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Ferroelectric Bi0.5(Na0.82K0.18)0.5TiO3 (NKBT) thick films have been prepared using screen printing on Pt electroded alumina substrates. The room-temperature dielectric constant of resulting 60 μm thick NKBT film reaches as high as 823 at 1 kHz and the depolarization temperature, Td, locates at 130 °C. The effect of amplitude and frequency of the applied ac field and the aging temperature as well as the Bi excess on the dielectric and piezoelectric aging characteristics are systemically studied. The results show that the dielectric and piezoelectric aging are associated with the reorientation of defect dipoles which stabilized the non-180° domain walls. By this reorientation the domain wall motions are clamped by a time dependent force resulting in the observed decrease in the dielectric and piezoelectric properties during the aging procedural. Moreover, the aging in NKBT thick films exhibits strong frequency dependence, which is caused by that the reorientation and alignment of the defect dipoles with the local polar domains provide a pinning field to the micropolar region, where the regions with larger micropolar volume will experience stronger pinning potential. The NKBT thick films added with 0.5 mol % Bi2O3 exhibit relative lower aging rate of the dielectric constant and piezoelectric coefficient, resulting from the compensation of the Bi3+ vacancies by the addition of small amount of excess Bi2O3. [ABSTRACT FROM AUTHOR]

La2O3-doped sodium–potassium bismuth titanate (Na0.82K0.18)0.5Bi0.5TiO3 (NKBT) lead-free thick films have been prepared on Pt-electroded alumina substrates using a combination of screen printing and subsequent infiltration of the corresponding composite sol. Their densification, microstructure, dielectric, ferroelectric, pyroelectric, and piezoelectric properties were investigated with variation of the La2O3 content. The resulting 40 μm-thick NKBT films doped with 1.0 mol% La2O3 show minimum leakage current density of 1.56 × 10−9 A/cm2 at an applied field of 100 kV/cm, remanent polarization of 21.6 μC/cm2, and coercive field of 58 kV/cm. The high pyroelectric coefficient of 2.0 × 10−4 C·(m2·°C)−1, the calculated detectivity figure of merit as high as 0.81 × 10−5 Pa−0.5, and the value of remanent d33eff of 108 pm/V at room temperature (20°C) were observed in 1.0 mol% La2O3-doped NKBT thick films, which can be comparable with that of the commonly used lead-based materials. The enhancement of the pyroelectric and piezoelectric performances is attributed to the reduction of lattice tetragonality, uniform microstructure, and improved densification in La-modified NKBT thick films. [ABSTRACT FROM AUTHOR]