Synthesis of potassium sodium niobate nanostructures by hydrothermal combining with the sol-gel method

Abstract

In this paper the K1−xNaxNbO3(KNN) nanostructures were synthesized by hydrothermal method using KNN gel powders as precursors. KNbO3-type orthorhombic KNN nanowires and perovskite KNN microfingers with a morphotropic phase boundary (MPB) between rhombohedral and tetragonal characterized by X-ray diffraction and Raman spectroscopy were obtained at 190°C and 220°C, respectively. KNbO3-type orthorhombic KNN nanowires had rectangular shape and the growth direction of these nanowires was [001]. The rhombohedral-tetragonal KNN microfingers were metastable, and changed the rhombohedral-tetragonal phase into the orthorhombic phase via thermal treatment at 600°C then cooled down to room temperature. Sodium dodecyl sulfate (SDS) as surfactant was added to the hydrothermal reaction. It was found that SDS could improve the crystallinity of the rhombohedral-tetragonal K0.52Na0.48NbO3 and reduce the impurity effectively. The tetragonal-cubic phase transition temperature (Tc) of the rhombohedral-tetragonal powders appeared at 555°C.