Solvothermal synthesis of dispersible homogeneous KNbO₃ nanocubes from K₄Nb₆O₁₇ microsheets

Abstract

The morphology- and size-controlled syntheses of KNbO₃ nanoparticles, which are demanded by ferroelectric and piezoelectric applications, have been attempted by hydrothermal and solvothermal methods in the typical Nb₂O₅–KOH reaction systems, but the resultant KNbO₃ nanoparticles generally had a wide particle size distribution and formed severe aggregations. In this study, dispersible homogeneous KNbO₃ nanocubes were synthesized from layered potassium niobate, K₄Nb₆O₁₇, by the solvothermal method. The K₄Nb₆O₁₇ microsheets could be completely converted into KNbO₃ at the lower K/Nb atomic ratio as compared to the Nb₂O₅ nanoparticles because it requires a relatively minor rearrangement of NbO₆-unit network in K₄Nb₆O₁₇ to form the KNbO₃ nuclei. The homogeneous KNbO₃ nanocubes with the ferroelectric orthorhombic phase were obtained at the higher K/Nb atomic ratio, and their colloidal suspensions were stabilized by the electrostatic repulsion between the negatively charged surfaces of the KNbO₃ nanocubes.