a1 Materials Department and Materials Research Laboratory, University of California, Santa Barbara, California 93106
a2 Materials Science Department 138–78, California Institute of Technology, 1200 California Boulevard, Pasadena, California 91125
a3 Materials Department and Materials Research Laboratory, University of California, Santa Barbara, California 93106
Orthorhombic KNbO3 and NaNbO3 powders were hydrothermally synthesized in KOH and NaOH solutions (6.7–15 M) at 150 and 200 °C. 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.
(Received July 22 2002)
(Accepted October 28 2002)