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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+Nb‴−VO··)′, 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-displa...

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.

Lead-free K1−xNaxNbO3 ceramics with x=0.48–0.54 were prepared by a conventional solid-state reaction method to investigate the influence of the K/Na ratio on phase structures and electrical properties. The results suggest that a typical morphotropic phase boundary exists at x=0.52–0.525, separating the monoclinic and orthorhombic phases. The sample with the composition near x=0.52 shows the maximum values of the piezoelectric constant (d33=160 pC/N) and the electromechanical coupling coefficient (kt=47%). The results provide a helpful guidance to consider the optimal ratio of K to Na for designing and developing new (K,Na)NbO3-based ceramics.

In addition to x-ray diffraction, Raman spectrum measurements provide direct evidence of the tetragonal and orthorhombic phases coexistence in lead-free ceramics (1−x)K0.5Na0.5NbO3 (KNN)–xLiTaO3 when x equals 5mol%. This is caused by the phase transition temperature between tetragonal and orthorhombic decreasing to around room temperature due to the Li and Ta doping in KNN, and not by constituting a region of morphotropic phase boundary as presented by most published papers. The results indicate that although this kind of ceramic displays good properties, it needs further study to verify if it is suitable to be used in a varying temperature environment.