(1-x)(0.8Bi_1/2Na_1/2TiO₃-0.2Bi_1/2K_1/2TiO₃)-xBi(Ni_2/3Nb_1/3)O₃ (BNKT-xBNN) solid solution ceramics were fabricated by high temperature solid-state reaction method. All the compositions possess relaxor ferroelectric features, among which the ergodic BNKT-0.02BNN exhibits large repeatable electrostrain value S_uni = 0.51% at electric field of 65 kV/cm, with high piezoelectric stain coefficient d₃₃∗ of 890 pm/V at 45 kV/cm, while the non-ergodic compositions present unrepeatable large strain response. Based on the electric field-composition phase diagram, the repeatability of strain response in ergodic compositions can be attributed to the reversible electric-field-induced phase transition. In addition, the effects of BNN contents on the macroscopic strain properties are explored by analyzing the existing states of the polar regions with corresponding thermal evolutions and electric-field-induced phase transitions. This research is expected to guide the design of lead free relaxor ferroelectric materials with desired electrostrain properties.

（1- x）（0.8Bi _1/2 Na _1/2 TiO ₃ -0.2Bi _{1 /} 2K _1/2 TiO ₃）-x Bi（Ni _2/3 Nb _1/3）O ₃（BNKT- x BNN固溶陶瓷是通过高温固相反应法制备的。所有组合物均具有弛豫铁电特性，其中遍历BNKT-0.02BNN 在65 kV / cm电场下表现出大的可重复电应变值S _uni = 0.51％，且压电染色系数d ₃₃*在45 kV / cm时为890 pm / V，而非遍历组合物则表现出不可重复的大应变响应。根据电场组成相图，遍历组合物中应变响应的可重复性可以归因于电场可逆引起的相变。此外，通过分析极性区域的存在状态以及相应的热演化和电场诱导的相变，探索了BNN含量对宏观应变性质的影响。预期该研究将指导具有所需电应变特性的无铅弛豫铁电材料的设计。