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Defect dipoles in acceptor-doped (K0.5Na0.5)NbO3-based ceramics have a significant influence on their electrical properties. The present study examined the influence of the sintering atmosphere on the electrical properties of MnO2-doped (K0.5Na0.5)NbO3. The poled and aged samples sintered in the Ar atmosphere depicted unusual behavior related to the formation of defect dipoles (Mn2+ó‴Nb - VÖ, aligned in the poling direction having larger polarity. The S-E loop of the poled and aged MnO2-doped (K0.5Na0.5)NbO3 ceramics sintered in the Ar atmosphere revealed larger strains in the poling direction and restrained strains in the opposite direction. Furthermore, it is observed that the unipolar electro-strain could reach 0.28% (d33*=800 pm/V) at 3.5 kV/mm, a value nearly 5.6-fold higher than those obtained in the air atmosphere (0.05%). This method based on the sintering atmosphere and process control provides a promising way to obtain substantial electro-strain values suitable for applications in high-displacement actuators. [ABSTRACT FROM AUTHOR]

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 (K0.46Na0.54)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. [ABSTRACT FROM AUTHOR]