Dielectric Susceptibility Research Articles

The hydrostatic pressure dependence of the phase transitions and dielectric properties for a potassium niobate crystal

The phase transitions, spontaneous polarizations, and dielectric properties of a potassium niobate (KNbO3) ferroelectric crystal were investigated under hydrostatic pressure from 0 to 21.3 GPa using the Landau–Ginsburg–Devonshire phenomenological theory. It was shown that the phase transition temperatures of cubic to tetragonal, tetragonal to orthorhombic, and orthorhombic to rhombohedric decreased as the hydrostatic pressure was increased and the derivative of the phase transition temperatures with respect to hydrostatic pressure could be estimated to be −33.1 °C/GPa. The spontaneous polarizations decreased nonlinearly with increasing hydrostatic pressure which could be attributed to the hydrostatic pressure-induced decrease of the interionic distance. The dielectric susceptibility ε33 increased by about 85% and the dielectric susceptibility ε11 decreased by about 50% when hydrostatic pressure increased from 0 to 4 GPa at 260 °C. It provides a new effective way to improve the pressure sensitivity in acoustic transducer and the energy storage performance of capacitor. The changes of dielectric susceptibilities induced by hydrostatic pressure had been explained by the flattening or steepness of Gibbs free energy profile. As the properties of the ceramics are related to those of the single crystal, results in this paper can be used to explore the general rule of performance change induced by pressure for lead free KNbO3-based ceramics.

Nonlinear optical properties of a slab of CdSe/ZnS quantum dot matrix

In this paper linear and nonlinear optical dielectric function of a slab of CdSe/ZnS quantum dot matrix associated with intersubband transitions is investigated theoretically. To this end, by using effective mass approximation and density matrix, the electronic structure and dielectric function of quantum dots are calculated. Afterwards, the Clausius-Mossotti relation and TKF model is used to calculate the effective dielectric function and susceptibility of slabs of ffc and randomly ordered quantum dots. The dependence of dielectric function, susceptibility, refractive index (RI) and absorption coefficient (AC) of the slab on the size and density of quantum dots have been studied. The results show that for all radii the AC and RI of fcc ordered quantum dots have higher magnitude than randomly ordered ones. It is also found that magnitude of the dielectric function of the slab increases by increasing radius and intensity. At fixed radii the dielectric function, RI and AC increases by increasing number density of quantum dots in the slab.

Mechanical spectral hole burning of an entangled polymer solution in the stress-controlled domain.

Nonresonant spectral hole burning has proven to be a versatile method to characterize the dynamics of complex fluids, including polymers. Early work focused on dielectric susceptibility measurements in glass forming liquids, while recent work from our lab used mechanical viscoelastic measurements to investigate polymer melts and solutions. While the observed results were similar, the interpretations were different, with the former being interpreted by attributing the "holes" in the response as being due to dynamic heterogeneity in the system that is related to the glass or other transition, while the latter was interpreted in a way that suggested that the observed holes depend on the type of dynamics (Rouse, terminal, etc.) rather than an identifiable spatial heterogeneity. In this work, we have expanded mechanical spectral hole burning (MSHB) into the stress-controlled domain and carried out experiments in the rubbery regime of a polystyrene solution, similar to one which was tested previously with strain-controlled MSHB. The effects of pump stress amplitude, pump frequency, and waiting time were investigated. The mechanical holes in both directions (vertical and horizontal) were successfully burned, unlike the strain-controlled MSHB experiments on the same polystyrene solution, in which vertical holes were at best incomplete. The hole intensity exhibits a linear relationship with the amount of energy dissipated in the system during the large mechanical pump modification. The results suggest that the stress-controlled MSHB can be combined with strain-controlled MSHB to build a more complete framework to investigate the dynamics of polymeric materials and is consistent with the dynamic heterogeneity being related to the type of dynamics rather than to localized heating effects.

Effect of uniaxial stress on phase transitions and dielectric properties of potassium niobate ferroelectric single crystal

The uniaxial compression stress dependence of the phase transitions and dielectric properties of a potassium niobate (KNbO3) ferroelectric crystal were investigated using Landau–Ginsburg–Devonshire phenomenological theory. The results showed that (1) uniaxial stress along [001]c could induce a spontaneous polarization change from the [001]c direction to the [010]c or [100]c directions and from the [011]c, [101]c directions to the [110]c direction; (2) the cubic to tetragonal and the tetragonal to orthorhombic phase transition temperatures increased, while the orthorhombic to rhombohedral phase transition temperature decreased as the uniaxial stress was increased; and (3) spontaneous polarization increased as the uniaxial stress was increased for the tetragonal and orthorhombic phases. The uniaxial stress dependence of the dielectric susceptibility also showed that a flatter Gibbs free energy profile corresponds with a greater expandability, contractibility, and rotationality of the polarization (which indicates a higher dielectric susceptibility), while a steeper Gibbs free energy profile corresponds with a reduced expandability, contractibility, and rotation of the polarization (which indicates a lower dielectric susceptibility).

Scanning differential microscopy for characterization of reflecting phase-gradient metasurfaces

Gap-plasmon based phase-gradient metasurfaces operating in reflection are widely used for the realization of diverse flat optical components, ranging from spectropolarimeters to efficient couplers for surface waves. Successful implementation of carefully designed metasurfaces is however often hampered by technological imperfections that could be related to deviations of geometrical parameters of fabricated nanostructures from the designed ones or material properties, such as the metal and/or dielectric susceptibilities, from the handbook data. While the overall performance of fabricated components might indicate the existence of a potential problem, it is very difficult to identify its origin, which, for example, can simply be related to the deviation in only one cell of the metasurface supercell. We suggest exploiting well-developed experimental techniques of scanning differential heterodyne microscopy (SDHM) to characterize fabricated phase-gradient metasurfaces designed to operate in reflection. We further establish that, by carefully measuring the SDHM response of a gradient metasurface, one should be able of detecting small (∼5%) amplitude and phase deviations (with respect to the design values) in the optical field reflected by an individual subwavelength-sized cell of the metasurface supercell.

Thomson scattering in inhomogeneous plasmas: The Role of the Fluctuation-Dissipation Theorem

A self-consistent kinetic theory of Thomson scattering of an electromagnetic field by a non-uniform plasma is derived. We draw the readers’ attention to the inconsistency in recent results on the Thomson scattering in inhomogeneous plasma, which leads to violation of the Fluctuation-Dissipation Theorem. We show, that not only the imaginary part, but also the derivatives of the real part of the dielectric susceptibility determine the amplitude and the width of the Thomson scattering spectral lines. As a result of inhomogeneity, these properties become asymmetric with respect to inversion of the sign of the frequency. A method is proposed for measuring local gradients of the electron density with the aid of Thomson scattering.Arising from: P. Kozlowski, et al. Sci. Rep. 6, 24283 (2016); https://doi.org/10.1038/srep24283.

Coupled dielectric permittivity and magnetic susceptibility in the insulating antiferromagnet Ba2FeSbSe5

We report on coupled changes in the dielectric permittivity and the magnetic susceptibility in the insulating antiferromagnet Ba2FeSbSe5. The real part of the dielectric permittivity (ε′) and the thermal conductivity (κ) shows pronounced anomalies at the Néel temperature (TN). Our findings show that there is a weak coupling between electric dipoles and magnetic spins, which is mediated by spin-lattice coupling possibly through exchange striction effects.

Theory of Thomson scattering in inhomogeneous plasmas.

A self-consistent kinetic theory of Thomson scattering of an electromagnetic field by a nonuniform plasma is derived. We show that not only the imaginary part, but also the time and space derivatives of the real part of the dielectric susceptibility determine the amplitude and the width of the Thomson scattering spectral lines. As a result of inhomogeneity, these properties become asymmetric with respect to inversion of the sign of the frequency. Our theory provides a method of a remote probing and measurement of electron density gradients in plasma; this is based on the demonstrated asymmetry of the Thomson scattering lines.

Hysteresis loops and dielectric properties of a mixed spin Blume–Capel Ising ferroelectric nanowire

The critical and hysteresis behaviors of a ferrielectric Blume–Capel nanowire are studied using the Ising model with mixed spins-(12, 1) in the presence of both an external longitudinal electric (Ez) and crystal anisotropy (D) fields. We use the Monte Carlo simulations (MCs) to examine the influence of Ez, D and the exchange interactions on the compensation and critical temperatures, the specific heat, the dielectric susceptibility and the internal energy of the system. Our theoretical predictions are in accordance with some experimental and theoretical results.

Nuclear Magnetic Resonance Spectroscopy

n/a

Electrowetting of Liquid Drops Revisited By XPS

Electrowetting behavior of liquid drops has been followed in-situ and in-vacuum using XPS in a chemically resolved fashion, under both D.C. and A.C. excitations. Various liquid drops, compatible with the UHV conditions, consisting of an Ionic Liquid, DEME-TFSI, [N,N-Diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide]), or Poly-Ethylene-Glycol (PEG, M.W. ~600 amu) and their mixtures. For the dielectric substrate, a ~300 nm thick silicon oxide (SiO2/Si) without and with a thin (~20 nm) hydrophobic amorphous fluoropolymer coating, CYTOP (Bellex International Co.), has been employed. XPS data have been recorded both in the conventional scan and also in the fast (<1s) snap-shot modes. Intensity and position of the peaks, representing the liquid drops (F1s in the case of the IL, or C1s/O1s of the PEG) as well as those of the substrates (Si2p for the oxide only and F1s for the hydrophobic coated one) have been recorded under various electrical excitations. Under AC excitation at a fixed frequency, intensity modulations in the XPS peaks reveal geometrical changes of the drops, while the peak position modulations reveal electrical potentials developed. Monitoring binding energy modulations as a function of the changes in the AC frequency (10-2 – 104 Hz) allows us tap into ionic, dipolar and electronic contributions of the dielectric susceptibility of both the liquid drops and the substrates. Experimental details and various applications will be presented and discussed. This work is partially supported by TUBITAK through Grant No. 215Z534

Simple model of coherent anti‐Stokes Raman scattering signals generated by means of linearly chirped ultrashort Gaussian laser pulses

AbstractTime and frequency dependences of coherent anti‐Stokes Raman scattering (CARS) are here found analytically for the increasingly popular experimental approach where the Raman preparation and probing are realized by means of very short linearly chirped laser pulses. These are chosen with Gaussian lineshapes that, besides being rather common in ultrashort laser physics, guarantee full solution to the nonlinear scattering problem at hand. The solution appears rather simple in spite of the complications arising from the treatment of optical nonlinearities of different nature (dielectric susceptibility of the third order for the Raman medium and quadratic phases of three laser fields). The simplicity of the solution allows versatile applications that are here shown for different chirp effects in vibrational and purely rotational N2 CARS whose spectral complexity provides an excellent ground to test the model. The comparison with known experiments shows a good agreement except for some limitations imposed by deviations of the nonresonant CARS signal from the Gaussian structure assumed in the model.

Nonlinear Dielectric Response of Nanocomposites Based on Potassium Dihydrogen Phosphate

Nonlinear properties of nanocomposites based on KH2PO4 embedded in nanosized silica matrices with pore sizes of 2.6 and 3.8 nm were investigated. It was found that the structural phase transition temperature for KH2PO4 nanoparticles was higher than that for bulk KH2PO4. Investigations of temperature dependence of the second ( $$\upchi_{2}^{\prime }$$ )- and third ( $$\upchi_{3}^{\prime }$$ )-order dielectric susceptibilities showed the presence of nonlinear properties in the paraelectric phase for the bulk and nanocomposite samples.

Is there a spontaneous ferroelectric phase transition in 0.83PbMg1/3Nb2/3O3-0.17PbTiO3 single crystal?

The macroscopic response of 0.83PbMg1/3Nb2/3O3-0.17PbTiO3 (PMN-17PT) single crystals has been investigated in order to resolve existing controversy about the structural phase transition in the rhombohedral side of (1-x)PbMg1/3Nb2/3O3-xPbTiO3 phase diagram. The combination of nonlinear dielectric spectroscopy, temperature dependant polarization and strain hysteresis loop measurements and ultrasonic spectroscopy revealed that ferroelectric phase occurs spontaneously in PMN-17PT single crystals. The experimental techniques applied in this work probe the bulk of the sample and can unambigously determine the existence of a spontaneous ferroelectric phase.The experiments showed that zero-field cooled sample has a normal ferroelectric hysteresis loop at room temperature. The electric-field dependence of induced polarization revealed that at a certain electric field the sample undergoes transformation from polydomain to monodomain-like states. The 1 s t order phase transition at 330 K was evidenced by the third order nonlinear dielectric susceptibility for monodomain sample. The nonlinear dielectric response of an unpoled sample does not show such abrupt jump and is more similar to the response of canonical relaxor PbMg1/3Nb2/3O3.Zero-field heating and zero-field cooling experiments also revealed very slow domain formation processes appearing at 300–320 K temperature. They are affected by the experimental conditions. There are evidences that on cooling the domains tend to grow in the sample.

Gaussian field model for polar fluids as a function of density and polarization: Toward a model for water.

This work is concerned with a simple model for a polar fluid, a Gaussian field model based on the excess density and on the polarization. It is a convenient framework to implement the dielectric properties of correlated liquids that stem from nanometric correlations between molecules. It allows us to study the effects of coupling terms between density and polarization on the structure of the fluid. Despite the simplicity of such a model, it can capture some interesting features of the response functions of water such as the quasi-resonant longitudinal dielectric susceptibility or the presence of two maxima in the structure factor. Explicit models of water generate high computational cost and implicit models sometimes fail to properly treat the electrostatic interactions. A Gaussian field theory could therefore be an interesting alternative to describe water.

Correlation between intensity fluctuations of polychromatic electromagnetic light waves on weak scattering

In the analysis of the correlation between intensity fluctuations (CIF) of light waves on scattering from a medium, it is implicitly assumed that the incident field is monochromatic. However, under usual circumstances, the field always has a certain frequency width. We examine the CIF of polychromatic electromagnetic light waves on scattering. It is found, in general, that the frequency components of the CIF may change on scattering from a medium whose dielectric susceptibility is a random function of position. The critical angle at which no frequency shift arises is introduced and the corresponding analytic expression is derived. The result shows that the critical angle is dominated by the physical properties of the medium and the source. Finally, we propose a scaling law for the normalized CIF for the scattering of polychromatic electromagnetic light waves. Our theory can be regarded as the vectorial extension of the scalar theory of Wolf et al. [E. Wolf, J. T. Foley, and F. Gori, J. Opt. Soc. Am. A 6, 1142 (1989)].

Comparative Investigation of the Thermoresponsive Behavior of Two Diblock Copolymers Comprising PNIPAM and PMDEGA Blocks.

The thermoresponsive behavior of two diblock copolymers PS- b-PNIPAM and PS- b-PMDEGA, which both comprise a hydrophobic polystyrene (PS) block but different thermoresponsive blocks, also differing in length, poly( N-isopropylacrylamide) (PNIPAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA), respectively, was comparatively investigated in a wide temperature range. Concentrated aqueous solutions containing 25 wt % polymer were studied by small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS). DSC measurements show that, during the demixing phase transition, the hydration number per oligo(ethylene glycol) side chain in the PS- b-PMDEGA solution decreases rather gradually, even up to 20 °C above the onset of the transition, i.e., the cloud point (CP). In contrast, the PS- b-PNIPAM solution exhibits an abrupt, stepwise dehydration behavior at its CP, indicated by the sharp, narrow endothermic peak. BDS measurements suggest that the organization of the expelled water during the phase transition and the subsequent evolution of the micellar aggregates are different for the two copolymers. In the PS- b-PMDEGA solution, the long-range charge transport process changes significantly at its CP and strong interfacial polarization processes appear, probably due to charge accumulation at the interfaces between the micellar aggregates and the aqueous medium. On the contrary, in the PS- b-PNIPAM solution, the phase transition has only a marginal effect on the long-range conduction process and is accompanied by a reduction in the high-frequency (1 MHz) dielectric permittivity, ε'. The latter effect is attributed to the reduced polarization strength of local chain modes due to an enhancement of intra- and interchain hydrogen bonds (HBs) in the polymer-rich phase during the water detaching process. Surprisingly, our BDS measurements indicate that prior to both the demixing and remixing processes the local chain mobility increases temporally. Our dielectric studies suggest that for PS- b-PNIPAM the water detaching process initiates a few degrees below CP and that the local chain mobility and intra- and/or interchain HBs of the PNIPAM blocks may control its thermoresponsive behavior. Dielectric "jump" experiments show that the kinetics of micellar aggregation in the PS- b-PMDEGA solution is slower than that in the PS- b-PNIPAM solution and is independent of the target temperature within the two-phase region. From the experimental point of view, it is shown that the dielectric susceptibility, especially, the dielectric permittivity, ε', is a well-suited probe for monitoring both the reversible changes in the molecular dipolar bond polarizability and the long-range interfacial polarization at the phase transition.

Higher-order Landau phenomenological models for perovskite crystals based on the theory of singularities: a new phenomenology of BaTiO3

ABSTRACTThe higher-order Landau phenomenological models for perovskite crystals based on the theory of singularities are proposed. The structural stabilities of some Landau potentials proposed for the phenomenology of BaTiO3 until now are discussed in the framework of the singularity theory. We confirm that the structurally stable Landau potential has to contain at least all the invariants up to the eighth power when the three parameters vary in the experiment. We propose the 10th-order Landau potential for adequate description of the various experimental data for BaTiO3 crystal. We show that the results of the phenomenology based on the 10th potential are in good agreement with the experimental data on spontaneous polarization, dielectric constants, dielectric susceptibility and piezoelectric coefficients versus the temperature and the electric field.

Full-waveform inversion using a stepped-frequency GPR to characterize the tack coat in hot-mix asphalt (HMA) layers of flexible pavements

The use of tack coats in the construction of road structures is a technique that ensures pavement layer bonding. Unfortunately, existing techniques commonly used in France to estimate tack coat conditions require coring structures for ad hoc characterization in the laboratory. This paper investigates a non-destructive approach to characterize changes in geometric and dielectric properties of the tack coats present inside the hot-mix asphalt (HMA) layers of flexible pavements, with the use of a stepped-frequency radar combined with a mono-static, off-ground, ultra-wideband Vivaldi antenna. The principle of this method is to consider the flexible pavement as a multi-layered medium with changing properties (thicknesses, dielectric susceptibilities and dispersion parameters). Then a full-waveform inversion is applied, which allows for the extraction of the dielectric and geometric parameters of each layer composing the structure. Following numerical validations, the multi-layered forward model, namely, a Green's function model integrating the 2-parameter variant of Jonscher's model, combined with Lambot's et al. radar full-wave method was experimentally validated using calibrating media (up to three layered media). Then, the link between both the dielectric and the geometric parameters of the tack coats and the emulsion quantity (bonding) was analyzed. The results showed good agreement between measured and modeled radar data. Radar data inversions showed in particular that the dielectric susceptibility and thickness of the transition zone increase with the emulsion quantity. Future research will focus on the establishment of a reference database of calibration curves linking dielectric susceptibility and tack coat characteristics.

Intelligent System for Active Dielectrics Parameters Research

The structure of the intellectual system and methods of automated measurements of active dielectric parameters are proposed. The intelligent system automates the process of measuring the dielectric parameters of materials depending on the temperature and electric field strength; decides on the choice of measurement methods; processes the measurement results and calculates the porosity of the measurement results. The original methods of measuring the capacitance and the active component of the resistance of a ferroelectric capacitor characterizing its dielectric losses are developed. Both methods are based on the modification of the Sawyer-Tower scheme proposed by the authors. The intelligent system implements methods for measuring the temperature dependences of the dielectric parameters of the active dielectrics. The algorithms, based for the methods, are founded on the measurement of the inverse dielectric susceptibility depending on temperature and are different for ferroelectrics with the phase transition of the first and second kind. These methods allowed to increase the measurements efficiency 3 times by reducing the number of measurement procedures, performing measurements in a narrow temperature range and modeling dielectric parameters in the desired temperature range.