Abstract: Due to the demand for environmental protection, developing eco-friendly piezoelectric applications/materials is an inevitable trend. The market share of lead-free materials is growing steadily every year. Among typical lead-free systems, Bi_0.5Na_0.5TiO₃ (BNT) has attracted wide attention due to its superior strain property (e.g., dynamic piezoelectric coefficient d₃₃* of most modified-BNT ceramics exceeds 600 pm/V, which is higher than commercial soft PZT ceramics PIC151). The excellent strain performance in BNT-based materials is thought to arise from the relaxor-ferroelectric transition, and currently, the mainstream strain regulation method is chemical modifying. So far, amounts of effective dopants have been investigated, while the intrinsic strain regulation mechanism is still ambiguous (e.g., how do dopants work?). Therefore, we review the intrinsic strain regulation mechanism, and strain origination and regulation methods are also investigated to comprehend the regulation mechanism. Significantly, the strain origination and regulation mechanism are investigated from different dimensions (e.g., macro perspective and micro perspective), which is vacant in previous reports. From the macro view, the particular tailored relaxor-ferroelectric crossover is the critical key for the giant electro-strain, while from the micro view, the electro-strain is dominated by the cracked ferroelectric order and relaxor-ferroelectric transition, resulting from the broken Bi-O bonds due to the local field effect. Exploring the strain origination and regulation mechanism of BNT-based ceramics is of great importance to exclude the blind researching mode and rationally design the experimental scheme.

Key words: Strain origin, Bi0.5Na0.5TiO3 (BNT), Strain regulation