Enhancement of the electrical-field-induced strain in sodium bismuth titanate-based lead-free ceramics by co-doping with Mn and Nb

Lead-free (Bi_0.5Na_0.5)_0.935Ba_0.065Ti_1−x(Mn_0.5Nb_0.5)_xO₃ piezoelectric ceramics with excellent strain properties were prepared by conventional solid state reaction route. The effects of Mn/Nb on the structure and electrical properties of the ceramics have been investigated. The replacement of Ti by Mn/Nb induced a ferroelectric–ergodic relaxor phase transition with the degradations of the long-term ferroelectric properties. Near the ferroelectric–ergodic phase boundary, the electric-field-induced strain was significantly enhanced and reached the highest strain value of 0.37% (80 kV/cm, corresponds to a S_max/E_max = 463 pm/V) at 0.005 Mn/Nb addition. Temperature dependent measurements of polarization, permittivity, large signal piezoelectric constant and strain indicate that a reversible field-induced phase transformation from ergodic relaxor phase to ferroelectric is the main reason for the large strain response. Moreover, due to the reversible field-induced phase transition, the material with high-strain showed good fatigue resistance (up to 10⁵ cycles), which can be considered as one of promising candidate used in actuator applications.