Gaint electric field-induced strain and ferroelectric behavior of Bi_0.5Na_0.4K_0.1TiO₃-Na_1-xLi_xNbO₃ lead-free ceramics

0.96 Bi_0.5Na_0.4K_0.1TiO₃-0.04Na_1-xLi_xNbO₃ (BNKT-100xLi, x = 0, 0.25, 0.5, 0.75, 1.0) lead-free ceramics were prepared using traditional solid-state reaction method. X-ray diffraction patterns confirmed the pure perovskite structure of sintered ceramics. Electric field and composition-dependent strain behavior was investigated. The highest bipolar strain of 0.45% and the unipolar strain 0.443% was achieved at x = 0.75 under the applied electric field of 70 kV/cm. Meanwhile, the corresponding normalized strain (d₃₃*) reached to 633 pm/V. Moreover, the giant strain exhibited excellent thermal stability and fatigue-resistance (within 10⁵ switching cycles) properties, and the large strain was attributed to the reversible electric field-induced transition between relaxor and ferroelectric phase.