Large electrostrain and high energy-storage properties of (Sr_1/3Nb_2/3)⁴⁺-substituted (Bi_0.51Na_0.5)TiO₃-0.07BaTiO₃ lead-free ceramics

In this study, we developed a novel (Sr_1/3Nb_2/3)⁴⁺ complex ion dopant to tailor the electrostrain and energy-storage properties of (Bi_0.5Na_0.5)TiO₃ (BNT)-based ferroelectric ceramics. The chemical formula of the investigated system is [0.93(Bi_0.51Na_0.5)0.07Ba)]Ti_1-x(Sr_1/3Nb_2/3)_xO₃, where x = 0.0025, 0.005, 0.0075, and 0.01. The crystal structures, microstructures, and dielectric/ferroelectric/electrostrictive/energy-storage properties of the ceramics synthesized by a solid-state reaction method were thoroughly investigated. For the x = 0.01 composition, an ultrahigh electrostrain of 0.59 % was achieved under an electric field of 130 kV/cm. The strain response of this composition increased progressively with increasing temperature from 30 to 150 °C while maintaining good symmetry. Interestingly, the electrostrictive coefficient Q₃₃ was shown to be strongly temperature-sensitive. The Q₃₃ value was 0.018 m⁴/C² at 30 °C and increased dramatically as the temperature increased, reaching a maximum value of 0.0378 m⁴/C² at 150 °C. Furthermore, under a relatively modest electric field of 100 kV/cm, a high recoverable energy-storage density of 1.36 J/cm³ was obtained for the x = 0.0075 composition. These findings demonstrate that the addition of (Sr_1/3Nb_2/3)⁴⁺ complex ions can effectively tailor the electrostrain and energy storage properties of BNT-based ceramics. Moreover, the doping ion design principle can be applied to other BNT-based ferroelectrics, with potential for dramatic improvements in electrostrain and energy storage properties.