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Bi0.5(Na0.82K0.18)0.5TiO3(NKBT) lead-free ferroelectric thick films with various porosities have been produced by screen printing. Their microstructures, pyroelectric and piezoelectric properties were investigated with variation of porosity. The results show that the relative dielectric constant of the resulting 90 μm NKBT thick films with 19% and 32% porosity was down to 161 and 56, respectively. The pyroelectric voltage figure of merit ( Fv) and detectivity figure of merit ( FD) of NKBT thick films were increased from 10.2 × 10−13 to 19.7 × 10−13 Cm/J and 1.1 × 10−5 to 3.8 × 10−5 Pa−0.5. Moreover, the hydrostatic voltage constant and hydrostatic figure of merit of the NKBT thick films with 32% porosity reached 81 × 10−3 V/mPa and 8200 × 10−15 Pa−1 respectively. The decreasing of relative dielectric constant, volume specific heat, and piezoelectric coefficient with increasing porosity was responsible for the improved pyroelectric and piezoelectric figures of merit of the NKBT thick films. Furthermore, screen printing with the addition of controlled fraction of organic vehicle in pastes has been proved to be an alternative method for fabrication of porous pyroelectric and piezoelectric thick films. Our work demonstrates that introduction of pores in ferroelectric thick films creates a matrix void composite resulting in high figures of merit for pyroelectric and piezoelectric applications. [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]