Relaxor phase evolution and temperature-insensitive large strain in B-site complex ions modified NBT-based lead-free ceramics

Lead-free Bi_0.495(Na_0.8K_0.2)_0.495Sr_0.01Ti_1−x (Fe_0.5Me_0.5) _x O₃ ceramics with x = 0−0.03/0.04 mol (Me = Nb, Sb and Ta, abbreviated as FN0.5–FN4, FS0.5–FS3 and FT0.5–FT3, respectively) were fabricated by a conventional solid-state reaction method. The effects of B-site complex ions content on relaxor phase evolution and electromechanical properties were systematically investigated. Results showed that the modification of FN, FS and FT complex ions can significantly reinforce the B-site compositional disorder, effectively destroy the long-range ferroelectric order and tune the ferroelectric–relaxor transition point (T _FR) to around room temperature. The relatively high strain performances (dynamic \(d_{{33}}^{*}\) values) of 567, 550 and 600 pm/V were obtained in FN2, FS1.5 and FT2 critical compositions, respectively. The large strain responses are closely associated with the reversible relaxor–ferroelectric phase transformation. Furthermore, the electrostrain of FT2 sample presents a temperature-insensitive characteristic with the variation less than 10% up to 120 °C. These findings indicate that the B-site complex ions modified NBT-based ceramics can be considered as promising candidates for lead-free electromechanical actuator applications.