Nonlinear Dielectric Constant Research Articles

Improving the optical properties of magnesium spinel chromites through Ni and Cu substitutions for optoelectronic applications.

In this study, we investigated the optoelectronic performance of magnesium spinel chromites with nickel (Ni) and copper (Cu) substitutions. Using the sol-gel method, we synthesized two spinel chromites: Mg0.6Ni0.4Cr2O4 (MNCO) and Mg0.6Cu0.4Cr2O4 (MCCO). We extensively characterized these samples to analyze their thermal, structural, elastic, and optical properties. Structural analysis reveals good agreement between the calculated and refined structural parameters, which supports the proposed cation distributions for the samples. By calculating stiffness constants from force constants, we derived elastic moduli such as bulk modulus, longitudinal modulus, and rigidity modulus. MCCO exhibited lower values for these moduli, as well as the Debye temperature, compared to MNCO. Both samples displayed a brittle mechanical nature according to the Pugh ratio, while the Poisson ratio remained constant at 0.25, indicating isotropic elasticity. UV-vis-NIR spectroscopy revealed that MNCO has higher band-gap (E g) and Urbach (E u) energies than MCCO. Further analysis of refractive index, penetration depth, extinction coefficients, nonlinear optical parameters, optical conductivity, and optical dielectric constants highlighted the promising optoelectronic applications of the synthesized materials. Our study found that the band-gap energy values of the as-synthesized samples were smaller than reported values for MgCr2O4 spinel chromites, indicating that Ni and Cu substitutions offer an opportunity to extend the sunlight absorption range of magnesium chromites.

Multi-Scale Modeling of Dielectric Polarization in Polymer/Ferroelectric Composites

Ferroelectric materials are attractive fillers for polymer composites due to their high and non-linear dielectric constants. In this study, the dielectric response of the epoxy/BaTiO3 composite is obtained by a Sawyer–Tower measurement. In addition, we propose a multiscale computational approach that allows simulation of the polarization behavior of polymer/ferroelectric composites on the timescale above 100 ms, which is several orders of magnitude longer than previous studies. The model is free of ad hoc parameters and therefore can simulate the polarization characteristics from first-principles. Both in experiments and simulations, non-linear hysteresis behavior was observed in the epoxy/BaTiO3 composite even when the electric field across the BaTiO3 is more than an order of magnitude lower than the coercive field. The computational results suggested that this originates from the domain wall motion in BaTiO3. Some practical implications drawn from the computational results are discussed.

IGSE-CD—An Electric-/Displacement-Field Related Steinmetz Model for Class II Multilayer Ceramic Capacitors Under Low-Frequency Large-Signal Excitation

Multilayer Ceramic Capacitors (MLCCs) are of paramount importance in electronics and ferroelectric Class II dielectrics enable outstanding energy-density values. However, the non-linear dielectric constant and associated low-frequency large-signal excitation losses of Class II MLCCs may cause critical overheating. A peak-charge based Steinmetz loss model entitled iGSE-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</sub> is known in literature and allows to accurately calculate MLCC low-frequency large-signal excitation losses under various operating conditions including biased and non-sinusoidal excitation voltage waveforms. Such a macroscopic iGSE-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</sub> model, however, is inherently limited to a specific MLCC, and in contrast to Steinmetz loss modeling for ferromagnetic inductor cores, the losses of other devices employing the same dielectric material cannot be predicted. Recent literature therefore proposed a microscopic and/or material specific MLCC Steinmetz Model entitled iGSE-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> which allows to calculate the losses of any MLCC of the same dielectric material based upon just a single set of Steinmetz parameters. However, due to the lack of information on the internal device geometry, the iGSE-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> could be verified only indirectly so far by means of a loss normalization based on the device capacitance and rated voltage. In this paper, we demonstrate the feasibility of a microscopic iGSE-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> MLCC loss model enabled by manufacturer data on the internal capacitor structure. The iGSE-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> is verified for two different MLCC series employing a conventional X7R dielectric and a novel Hiteca (with reduced non-linearity) Class II dielectric material with loss estimation error below 22%. This error results due to component tolerances and is acceptable, especially when compared to the loss calculation based on the datasheet information which can be off by up to a factor of ten. The analysis of the Hiteca dielectric reveals a frequency behavior different to the X7R material, and is discussed in the Appendix of this paper.

Semi-Experimental Determination of the Linear Clamped Electro-Optical Coefficients of Polar Crystals from Vibrational Spectroscopic Data

The present work highlights a new general method devoted to computations of the clamped linear electro-optical coefficients from the measured fundamental vibrational frequencies and the nonlinear dielectric susceptibility constants. The calculations are based on the formula analog to that of the Lyddane–Sachs–Teller relation, which is systematically used for the calculations of the clamped linear electro-optical coefficient of oxide ferroelectric crystals such as LiNbO3, LiTaO3, BaTiO3, PbTiO3, and KNbO3. The computed electro-optical coefficients are in good agreement with those obtained from direct measurements and the first-principles calculations or other semi-empirical models. In addition, the famous r51 or r42 coefficients of the tetragonal BaTiO3, PbTiO3, and KNbO3 crystals are finally calculated with high accuracy and discussed in connection with the soft mode behavior.

Propagation of two relativistic hollow Gaussian laser beams in magnetized plasma: extended paraxial theory

This work presents an analytical and numerical study for the mutual interaction and propagation of two intense hollow Gaussian laser beams (HGLBs) at difference frequency in a magnetized plasma. This work has been done in the presence of relativistic nonlinearity, which depends on the intensity of both laser beams. In this process, the propagation of both laser beams in the plasma is described by cross-focusing, as the behavior of one laser beam affects that of another laser beam. The nonlinear differential equations for the beamwidth of HGLBs have been obtained within the Wentzel–Kramers–Brillouin (WKB) method and higher-order paraxial theory. The expression for the nonlinear dielectric constant of the plasma has been obtained from the maximum irradiance of the HGLBs. The obtained equations have been solved numerically to explore the effect of the well-established laser and plasma parameters on the focusing of both laser beams in a magnetized plasma. The results have been compared with paraxial ray theory and Gaussian profile of the laser beams. The focusing/intensity of both laser beams increases in the extended paraxial region compared to the paraxial region in the magnetized plasma. The focusing of both laser beams increases even at high values of beam order and electron cyclotron frequency in the extended paraxial region.

Influence of polarization, multi-valences and multi-coordination of cobalt: Third-order nonlinear, dielectric and Faraday properties of Bi0.5Co1.5S3/high optical basicity glass

In this study, we have successfully grown Co doped Bi0.5Co1.5S3 nanocrystals inside heavy metal oxide diamagnetic 42PbO-48TeO2-10B2O3 glass whose morphology, structure and properties were characterized using various techniques. The optimum parameters for Bi0.5Co1.5S3 nanocrystals formation is 380°C for 10hours. Glasses having different amounts of Bi0.5Co1.5S3presented colors from light yellow to green and pure blue due to the different optical absorption of Co2+ ions in octahedral and tetrahedral coordination units. X-ray diffraction pattern revealed the formation of orthorhombic Bi2S3 nanocrystals in glass and Raman spectra demonstrated modification on structure such as TeO4 → TeO3 and BO → NBO conversion. The red shift in transmission cutoff edge of glasses showed experimental evidence of quantum confinement effect. Due to the high optical basicity system, X-ray photoelectron spectra studies confirmed the co-existence of Co2+, Co3+ and Co4+ which presented characteristic absorption in ultraviolet-visible spectra. The introduction of Bi0.5Co1.5S3 greatly increased the polarizability of glass, resulting in significant improvement on third-order nonlinearity, AC conductivity and dielectric constant. 1% Bi0.5Co1.5S3 doped glass presents giant Verdet constant of 62 rad/T.m at 633nm, promising nonlinear refractive index (5.662 × 10−11 esu) and large dielectric constant (78). This result proved that the synthesis of multivalence states of Co doped Bi2S3 in glass is an efficient method to improve the optical, dielectric and magneto optical performance of glass. Such dilute magnetic semiconductor nanocrystals-glass system has great potential applications in nonlinear, dielectric and magneto optical current sensors and isolators devices.

Modeling nonlinear dielectric properties of laminated composites

sThe article is devoted to the development of a method for predicting the nonlinear dielectric properties of layered composites with complex dependences of the dielectric constant on the electric field strength, which consider the effects of a sharp increase and subsequent decrease in the dielectric constant with increasing field strength. The method is based on the use of the theory of asymptotic averaging proposed by N.S. Bakhvalov, E. Sanchez-Palencia, in relation to the nonlinear problem of electrostatics in a layered medium. As a result of applying this method, local nonlinear problems of electrostatics on a periodicity cell are formulated, and an algorithm for calculating effective nonlinear dielectric constants is proposed. It is shown that a layered composite is a transversely isotropic nonlinear dielectric material if its layers are isotropic materials. A numerical example of calculating the nonlinear properties of a 2-layer composite based on barium titanate and ferroelectric ceramic varicond VK4 is considered. Calculations have shown that the developed method for calculating the nonlinear-dielectric ratios of composites is quite effective and makes it possible to predict the dielectric properties of composites at various values of the electric field strength, including the regions where the dielectric permittivities of the layer materials are saturated. The developed technique can serve as a basis for designing new nonlinear dielectric composite materials with unusual properties.

Nanoplasma properties in metallic clusters driven by a Gaussian laser beam in the presence of helical magnetic undulator

The motivation of present paper is the investigation of effective permittivity and absorption cross section of cluster nanoplasmas in the interaction of a Gaussian laser beam with a cluster of metallic nanoparticles, in the presence of a helical magnetic undulator. The static magnetic field of the undulator couples with the field of the laser wave, and forms a nonlinear force in the interaction region. As a result, the nonlinear force varies the plasmonic oscillations of the electron of nanoplasmas that leads to electron density modulation, which modifies absorption cross section and effective permittivity of nanoparticles. Using a perturbative method, we analytically derived the nonlinear dispersion waves and dielectric constant of metallic nanoparticles lattice (gold, silver, and copper) in the presence of a helical magnetic undulator. Numerical results indicate that with increasing the undulator magnetic field strength, absorption cross section of cluster nanoplasmas increases and absorption phenomenon occurs at frequencies close to the effective plasma frequency. Besides, with decreasing distance of nanoparticles in the cluster (and with increasing the nanoparticles radius), absorption cross section increases. We also found that the dielectric constant of the cluster nanoplasma medium increases with enhancing undulator magnetic field strength only near the effective plasmonic frequency. This concept opens a path toward new properties of cluster nanoplasmas as quantum dots, diagnostics, and sensors based on magnetic undulator structures.

Acousto-elastic theory for the coupling parameters in terms of nonlinear elastic, piezoelectric, electrostrictive, and dielectric constants in trigonal and hexagonal crystalline systems: applied in the crystal and solid-state physics

The aim of the acousto-elastic theory was to measure ultrasonic velocity changes which characterize the mechanical nonlinearity of a prestressed material. In this context, our purpose is to tabulate the invariant third-order elastic coefficients including the piezoelectric, electrostrictive, and dielectric corrections. The investigation is limited to trigonal and hexagonal crystalline structures, which represent the most often encountered symmetry classes for the piezoelectric materials. In fact, the enumeration includes the high-order tensors involved in the analysis of nonlinear behaviors associated with various electromechanical coupling forms. The obtained results are extensions to previous calculations in this area which bring some corrections to certain published combinations related to the invariance rules. The numerical procedure built using the software MATLAB is based on coordinate system transformations performed on the eigenbasis of their corresponding symmetry axes three- and sixfold. In this purpose, we found some contradictions between our results and a former paper published in Journal of Applied Physics. To the authors’ knowledge, rechecking of the relationships between the invariant third-order constants and comparison with this last reference has not been discussed yet. The relationships between the invariant third-order coefficients presented in this work provide a number of attractive properties for use in mechanical and physical applications.

Improved memristive switching of graphite/Nb:SrTiO3 interfaces by tuning Fermi levels and dielectric constants

Layered electrodes based on graphene or transition metal dichalcogenides have enriched the development of nanoelectronics due to their uniqueness in flexibility, transparency, thermal stability, and electronic structure. Here, we report on resistive switching behavior observed in graphite/Nb:SrTiO3 (Gr/NbSTO) junctions. Straightforward in situ bromine intercalation of graphite modulates the transport properties of Gr/NbSTO devices, an effect which cannot be achieved using traditional metal electrodes. At low temperatures, the strong electric field dependence of the dielectric constant of NbSTO also plays an important role in further enhancing the resistive switching performance. Our findings here suggest that to optimize the performance and to perform more complex functions, tunability of the Fermi level of the layered graphite electrode in combination with the nonlinear dielectric constant of the NbSTO substrate is critically important for interface-type resistive switching devices.

Quantitative thickness measurement of polarity-inverted piezoelectric thin-film layer by scanning nonlinear dielectric microscopy

A quantitative measurement method for a polarity-inverted layer in ferroelectric or piezoelectric thin film is proposed. It is performed nondestructively by scanning nonlinear dielectric microscopy (SNDM). In SNDM, linear and nonlinear dielectric constants are measured using a probe that converts the variation of capacitance related to these constants into the variation of electrical oscillation frequency. In this paper, we describe a principle for determining the layer thickness and some calculation results of the output signal, which are related to the radius of the probe tip and the thickness of the inverted layer. Moreover, we derive an equation that represents the relationship between the output signal and the oscillation frequency of the probe and explain how to determine the thickness from the measured frequency. Experimental results in Sc-doped AlN piezoelectric thin films that have a polarity-inverted layer with a thickness of 1.5 µm fabricated by radio frequency magnetron sputtering showed a fairly good value of 1.38 µm for the thickness of the polarity-inverted layer.

Propagation of two intense cosh-Gaussian laser beams in plasma in the relativistic-ponderomotive regime

This work presents an investigation of the propagation of two intense cosh-Gaussian laser beams (CGLBs) in collisionless plasma taking into account the combined effects of relativistic and ponderomotive nonlinearities. Due to mutual interaction of two CGLBs, the self-focusing of one beam is affected by the presence of another beam in plasma, and cross-focusing takes place. A paraxial-like approach has been used to investigate the cross-focusing of CGLBs in plasma. An appropriate expression for the nonlinear dielectric constant of plasma has been evaluated in the presence of relativistic-ponderomotive force and used to study the propagation of CGLBs in plasma. The effect of various well-established laser and plasma parameters on the cross-focusing of two beams in plasma has been explored and the results are compared with only relativistic nonlinearity and the Gaussian profile of laser beams. Numerical results show that the decentered parameter (b) plays a crucial role in the cross-focusing of the CGLBs. It is observed that CGLBs focused earlier than Gaussian beams. This study is useful in beat wave excitation of electron plasma wave and collective laser particle accelerators.

Enhancement of nonlinear optical properties of compounds of silica glass and metallic nanoparticle

The aim of this paper is to introduce a method for enhancing the nonlinear optical properties in silica glass by using metallic nanoparticles. First, the T-matrix method is developed to calculate the effective dielectric constant for the compound of silica glass and metallic nanoparticles, both of which possess nonlinear dielectric constants. In the second step, the Maxwell–Garnett theory is exploited to replace the spherical nanoparticles with cylindrical and ellipsoidal ones, facilitating the calculation of the third-order nonlinear effective susceptibility for a degenerate four-wave mixing case. The results are followed by numerical computations for silver, copper and gold nanoparticles. It is shown, graphically, that the maximum and minimum of the real part of the reflection coefficient for nanoparticles of silver occurs in smaller wavelengths compared to that of copper and gold. Further, it is found that spherical nanoparticles exhibit greater figure-of-merit compared to those with cylindrical or ellipsoidal geometries.

Understanding Nonlinear Dielectric Properties in a Biaxially Oriented Poly(vinylidene fluoride) Film at Both Low and High Electric Fields.

Understanding nonlinear dielectric behavior in polar polymers is crucial to their potential application as next generation high energy density and low loss dielectrics. In this work, we studied nonlinear dielectric properties of a biaxially oriented poly(vinylidene fluoride) (BOPVDF) film under both low and high electric fields. For fundamental nonlinear dielectric constants at low fields (<30 MV/m), Novocontrol high-voltage broadband dielectric spectroscopy (HVBDS) was accurate enough to measure up to the third harmonics. It was observed that the low-field dielectric nonlinearity for the BOPVDF disappeared above 10 Hz at room temperature, suggesting that the low-field dielectric nonlinearity originated from ionic migration of impurity ions rather than dipolar relaxation of the amorphous segments. Above the coercive field (EC ≈ 70 MV/m), bipolar electric displacement-electric field (D-E) loop tests were used to extract the nonlinear behavior for pure PVDF crystals, which had a clear origin of ferroelectric switching of polar crystalline dipoles and domains and nonpolar-to-polar (α → δ → β) phase transformations. By using HVBDS, it was observed that the ferroelectric switching of polar crystalline dipoles and domains in BOPVDF above the EC always took place between 20 and 500 Hz regardless of a broad range of temperature from -30 to 100 °C. This behavior was drastically different from that of the amorphous PVDF dipoles, which had a strong dependence on frequency over orders of magnitude.

Selective excitation of lasing modes by controlling modal interactions.

Using the correspondence between (saturated) nonlinear and (unsaturated) linear dielectric constants, we propose a simple and systematic method to achieve selective excitation of lasing modes that would have been dwarfed by more dominant ones of lower thresholds. The key element of this method is incorporating the control of modal interactions into the spatial pump profile, and it is most valuable in the presence of spatially and spectrally overlapping modes, where it would be difficult to achieve selective excitation otherwise.

Self-Focusing of Quadruple Gaussian Laser Beam in an Inhomogenous Magnetized Plasma with Ponderomotive Non-Linearity: Effect of Linear Absorption

The propagation of quadruple Gaussian laser beam in a plasma characterized by axial inhomogeneity and nonlinearity due to ponderomotive force in the paraxial ray approximation is investigated. An appropriate expression for the nonlinear dielectric constant has been developed in the presence of external magnetic field, with linear absorption and due to saturation effects for arbitrary large intensity. The effects of different types of plasma axial inhomogeneities on self-focusing of laser beam have been studied with the typical laser and plasma parameters. Self-focusing of quadruple Gaussian laser beam in the presence of externally applied magnetic field and saturating parameter is found significantly improved in the case of extraordinary mode. Our results reveal that initially converging beam shows oscillatory convergence whereas initially diverging beam shows oscillatory divergence. The beam is more focussed at lower intensity in both cases viz. extraordinary and ordinary mode.

The effect of strain on the domain switching of ferroelectric polycrystals

The effect of external strain on the non-linear electromechanical behavior of a ferroelectric poly-crystal is investigated under different applied electric fields by using a phase field model. Simulation results show that the domain switching induced by electric field under a tensile strain is much easier than that under a compressive strain, which is attributed to that a multi-domain structure can be more easily formed under the tensile strain than in the case of compressive strain when the electric field is absent. It is also found that a compressive misfit strain increases the macroscopic coercive field and remnant polarization while a tensile misfit strain decreases both of them. In addition, a compressive strain decreases the non-linear dielectric constant while a tensile strain increases it.

Nano-domains and related phenomena in congruent lithium tantalate single crystals studied by scanning nonlinear dielectric microscopy.

Nanodomains and their related phenomena in congruent lithium tantalate (CLT) single crystals are studied using scanning nonlinear dielectric microscopy (SNDM). We carried out two specific investigations: super higher order nonlinear dielectric spectroscopy studies on thick multi-domain congruent CLT single crystals and electrical conduction in nanodomains in thin CLT single crystals. First, without using a special sharp tip, we achieve improved lateral resolution in SNDM through the measurement of super higher order nonlinearity up to the fourth order. We also found a marked enhancement of nonlinear dielectric constants when the applied tip-sample voltage exceeded a particular threshold value. This is due to domain nucleation activated by a huge electric field under the tip. Low frequencies (less than a few hundred hertz) do not enhance nonlinearity. An effectively lower electric field caused by ion conduction in the sample under the tip is a possible reason for the frequency-dependent characteristics of the enhanced nonlinearity for the applied voltage. Finally, electrical current flow behavior was investigated for nanodomains formed in a thin CLT single-crystal plate. When the nanodomains are relatively large, with diameters of about 100 nm, current flow is detected along the domain wall. However, when the nanodomains were about 40 nm or smaller in size, current flowed through the entire nanodomain. Schottky-like rectifying behavior was observed. A clear temperature dependence of the current is found, indicating that the conduction mechanism for nanodomains in CLT may involve thermally activated carrier hopping.

Influencing dielectric properties of relaxor polymer system by blending vinylidene fluoride–trifluoroethylene-based terpolymer with a ferroelectric copolymer

We report the influence of blending the poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) terpolymer [P(VDF–TrFE–CFE), a member of the relaxor polymer family that exhibits fast response speeds, giant electrostriction, high electric energy density, and large electrocaloric effect] with the ferroelectric poly(vinylidene fluoride–trifluoroethylene) copolymer [P(VDF–TrFE)] on its dielectric response. Although both components form separate crystalline phases, at low copolymer content, the P(VDF–TrFE–CFE)/P(VDF–TrFE) blends entirely exhibit a relaxorlike linear dielectric response, since the interfacial couplings to the bulky defects in the terpolymer convert the normal ferroelectric copolymer into a relaxor. On the other hand, the linear and particularly nonlinear dielectric experiments, i.e., temperature dependences of the second and the third harmonic dielectric response, clearly evidence that in blends with 20–50 wt. % of P(VDF–TrFE), the ferroelectric and relaxor states coexist. The nonlinear dielectric response further reveals the onset of ferroelectric behavior also in blends with low copolymer amount, due to a high VDF content in the terpolymer, which increases the ferroelectric interactions: While in relaxor polymers with lower VDF content, the third order nonlinear dielectric constant, in accordance with the theoretical predictions, exhibits solely positive values, here it changes sign even in the pure P(VDF–TrFE–CFE).

Relativistic Propagation of Linearly/Circularly Polarized Laser Radiation in Plasmas

Paraxial theory of relativistic self-focusing of Gaussian laser beams in plasmas for arbitrary magnitude of intensity of the beam has been presented in this paper. The nonlinearity in the dielectric constant arises on account of relativistic variation of mass. An appropriate expression for the nonlinear dielectric constant has been used to study laser beam propagation for linearly/circularly polarized wave. The variation of beamwidth parameter with distance of propagation, self-trapping condition, and critical power has been evaluated. The saturating nature of nonlinearity yields two values of critical power of the beam ( and ) for self-focusing. When the beam diverges. When the beam first converges then diverges and so on. When the beam first diverges and then converges and so on. Numerical estimates are made for linearly/circularly polarized wave applicable for typical values of relativistic laser-plasma interaction process in underdense and overdense plasmas. Since the relativistic mechanism is instantaneous, this theory is applicable to understanding of self-focusing of laser pulses.