Phase and domain engineering strategy for enhancement of piezoelectricity in the lead-free BiFeO3-BaTiO3 ceramics

Lead-free BiFeO3-BaTiO3 ceramics attract widespread attention over the last two decades due to their high Curie temperature (TC) and excellent piezoelectric performance. Here, in the Nd-modified 0.67BiFeO3-0.33BaTiO3 ceramics, an excellent piezoelectric constant (d33) of 325 pC/N was achieved by applying a novel poling method (AC-bias + DC-bias) with a high TC of 455 °C. In addition, an ultrahigh normalized piezoelectric strain (d33∗ = Smax/Emax) of 808 pm/V was obtained at the normal/typical and relaxor-ferroelectrics phase boundary simultaneously with good thermal stability (Δd33∗(T) ≈ 20%) in the temperature range of 25–125 °C. The piezoelectric force microscopy results show the domain miniaturization from micro to nanoscale/polar nano-regions due to local structure heterogeneity caused by Nd doping. The mechanism for the giant piezoelectric strain is attributed to the thermal quenching, nano-domains, and reverse switching of the short-range order to the long-range order under the applied electric field. The strategic design of domain engineering and a proposed model for the high piezoelectricity is successfully supported by the phenomenological relation and Gibbs free energy profile. In this work, a new lead-free single-element modified BiFeO3-BaTiO3 ceramics was developed by applying a synergistic approach of domain engineering and phase boundary for the high-temperature piezoelectric performance.