Baojin Chu

Bio: Baojin Chu is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Dielectric & Ferroelectric ceramics. The author has an hindex of 13, co-authored 41 publications receiving 579 citations. Previous affiliations of Baojin Chu include Pennsylvania State University.

Flexoelectricity in several thermoplastic and thermosetting polymers

Abstract: The flexoelectricity of several thermoplastic and thermosetting polymers was investigated by testing the dielectric polarization response under bending deformation of polymer cantilevers. All the polymers studied showed a flexoelectric response with a flexoelectric coefficient of the order of the 10−9–10−8 C/m. Based on a comparison of the flexoelectric response of the different polymers studied, we discuss factors that may influence the generation of flexoelectricity in polymeric materials.

Lead‐Free Metamaterials with Enormous Apparent Piezoelectric Response

Abstract: Lead-free flexoelectric piezoelectric metamaterials are created by applying an asymmetric chemical reduction to Na1/2 Bi1/2 TiO3 -BaTiO3 ceramics. The reduction induces two gradient-generating mechanisms, curvature structure and chemical inhomogeneity, and enhances the flexoelectric effect. The ceramics behave like piezoelectric materials, exhibiting an enormous and high-temperature stable apparent piezoelectric response, outperforming existing lead-oxide-based piezoelectrics.

Piezoelectric responses in poly(vinylidene fluoride/hexafluoropropylene) copolymers

Abstract: The authors show that a high transverse piezoelectric response with both high piezoelectric d31 (d31=43.1pm∕V) and electromechanical coupling k31 coefficients (k31=0.187), much higher than those in the piezoelectric poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) copolymers, can be obtained in poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] 10wt% copolymers under quasistatic condition. Furthermore, the copolymers also display a higher d31 coefficient compared to the d33 coefficient, which seems to be unusual compared with most other piezopolymers. The experimental data suggest that the origin of the unusual piezoelectric response in these P(VDF-HFP) copolymers originates from a reversible change between a poled α-like structure and β-like structure. The phase change nature also results in a large frequency dispersion of the piezoelectric response and a smaller d31 (=20.5pm∕V) at 50kHz.

Large Flexoelectriclike Response from the Spontaneously Polarized Surfaces in Ferroelectric Ceramics.

Abstract: Nonpoled ferroelectric ceramics are thought to be nonpolar because of randomly oriented grains and the formation of ferroelectric domains in the grains. Here, we discover the surfaces ($\ensuremath{\sim}\mathrm{several}\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ thick) of ferroelectric ceramics are spontaneously polarized. Because the orientations of ferroelectric polarization of the opposite surfaces are antiparallel, ferroelectric ceramics are nonpolar as a whole. However, the ceramics exhibit a strong flexoelectriclike electromechanical response from the piezoelectric response of the polarized surfaces if they are asymmetrically strained (such as bending). Our results reveal a major mechanism to resolve one important but largely unresolved issue: the experimentally measured flexoelectric effect is typically orders of magnitude larger than the theoretically predicted value in ferroelectrics.

Effect of metal-polymer interface on the breakdown electric field of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

Abstract: The authors investigate the effect of electrode material and charge injection on the breakdown electric field of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer. The results indicate that the breakdown is mainly initiated at electrode-polymer interfaces, the properties of which are controlled by metal materials and deposition conditions. Interfaces with lower leakage currents display higher breakdown fields. Terpolymer films with Al and Cr electrodes have lower leakage current and higher breakdown field compared to those with Au and Ag electrodes. The difference in charge injection and breakdown field is attributed to both the existence of interfacial blocking layers and the difference in Schottky barrier height.

Electroactive phases of poly(vinylidene fluoride) : determination, processing and applications

Abstract: Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed.

Advances in dielectric elastomers for actuators and artificial muscles.

Abstract: A number of materials have been explored for their use as artificial muscles Among these, dielectric elastomers (DEs) appear to provide the best combination of properties for true muscle-like actuation DEs behave as compliant capacitors, expanding in area and shrinking in thickness when a voltage is applied Materials combining very high energy densities, strains, and efficiencies have been known for some time To date, however, the widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames Recent advances seem poised to remove these restrictions and allow for the production of highly reliable, high-performance transducers for artificial muscle applications

Flexoelectric Effect in Solids

Abstract: Flexoelectricity—the coupling between polarization and strain gradients—is a universal effect allowed by symmetry in all materials. Following its discovery several decades ago, studies of flexoelectricity in solids have been scarce due to the seemingly small magnitude of this effect in bulk samples. The development of nanoscale technologies, however, has renewed the interest in flexoelectricity, as the large strain gradients often present at the nanoscale can lead to strong flexoelectric effects. Here we review the fundamentals of the flexoelectric effect in solids, discuss its presence in many nanoscale systems, and look at potential applications of this electromechanical phenomenon. The review also emphasizes the many open questions and unresolved issues in this developing field.

Novel Ferroelectric Polymers for High Energy Density and Low Loss Dielectrics

Abstract: The state-of-the-art polymer dielectrics have been limited to nonpolar polymers with relatively low energy density but ultralow dielectric losses for the past decades. With the fast development of power electronics in pulsed power and power conditioning applications, there is a need for next-generation dielectric capacitors in areas of high energy density/low loss and/or high temperature/low loss polymer dielectrics. Given limitations in further enhancing atomic and electronic polarizations for polymers, this Perspective focuses on a fundamental question: Can orientational polarization in polar polymers be utilized for high energy density and low loss dielectrics? Existing experimental and theoretical results have suggested the following perspectives. For amorphous polar polymers, high energy density and low loss can be achieved below their glass transition temperatures. For liquid crystalline side-chain polymers, dipole mobility is so high that they saturate at relatively low electric fields, and only li...

Interface design for high energy density polymer nanocomposites

Abstract: This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area.