scispace - formally typeset
Search or ask a question
Author

Xin Zhou

Bio: Xin Zhou is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Dielectric & Capacitor. The author has an hindex of 18, co-authored 34 publications receiving 3118 citations. Previous affiliations of Xin Zhou include Foundation University, Islamabad.

Papers
More filters
Journal ArticleDOI
21 Jul 2006-Science
TL;DR: It is demonstrated that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants.
Abstract: Dielectric polymers with high dipole density have the potential to achieve very high energy density, which is required in many modern electronics and electric systems. We demonstrate that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers. This is achieved by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants, to avoid the electric displacement saturation at electric fields well below the breakdown field. The results indicate that a very high dielectric constant may not be desirable to reach a very high energy density.

2,008 citations

Journal ArticleDOI
Yong Wang1, Xin Zhou1, Qin Chen1, Baojin Chu1, Qiming Zhang1 
TL;DR: Aromatic polyurea thin films were developed through vapor phase deposition, exhibiting relatively high dielectric constant, low loss, high breakdown field (>800 MV/m) and consequently high energy density (>12 J/cm3) as mentioned in this paper.
Abstract: High energy density dielectric materials are desirable for capacitors and other energy storage systems. Two approaches were developed to achieve high electric energy density: explore high dielectric constant (K) materials and improve high operation electric field. Relaxor ferroelectric polyvinylidene fluoride (PVDF) based copolymers P(VDF-HFP), P(VDF-CTFE) and terpolymer P(VDF-TrFE-CFE) have been proven to possess high electric energy density. An energy density of over 25 J/cm3 has been achieved in PVDF-based polymers, which represents the state of art in high energy density polymers. Aromatic polyurea thin films were developed through vapor phase deposition, exhibiting relatively high dielectric constant, low loss, high breakdown field (>800 MV/m) and consequently high energy density (>12 J/cm3). Its thermal stability up to 200°C and high charge-discharge efficiency (>90%) make it attractive for high temperature capacitors. Investigation through SEM, AFM and other experiments indicated unbalanced aromatic polyurea could exhibit apparent high-K (~15) due to the non-uniformity of film thickness and surface morphology. This article reviews the recent development of these high performance polymers.

263 citations

Journal ArticleDOI
TL;DR: In this paper, the electrical breakdown of a polar fluoropolymer, poly(vinylidene fluoride-hexafluoropropylene) which exhibits an exceptionally high discharged electrical energy density (>25 J/cm3), was investigated.
Abstract: This paper investigates the electrical breakdown of a polar fluoropolymer, poly(vinylidene fluoride-hexafluoropropylene) which exhibits an exceptionally high discharged electrical energy density (>25 J/cm3). It is shown that above room temperature, the breakdown strength decreases with temperature. It is further shown that such a temperature dependence of breakdown strength is consistent with the electromechanical breakdown model by taking into consideration of the plastic deformation of semicrystalline polymers.

239 citations

Journal ArticleDOI
Xin Zhou1, Baojin Chu1, Bret Neese1, Minren Lin1, Qiming Zhang1 
TL;DR: In this paper, the authors investigated the dielectric and discharge behavior of polyvinylidene fluoride-based copolymer film capacitors and found that the discharge energy density decreases with frequency and the discharged energy density is also reduced at shorted discharge time.
Abstract: The high electric displacement (D>0.1 C/m2) and breakdown field (600 MV/m) in polyvinylidene fluoride based polymers suggest high electrical energy density in this class of polymers. By defect modifications which reduce or eliminate the remnant polarization in the polymer, a high electrical energy density can indeed be obtained. This paper shows that in properly prepared P(VDF-CTFE) copolymer film capacitors, an electrical energy density ~25 J/cm3 can be obtained with a breakdown field higher than 600 MV/m. The dielectric and discharge behavior of the polymer films were investigated. The results reveal that there are strong frequency dispersions in both the dielectric and discharge behavior. The dielectric constant decreases with frequency and the discharged energy density is also reduced at shorted discharge time (~1 mus) due to increased ESR for fast discharge. The results indicate the potential of this class of polymers for high energy density capacitors and suggest the need for further tuning of the polymer compositions to reduce the frequency dispersion.

199 citations

Journal ArticleDOI
Baojin Chu1, Xin Zhou1, Bret Neese1, Qiming Zhang1, F. Bauer 
TL;DR: In this paper, the relaxor ferroelectric polymer-poly(vinylidene fluoride/trifluoroethylene/chlorofluoro methylene) terpolymer for energy storage capacitors was investigated and it was found that the high dielectric constant (>50 at 1 kHz) and high reversible polarization in the terpolymers lead to high electric energy density ~ 10 J/cm3, achieved under an electric field of more than 350 MV/m.
Abstract: This paper investigates the relaxor ferroelectric polymer-poly(vinylidene fluoride/trifluoroethylene/chlorofluoroethylene) terpolymer for energy storage capacitors. It is found that the high dielectric constant (>50 at 1 kHz) and high reversible polarization in the terpolymer lead to a high electric energy density ~ 10 J/cm3 , achieved under an electric field of more than 350 MV/m. The high dielectric constant also causes the polarization saturation at fields much below the breakdown field and whereby the discharged energy density increases nearly linearly with applied field, distinctively different from the low dielectric constant linear dielectric polymers whose energy density rises with square of the applied field. The strong frequency dispersion and nonlinear polarization response (polarization saturation) of the relaxor terpolymer result in a low effective capacitance at the beginning of the discharge and the effective capacitance increases with time during the discharge. Furthermore, due to the frequency dispersion and nonlinear effect, the discharged energy density of the terpolymer to a resistor load RL increases with RL. A large R L will lead to high discharge efficiency in the terpolymer capacitor

122 citations


Cited by
More filters
Reference EntryDOI
31 Oct 2001
TL;DR: The American Society for Testing and Materials (ASTM) as mentioned in this paper is an independent organization devoted to the development of standards for testing and materials, and is a member of IEEE 802.11.
Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

3,792 citations

Journal ArticleDOI
TL;DR: In this article, the main characteristics of the electroactive phases of polyvinylidene fluoride and copolymers are summarized, and some interesting potential applications and processing challenges are discussed.

2,242 citations

Journal ArticleDOI
TL;DR: Electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin akin to human skin.
Abstract: Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

1,950 citations

01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

1,652 citations

Journal ArticleDOI
30 Jul 2015-Nature
TL;DR: Crosslinked polymer nanocomposites that contain boron nitride nanosheets have outstanding high-voltage capacitive energy storage capabilities at record temperatures and have been demonstrated to preserve excellent dielectric and capacitive performance after intensive bending cycles, enabling broader applications of organic materials in high-temperature electronics and energy storage devices.
Abstract: Dielectric materials, which store energy electrostatically, are ubiquitous in advanced electronics and electric power systems. Compared to their ceramic counterparts, polymer dielectrics have higher breakdown strengths and greater reliability, are scalable, lightweight and can be shaped into intricate configurations, and are therefore an ideal choice for many power electronics, power conditioning, and pulsed power applications. However, polymer dielectrics are limited to relatively low working temperatures, and thus fail to meet the rising demand for electricity under the extreme conditions present in applications such as hybrid and electric vehicles, aerospace power electronics, and underground oil and gas exploration. Here we describe crosslinked polymer nanocomposites that contain boron nitride nanosheets, the dielectric properties of which are stable over a broad temperature and frequency range. The nanocomposites have outstanding high-voltage capacitive energy storage capabilities at record temperatures (a Weibull breakdown strength of 403 megavolts per metre and a discharged energy density of 1.8 joules per cubic centimetre at 250 degrees Celsius). Their electrical conduction is several orders of magnitude lower than that of existing polymers and their high operating temperatures are attributed to greatly improved thermal conductivity, owing to the presence of the boron nitride nanosheets, which improve heat dissipation compared to pristine polymers (which are inherently susceptible to thermal runaway). Moreover, the polymer nanocomposites are lightweight, photopatternable and mechanically flexible, and have been demonstrated to preserve excellent dielectric and capacitive performance after intensive bending cycles. These findings enable broader applications of organic materials in high-temperature electronics and energy storage devices.

1,324 citations