Bi2Ti2O7 modification-induced large strain characteristics in BNT-6BT piezoelectric ceramics

Lead-free sodium bismuth titanate and related compounds are promising piezoelectric materials. A comprehensive understanding of this series of materials remains a challenge, partly due to their structural complexity and the differences in structure and properties caused by the application of an external electric field. This study investigates the effect of doping Bi2Ti2O7 (BTO) into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-6BT) ceramics. The results show that the introduction of BTO increases the pseudo-cubic phase structure of BNT-6BT and breaks the ferroelectric long-range order to form more polar nanoregions. The composition induces a phase transition from the ferroelectric phase to the relaxor phase, in which oxygen vacancies may play a certain role, and the relaxor property of the ceramics is enhanced. The BNT-6BT-4wt%BTO ceramic achieves a high positive strain (0.43%) at room temperature, which is attributed to the huge strain generated during the reversible transition between the ergodic relaxor phase and the long-range ordered ferroelectric phase. Overall, BTO doping significantly modifies the properties of BNT-6BT ceramics, enabling them to exhibit reversible long-range ordered transitions under an electric field, thus providing potential for applications in precision actuators.