Ferroelectric polarization and domain walls in orthorhombic (K _1-x Na_x) NbO₃ lead-free ferroelectric ceramics

Combining aberration-corrected high-resolution transmission electron microscopy with first-principles calculations, we have investigated the ferroelectric polarization and the atomic structures of 60°/120° domain walls in orthorhombic (K_0.46 Na_0.54) NbO₃ lead-free ferroelectric ceramics. The projections of cation-oxygen dipoles across the 60°/120° domain walls were determined using the recently developed negative spherical-aberration imaging technique. The measured ferroelectric distortion matched well with that obtained from first-principles calculations. The width across the wall was measured to be ∼1.1 nm.