Trirelaxor Ferroelectric Material with Giant Dielectric Permittivity over a Wide Temperature Range

Lead-Free Relaxor Ferroelectric Ceramics with Ultrahigh Energy Storage Densities via Polymorphic Polar Nanoregions Design

One of the long-standing challenges of current lead-free energy storage ceramics for capacitors is how to improve their comprehensive energy storage properties effectively, that is, to achieve a synergistic improvement in the breakdown strength (E_b ) and the difference between maximum polarization (P_max ) and remnant polarization (P_r ), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO₃ into Bi_0.5 Na_0.5 TiO₃ is proposed to construct the morphotropic phase boundary with coexisting structures of micrometer-size domains and polymorphic nanodomains, enhance the electric field-induced polarization response (increase P_max ). Then Sr(Al_0.5 Ta_0.5 )O₃ (SAT)-doped 0.94 Bi_0.5 Na_0.5 TiO₃ -0.06BaTiO₃ (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease P_r ). Finally, a large recoverable energy density (W_rec ) of 8.33 J cm^-3 and a high energy efficiency (η) of 90.8% under 555 kV cm^-1 are obtained in the 0.85BNBT-0.15SAT ceramic prepared by repeated rolling process method (enhance E_b ), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (W_rec > 5.0  cm^-3 , η > 90%) at 400 kV cm^-1 . This strategy provides a new conception for the design of other-based multifunctional energy storage dielectrics.

High-Performance Electrostrictive Relaxors with Dispersive Endotaxial Nanoprecipitations

Ultrahigh-precision manufacturing and detection have highlighted the importance of investigating electrostrictive materials with a weak stimulated extrinsic electric field and a simultaneous large hysteresis-free strain. In this study, a new type of electrostrictive relaxor ferroelectric is designed by constructing a complex inhomogeneous local structure to realize excellent electrostrictive properties. A remarkably large electrostrictive coefficient, M₃₃ (8 × 10^-16 m² V^-2 ) is achieved. Through a combined atomic-scale scanning transmission electron microscopy and advanced in situ high-energy synchrotron X-ray diffraction analysis, it is observed that such superior electrostrictive properties can be ascribed to a special domain structure that consists of endotaxial nanoprecipitations embedded in a polar matrix at the phase boundary of the rhombohedral/tetragonal/cubic phases. The matrix contributes to the high strain response under the weak extrinsic electric field because of the highly flexible polarization and randomly dispersed endotaxial nanoprecipitations with a nonpolar central region, which provide a strong restoring force that reduces the strain hysteresis. The approach developed in this study is widely applicable to numerous relaxor ferroelectrics, as well as other dielectrics, for further enhancing their electrical properties, such as electrostriction and energy-storage capacity.

Achieving Good Temperature Stability of Dielectric Constant by Constructing Composition Gradient in (Pb1-x,Lax)(Zr0.65,Ti0.35)O3 Multilayer Thin Films

Ferroelectrics with a high dielectric constant are ideal materials for the fabrication of miniaturized and integrated electronic devices. However, the dielectric constant of ferroelectrics varies significantly with the change of temperature, which is detrimental to the working stability of electronic devices. This work demonstrates a new strategy to design a ferroelectric dielectric with a high temperature stability, that is, the design of a multilayer relaxor ferroelectric thin film with a composition gradient. As a result, the fabricated up-graded (Pb,La)(Zr_0.65,Ti_0.35)O₃ multilayer thin film showed a superior temperature stability of the dielectric constant, with variation less than 7% in the temperature range from 30 °C to 200 °C, and more importantly, the variation was less than 2.5% in the temperature range from 75 °C to 200 °C. This work not only develops a dielectric material with superior temperature stability, but also demonstrates a promising method to enhance the temperature stability of ferroelectrics.

Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering

It is challenging to achieve highly tunable multifunctional properties in one piezoelectric ceramic system through a simple method due to the complicated relationship between the microscopic structure and macroscopic property. Here, multifunctional potassium sodium niobate [(K, Na)NbO₃ (KNN)]-based lead-free piezoceramics with tunable piezoelectric and electrostrictive properties are achieved by controlling the long-range ferroelectric ordering (LRFO) through antimony (Sb) doping. At a low Sb doping, the slightly distorted NbO₆ octahedron and the softened B-O repulsion well maintain the LRFO and induce plenty of nanoscale domains coexisting with a few polar nanoregions (PNRs). Thereby, the diffused rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence with distinct dielectric jumping is constructed near room temperature, by which the nearly 2-fold increase in the piezoelectric coefficient (d₃₃ ∼ 539 pC/N) and the temperature-insensitive strain (the unipolar strain varies less than 8% at 27-120 °C) are obtained. At a high Sb doping, the LRFO is significantly destroyed, leading to predominant PNRs. Thus, a typical relaxor is obtained at the ferroelectric-paraelectric phase transition near room temperature, in which a large electrostrictive coefficient (Q₃₃ = 0.035 m⁴/C²), independent of the electric field and temperature, is obtained and comparable to that of lead-based materials. Therefore, our results prove that controlling the LRFO is a feasible way to achieve high-performance multifunctional KNN-based ceramics and is beneficial to the future composition design for KNN-based ceramics.