Hydrothermal synthesis of KNbO3 and NaNbO3 powders

Orthorhombic KNbO3 and NaNbO3 powders were hydrothermally synthesized in KOH and NaOH solutions (6.7-15 M) at 150 and 200 degreesC. An intermediate hexaniobate species formed first before eventually converting to the perovskite phase. For synthesis in KOH solutions, the stability of the intermediate hexaniobate ion increased with decreasing KOH concentrations and temperatures. This led to significant variations in the induction periods and accounted for the large disparity in the mass of recovered powder for different processing parameters. It is also believed that protons were incorporated in the lattice of the as-synthesized KNbO3 powders as water molecules and hydroxyl ions.