Electric Polarization Effects Research Articles

Molecular dynamics simulation of polarizable carbon nanotubes

This paper is aimed to develop a modified force field for molecular dynamics (MD) simulations of polarizable carbon nanotubes (CNTs). The effects of electrical polarization and the associated electronic degrees of freedom are represented by a network of negative charged shell particles which move relative to the surrounding positively charged carbon atoms in response to an applied electric field. In this setting, the negative and positive charges are exactly balanced so that the total system remains electrically neutral, and the motion of the shell particles relative to their equilibrium positions leads to polarization within the nanotube. Potential applications of the proposed model include simulations of controlled translocation of ions, water and polymers through solid-state CNT membranes.

Effects of in-plane electric fields on the toughening behavior of ferroelectric ceramics

Mode-I steady state crack growth in poled ferroelectric ceramics subjected to simultaneous electrical and mechanical loading is analyzed to investigate the effect of in-plane electric fields and polarization on the toughening behavior. A multiaxial, incremental constitutive law for domain switching is implemented within the finite element method to obtain the electromechanical crack tip fields. Simulation results are presented for the cases of initial remanent polarization states and applied electric fields perpendicular to the crack plane and parallel to the crack growth direction. Specific results from the calculations include the shapes and sizes of switching zones, and the toughening effects due to domain switching near the crack tip. Ferroelectric ceramics have been widely used in smart structure applications due to their large electromechanical coupling effects. Since ferroelectricdevices oftenoperate understrong mechanicaland electrical loading conditions, the brittle ferroelectric ceramic material is susceptible to fracture. Therefore, an understanding of ferroelectric fracture is a key issue for the efficient and reliable design of these devices. This paper is concerned with the study of the Mode-I fracture behavior of ferroelectric ceramics under combined in-plane electrical and mechanical loading. The scenario investigated here is illustrated in Figure 1. A ferroelectric material is initially poled by an electric field either perpendicular or parallel to the direction of crack growth. After the initial poling, an electric field is applied along (positive electric field) or opposite (negative electric field) to the initial poling direction. Finally, mechanical loading is applied and crack growth occurs. Experimental observations of the fracture properties of ferroelectrics under such conditions have been obtained on several materials from indentation tests and compact tension specimens. Using indentation tests on a PZT-8 material composition, Tobin and Pak [1993] showed that for cracks perpendicular to the poling direction, the apparent fracture toughness decreases with positive electric field and increases with a negative field. For cracks parallel to the poling direction, their results indicated that both positive and negative electric fields have little influence on the toughening. Tobin and Pak [1993] also observed that with no applied electric field the fracture toughness was greater for cracks parallel to the poling direction than for cracks perpendicular to the poling direction. Park and Sun [1995] investigated electric field effects on crack growth in a PZT-4 ceramic by using conventional compact tension fracture tests. Their results agree with those of Tobin and Pak [1993] for the case of electric field applied perpendicular to the cracksurface. However, theVickersindentationtestsofWangandSingh[1997]showedthatiftheapplied electricfields are perpendicular to the crack in a PZT EC-65 ceramic, then a positive electricfield impedes

Features of the magnetoelectric behavior of the family of multiferroics RMn2O5 at high magnetic fields (Review)

The family of multiferroics comprised of the orthorhombic manganates RMn2O5 (R=Eu,Gd,Er,Y), in which the coexistence of antiferromagnetism and ferroelectricity has been reported previously, is investigated at high magnetic fields. These compounds, unlike the members of the family RMnO3 (where R=Eu,Ge,Tb,Dy) have two subsystems of magnetic mixed-valence d ions Mn3+ and Mn4+, the direct and indirect interactions between which, being of the ferro- or antiferromagnetic type, depending on the particulars of the environment and properties of the rare-earth ions, enhance substantially the role of the frustrations observed in RMnO3 compounds. These systems, as a consequence of the specific combination of the additional magnetic degeneracy realized in them (due to competition between nearest- and next-nearest-neighbor interactions of nearly equal magnitude) and their strong magnetoelastic coupling, display a cascade of magnetic phase transitions, with the appearance/disappearance of incommensurate (modulated) magnetic structure independently along the a and c axes. The substantial magnetoelectric interactions observed in these systems provide the prerequisites not only for efficiently influencing the phase transitions by means of a magnetic field but also hold forth the possibility of magnetic control of electrical polarization effects.

Effect of Electrical Polarization of Hydroxyapatite Ceramics on New Bone Formation

Large surface charges can be induced on hydroxyapatite (HAp) ceramics by proton transport polarization, but this does not affect beta-tricalcium phosphate (TCP) because of its low polarizability. We wished to examine differences in osteogenic cell activity and new bone growth between positively or negatively surface-charged HAp and HAp/TCP plates using a calvarial bone defect model. In the first group of rats, test pieces were placed with their positively charged surfaces face down on the dura mater. In the second group, test pieces were placed with their negatively charged surfaces face down on the dura mater. A third group received noncharged test pieces. Histological examination, including enzymatic staining for osteoblasts and osteoclasts, was carried out. While no bone formation was observed at the pericranium, direct bone formation on the cranial bone debris and new bone growth expanded from the margins of the sites of injury to bridge across both the positively and negatively charged surfaces of HAp and HAp/TCP plates occurred. Electrical polarization of implanted plates, including positive charge, led to enhanced osteoblast activity, though decreased osteoclast activity was seen on the positively charged plate surface. Thus, polarization of HAp ceramics may modulate new bone formation and resorption.

Polarization effects induced by a magnetic field in intrinsically granular superconductors

Based on the previously suggested model of nanoscale dislocations induced Josephson junctions and their arrays, we study the magnetic field induced electric polarization effects in intrinsically granular superconductors. In addition to a new phenomenon of chemomagnetoelectricity, the model predicts also a few other interesting effects, including charge analogues of Meissner paramagnetism (at low fields) and "fishtail" anomaly (at high fields). The conditions under which these effects can be experimentally measured in non-stoichiometric high-T_c superconductors are discussed.

Quantum control of molecular motion including electronic polarization effects with a two-stage toolkit

A method for incorporating strong electric field polarization effects into optimal control calculations is presented. A Born-Oppenheimer-type separation, referred to as the electric-nuclear Born-Oppenheimer (ENBO) approximation, is introduced in which variations of both the nuclear geometry and the external electric field are assumed to be slow compared with the speed at which the electronic degrees of freedom respond to these changes. This assumption permits the generation of a potential energy surface that depends not only on the relative geometry of the nuclei but also on the electric field strength and on the orientation of the molecule with respect to the electric field. The range of validity of the ENBO approximation is discussed in the paper. A two-stage toolkit implementation is presented to incorporate the polarization effects and reduce the cost of the optimal control dynamics calculations. As an illustration of the method, it is applied to optimal control of vibrational excitation in a hydrogen molecule aligned along the field direction. Ab initio configuration interaction calculations with a large orbital basis set are used to compute the H-H interaction potential in the presence of the electric field. The significant computational cost reduction afforded by the toolkit implementation is demonstrated.

Flexoelectric effect in ceramic lead zirconate titanate

Mechanical strain gradient generated electric polarization or flexoelectric effect was investigated in unpoled lead zirconate titanate (PZT) ceramics in the ferroelectric state by using a cantilevered beam based approach. Flexoelectric coefficient μ12 at room temperature was measured to be 1.4μC∕m in the PZT ceramic at small level of strain gradient. Temperature-dependent experimental investigations clearly showed that high dielectric permittivity in the ferroelectrics enhanced flexoelectric polarization: essentially a linear relation was found to exist between μ12 and dielectric susceptibility χ at lower permittivity level (2100–2800), while μ12 versus χ curve started to deviate from the straight line at the χ∼2800 and nonlinear enhancement of μ12 with χ was observed, with μ12 value reaching 9.5 at χ∼11000. The nonlinearity in the flexoelectric effect was associated with domain-related processes. It is suggested that flexoelectric effect can have a significant impact on epitaxial ferroelectric thin films and mesoscopic structures.

THE PERFORMANCE OF POLARIZATION DIVERSITY SCHEMES IN OUTDOOR MICRO CELLS

The application of polarization diversity reception at the mobile terminal in micro cells at 2 GHz is presented in this paper. Raytracing tool is used to study effects of electric field polarization on the received power in outdoor environments. The performance of diversity schemes with vertical/ horizontal polarization and +45◦/−45◦ slanted polarization are compared in different line-of-sight (LOS) and nonlineof-sight (NLOS) environments. Based on the evaluation of cross polarization discrimination (XPD) parameters, it is clarified that different environments will affect XPD values in micro cells. Then, the vertical/horizontal polarization diversity and +45◦/− 45◦ slanted polarization diversity are chosen to compare with space diversity. Several different combining techniques of polarization and space diversity schemes are also compared in different environments. It is found that dual-polarized antennas for mobile terminal are a promising alternative for two spaced antennas.

Electric polarization effects on the electronic spectral shift of centrosymmetric compounds

The classic dielectric dipolar Onsager model was extended to include quadrupolar interactions between solute molecules and solvents with different polarities. A multiparametric solvatochromic expression, based on the point quadrupole moment inside a spherical cavity embedded in a dielectric continuum, is applied to centrosymmetric sulfonamide porphyrins, zinc tetraphenyl porphyrin, squaraine and 9,10-dicyanoanthracene, in order to account for the quadrupolar polarization effect of solute molecules. The reaction field polarity functions created respectively by dipole and quadrupole moments are compared and found to be linearly correlated.

Electrical polarization effects on LDPE morphology

AbstractThe thermal and dynamic mechanical behavior of polarized low‐density polyethylene (LDPE) was investigated, by applying electric fields in the range of 5.37 to 31.7 MV/m, for 2.75 to 43.5 h. The polarization strongly affected DSC and DMA spectra, indicating that a new and more ordered phase is formed, which disappears gradually after the removal of the electrical field. A shift of −21.3°C was found in the DMTA spectra for the Tg of the polarized material, and no changes could be found in comparing the results of WAXS analyses of the original and treated materials. Very similar effects were observed with mechanical loading of the materials, leading to the conclusion that the amorphous phase of LDPE might be orienting under high electric fields in a similar manner. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3107–3114, 2003

Experimental study of the thermal behavior of a water cooled Ni–Cd battery

Abstract In this paper, the Ni–Cd battery principle and exothermal processes are first recalled. It is pointed out that heat generation can be decomposed into irreversible losses (entropic effect), battery electric resistance and polarization effect. It is shown how these effects can be analyzed from overall battery heat balance. The calorimetric test bench is described. Battery cycles are composed of charge, overcharge, rest and discharge. Typically, the total heat losses range around 25% with an increase up to 33% at 200 A. Only during overcharge, gas losses are shown to be a high contribution. The paper shows that the calorimetric study permits not only further insight into local temperatures and heat losses, but also to deduce such parameters as entropy generation and, above all, total resistance (Joule effect and polarization). In this case, resistance was estimated to increase from 2 to 6 mΩ with depth of discharge from 0 to 100%.

Suppression of electron–hole-pair recombination in edge states in quantum Hall regimes

Far-infrared (FIR) photoconductivity induced by cyclotron resonance in edge states of quantum Hall devices are studied by carrying out time-resolved measurements. It is found that the recombination of electron–hole pairs excited via cyclotron resonance in edge states is significantly suppressed, yielding a surprisingly long recombination lifetime (∼10ms). This is in marked contrast to much shorter recombination lifetimes (∼1ms) in bulk states. The experimental results lead us to suggest that the edge-state FIR photoconductivity is induced by an effect of electric polarization. This implies also that edge states can be a promising candidate for application as a FIR detector.

A Micromechanics-Based Hysteresis Model for Ferroelectric Ceramics

Based on the mechanics of domain switch and irreversible thermodynamics, a micromechanics-based model that incorporates the effect of polarization strain and electric polarization in the switched domain is developed to predict the evolution of new domain and the associated hysteresis loops of a ferroelectric ceramic. The new domain concentration c r associated with the remanent polarization P r, and the new domain concentration c c at the coercive field E c, are also found in terms of the saturation polarization P s, the coercive field E c, and the dielectric permittivity of the parent domain. The theory is developed with a homogenization technique for a coupled, dual-phase electromechanical system with an evolving microstructure, whose driving force arises from the reduction of Gibbs’ free energy and whose resistance force comes from the energy dissipation due to domain wall movement. The developed theory is applied to a lanthanum doped lead zirconate titanate (PLZT), first for the calculation of its hysteresis electric displacement versus electric field ( D vs. E) relation and the butterfly-shaped longitudinal strain versus electric field (∊ vs. E) relation, and then for its nonlinear compressive stress-strain relation and nonlinear depolarization. The results are shown to provide the essential features of the hysteresis behavior and found to be in quantitative accord with the experimental data.

A Polarization Model Overcoming the Geometric Restrictions of the Laplace Solution for Spheroidal Cells: Obtaining New Equations for Field-Induced Forces and Transmembrane Potential

We present a new model for a variety of electric polarization effects on oblate and prolate homogeneous and single-shell spheroids. For homogeneous spheroids the model is identical to the Laplace model. For single-shell spheres of cell-like geometry the calculated difference of the induced dipole moments is in the thousandths range. To solve Laplace's equation for nonspherical single-shell objects it is necessary to assume a confocal shell, which results in different cell membrane properties in the pole and equator regions, respectively. Our alternative model addresses this drawback. It assumes that the disturbance of the external field due to polarization may project into the medium to a characteristic distance, the influential radius. This parameter is related to the axis ratio of the spheroid over the depolarizing factors and allows us to determine the geometry for a finite resistor-capacitor model. From this model the potential at the spheroid's surface is obtained and, consequently, the local field inside a homogeneous spheroid is determined. In the single-shell case, this is the effective local field of an equivalent homogeneous spheroid. Finally, integration over the volume yields the frequency-dependent induced dipole moment. The resistor-capacitor approach allowed us to find simple equations for the critical and characteristic frequencies, force plateaus and peak heights of deformation, dielectrophoresis and electrorotation for homogeneous and single-shell spheroids, and a more generalized equation for the induced transmembrane potential of spheroidal cells.

Effects of Electric Double Layer and Space Charge Polarization by Plural Kinds of Ions on Complex Dielectric Constant of Liquid Crystal Materials

The complex dielectric constant of a liquid crystal material, 4-cyano-4′-alkyl-biphenyl (5CB), was measured in low-frequency regions below 1000 Hz. The anomalous increasing behavior was analyzed using an equivalent circuit which takes two kinds of contributions into account: one is from the electric double layer and the other is from the space charge polarization. It was found by numerical calculations that these two effects exhibit different dependences of dielectric dispersion on the thickness of a specimen, and both effects were successfully distinguished in the experimental results. In the analysis of the space charge polarization, the experimental results were best fitted by the calculated results with five kinds of ions in terms of the diffusion coefficient. These measurements can be applied to a precise determination of the attributes of plural kinds of ions, such as the diffusion coefficient and the number density.

Rotor-blade modulation on antenna amplitude pattern and polarization: predictions and measurements

The rotation of lift- and thrust-generating airfoils causes a periodic variation in aircraft communication signals. This effect is called rotor-blade modulation (RBM). The RBM on the radiation characteristics of helicopter-mounted antennas are predicted using the uniform theory of diffraction (UTD) and the finite-difference time-domain (FDTD) method and are compared with scale model measurements and full-scale in-flight measurements. In addition, the effects of electric field polarization on RBM are studied using the FDTD.

Polarization and band offsets of stacking faults in AlN and GaN

We have performed systematic first-principles pseudopotential local density functional calculations of stacking faults in GaN and AlN. Their band offsets and the charge accumulation at stacking fault interfaces has been investigated, taking fully into account the effects of lattice relaxation and electric polarization. We find the stacking fault junctions to be of type I in both materials. However, the intrinsic valence band offsets are close to zero, so that the conduction band offsets result mostly from the differences in the energy gaps between the cubic and wurtzite phases. The charge accumulated at the interface between the cubic and wurtzite phase is found to be 0.009 and 0.003 C/m2 for the AlN and GaN stacking fault, respectively.

Wave flows in a thin layer of a viscous liquid. Influence of a constant electric field

The influence of a constant transverse electric field on the dynamics of longwave, weakly nonlinear flow of a viscous dielectric liquid film down a vertical wall is studied. An amplitude integrodifferential equation in partial derivatives of the Kuramoto-Sivashinskii equation type, which describes the behavior of the free surface of the layer, is derived using the method of multiscale stretching. In the case considered, the potential energy of the electric field is a source of longwave perturbations, but, on the whole, secondary regimes are apparently nonlinearly steady. Probably, the electric polarization effects studied can be used as a factor that governs the dynamics of film flow.

Dielectrophoresis: Using Inhomogeneous AC Electrical Fields to Separate and Manipulate Cells

Dielectrophoresis is the motion of particles caused by electrical polarization effects in inhomogeneous (nonuniform) electric fields. Unlike electrophoresis, the particles do not require a net electrical charge for motion to occur and AC rather than DC fields are employed to exploit the dielectric properties of the particles. Factors controlling the effective dielectric properties of cells and microorganisms include electrical double layers associated with surface charges, the conductivity and permittivity of their membranes and any cell walls, and their morphologies and structural architectures. In recent years, several laboratories have developed separation and manipulation techniques for cells and microorganisms based on dielectrophoresis, using both static and traveling AC fields. In this article, the basic physical factors influencing the dielectrophoretic behavior of particles are outlined, and ways in which these can be employed to achieve selective separation of cells and microorganisms are described.

Theoretical analysis of the bonding of oxygen to Cu(100).

The chemisorption of O/Cu(100) has been modeled by a ${\mathrm{Cu}}_{5}$O cluster; ab initio self-consistent-field electronic wave functions have been obtained for this cluster. The bonding has been analyzed using several new theoretical methods: (1) the variation of the ${\mathrm{Cu}}_{5}$O dipole moment with the distance of O from the surface; (2) the projection of the O orbitals from ${\mathrm{Cu}}_{5}$O; and (3) the constrained space orbital variation (CSOV) method for the development of the bond. It is concluded that the bond is dominantly ionic but with a significant covalent contribution. Our results indicate that the excess charge on O is \ensuremath{\sim}1.5 electrons. We have computed the CSOV analysis for ${\mathrm{Cu}}_{5}$O and for ${\mathrm{Cu}}_{5}$ with point charges. The comparison of these two clusters has allowed us to have a definitive measure of the contribution of the Cu d electrons to the covalent bond. The total contribution of the d electrons to the bond is rather large (1.2 eV). Once the different contributions are separated, it is shown that purely electrical polarization effects account for \ensuremath{\sim}0.5 eV, while the direct participation of the d electrons in the covalent bond is \ensuremath{\sim}0.7 eV.