Next‐generation microelectronics and electrical power systems call for high‐energy‐density dielectric polymeric materials that can operate efficiently under elevated temperatures. However, the ...currently available polymer dielectrics are limited to relatively low working temperatures. Here, the solution‐processable polymer nanocomposites consisting of readily prepared Al2O3 fillers with systematically varied morphologies including nanoparticles, nanowires, and nanoplates are reported. The field‐dependent electrical conduction of the polymer nanocomposites at elevated temperatures is investigated. A strong dependence of the conduction behavior and breakdown strength of the polymer composites on the filler morphology is revealed experimentally and is further rationalized via computations. The polymer composites containing Al2O3 nanoplates display a record capacitive performance, e.g., a discharged energy density of 3.31 J cm−3 and a charge–discharge efficiency of >90% measured at 450 MV m−1 and 150 °C, significantly outperforming the state‐of‐the‐art dielectric polymers and nanocomposites that are typically prepared via tedious, low‐yield approaches.
High‐temperature dielectric polymer nanocomposites with facilely prepared nanostructured Al2O3 fillers exhibit remarkable electrical energy storage and discharge capabilities at elevated temperatures and high electric fields, outperforming state‐of‐the‐art polymer dielectrics. The significant impact of the filler morphology on conduction behavior and capacitive performance of the composites is revealed.
Long‐range ordering of dipoles is a key microscopic signature of ferroelectrics. These ordered dipoles form ferroelectric domains, which can be reoriented by electric fields. Relaxor ferroelectrics ...are a type of ferroelectric where the long‐range ordering of dipoles is disrupted by cation disorder, exhibiting complex polar states with a significant amount of local structural heterogeneity at the nanoscale. They are the materials of choice for numerous devices such as capacitors, nonlinear optical devices, and piezoelectric transducers, owing to their extraordinary dielectric, electro‐optic, and electromechanical properties. However, despite their extensive applications in these devices, the origins of their unique properties are yet to be fully understood, hindering the design and exploration of new relaxor ferroelectric‐based materials. Herein, the complex polar states and applications of relaxor ferroelectrics are first introduced. Attention is then focused on their electromechanical properties, where the relationship between local structural heterogeneity and the extraordinary electromechanical properties is discussed. Based on the understanding of relaxor ferroelectrics, potential strategies to exploit the local structural heterogeneity to design ferroelectrics for drastically enhancing their electromechanical performances are also discussed. It is expected that this article will stimulate future studies on the important roles of local structural heterogeneity in improving the properties of various functional materials.
Relaxor ferroelectrics are a type of ferroelectrics where long‐range ordering of dipoles is disrupted by cation disorder, and thus exhibiting complex polar states at the nanoscale. Due to the outstanding electromechanical properties, relaxor ferroelectrics have received continued interest during the last decades. This review attempts to clarify the relationship between local structural heterogeneity and extraordinary electromechanical properties in relaxor ferroelectrics.
Piezoelectric materials, which respond mechanically to applied electric field and vice versa, are essential for electromechanical transducers. Previous theoretical analyses have shown that high ...piezoelectricity in perovskite oxides is associated with a flat thermodynamic energy landscape connecting two or more ferroelectric phases. Here, guided by phenomenological theories and phase-field simulations, we propose an alternative design strategy to commonly used morphotropic phase boundaries to further flatten the energy landscape, by judiciously introducing local structural heterogeneity to manipulate interfacial energies (that is, extra interaction energies, such as electrostatic and elastic energies associated with the interfaces). To validate this, we synthesize rare-earth-doped Pb(Mg
Nb
)O
-PbTiO
(PMN-PT), as rare-earth dopants tend to change the local structure of Pb-based perovskite ferroelectrics. We achieve ultrahigh piezoelectric coefficients d
of up to 1,500 pC N
and dielectric permittivity ε
/ε
above 13,000 in a Sm-doped PMN-PT ceramic with a Curie temperature of 89 °C. Our research provides a new paradigm for designing material properties through engineering local structural heterogeneity, expected to benefit a wide range of functional materials.
Ferroelectric polymers have been regarded as the preferred matrix for high‐energy‐density dielectric polymer nanocomposites because of their highest dielectric constants among the known polymers. ...Despite a library of ferroelectric polymer‐based composites having been demonstrated as highly efficient in enhancing the energy density, the charge–discharge efficiency remains moderate because of the high intrinsic loss of ferroelectric polymers. Herein, a systematic study of the oxide nanofillers is presented with varied dielectric constants and the vital role of the dielectric match between the filler and the polymer matrix on the capacitive performance of the ferroelectric polymer composites is revealed. A combined experimental and simulation study is further performed to specifically investigate the effect of the nanofiller morphology on the electrica properties of the polymer nanocomposites. The solution‐processed ferroelectric polymer nanocomposite embedded with Al2O3 nanoplates exhibits markedly improved breakdown strength and discharged energy density along with an exceptional charge–discharge efficiency of 83.4% at 700 MV m−1, which outperforms the ferroelectric polymers and nanocomposites reported to date. This work establishes a facile approach to high‐performance ferroelectric polymer composites through capitalizing on the synergistic effect of the dielectric properties and morphology of the oxide fillers.
This work reports the dielectric properties and capacitive performance of ferroelectric polymer composites containing a series of inorganic fillers with varied dielectric constants and morphologies. Solution‐processed ferroelectric polymer nanocomposites incorporated with 2D oxide fillers with a dielectric constant comparable to that of the matrix exhibit markedly improves energy densities along with exceptional charge–discharge efficiency.
The existence of polar nanoregions is the most important characteristic of relaxor‐based ferroelectric materials. Recently, the contributions of polar nanoregions to the shear piezoelectric property ...of relaxor‐PbTiO3 (PT) crystals are confirmed in a single domain state, accounting for 50%–80% of room temperature values. For electromechanical applications, however, the outstanding longitudinal piezoelectricity in domain‐engineered relaxor‐PT crystals is of the most significance. In this paper, the contributions of polar nanoregions to the longitudinal properties in 001‐poled Pb(Mg1/3Nb2/3)O3‐0.30PbTiO3 and 110‐poled Pb(Zn1/3Nb2/3)O3‐0.15PbTiO3 (PZN‐0.15PT) domain‐engineered crystals are studied. Taking the 110‐poled tetragonal PZN‐0.15PT crystal as an example, phase‐field simulations of the domain structures and the longitudinal dielectric/piezoelectric responses are performed. According to the experimental results and phase‐field simulations, the contributions of polar nanoregions (PNRs) to the longitudinal properties of relaxor‐PT crystals are successfully explained on the mesoscale, where the PNRs behave as “seeds” to facilitate macroscopic polarization rotation and enhance electric‐field‐induced strain. The results reveal the importance of local structures to the macroscopic properties, where a modest structural variation on the nanoscale greatly impacts the macroscopic properties.
The contributions of polar nanoregions to piezoelectric responses are successfully quantified for domain‐engineered relaxor‐ferroelectric crystals. A mesoscale mechanism is proposed to explain the ultrahigh longitudinal piezoelectric responses and strain behaviors of relaxor‐PbTiO3 ferroelectrics, where the polar nanoregions act as “seeds” to facilitate polarization rotation and enhance the piezoelectric response.
Piezoelectricity of ferroelectric crystals is widely utilized in electromechanical devices such as sensors and actuators. It is broadly believed that the smaller the ferroelectric domain size, the ...higher the piezoelectricity, arising from the commonly assumed larger contributions from the domain walls. Herein, the domain‐size dependence of piezoelectric coefficients of prototypical ferroelectric crystals is theoretically studied based on thermodynamic analysis and phase‐field simulations. It is revealed that the inverse domain‐size effect, i.e., the larger the domain size, the higher the piezoelectricity, is entirely possible and can be just as common. The nature of the domain‐size dependence of piezoelectricity is shown to be determined by the propensity of polarization rotation inside the domains instead of the domain wall contributions. A simple, unified, analytical model for predicting the domain‐size dependence of piezoelectricity is established, which is valid regardless of the crystalline symmetry, the materials chemistry, and the domain structures of a ferroelectric crystal, and thus can serve as a guiding tool for optimizing piezoelectricity of ferroelectric materials beyond the “nanodomain” engineering. In addition, the theoretical approach can be extended to understand the microstructural size effect of multifunctional properties in ferroic and multiferroic materials.
Theoretical simulation reveals that the piezoelectricity of ferroelectric crystals does not necessarily increase with smaller domain size as conventionally believed. A simple thermodynamic model applicable to ferroelectrics of arbitrary symmetry is proposed to guide the design of high‐performance piezoelectrics.
Both experimental results and theoretical models suggest the decisive role of the filler–matrix interfaces on the dielectric, piezoelectric, pyroelectric, and electrocaloric properties of ...ferroelectric polymer nanocomposites. However, there remains a lack of direct structural evidence to support the so‐called interfacial effect in dielectric nanocomposites. Here, a chemical mapping of the interfacial coupling between the nanofiller and the polymer matrix in ferroelectric polymer nanocomposites by combining atomic force microscopy–infrared spectroscopy (AFM–IR) with first‐principles calculations and phase‐field simulations is provided. The addition of ceramic fillers into a ferroelectric polymer leads to augmentation of the local conformational disorder in the vicinity of the interface, resulting in the local stabilization of the all‐trans conformation (i.e., the polar β phase). The formation of highly polar and inhomogeneous interfacial regions, which is further enhanced with a decrease of the filler size, has been identified experimentally and verified by phase‐field simulations and density functional theory (DFT) calculations. This work offers unprecedented structural insights into the configurational disorder‐induced interfacial effect and will enable rational design and molecular engineering of the filler–matrix interfaces of electroactive polymer nanocomposites to boost their collective properties.
Using atomic force microscopy–infrared spectroscopy together with first‐principles calculations and phase field simulations, a spatial structure analysis of the filler–matrix interfaces in ferroelectric polymer nanocomposites is provided. The unprecedented insights into the interfacial coupling effect at the molecular level would enable interfacial engineering strategies to realize improved properties and unlock new functionalities of the nanocomposites.
Dielectric capacitors with ultrahigh power densities are fundamental energy storage components in electrical and electronic systems. However, a long-standing challenge is improving their energy ...densities. We report dielectrics with ultrahigh energy densities designed with polymorphic nanodomains. Guided by phase-field simulations, we conceived and synthesized lead-free BiFeO
-BaTiO
-SrTiO
solid-solution films to realize the coexistence of rhombohedral and tetragonal nanodomains embedded in a cubic matrix. We obtained minimized hysteresis while maintaining high polarization and achieved a high energy density of 112 joules per cubic centimeter with a high energy efficiency of ~80%. This approach should be generalizable for designing high-performance dielectrics and other functional materials that benefit from nanoscale domain structure manipulation.
Polymer dielectrics are the preferred materials of choice for power electronics and pulsed power applications. However, their relatively low operating temperatures significantly limit their uses in ...harsh‐environment energy storage devices, e.g., automobile and aerospace power systems. Herein, hexagonal boron nitride (h‐BN) films are prepared from chemical vapor deposition (CVD) and readily transferred onto polyetherimide (PEI) films. Greatly improved performance in terms of discharged energy density and charge–discharge efficiency is achieved in the PEI sandwiched with CVD‐grown h‐BN films at elevated temperatures when compared to neat PEI films and other high‐temperature polymer and nanocomposite dielectrics. Notably, the h‐BN‐coated PEI films are capable of operating with >90% charge–discharge efficiencies and delivering high energy densities, i.e., 1.2 J cm−3, even at a temperature close to the glass transition temperature of polymer (i.e., 217 °C) where pristine PEI almost fails. Outstanding cyclability and dielectric stability over a straight 55 000 charge–discharge cycles are demonstrated in the h‐BN‐coated PEI at high temperatures. The work demonstrates a general and scalable pathway to enable the high‐temperature capacitive energy applications of a wide range of engineering polymers and also offers an efficient method for the synthesis and transfer of 2D nanomaterials at the scale demanded for applications.
Hexagonal boron nitride films grown by chemical vapor deposition are readily transferred onto polymers, yielding sandwiched films exhibiting superior energy densities and greater efficiencies at high temperatures. This work enables the capacitive applications of engineering polymers in high‐temperature electronics and energy devices, and also offers an efficient synthesis method for 2D nanomaterials at the scale demanded for applications.
Stimuli‐responsive micro/nanostructures that can dynamically and reversibly adapt their configurations according to external stimuli have stimulated a wide scope of engineering applications, ranging ...from material surface engineering to micromanipulations. However, it remains a challenge to achieve a precise local control of the actuation to realize applications that require heterogeneous and on‐demand responses. Here, a new experimental technique is developed for large arrays of hybrid magnetic micropillars and achieve precise local control of actuation using a simple magnetic field. By manipulating the spatial distribution of magnetic nanoparticles within individual elastomer micropillars, a wide range of the magnetomechanical responses from less than 5% to ≈50% for the ratio of the bending deflection to the original length of the pillars is realized. It is demonstrated that the micropillars with different degrees of bending deformation can be configured in any spatial pattern using a photomask‐assisted template‐casting technique to achieve heterogeneous, site‐specific, and programmed bending actuations. This unprecedented local control of the micropillars offers exciting novel applications, as demonstrated here in encryptable surface printing and stamping, direction‐ and track‐programmable microparticle/droplet transport, and smart magnetic micro‐tweezers. The hybrid magnetic micropillars reported here provide a versatile prototype for heterogeneous and on‐demand actuation using programmable stimuli‐responsive micro/nanostructures.
A new experimental technique for hybrid magnetic micropillar arrays is developed to realize site‐specific, on‐demand, and programmed bending actuation. Several exciting applications for surface engineering and micromanipulations, including encryptable surface printing/stamping, direction‐ and track‐programmable microtransport, and magnetic micro‐tweezers that can smartly grip and release microscale objects, are demonstrated using the micropillar arrays.
PDF
