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The structure and properties of Mn‐doped 0.67BiFeO3‐0.33BaTiO3 ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air‐quenching induces a change in crystal structure from pseudo‐cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well‐defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature‐dependent relative permittivity for the as‐sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature‐stability of piezoelectric properties. It is proposed that the formation of defect clusters by A‐site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties. [ABSTRACT FROM AUTHOR]

The structures and functional properties of Na0.5Bi0.5TiO3- xKNbO3 (NBT-xKN) solid solutions, with x in the range from 0.01 to 0.09, were investigated using a combination of high-resolution synchrotron X-ray powder diffraction (SXPD) and ferroelectric property measurements. For low KN contents, an irreversible transformation from cubic to rhombohedral phases was observed after the application of a high electric field, indicating that the polar nanoregions (PNRs) in the unpoled state can be transformed into metastable long-range ordered ferroelectric domains in the poled state. In contrast, the near-cubic phase of the unpoled ceramics was found to be remarkably stable and was retained on cooling to a temperature of −175°C. Upon heating, the field-induced metastable ferroelectric rhombohedral phase transformed back to the nanopolar cubic state at the structural transformation temperature, TST, which was determined as approximately 225°C and 125°C for KN contents of 3% and 5% respectively. For the field-induced rhombohedral phase in the poled specimens, the pseudo-cubic lattice parameter, ap, exhibited an anomalous reduction while the inter-axial angle increased towards a value of 90° on heating, resulting in an overall increase in volume. The observed structural changes were correlated with the results of temperature-dependent dielectric, ferroelectric and depolarization measurements, enabling the construction of a phase diagram to define the stable regions of the different ferroelectric phases as a function of composition and temperature. [ABSTRACT FROM AUTHOR]