Enhanced Bipolar Strain Response in Lithium/Niobium Co-Doped Sodium–Barium Bismuth Titanate Lead-Free Ceramics

The (Na_0.484Bi_0.456Ba_0.06)Ti_0.97Nb_0.03O₃ − xLi⁺ (x = 0, 0.005, 0.01, 0.015) lead-free piezoelectric ceramics are prepared by conventional solid-state reaction technique. X-ray diffraction and surface scanning electron microscope images confirm the pure perovskite structure of sintered ceramics. Electric field and composition-dependent strain behavior are investigated. The highest bipolar strain of 0.47% is achieved at x = 0.01 with the applied electric-field of 70 kV cm⁻¹, and the corresponding normalized strain (d₃₃^*) reaches up to 671 pm V⁻¹. Moreover, the giant strain exhibits excellent thermal stability and fatigue-resistance (within 10⁵ switching cycles) properties. The origin of the strain can be attributed to transition between ferroelectric and relaxor ferroelectric induced by the applied electric field, and introduction of Li cations further enhances the strain behavior. AC impedance analysis indicate the appearance of grain boundary effect with increasing Li⁺ addition, which is also reflected on the dielectric and dielectric loss curves. It is believed that the environmental friendly binary system can be a promising candidate for piezoactuators.