Superior electrostrictive coefficient of 6BNT-4SC BT lead-free relaxor ferroelectrics with Ca2+ substitution

In this study, lead-free 0.6(Bi0.5Na0.5)TiO3-0.4(Sr0.7-xCaxBi0.2)TiO3 ceramics (abbreviated as 6BNT-4SCxBT, x=0, 0.05, 0.10, 0.15 and 0.20 mol) were prepared by a traditional solid-state method. The effects of Ca2+ on phase structure, state transformation, ferroelectric and energy storage properties, and electrostrictive performance of 6BNT-4SCBT-x ceramics were comprehensively investigated. Co-occupied Bi3+, Na+, Sr2+ and Ca2+ ions induced the inhomogeneous distribution of A-site ions and charge, which resulted in polar nano-regions (PNRs) for relaxor ferroelectrics. 6BNT-4SCxBT ceramics present the ergodic relaxor state of polar rhombohedral PNRs and weakly polar tetragonal PNRs at room temperature. When the Ca2+ content was increased, 6BNT-4SC0.01BT ceramics showed the properties of weakly polar tetragonal PNRs (with lowest Tp~71 °C). 6BNT-4SCxBT ceramics exhibit electrostrictive effect Q33 (~0.045 m4/C2) and high energy storage efficiency. Moreover, large Q33 (>0.0421 m4/C2) indicates good electrical field stability. This result is a significant advancement in the area of lead-free electrostrictive materials, which has a great prospect in BNT-based ceramics.