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Large electrostrains with high temperature stability and low hysteresis are essential for applications in high-precision actuator devices. However, achieving simultaneously all three of the aforementioned features in ferroelectric ceramics remains a considerable challenge. In this work, we firstly report a high unipolar electrostrain (0.12% at 60 kV/cm) in (1–x)NaNbO3-x[(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3] (NN-xBCZT) ferroelectric polycrystalline ceramics with excellent thermal stability (variation less than 10% in the temperature range of 30–160 °C) and ultra-low hysteresis (

Lead-free (Bi0.5Na0.5)TiO3 (BNT)-based relaxor ferroelectric (RFE) ceramics have attracted a lot of attention due to their high power density and rapid charge-discharge capabilities, as well as their potential application in pulse power capacitors. However, because of the desire for smaller electronic devices, their energy storage performance (ESP) should be enhanced even further. We describe a defect engineering strategy for enhancing the antiferroelectric-like RFE feature of BNT-based ceramics by unequal substitution of rare-earth La3+ in this paper. The ESP of La3+-doped samples is raised by 25% with the same synthetic procedure and thickness, due to an increase in the critical electric field (E-field) and saturated E-field during polarization response, which is induced by a modification in the energy barrier between the lattice torsion. More impressively, an ultrahigh recoverable energy storage density Wrec of 8.58 J/cm3 and a high energy storage efficiency η of 94.5% are simultaneously attained in 3 at.% La3+-substituted 0.6(Bi0.5Na0.4K0.1)1-1.5xLaxTiO3-0.4[2/3SrTiO3-1/3Bi(Mg2/3Ni1/3)O3] RFE ceramics with good temperature stability (Wrec = 4.6 ± 0.2 J/cm3 and higher η of ≥90% from 30 °C to 120 °C), frequency stability, and fatigue resistance. The significant increase in ESP achieved through defect engineering not only proves the effectiveness of our strategy, but also presents a novel dielectric material with potential applications in pulse power capacitors.

Owing to the complex composition architecture of these solid solutions, some fundamental issues of the classical (1−x)Bi1/2Na1/2TiO-xBi1/2K1/2TiO3 (BNT-xBKT) binary system, such as details of phase evolution and optimal Na/K ratio associated with the highest strain responses, remain unresolved. In this work, we systematically investigated the phase evolution of the BNT-xBKT binary solid solution with x ranging from 0.12 to 0.24 using not only routine X-ray diffraction and weak-signal dielectric characterization, but also temperature-dependent polarization versus electric field (P-E) and current versus electric field (I-E) curves. Our results indicate an optimal Na/K ratio of 81/19 based on high-field polarization and electrostrain characterizations. As the temperature increased above 100 °C, the x = 0.19 composition produces ultrahigh electrostrains (> 0.5%) with high thermal stability. The ultrahigh and stable electrostrains were primarily due to the combined effect of electric-field-induced relaxor-to-ferroelectric phase transition and ferroelectric-to-relaxor diffuse phase transition during heating. More specifically, we revealed the relationship between phase evolution and electrostrain responses based on the characteristic temperatures determined by both weak-field dielectric and high-field ferroelectric/electromechanical property characterizations. This work not only clarifies the phase evolution in BNT-xBKT binary solid solution, but also paves the way for future strain enhancement through doping strategies.