Enhanced pyroelectric properties of lead‐free BNT‐BA‐KNN ceramics for thermal energy harvesting

In this work, (1-x)(0.98Bi(0.5)Na(0.5)TiO(3)-0.02BiAlO(3))-x(Na0.5K0.5)NbO3 (BNT-BA-xKNN) lead-free pyroelectric ceramics were prepared by a solid-state reaction method. The effect of Na0.5K0.5NbO3 (KNN) content on microstructure, phase transition, and electrical properties of the BNT-BA-xKNN ceramics were systematically investigated. The results show that the appropriate content of KNN can induce the formation of the tetragonal structure, which results in the decreased ferroelectric-antiferroelectric phase transition temperature as a result of the break of long-range translational symmetry of BNT lattices. Therefore, the ferroelectric and pyroelectric properties of the BNT-BA-xKNN near room temperature are improved. The room-temperature pyroelectric coefficient significantly increases from 3.66x10(-4)C/m(2)/K at x=0 to 8.04x10(-4)C/m(2)/K at x=0.02, making a great contribution to the superior pyroelectric energy harvesting. The output energy density in one cycle of the BNT-BA-0.02KNN is 23.32J/cm(3), which is twice as high as that of the pristine samples. The enhancement of material properties suggests that the pyroelectric energy harvesting can be efficiently optimized by the adequate control of the phase structure.