Possible origin of stabilized monoclinic structure of KNbO3 nanomaterials at room temperature.

We have investigated the structural phase transition and phase stability of newly discovered monoclinic crystal structure of KNbO 3 nanomaterials. Through x-ray diffraction, Raman scattering, and neutron diffraction measurements, we have found that the KNbO 3 grown at low temperature undergoes a successive structural transition from monoclinic, tetragonal, to cubic, while the KNbO 3 grown at high temperature does from monoclinic, orthorhombic, tetragonal, to cubic with the increase of temperature. After heat treatment, the monoclinic structure of KNbO 3 is transformed to an orthorhombic structure at room temperature. Accompanying the structural transformation, the Raman peaks corresponding to surface and lattice hydroxyl groups are strongly suppressed. These results imply that the hydroxyl defects should play a crucial role for the monoclinic structure of KNbO 3 at room temperature. [ABSTRACT FROM AUTHOR]