Thermally stable electrostrains and composition-dependent electrostrictive coefficient Q₃₃ in lead-free ferroelectric ceramics

The electrostrictive effect plays an important role in the electric-field-induced strain (electrostrain) of ferroelectric ceramics. This is especially true in high-electric-field regions because of the high-order coupling effect between electric-field-induced polarization and electrostrain. In this study, the electrostrictive properties of (1-x)(Bi_0.5Na_0.5)TiO₃-x(Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BNT-xBCZT, x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) ferroelectric ceramics were investigated in the temperature range 30 °C–120 °C for obtaining high thermally stable electrostrains and for understanding the effect of composition on the longitudinal electrostrictive coefficient Q₃₃. High electrostrains (>0.2% at 60 kV/cm) with good thermal stability (variation of less than 10%) in the tested temperature range were obtained for x = 0.1. Most importantly, Q₃₃ of BNT-xBCZT ceramics increased almost linearly from 0.0244 m⁴/C² to 0.0374 m⁴/C² when x increased from 0.1 to 0.6, suggesting a composition-dependent nature. In addition, Q₃₃ of pure BNT (0.0215 m⁴/C²), which has been unavailable to date, was extracted from this linear relationship. Furthermore, we revealed that the increase in Q₃₃ is mainly due to the increase in the cell volume. Our results not only clarify the composition effect on Q₃₃ in BNT-xBCZT ceramics but also provide a way to enhance Q₃₃ by increasing the cell volume through appropriate doping of ions or perovskite ferroelectric compounds.