Narrow Results

The Lifshitz theory provides a semiclassical description of the Casimir–Polder atom-plate interaction, where the electromagnetic field is quantized, whereas the material of the plate is considered as a continuous medium. This places certain restrictions on its application regarding the allowable atom-plate separation distances and the dielectric properties of the plate material. Below, we demonstrate that in some recent literature the application conditions of the Lifshitz theory established by its founders are violated by applying it at too short separations and using the dielectric permittivities possessing the negative imaginary parts in violation of the second law of thermodynamics.

The experiment investigated the dielectric properties of copper ferrite nanoparticle-doped cotton and cotton–polyester mixture and observed the higher dielectric permittivity of cotton–copper ferrite nanoparticles mixture than the cotton–polyester–copper ferrite nanoparticles mixture. This work describes the effects of copper ferrite nanoparticles on the dielectric properties of cotton and cotton–polyester mixture theoretically. The real and imaginary parts of the complex dielectric permittivity as function of temperature and concentration of copper ferrite nanoparticles are calculated. The decrease of dielectric permittivity of cotton–copper ferrite nanoparticles mixture and cotton–polyester–copper ferrite nanoparticles mixture with the increase of frequency has been observed. The comparison between theoretical and experimental results has been presented.

Additional information is provided on the effect of the significant (up to 35%) reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film which was observed after UV treatment of the latter. A striking feature of this effect is that the reduction is not accompanied with a corresponding variation of the dielectric permittivity, as confirmed by direct ellipsometry measurements. The measurement data are compared with computations using the Lifshitz theory. It is shown that the data for the untreated sample are in a very good agreement with theory taking into account the free charge carriers in the indium tin oxide. The data for the UV-treated sample exclude the theoretical results obtained with account of free charge carriers. These data are found to be in a very good agreement with theory disregarding the free charge carriers in an indium tin oxide film. A possible theoretical explanation of our observations as a result of phase transition of indium tin oxide from metallic to dielectric state is discussed in comparison with other related experiments.

Sm-doped BaTiO₃ thin films with ~200 nm thickness fabricated by rf magnetron sputtering system onto Pt/Ti/SiO₂/Si substrates have been investigated. The effects of postannealing and the dopant content in a range of 0.1 to 2.2 at.% on microstructure and electrical properties were studied. The films were found to be amorphous in the as-deposited state and became fully crystallized after annealing at 750°C and above. The addition of Sm in the BaTiO₃ films resulted in the inhibition of grain growth. Electrical characterizations show that the dielectric permittivity increased with increasing annealing temperatures and the 2.2% Sm-doped film had the low leakage current of 1.29×10^-9 A at an applied electric field of 100 KV/cm.

Ab initio density functional calculations are performed to investigate the dielectric properties of LnBSiO₅ (Ln = Ce, Pr, Nd) with the stillwellite structure. The calculated structural parameters are found to agree well with existing experimental results. The three compounds possess insulating electronic structure with nearly isotropic high frequency dielectric permittivity tensors. On the other hand, the static dielectric permittivity tensors are found to be less isotropic. The anisotropy of static dielectric tensors are found to increase as the atomic number of the lanthanide increases.

The temperature and pressure dependence of the static dielectric permittivity in the isotropic phase of the isotropic to cholesteric phase transition is calculated using Landau–de Gennes’s fluctuation theory, allowing spatial variation of the orientational order parameter. A comparison is made with experimental data available in the isotropic phase of the isotropic to cholesteric phase transition.

The permittivity as a function of temperature and dc bias in the poly(vinylindene fluoride-trifluorethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer was measured and analyzed using both the Vogel–Fulcher and universal Curie–Weiss law. The decreased permittivity with increasing dc bias has been observed. The lower permittivity in dc bias is due to the suppressed diffusion of phase transition rather than the nonlinear dielectric contribution. Furthermore, the suppression of phase diffusion can be explained by the molecular conformation conversion in dc bias.

Within the density functional theory, the Hartree–Fock/Kohn–Sham-coupled perturbation method using the basis of localized orbitals, the gradient PBE functional with dispersion correction D3(BJ) and hybrid PBE0 and B3LYP functionals, the structural, dielectric, and piezoelectric properties of hexagonal alkali fluorocarbonates ABCO₃F (A: K, Rb, Cs; B: alkaline earth (Mg, Ca, Sr) and $d^{10}$ (Zn, Cd, Pb)) were evaluated. In the series of crystals, fluorocarbonates with lead have the highest values of the calculated components of the dielectric constant tensor, piezoelectric constants, and nonlinear optical (NLO) coefficients.

In this work, an attempt has been made to correlate the dielectric permittivity of polyacrylamide based tissue mimicking phantoms with their mechanical properties such as breaking stress, breaking strain and Young's modulus. The tissue mimicking phantoms of various concentrations were prepared as per the standard protocol and their permittivity was measured using a precision impedance analyzer. The mechanical properties of the phantoms were measured by conducting tensile tests using a Universal Testing Machine. The measured mechanical properties were correlated with the dielectric permittivity by performing statistical analysis. Results demonstrate that the percentage variation in the mechanical properties correlate well with the percentage variation in the permittivity of the tissue mimicking phantoms. Further, it appears that the changes in the mechanical properties of the phantoms can be estimated by quantifying the changes in their dielectric permittivity. In this paper, the objectives of the study, methodology and significant observations are discussed in detail.

The anomalous electrodynamic characteristics (dielectric permittivity and electrical conductivity) of MRET water subjected to applied EMF (electromagnetic field) in the area of a very low range of frequencies were discovered during experiments conducted at Moscow State University, Russia. This confirmed the high level of long range dynamic structuring of water molecules in polarized-oriented multilayer formations in activated water produced with the help of the MRET activation process. The similarity of molecular formations of cell water and MRET-activated water contributes to their compatibility, easy bioavailability and assimilation of MRET-activated water into biological systems. The introduction of MRET water into biological systems can contribute to the enhancement of the cellular transduction mechanism and the proper functioning of cells in biological systems. The significant positive effect of MRET-activated water regarding tumor resistance in animals was observed in experiments conducted on 500 mice at Kiev Institute of Experimental Pathology, Oncology and Radiobiology, Ukrainian Academy of Science.

In this paper, we show the possibility of rebuilding of the structure of wave vector surface and the appearance of its local parts with near zero curvature for epsilon-near-zero hyperbolic metamaterials. It is established that when evanescent Bessel light beam falls in special directions related to these local parts, it is transformed into propagating one. The features of transformed beam are analyzed.

2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanines were synthesized from 4-(4-amino-3-nitrophenoxy)phthalonitrile which was obtained from 4-nitro-1,2-dicyanobenzene and 4-amino-3-nitrophenol. 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) were synthesized in a one-step condensation reaction of ferrocenylaldehyde with 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), respectively. The novel compounds were characterized by elemental analysis, Inductively Coupled Plasma (ICP-MS), UV-vis, IR and ¹H NMR spectroscopy. The effects of temperature and frequency on the conduction properties (a.c. and d.c.) and the dielectric constant were studied on pellet samples of 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), with evaporated, ohmic gold electrodes in the frequency range 40-10⁵ Hz. and within the temperature range 290-400 K. Unlike many metallophthalocyanines, a variable-range hopping model is found to most appropriately fit the experimental conductivity data of 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), while for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), thermally activated conduction with single activation energy is valid. Frequency and temperature dependence of the a.c conductivity were analyzed in terms of existing theory for 2,9,16,23-tetra-(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II). It was found that the a.c. conductivity of the compounds depends on the frequency, obeying the empirical formula, σ_ac = A(T)ω^s. The model parameters calculated are reasonable and consistent with the prediction of the correlated barrier hopping model for 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) and the quantum mechanical tunneling model for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II). The dielectric constant of the compounds increased with temperature and decreased with frequency in the investigated range.

This paper conducts theoretical study on the mechanical, thermal and electrical properties of graphene reinforced composites by effective medium theory (EMT). Considering the imperfect bonding between the reinforcing fillers and the matrix, an interphase surrounding the graphene fillers is introduced during the EMT modeling. The coated graphene fillers are homogenized as effective reinforcements dispersed in a matrix. The EMT model is validated by comparing the predicted material properties with previously reported results. Parametric study is carried out to investigate the influences of several parameters, including concentration and geometry of graphene fillers, the attributes of the introduced an interphase and the alternating current (AC) frequency, upon the effective material properties of the reinforced composites. The results demonstrate that the increase of the thickness of the interphase results in the decrease of Young’s modulus, thermal conductivity and electrical conductivity of the composites while it is favorable to enhance the dielectric properties of the composites. The increase in the aspect ratio of the graphene filler enhances all material properties involved. Percolation behaviors are observed for the dielectric properties of the composites. Moreover, the dielectric properties of the composites are very sensitive to the change of the AC frequency within a certain range, which suggests the achievement of active tuning of material properties.

Specific features of the dielectric response of colloid systems with electrically interacting components (polar liquid matrix and solid spherical inclusions) have been revealed. A theory was developed to describe dielectric dispersion and anisotropy of the liquid phase caused by the electric field of surface charges on the solid particles. It was found that the local dielectric permittivity in different directions can vary over a wide range and strongly depends on the strength of the inner field. The existence of the interphase interaction leads to the formation of thin structured liquid layers in the contact area of two phases and, therefore, to a decrease in the average dielectric permittivity of the considered system. Nonuniform structure of the polar liquid was taken into account while the derivation of a mixing formula which clearly demonstrates the contribution of the interphase interaction to the dielectric response of the investigated colloid system.

This paper presents a study of the structure and microwave properties of substituted into the Ti⁴⁺ site of calcium titanate ceramics. The structural and dielectric properties of solid solutions in CaTi_1-x(Nb_1/2Fe_1/2)_xO₃, was done. The microwave dielectric properties of solid solutions in CaTi_1-x(Nb_1/2Fe_1/2)_xO₃, (CNFTOX with x = 0.1 to x = 1) is discussed. The modified CaTiO₃ (CTO) ceramics were prepared by a new procedure in the solid-state method. A study of the variations of the ball-milling process was done. The calcinations were done at 900°C for 3 and 5 h respectively, and the sintering at 1100°C, for 3 h. The structural property studies of the ceramics were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The X-ray analysis showed that all samples have an orthorhombic structure. The refinement analysis of all samples were also duly performed and discussed. The nine scattering bands centered at 183, 227, 247, 288, 338, 470, 490 and 805 cm^-1 were observed. Several peaks presented a small shift as a function of the x value. All Raman spectra in the studied samples showed a small band at 805 cm^-1, which is a function of the x value. The dielectric permittivity and loss at microwave frequencies (MW) were investigated. For both calcination treatments (900°C for 3 and 5 h), the dielectric permittivity decreased with a decrease of the titanium content. Dielectric permittivity values in the range of 20 to 80 were obtained. It was also observed that a higher number of balls in the milling process contribute to the increase of the ε_r values. The CNFTO has an excellent microwave property at x = 0.6, with a temperature coefficient of resonant frequency (τ_f) near zero (τ_f = 2.8 ppm/°C).

Ferroelectric ceramics are important materials with a wide range of industrial and commercial applications. Since the discovery of the phenomenon of ferroelectricity, they have been the heart and soul of several multibillion dollar industries, ranging from high-dielectric-permittivity capacitors to developments in piezoelectric transducers, pyroelectric sensors, medical diagnostic transducers, electro-optical devices, etc. Materials based on barium titanate and lead zirconate titanate have dominated the field throughout their history. Actually, the ferroelectric ceramics from the Aurivillius family receive great attention due to their large remanent polarization, lead-free nature, relatively low processing temperatures, high Curie temperatures and excellent piezoelectric properties, which made them good candidates for multiple applications. This review presents a general overview of the progress in the studies on the ferroelectric ceramics from the Aurivillius family. The progress includes several aspects: (i) structural studies, (ii) dielectric and electric behavior, (iii) piezoelectricity, and (iv) pyroelectricity.

The depolarization decaying currents were measured for the PZT compound with morphotropic composition modified by the Fe_1/3Sb_2/3 cations, i.e., Pb[(Fe_1/3Sb_2/3)_xTi_yZr_z]O₃ with x + y + z = 1, x = 0.1, y = 0.44 (morphotropic boundary) and y = 0.47. The measurements were performed at room temperature and a few temperatures above (up to 473 K), as well as at a few lower temperatures (down to 77 K). The samples were poling at fields 0.02 kV/cm and 0.2 kV/cm at higher and lower temperatures, respectively. In the high temperature range, the time dependence depolarization current follows the fractional power law with two different exponents (n < 1 and m > 1), while in the low temperature range with a single exponent (n). The appropriate procedure has been used to transform the results obtained in the time domain into the frequency domain in order to calculate real and imaginary parts of the dielectric permittivity in the frequency range 5 × 10^-5-0.1 Hz. The possible dielectric relaxation mechanisms have been discussed.

The polyaniline/copper oxide (PANI/CuO) nanocomposite was prepared by mixing solutions of polyaniline and copper oxide nanoparticles in dimethyl sulfoxide (DMSO). The synthesized polymer nanocomposites were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and UV–visible spectroscopy. The characteristic peaks in XRD and UV–visible spectra confirmed the presence of CuO in the polymer structure. SEM images indicated morphological changes in the composite matrix as compared to the pristine PANI. The DC conductivity measurements were performed using two-probe method for various temperatures. AC conductivity and dielectric response of the composites were investigated in the frequency range of $10^2$–$10^6$Hz using LCR meter. Dielectric permittivity ${ϵ}^{\prime }(w)$ and dielectric loss factor ${ϵ}^{\prime \prime }(w)$ were investigated. It was observed that ${ϵ}^{\prime }(w)$ and ${ϵ}^{\prime \prime }(w)$ decrease with increase in frequency at all temperatures. At a particular frequency it is observed that both ${ϵ}^{\prime }(w)$ and ${ϵ}^{\prime \prime }(w)$ increase with increase in temperature. It was also observed that AC conductivity increased with increase in frequency and temperature.

The comparative analysis of the dielectric properties of bismuth-containing pyrochlores with different manifestation of atomic order/disorder was carried out. We examined the dielectric properties (including behavior in electric fields) of two pyrochlore compounds: BZN (presumably a composition close to ${\text{Bi}}_{1.5}$${\text{Zn}}_{0.5}$${\text{Nb}}_{1.5}$${\text{O}}_{6.5})$ ceramics with chemical disorder in both A and B cation sublattices and Bi₂Ti₂O₇ single crystal with fully chemical ordered structure. The fundamental differences between the dielectric properties of the BZN ceramics and Bi₂Ti₂O₇ single crystal were shown. In particular, in the dielectric relaxation behavior (which cannot be described via Arrhenius law in the Bi₂Ti₂${\text{O}}_7)$ or in the influence of the electric fields on the dielectric permittivity (splitting of the field-cooled and zero-field-cooled behaviors was observed for Bi₂Ti₂O₇ below estimated freezing temperature). The results of this study highlights the special role of Bi₂Ti₂O₇ as a candidate material for studying aspects of geometric frustration related with pyrochlore structure in non-magnetic medium and specifies the future directions of research.

This paper presents the results of an experimental study of the percolation behavior of the complex dielectric constant of ceramic matrix composites (CMC). Samples of piezoactive CMC were obtained by joint sintering of synthesized PZT piezoceramic powder (matrix) and crushed particles of sintered PZT piezoceramics (filler) of different compositions. The experimental dependencies of real and imaginary parts of the complex dielectric constant of CMC on the porosity of piezoceramic matrix and volume content of ceramic filler particles were measured and analyzed. It was shown that the additional porosity of the ceramic matrix resulting from sintering of the CMC masks the dielectric percolation transition, that actually occurs at the volume concentration of ceramic filler close to percolation threshold (V ∼ 1/3).