Donor multiple effects on the ferroelectric and piezoelectric performance of lead-free BiFeO3-BaTiO3 ceramics

•Large d33 = 285 pC/N and high TC = 473 °C were achieved simultaneously.•A large d33* ≈ 400 pm/V was obtained at a very low electric field of 25 kV/cm.•Temperature stability, ΔS = 25% in d33* shows significant progress Pb-free ceramics.•Small strain hysteresis, HS = 20% have a high potential for piezoelectric actuators. Nb-modified lead-free 0.67Bi1.03FeO3-0.33BaTi1-xNbxO3 ceramics were synthesized by a solid-state reaction combined with a quenching process and investigated in terms of ferroelectric and piezoelectric properties. The Nb modification induced a phase change from the rhombohedral and tetragonal mixed-phase to the pseudocubic phase. This chemical modification transforms the long-range ferroelectric state to a short-range relaxor ferroelectric state. As a result, an excellent piezoelectric performance (d33 = 285 pC/N and d33* = 403 pm/V) with high a Curie temperature, 473 °C and low piezoelectric strain hysteresis, 20% were achieved. Furthermore, high d33* at a very low field 25 kV/cm and the temperature-insensitive piezoelectric response suggest highly promising results in the lead-free BF-BT ceramics. It is believed that the high piezoelectric response is related to multiple effects such as crystal structure of morphotropic phase boundary, an optimum grain size (≈5 μm), high lattice distortion (cT/aT = 1.01) and soft-ferroelectric effect induced by the donor-doping.