On the formation mechanism of Ba0.85Ca0.15Zr0.1Ti0.15O3 thin films by aqueous chemical solution deposition

Here we report on the development of an environmentally friendly, simple and robust aqueous chemical solution route for the fabrication of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) thin films. Using a stable aqueous precursor solution, thin films were prepared by spin coating and the impact of thermal processing on the microstructure and phase purity of the thin film was revealed by X-ray diffraction and transmission electron microscopy. We find, that barium oxycarbonate formation during the pyrolysis plays a key role in the formation of dense, homogeneous single phase BCZT films. The formation of barium oxycarbonate leads to undesirable segregation of cations, resulting in barium depletion on the BCZT grain boundaries and occurrence of a secondary phase (CaZrTi2O7). Based on this insight the thermal processing was optimized and dense, oriented and single-phase BCZT films were fabricated by combining a low pyrolysis temperature with rapid heating to the annealing temperature

Self-Poling of BiFeO₃ Thick Films

Bismuth ferrite (BiFeO₃) is difficult to pole because of the combination of its high coercive field and high electrical conductivity. This problem is particularly pronounced in thick films. The poling, however, must be performed to achieve a large macroscopic piezoelectric response. This study presents evidence of a prominent and reproducible self-poling effect in few-tens-of-micrometer-thick BiFeO₃ films. Direct and converse piezoelectric measurements confirmed that the as-sintered BiFeO₃ thick films yield <i>d</i>₃₃ values of up to ∼20 pC/N. It was observed that a significant self-poling effect only appears in cases when the films are heated and cooled through the ferroelectric-paraelectric phase transition (Curie temperature <i>T</i>_C ∼ 820 °C). These self-poled films exhibit a microstructure with randomly oriented columnar grains. The presence of a compressive strain gradient across the film thickness cooled from above the <i>T</i>_C was experimentally confirmed and is suggested to be responsible for the self-poling effect. Finally, the macroscopic <i>d</i>₃₃ response of the self-poled BiFeO₃ film was characterized as a function of the driving-field frequency and amplitude