Electric polarization modulation through continuous phases regulation of KNbO 3 nanocrystal at room temperature

Abstract

Phase variation always brings the noncentrosymmetrical materials with different polarization properties. Here, we prepared the KNbO3 nanocrystals with three different phases using the traditional hydrothermal method. Through simply changing the KOH concentration, the tetragonal (T-KNbO3), monoclinic (M-KNbO3) and orthorhombic (O-KNbO3) phase were obtained. The anisotropy growth mechanism driven by OH- concentration plays a dominant role in manipulating the morphology and phase. Due to the large off-center ratio of O-KNbO3 and T-KNbO3, they show strong spontaneous polarization along [010] and [001] directions. However, the further decrease in lattice symmetry endows the M-KNbO3 crystal with two perpendicular spontaneous polarization axes, [100] and [001], as confirmed by theoretical calculations and second-harmonic generation characterizations. This work provides a facile strategy for modulating the nonlinear performance of perovskite oxide materials and devices.