Significant impact of TiO₂ purity on the phase structure and electrical properties of BiFeO₃–BaTiO₃ lead-free piezoelectric ceramics

In many studies, the properties of BiFeO₃–BaTiO₃ (BF–BT) ceramics vary greatly using different raw reagents, which makes it challenging to obtain reliable and repeatable properties of BF–BT-based devices. In this work, 0.7BiFeO₃–0.3BaTiO₃ (0.7BF–0.3BT) ceramics were fabricated by a conventional solid-phase synthesis using TiO₂ reagents with varied purities of 98%, 99%, 99.9%, and 99.99%, respectively. The phase structure, microstructure, ferroelectric, and piezoelectric properties were comprehensively studied. All compositions of the ceramics exhibit a pseudo-cubic phase perovskite structure, and the fraction of the rhombohedral phase increases with increasing the TiO₂ purity. Additionally, backscattered electron images and energy-dispersive spectroscopy revealed an obvious core–shell structure within grains. In particular, the 0.7BF–0.3BT ceramics prepared with 98% purity TiO₂ exhibited superior ferroelectric and piezoelectric properties, d₃₃ ∼ 220 pC/N and (Formula presented.) ∼ 230 pm/V. The ceramics prepared with higher purity TiO₂ suffered from severe leakage conduction, which can be well addressed by adding excess TiO₂. Our work reveals the importance of different grades of purity TiO₂ on the electrical properties of BF–BT ceramics.