Hydrothermal synthesis and characterization of KNbO3nanorods

Abstract

Single-crystalline KNbO₃nanorods were prepared from Nb₂O₅ by hydrothermal synthesis at 180 °C in a KOH solution using sodium dodecyl sulfate surfactant. The morphology of the KNbO₃ product was strongly influenced by the addition of the surfactant, the concentration of the reactants, the reaction time and temperature, demonstrating that KN nanorods were only obtained in a narrow window of synthesis parameters. At the optimized conditions the orthorhombic KNbO₃nanorods were 100–300 nm in diameter, up to 5 µm in length and grew along the [001] direction. The proposed growth mechanism is based on self-assembly of cube-shaped or facetted KNbO₃nanocrystals into mesocrystals, which further ripen into nanorods. High temperature X-ray diffraction, calorimetry and Raman spectroscopy evidenced that the orthorhombic to tetragonal and tetragonal to cubic phase transition of KNbO₃nanorods occurred at significantly lower temperatures than for bulk KNbO₃, reflecting finite size or disorder effects.