Giant strains in (Bi_0.5Na_0.5)TiO₃ based ceramics are usually attributed to electric field induced nonpolar to polar phase transition. Whether it is an ergodic relaxor R3c/P4mm ferroelectric (FE) to long-range ordered FE phase transformation or a reversible P4bm antiferroelectric (AFE) to FE phase transition is still unclear. Herein, lead-free (0.88-x)(Bi_0.5Na_0.5)TiO₃-0.12BaTiO₃-xNaNbO₃ ceramics exhibit a composition-modulated FE tetragonal P4mm to relaxor AFE tetragonal P4bm phase transition, in which double hysteresis loop, sprout-shaped S-E curves, near-zero quasi-static d₃₃ together with a large volume change suggest the AFE characteristics of P4bm phase. An interesting finding is that the reversibility of field-induced AFE P4bm phase to FE P4mm phase transition strongly depends on the NN content, from being completely irreversible at x = 0.01–0.02, to partially reversible at x = 0.03–0.05, and finally to completely reversible at x = 0.06–0.08. It is indicated that the variation of reversibility should be attributed to the change of relative free energy caused by decreasing the FE to AFE phase transition temperature with increasing the NN content.

_{(Bi 0.5} Na _0.5 )TiO ₃基陶瓷中的巨应变通常归因于电场诱导的非极性到极性的相变。无论是遍历弛豫R 3 c / P 4 mm铁电体 (FE) 到长程有序 FE 相变还是可逆P 4 bm反铁电体 (AFE) 到 FE 相变，目前还不清楚。在此，无铅(0.88- x )(Bi _0.5 Na _0.5 )TiO ₃ -0.12BaTiO ₃ - x NaNbO ₃陶瓷表现出成分调制的 FE 四方P 4 mm到弛豫 AFE 四方P 4 bm相变，其中双磁滞回线、芽形SE曲线、接近零的准静态d ₃₃以及大的体积变化表明 AFE P 4 bm相的特性。一个有趣的发现是，场致 AFE P4bm 相到 FE P 4 mm相变的可逆性很大程度上取决于 NN 含量，从在x  = 0.01-0.02 时完全不可逆到在 x 时部分可逆 = 0.03–0.05，最后在x  = 0.06–0.08 处完全可逆。表明可逆性的变化应归因于随着NN含量的增加，FE向AFE相变温度降低引起的相对自由能的变化。