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Quenching procedures are effective in enhancing the low depolarization temperature of sodium bismuth titanate (NBT) relaxor ferroelectrics. In the present work, the influence of thermal processing parameters on the structure and electrical properties of NBT ceramics modified with 5 mol% sodium niobate (NBT-5NN) are evaluated. It is shown that quenching leads to higher electrical conductivity due to reduction at high temperatures, resulting in a higher oxygen vacancy concentration. The quenched materials also exhibit enhanced rhombohedral distortion and ferroelectric properties. The reduction process is largely reversible by reoxidation during annealing at intermediate temperatures in the region of 550 °C, which helps to recover the bulk resistivity to values close to those of the as-sintered materials. On the other hand, the rhombohedral distortion and ferroelectric properties were not affected significantly by the annealing procedure, indicating that the mechanisms responsible for the modification of electrical conductivity and structural distortion/ferroelectric properties have a different origin. [ABSTRACT FROM AUTHOR]

• Domain switching and lattice strain in polycrystalline K 0.5 Bi 0.5 TiO 3 -BiFeO 3 -PbTiO 3 is evaluated by in-situ high energy synchrotron XRD. • The tetragonal {200} grain family exhibited the highest effective lattice strain up to 8.2 × 10−3 at an electric field of 5 kV/mm. • A partial phase transformation from tetragonal to rhombohedral occurred at high electric field levels, with an average strain of −1.54 × 10−3. • Relaxation of intergranular stress gives rise to enhanced domain switching in KBT-BF-PT ceramics. • The observed self-adapting mechanism could also be exploited in other high performance, high temperature piezoelectric ceramics. We report an in-situ synchrotron X-ray diffraction study of K 0.5 Bi 0.5 TiO 3 -BiFeO 3 -PbTiO 3 ceramics, which exhibit a T c of around 450 °C. The electromechanical actuation mechanisms comprise contributions from coexisting tetragonal and rhombohedral phases. The tetragonal {200} grain family exhibited the highest effective lattice strain, up to 8.2 × 10−3 at 5 kV/mm. Strong strain anisotropy in the tetragonal phase and field-induced intergranular stresses facilitate a partial transformation from tetragonal (high strain anisotropy) to rhombohedral (low strain anisotropy) at high electric field levels, with an average linear transformation strain of -1.54 × 10-3. The domain switching behavior was effectively enhanced in both tetragonal and rhombohedral phases after the phase transformation, due to the release of intergranular stress. This observed self-adapting mechanism in tuning intergranular stress through partial phase switching in the morphotropic KBT-BF-PT composition with large lattice distortion could also be exploited in other perovskite systems in order to achieve high performance high temperature piezoelectric ceramics. [ABSTRACT FROM AUTHOR]