Free-standing 0.9Na0.5Bi0.5TiO3-0.1Sr0.7Bi0.2TiO3 thick films produced by water-based tape-casting method

(1-x)Na_0.5Bi_0.5TiO₃-xSr_1-1.5yBi_yTiO₃ solid solutions attract increased interest as lead-free ferroelectrics perspective for sensors, actuators, and energy storage applications. However, thick films of this composition are of great demand, as they could serve as a good compromise between the bulk ceramics and thin films—due to the advantage in realization of miniaturized devices without reducing the power and sensitivity of target devices, as in the case of thin films, and ability to accommodate application of much higher electric fields compared to bulk ceramics. In the present research, for the first time, we have produced free-standing 0.9Na_0.5Bi_0.5TiO₃-0.1Sr_0.7Bi_0.2TiO₃ thick films by water-based tape-casting method, using just two organic chemicals, which is an eco-friendly production approach having only several successful attempts in the case of ferroelectric materials before. We conducted a detailed study focusing on development of microstructure at various sintering temperatures and consequences of evaporation of Bi during the production. Our findings show how the choice of the sintering temperature can help in improvement of density of the thick films, reaching 98.9%, and changing the grain size. It is demonstrated that a secondary phase appears predominantly on the free surface of the films. We propose a method for effective minimization of its formation—by the choice of appropriate embedding powder media during the sintering.