Large strain response with low driving field in Bi_1/2Na_1/2TiO₃–Bi_1/2K_1/2TiO₃–Bi(Mg_2/3Nb_1/3)O₃ ceramics

The (1−x)(0.8Bi_1/2Na_1/2TiO₃–0.2Bi_1/2K_1/2TiO₃)−xBiMg_2/3Nb_1/3O₃ (100xBMN) ternary solid solutions were designed and prepared using a conventional solid-state reaction. Temperature and compositional dependent ferroelectric, piezoelectric, dielectric features, and structural evolution were systematically studied. At the critical composition of 2BMN, a large bipolar strain of 0.43% was achieved at 55 kV/cm, and the normalized strain reaches to 862 pm/V at a low driving electric field of 40 kV/cm. It was found that the substitution of BiMg_2/3Nb_1/3O₃ induces a transformation from ferroelectric to relaxor phase by disrupting the long range ferroelectric order. Therefore, as the external electric field was applied, a relaxor-ferroelectric phase transition will be induced. This is contributed to the giant strain. The results above suggest that such a ternary composition is a promising candidate for application to actuator.