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, 0.7BiFeO(3)-0.3BaTiO(3) (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, d(33) similar to 220 pC/N and d(33)(& lowast;) similar to 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.