Enhanced Pyroelectric and Piezoelectric Figure of Merit of Porous Bi0.5(Na0.82K0.18)0.5TiO3 Lead‐Free Ferroelectric Thick Films

Abstract

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.