Nonlinear Dielectric Susceptibility Research Articles

Linear and Nonlinear Dielectric Response of Intrinsically Disordered Proteins.

Linear and nonlinear dielectric responses of solutions of intrinsically disordered proteins (IDPs) were analyzed by combining molecular dynamics simulations with formal theories. A large increment of the linear dielectric function over that of the solvent is found and related to large dipole moments of IDPs. The nonlinear dielectric effect (NDE) of the IDP far exceeds that of the bulk electrolyte, offering a route to interrogate protein conformational and rotational statistics and dynamics. Conformational flexibility of the IDP makes the dipole moment statistics consistent with the gamma/log-normal distributions and contributes to the NDE through the dipole moment's non-Gaussian parameter. The intrinsic non-Gaussian parameter of the dipole moment combines with the protein osmotic compressibility in the nonlinear dielectric susceptibility when dipolar correlations are screened by the electrolyte. The NDE is dominated by dipolar correlations when electrolyte screening is reduced.

Colossal magneto-nonlinear-dielectric effect in magnetoelectric antiferromagnet tetracobalt diniobate

The magnetic field effect on nonlinear dielectric susceptibilities of magnetoelectric antiferromagnet tetracobalt diniobate (Co4Nb2O9) around Néel temperature (TN) is studied. Under a magnetic field of H = 5 T, the real part of second order nonlinear dielectric susceptibility χ'2 shows a valley at TN, whereas those of linear and third order nonlinear dielectric susceptibilities (χ'1 and χ'3) show peaks. The magnetic field has much more colossal effects on χ'2 and χ'3 than on χ'1. The fact that χ'3 keeps positive around TN under H = 5 T suggest discontinuousness of the magnetic field induced ferroelectric transition, but absence of thermal hysteresis on heat capacity indicates continuousness of transition. The reason why nonlinear dielectric spectra fail to identify the type of ferroelectric transition can be explained by the deviation of critical exponent β from the value for the Landau universality class.

Optical basicity, polarizability and spectroscopic investigations of CuO doped TeO2–B2O3 glass system

A study of the spectroscopic properties, as well as polarizability and optical basicity of TeO2–B2O3 glasses doped with CuO using density, XRD, and UV–Vis analysis, is presented in this paper. The TeO2–B2O3 – CuO glasses are fabricated using the melt-quenching method. The glasses proved to be amorphous in nature from the XRD which was confirmed by the UV–Vis spectra. The peak observed in the pattern of the 0% CuO sample represents the presence of a crystalline phase of α-TeO2 and/or γ-TeO2. Important optical and physical parameters are discussed such as the refractive index (2.318–2.378), metallization criterion (0.4069–0.3919), optical basicity (0.7995–0.8057), electronic polarizability (0.2358–0.2410), linear dielectric susceptibility (0.3480–0.3704 esu), and third order non-linear dielectric susceptibility (1.466 × 1012–1.882 × 1012 esu). Based on the refractive index, metallization criterion, electronic polarizability, optical basicity, and dielectric susceptibility values, the glasses could present great potential applications in fiber optics and laser applications.

Bi2WO6‐based Z-scheme photocatalysts: Principles, mechanisms and photocatalytic applications

The development of novel photocatalysts for efficient utilization of solar energy is highly essential for the most critical humanitarian challenges, i.e., energy and water crises as well as environmental pollution. Bismuth tungstate (Bi2WO6), an outstanding Aurivillius phase perovskite, has attracted intensive attention as a visible-light-responsive photocatalyst because of its non-toxicity, low cost, and outstanding physicochemical characteristics, i.e., nonlinear dielectric susceptibility, ferroelectric piezoelectricity, pyroelectricity, catalytic behavior, modifiable morphology, strong oxidation power, and good photochemical stability. However, the photocatalytic activity of bare Bi2WO6 is restricted because of the inherent drawbacks such as poor light-harvesting efficiency, weak reduction potential, relatively low specific surface area, the fast recombination rate of photoinduced charge carriers, and thus poor quantum yields of photocatalytic reactions. Moreover, the impossibility of simultaneous strong redox ability (demanding wide bandgap) and high light-harvesting efficiency (requiring narrow bandgap) is considered as a big challenge for the practical application of Bi2WO6. Undeniably, the construction of Z-scheme photocatalytic systems is recommended strategy to overcome the above-mentioned disadvantages because of the efficient spatial separation of photogenerated charge carriers and the boosting the redox performance. This review summarizes the principles and recent developments on Z-scheme photocatalytic systems with special emphasis on the Bi2WO6-based photocatalysts, including the types, photocatalytic mechanisms and practical applications. Moreover, major differences between type-II heterojunction and Z-scheme photocatalyst have also been discussed. Additionally, the significant role of unique structures (e.g., core-shell and 2D/2D) for the improvement of photocatalytic activity of Z-scheme photocatalyst has been presented. Indeed, Bi2WO6-based Z-scheme photocatalysts have exhibited superior photocatalytic activity for various applications. For example, they show high photocatalytic activity towards water/wastewater treatment (removal of organic and inorganic pollutants, as well as microorganisms), air purification (decomposition of volatile organic compounds and inorganic matters), “green” energy conversion (e.g., generation of H2 and CH4 fuels under solar irradiation), and organic synthesis. It is thought that this remarkable activity of Bi2WO6-based Z-scheme photocatalysts might be attributed to the efficient solar light harvesting, separation and further transfer of charge carriers and strong redox ability. To the best of our knowledge, the present paper is the first attempt to summarize the Bi2WO6-based Z-scheme photocatalytic reactions, providing important insights and up-to-date information for the scientific community to fully explore the potential of Bi2WO6-based photocatalysts for renewable environmental remediation, energy conversion, and chemical synthesis.

Understanding Relaxor Ferroelectrics with Simple Landau Theory

Third-order nonlinear dielectric susceptibility is measured in the paraelectric phase of Pb(Sc1/2Ta1/2)O3. The linear and nonlinear dielectric susceptibility results can be consistently explained based on the Landau-type free-energy density.

Генерация второй гармоники в поверхностном слое диэлектрической сфероидальной частицы. I. Аналитическое решение

The problem of second-harmonic generation by a plane elliptically polarized electromagnetic wave in a thin optically nonlinear surface layer of a dielectric particle shaped as an ellipsoid of revolution is solved. The generalized Rayleigh–Gans–Debye approximation is used for an analytical description with taking into account the difference in refractive indices of the medium corresponding to the frequencies of the exciting and generated radiation. The limiting forms of functions are obtained, with the use of which the electric field strength of the generated radiation is expressed. The order of dependence of these functions on the linear dimensions is found, when the lengths of the semiaxes of the particle are small compared to the wavelength of the exciting radiation and their ratio remains constant. It was found that the power density of the generated radiation in this case is determined to a greater extent by the chiral components of the nonlinear dielectric susceptibility tensor and is proportional to the fourth power of the length of the semiaxis of the particle, if the shape of the spheroidal particle differs significantly from the spherical one. The solution of this problem, obtained by other authors, is supplemented for the possibility of applying to the description of generation in the surface layer of a dielectric particle not only in the form of a prolate, but also in the form of an oblate spheroid. Corrections of inaccuracies and misprints made in similar works by other authors are proposed. The relationships between the formulas used in these works are found, taking into account the corrections and the formulas used in this work.

Second-harmonic generation in the surface layer of a dielectric spheroidal particle: I. Analytical solution

The problem of second-harmonic generation by a plane elliptically polarized electromagnetic wave in a thin optically nonlinear surface layer of a dielectric particle shaped as an ellipsoid of revolution is solved. The generalized Rayleigh-Gans-Debye approximation is used for an analytical description with taking into account the difference in refractive indices of the medium corresponding to the frequencies of the exciting and generated radiation. The limiting forms of functions are obtained, with the use of which the electric field strength of the generated radiation is expressed. The order of dependence of these functions on the linear dimensions is found, when the lengths of the semiaxes of the particle are small compared to the wavelength of the exciting radiation and their ratio remains constant. It was found that the power density of the generated radiation in this case is determined to a greater extent by the chiral components of the nonlinear dielectric susceptibility tensor and is proportional to the fourth power of the length of the semiaxis of the particle, if the shape of the spheroidal particle differs significantly from the spherical one. The solution of this problem, obtained by other authors, is supplemented for the possibility of applying to the description of generation in the surface layer of a dielectric particle not only in the form of a prolate, but also in the form of an oblate spheroid. Corrections of inaccuracies and misprints made in similar works by other authors are proposed. The relationships between the formulas used in these works are found, taking into account the corrections and the formulas used in this work. Keywords: second-harmonic generation, dielectric spheroidal particle, generalized Rayleigh-Gans-Debye model, small particle approximation, chiral component.

Second-harmonic generation in the surface layer of a dielectric spheroidal particle: II. Analysis of the solution

The vectors used in the solution of the problem of second-harmonic generation in the surface layer of a dielectric spheroidal particle are explicitly expressed in terms of the basis vectors of the spherical, cylindrical, and Cartesian coordinate systems. Three-dimensional directivity patterns characterizing the spatial distribution of the generated radiation in the far-field region and its polarization are constructed. It is found that for a small size of a spheroidal particle, the directivity pattern due to each of the non-chiral components of the nonlinear dielectric susceptibility tensor has its own individual shape. A proportional increase in the linear dimensions of the particle leads to separation of several directions of predominant radiation with a high directivity in the directivity pattern. If the exciting radiation has a linear polarization, then the generated radiation due to one (any) of the independent components of the tensor is also linearly polarized. Mathematical properties characterizing the spatial distribution of the generated radiation in the far-field region and properties associated with the change of problem parameters are found for the functions used in the solution. A relationship between the symmetries of the directivity patterns of doubled-frequency radiation and the indicated properties is revealed. The conditions under which the generation of radiation does not occur and the conditions under which the generated radiation has a linear polarization are found. The above conditions are related to the features of the spatial distribution of the generated radiation and its polarization, illustrated in the directivity patterns. Methods for estimating the independent components of the nonlinear dielectric susceptibility tensor using these conditions are proposed. Keywords: second-harmonic generation, spheroidal dielectric particle, symmetry of the spatial distribution of radiation, conditions for the absence of generation, conditions for the generation of linearly polarized radiation.

Генерация второй гармоники в поверхностном слое диэлектрической сфероидальной частицы: II. Анализ решения

The vectors used in the solution of the problem of second-harmonic generation in the surface layer of a dielectric spheroidal particle are explicitly expressed in terms of the basis vectors of the spherical, cylindrical, and Cartesian coordinate systems. Three-dimensional directivity patterns characterizing the spatial distribution of the generated radiation in the far-field region and its polarization are constructed. It is found that for a small size of a spheroidal particle, the directivity pattern due to each of the non-chiral components of the nonlinear dielectric susceptibility tensor has its own individual shape. A proportional increase in the linear dimensions of the particle leads to separation of several directions of predominant radiation with a high directivity in the directivity pattern. If the exciting radiation has a linear polarization, then the generated radiation due to one (any) of the independent components of the tensor is also linearly polarized. Mathematical properties characterizing the spatial distribution of the generated radiation in the far-field region and properties associated with the change of problem parameters are found for the functions used in the solution. A relationship between the symmetries of the directivity patterns of doubled-frequency radiation and the indicated properties is revealed. The conditions under which the generation of radiation does not occur and the conditions under which the generated radiation has a linear polarization are found. The above conditions are related to the features of the spatial distribution of the generated radiation and its polarization, illustrated in the directivity patterns. Methods for estimating the independent components of the nonlinear dielectric susceptibility tensor using these conditions are proposed.

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.

Modeling non-linear dielectric susceptibilities of supercooled molecular liquids.

Advances in high-precision dielectric spectroscopy have enabled access to non-linear susceptibilities of polar molecular liquids. The observed non-monotonic behavior has been claimed to provide strong support for theories of dynamic arrest based on the thermodynamic amorphous order. Here, we approach this question from the perspective of dynamic facilitation, an alternative view focusing on emergent kinetic constraints underlying the dynamic arrest of a liquid approaching its glass transition. We derive explicit expressions for the frequency-dependent higher-order dielectric susceptibilities exhibiting a non-monotonic shape, the height of which increases as temperature is lowered. We demonstrate excellent agreement with the experimental data for glycerol, challenging the idea that non-linear response functions reveal correlated relaxation in supercooled liquids.

Description of intermodulation generation of nonlinear responses beyond the validity of the power series expansion

Weakly nonlinear responses are commonly described by a power series expansion. However, intermodulation distortion products that cannot be described by a power series have been observed in a variety of physical systems. As the power series description is only applicable within its radius of convergence, we choose an alternative approach based on Fourier coefficients to describe intermodulation levels beyond the convergence of the power series. The description over a wide power range allows us to make a decision about models and to determine previously inaccessible model parameters. We apply the approach to data obtained from the characterization of the nonlinear dielectric susceptibility of a glass ceramic in the microwave range. The data are accurately modeled by a saturable absorber's response. We obtain the absorber's linear contribution to the polarization (χ1=10−5) as well as its characteristic ratio of nonlinear and linear polarization (χ3/χ1=10−9 m2/V2). Due to the small contribution of the saturable absorber to the overall polarization, the material shows a highly linear response (χ3=10−14 m2/V2).

Наведенное двулучепреломление в квантовых точках CdSe в матрице фосфатного стекла

In this paper, we report on the experimental observation of light-induced anisotropy (the optical Kerr effect) due to third-order nonlinear dielectric susceptibility (3) in a nanocomposite material consisting of CdSe quantum dots in a phosphate glass matrix. The signs and values of the off-diagonal components of the tensor (3) are determined using z-scanning techniques and nonlinear ellipsometry. It was shown that the nonlinear response contains three time components, the fastest of which does not exceed 20 ps, the average has an exponential form and amounted to 90 11 and 38530 ps for different samples, and the longest nonexponential and amounts to times of the order of a few nanoseconds. The switching of an optical signal with a time not exceeding 20 ps is demonstrated.

Генерация второй гармоники-суммарной частоты в тонком сферическом слое: III. Свойства решения

Mathematical properties of functions characterizing symmetries of spatial distribution of second harmonic–sum frequency radiation are determined. The conditions at which there occurs no generation and the conditions at which the polarization of the generated radiation is linear are found. The revealed properties are systematized by their manifestations in the directivity patterns of the generated radiation. Methods based on these properties for determining the components of the nonlinear dielectric susceptibility tensor are proposed. The relationship is described between the revealed properties as well as conditions and previously found similar properties and conditions for the phenomena of second–harmonic generation and sum–frequency generation.

The composition induced crossover in nonlinear dielectric response in (1\u2009\u2212\u2009x) Pb(Zr0.70Ti0.30)O3\u2013x BiMn2O5 (x\u2009=\u20090, 0.02, 0.055, 0.11, 0.15, 0.22, and 1) ceramics

Ceramics based on lead zirconate-titanate Pb(Zr0.70Ti0.30)O3 (PZT), bismuth manganite (BM) and the composite (1 − x) PZT–x BM were obtained. A systematic study of linear and nonlinear dielectric susceptibilities temperature and frequency dependences was conducted. A composition-induced crossover in nonlinear dielectric susceptibility was detected. The so-called scaled nonlinear susceptibility, a3, was obtained from experimental values of the real part of the linear and third-order nonlinear dielectric susceptibilities. The value for a3 was negative for low BM content in the whole temperature range specific to discontinuous ferroelectric phase transitions and relaxor behavior. In contradiction, a3 was positive for BM and for the composite with sufficiently high BM content. The positive a3 was attributed to a subsystem of dipoles created by trapped charges. Hopping charge transfer, which is a dominant mechanism for conduction in manganites, is responsible for the positive a3 and for the colossal magnitude of the imaginary part of the linear dielectric susceptibility. The concentration of the ions was determined using scanning electron microscopy. The chemical disorder and the precipitation of ions determined using time of flight–secondary ion mass spectrometry correspond to a crossover in the electrical features.

Study of the linear and nonlinear response properties of the zinc-blende AlP, GaP and their AlxGa1-xP ternary alloys using first principle calculations

The structural, electronic, thermodynamic, vibrational, elastic, linear and nonlinear optical properties of AlxGa1-xP ternary alloys are studied using plane-wave pseudopotential method based on the density functional theory. The alchemical mixing method is used to construct an alloy by mixing the pseudopotentials in an appropriate way. The local density approximation is used for the exchange and correlation potentials calculations using the ABINIT code. The Born effective charges, phonon frequencies, longitudinal-transvers optical splitting and thermal properties are calculated using density functional perturbation theory. By applying the many-body effects within the Bethe-Salpeter approach using the Tam-Dancoff approximation, the frequency-dependent macroscopic dielectric function is calculated. The nonlinear dielectric (electronic) susceptibility, the electro-optic tensor and the Raman tensor are investigated in the framework of density functional perturbation theory using the 2n+1 theorem. Moreover, due to density functional theory band gap problem, the band-gap correction is performed within the one-shot GW approximation of many-body perturbation theory. The calculated results of AlP and GaP compounds are in acceptable agreement with available theoretical and experimental results, so the present study on the AlxGa1-xP alloys would be helpful for future experimental and theoretical investigations.

Second-Harmonic Generation from a Thin Cylindrical Layer: II. Analysis of Solution

The problem of second-harmonic generation by a plane elliptically polarized electromagnetic wave from a thin optically nonlinear layer on the surface of a cylindrical dielectric particle of finite dimensions placed in a dielectric medium has been solved analytically in the Rayleigh–Gans–Debye approximation. The result has been presented in the tensor and vector forms in the general case, in which the nonlinear dielectric susceptibility tensor has four independent components (one chiral component and three nonchiral components). It has been shown for the first time that the contribution of chiral components to the generation from the butt-end surfaces of a cylindrical particle differs in phase from the contribution of nonchiral components. It has also been revealed that, if the linear dimensions of a cylindrical particle (height and base radius) are small, the radiation determined by the chiral component of the second-order nonlinear dielectric susceptibility tensor makes a predominant contribution to the second-harmonic generation from a nonlinear cylindrical layer (butt-end and lateral surfaces).

Elucidation of dipolar dynamics and the nature of structural phases in the [(CH3)2NH2][Zn(HCOO)3] hybrid perovskite framework

We demonstrate improper ferroelectric and non-relaxor behaviour of the [(CH3)2NH2][Zn(HCOO)3] hybrid perovskite framework.

Генерация второй гармоники от тонкого цилиндрического слоя. I. Аналитическое решение

In the Rayleigh–Gans–Debye approximation an analytical solution is obtained for the problem of second harmonic generation by a plane electromagnetic wave with elliptical polarization from a thin optically nonlinear layer on the surface of a cylindrical dielectric particle of finite size placed in a dielectric. The result is presented in tensor and vector forms in general case, in which the nonlinear dielectric susceptibility tensor has four independent components (one chiral and three non-chiral). For the first time it is shown that at generation from the end plane surfaces of a cylindrical particle the contribution of chiral components differs in phase from that of non-chiral components. It is also found that for small linear dimensions of the cylindrical particle (height and radius of the base), the radiation due to the chiral component of the second-order nonlinear dielectric susceptibility tensor makes a dominant contribution to the second harmonic generation from a non-linear cylindrical layer (end and side surfaces).

Nonlinear dielectric constant in Pb(Mg1/3Nb2/3)O3–PbTiO3 relaxor ferroelectrics

The nonlinear dielectric constant ε3 induced by the cube of the electric field was investigated in the paraelectric phase of the relaxor ferroelectric 70.5% Pb(Mg1/3Nb2/3)O3–29.5% PbTiO3. ε3 was confirmed to be positive near Tm at which the linear permittivity is maximum, and becoming negative at 158.5 °C. The temperature dependences of the linear and nonlinear dielectric susceptibilities are discussed on the basis of the Landau-type free energy function.