Direct observation of monoclinic ferroelectric phase and domain switching process in (K0.25Na0.75)NbO3 single crystals

Abstract

In situ observations of the phase symmetry and domain evolution of (K_0.25Na_0.75)NbO₃ single crystals under bipolar electric fields have been performed for both pseudocubic (110) and (001) orientations using polarized light microscopy and X-ray diffraction. The macroscopic symmetry was identified to be a monoclinic C type phase with the spontaneous polarization direction close to <054>. The electric field-driven domain morphology and evolution model were also presented. It was found that, under an antiparallel electric field, the approximately 180° domain switching process in a pseudocubic (101) sample consists of three steps: two ~60° domain switching and a ~90° domain switching, and the ~90° domain switching process in the pseudocubic (001) sample is composed of two ~60° switching steps.