydrothermal conditions at 160 °C. The reaction ruptured the corner-sharing of NbO6 octahedra in the reactant Nb2O5, yielding various niobates, and the structure and composition of the niobates depended on the [OH−] and reaction time. The fine Nb2O5 powder first aggregated to large particles and then turned to metastable intermediates with multifarious morphology. The reaction was fast for the situation of [OH−] = 2 M. The [OH−] determined the structure of final products, and three types of NaNbO3 powder with the orthorhombic, tetragonal and cubic symmetries were obtained, respectively, depending on the [OH−]. The low [OH−] was propitious to yield orthorhombic NaNbO3. The present work demonstrated that higher [OH−] was not favored to synthesize NaNbO3 powders and the conversion speed in this reaction was not in proportion to the [OH−].