Behavior Of Dielectric Permittivity Research Articles

Hydrogenation Influences the Created Giant Dielectric Behaviors of (Bi+W) Codoped Anatase TiO2

Introductions: TiO2 nanoparticles ceramic (NPs) codoped with Bi and W ions have been synthesized by a hydrothermal technique. A portion of the prepared ceramic was posthydrogenated. Ceramic NPs were characterized by traditional methods. Crystalline structures and optical properties were investigated using X-Ray diffraction (XRD) and diffuse reflection spectroscopy, respectively. Methods: The present work has focused on the creation of a colossal (giant) dielectric permittivity (GP) behavior with the TiO2 host NCs through the Bi/W codoping to construct electronic core/shell structures. In addition, the influence of post-hydrogenation on the created GP was also examined. Results: It was found a high permittivity of 3.69×104 at 1 kHz, which was reduced to 3.29×104 by the hydrogenation of the sample. This is attributed to the densification of the itinerant electrons by the effect of the catalytic power of the doping W5+ ions to dissociate the adsorbed H2. Conclusion: The present values of GP are much higher than the permittivity of the pure TiO2 and the Bi-doped TiO2 ceramic, which was attributed to the construction of core/shell electronics structures. As a result, the doping process has been studied in detail in relation to scientific expectations.

Thermally activated processes: the underlying mechanism of activated state formation.

In the present manuscript, we highlight the contradictions in the thermally activated processes theory which treats a system's activated state as a state of the phonon subsystem. We offer an alternative model, in which the activated state is treated as an electron subsystem state. The mechanism of the activated state formation is as follows: thermal fluctuations excite electrons of some particles within the activation zone. This excitation is then shared with other particles in the ground state. This creates a locally-equilibrium activated state. We estimate the lifetime of such a state and derive expressions for the activation energy and entropy, necessary to calculate the number of excited particles in the activation zone and the energy of the particle's excitation. We validate the model experimentally, by examining the behavior of nanocrystals of undecylenic acid in pores of silica gels using dielectric spectroscopy and the analysis of the complex dielectric permittivity behavior at different temperatures and with different frequencies of the external field. The estimated number of excited particles in the activation zone of the nanocrystals and the particle excitation energy for the dielectric relaxation process observed in undecylenic acid confirm that the results of the experiment align well with the proposed model.

Influence of LiNbO3 layer thickness on structural and dielectric properties of CoFe2O4\\LiNbO3 multiferroic bilayers prepared by laser ablation

Multiferroic bilayer thin films composed by LiNbO3 and CoFe2O4 were prepared by laser ablation over (100) platinum-covered Si substrates, to understand the influence of the LiNbO3 layer thickness on their structural, electric and dielectric properties. The films were dense and polycrystalline, presenting rhombohedral LiNbO3 and cubic spinel CoFe2O4 layers. The CoFe2O4 unit cell experienced compression along the growth direction of the films, whereas the LiNbO3 layer exhibited a structural distortion in its unit cell. These strain effects were due to the mechanical interaction between both layers and to the presence of a higher amount of point defects in the thinner LiNbO3 samples, which gradually relaxed as the LiNbO3 layer thickness increased. The DC conductivity and activation energies of LiNbO3, determined from low-frequency dielectric permittivity behavior, were found to be dependent on the layer thickness. Thicker LiNbO3 layers displayed bulk-like characteristics, with a transition from polaronic to ionic conduction with increasing temperature. In contrast, thinner LiNbO3 layer films displayed polaronic behavior up to higher temperatures, due to the formation of bound polarons associated with lithium defects during deposition. AC conductivity analysis revealed that the CoFe2O4 layer conductivity mechanism primarily involved hopping between ions located at octahedral sites in the ferrite. These findings provide valuable insights into structure-function relationships and dynamical behavior within multiferroic bilayer thin films, promoting their applicability for emerging magneto-electric technologies.

A network of hydrogen bonds in the lattice of heavy atoms of single crystals of the KDP group: quantum nature of dipole interactions

In the work presented, the distinctive features of temperature behavior of dielectric permittivity ε, dielectric loss tangent tanδ and pyroelectric coefficient γ of classical ferroelectric KDP and crystals of its family, which have a network of strong OH…O hydrogen bonds, are discussed. Particular attention is focused on the evidence of quantum-chemical interactions in network of hydrogen bonds in the matrix of heavy nuclei.

Эффект оптической невзаимности в многослойных наноостровковых системах на основе Bi

In multilayer non-magnetic structures with island layers Bi ([Bi-Al2O3]N) - at room temperature, an abnormally large optical non-reciprocity effect was detected. It is shown that this effect can be closely related to the behavior of dielectric permittivity in Bi nanostructured layers. It is found that in these multilayer island systems, the metallic nature of the optical response of the dielectric constant (Re(ε) is observed<0) in the optical range when the thickness of the dielectric layer of Al2O3 is less than 1.6 nm. It is assumed that the island systems [Bi-Al2O3]N exhibit the properties of "left" metamaterials with negative μ and ε in the optical range.

New insight into the colossal dielectric permittivity and AC conductivity behavior of polycrystalline non-ferroelectric ceramics

The correlation of polarization with AC conductivity behavior of polycrystalline non-ferroelectric ceramics is more satisfied to be interpreted by three zones indicated in permittivity and AC conductivity spectra. These three zones concerning the dielectric and conductivity processes governing the response to an AC field have been identified in terms of the cluster model within the framework of percolation theory. Colossal dielectric permittivity of non-ferroelectric materials can be attributed to hopping polarization aligned via developing percolation clusters with high electron concentrations. The physical origin of the correlation between dielectric permittivity and AC conductivity of polycrystalline ceramics with respect to the effect of grain boundary has been clarified.

The polar properties of calcium orthovanadate crystals doped with manganese and thulium ions

In this work, on the base of piezoelectric and pyroelectric measurements, it was shown that the calcium orthovanadate crystals pure and doped exhibit a natural unipolar state. Doping these crystals with manganese and thulium ions did not affect the magnitude and behavior of dielectric permittivity. However, the presence of doping ions led to reducing the local piezoelectric response and stabilizing the unipolar state.

Investigation of large dielectric permittivity and relaxation behavior of DyMnO[formula omitted] single crystal

We have investigated the frequency-dependent dielectric properties of DyMnO3 single crystal in the temperature region from 100 K to 320 K. The material shows a large dielectric permittivity in the low-frequency range around room temperature. The dielectric permittivity exhibits a strong temperature dependence at all frequency and two anomalies which can be associated with the Debye-type relaxation with activation energies of 0.66 eV and 0.23 eV in the higher (around 300 K) and lower (around 150 K) temperature regions, respectively. The high value of activation energy around room temperature suggests that the relaxation is associated to the charge carriers hopping resulting from the second ionization of oxygen vacancies. However, the impedance analysis suggests that the low-temperature relaxation is due to the Maxwell–Wagner type effects originating from the dipoles at the surface.

THE OVERVIEW OF DIELECTRIC PROPERTIES OF LIQUID CRYSTALS WITH THE FUNCTION OF FREQUENCY AND TEMPERATURE

In this review article, we have analysed the overview of the dielectric parameters of liquid crystals (LCs) such as nematic, smectic with the function of frequency and temperature.LCs are isotropic with anisotropic dielectric nature. When the dielectric anisotropy was affected by the cause director reorientation in an applied electric field, deepening our understanding of dielectric response has been a leading theme in the development of LC science. Herein, we have studied the dielectric permittivity, dielectric loss and relaxation behaviour of nematic and smectic LCs. The molecular theory of LC has been explained by Maier and Saupe and then used it to explain how nematic order influences dielectric relaxation in LCs.

Optical, dielectric and photocatalytic investigation on Dy1-xHoxCrO3 (x = 0, 0.5) perovskites

Holmium (Ho) substituted Dysprosium orthochromite Dy1-xHoxCrO3(x = 0, 0.5) nanoparticles were fabricated using the sol-gel method to investigate the effect of Ho substitution (at Dy-sites) on the structural, optical, dielectric and photocatalytic properties of DyCrO3 (DCO) compound. Both compounds crystallized into distorted orthorhombic structure with Pbnm space group. The lattice volume was found to decrease whereas the orthorhombic strain increased in Dy0.5Ho0.5CrO3 (DHCO) compound in comparison to DCO. This resulted in the generation of more defect states (oxygen vacancies), which influenced the optical, electrical and photocatalytic properties. Optical studies demonstrated the presence of oxygen vacancies and the bandgap was found to reduce to 2.91 eV for DHCO from 2.96 eV for DCO compound. Dielectric constant (ε ′) was smaller in DHCO compound in comparison to the pristine compound. Phase transformation occurred in both compounds around 200 οC in dielectric permittivity versus temperature behaviour under an applied a.c. electric field (frequency range from 0.160 MHz to 3 MHz). Depressed single semicircular patterns in Nyquist plots between real and imaginary parts of the impedance spectra revealed the non-Debye type relaxation mechanism in these materials. Prepared nanoparticles exhibited degradation of Rhodamine B (RhB) dye with efficiency 54% (DCO) and 69% (DHCO) in 255 min under visible light irradiation. The degradation rate of DHCO compound was found to be 64% higher than that of the pristine compound. These studies prove the usefulness of DHCO compound as an important dielectric and photocatalytic material.

High dielectric permittivity and dielectric relaxation behavior in a Y2/3Cu3Ti4O12 ceramic prepared by a modified Sol−Gel route

In this work, Y2/3Cu3Ti4O12 ceramics were fabricated via a modified sol−gel route. Structural, dielectric, and electrical parameters were systematically investigated. The XRD results indicate that a CaCu3Ti4O12 phase (JCPDS No. 75–2188) is present in every sintered sample. SEM images of Y2/3Cu3Ti4O12 ceramics disclose a fine-grained ceramic microstructure. Interestingly, high dielectric permittivity, ∼6600–7600, with loss tangents of ∼0.918–1.086 were achieved in the sintered Y2/3Cu3Ti4O12 samples. Density functional theory (DFT) calculations were used to investigate the most stable structure of the Y2/3Cu3Ti4O12 ceramics. Our DFT results reveal that two calcium vacancies (VCa) are isolated from each other. We also determined the lowest energy configuration of an oxygen vacancy (VO) in the Y2/3Cu3Ti4O12 ceramics occurred during the sintering process. We found that the VO is trapped close to the Y atom in this structure. Both computational and experimental studies specify that the oxygen vacancy is located close to the Y atom in the Y2/3Cu3Ti4O12 lattice and it might be a bivalent oxygen vacancy. As a result, due to charge balance, charge compensation of the transition ions, i.e., Cu and Ti ions, might take place. The charge compensation mechanisms in the Y2/3Cu3Ti4O12 lattice were verified using an XPS technique. Impedance spectroscopy confirms the presence of an inhomogeneous microstructure consisting of semiconducting grains and insulating grain boundaries in the sintered Y2/3Cu3Ti4O12 ceramics. This electrical result is consistent with the computational analysis, showing that a charge compensation mechanism might be involved in generation of the grains' semiconductive region due to the presence of a VO. Consequently, high dielectric permittivity in Y2/3Cu3Ti4O12 may have originated from an internal barrier layer capacitor (IBLC) effect.

New Insight into the Colossal Dielectric Permittivity and AC Conductivity Behavior of Polycrystalline Non-Ferroelectric Ceramics

New Insight into the Colossal Dielectric Permittivity and AC Conductivity Behavior of Polycrystalline Non-Ferroelectric Ceramics

A special role of water in dielectrics of different structural organization

The paper presents some general patterns of the temperature behavior of thermodepolarization currents, dielectric permittivity and conductivity of dielectric materials containing water molecules or hydrogen bonds – crystallohydrates, polyelectrolytes, and biopolymers. The results indicate that the anomalies of these properties are observed at 4, 20, 35, 46, 65–76°С, which are “threshold points” of water, when its structure changes abruptly. The observed anomalies are probably due to a change in the proton energy at a transition to an excited level in the double-well potential at heating, while the equilibrium of the system is achieved by slow stepwise heating.

Revision of the freezing concept in relaxor ferroelectrics: the case of Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions

Presence of a frequency-independent maximum and a frequency-dependent shoulder in temperature-frequency dependence of dielectric permittivity are characteristic features of NBT-based solid solutions, while interpretation of these features is insufficient. In the present work, dielectric dispersion is studied in a wide frequency range (20 mHz–30 GHz) in (1-x)NBT-xSr0.7Bi0.2TiO3 solid solutions, in which a continuous transfer from NBT-like to pure relaxor-like behaviour is observed upon increasing of Sr0.7Bi0.2TiO3 concentration. Temperature dependence of dielectric dispersion and static dielectric permittivity in different compositions of this solid solutions group is analysed. The observed behaviour of static dielectric permittivity upon increasing of x is interpreted as a diminishing of transition between the low and the high-temperature states, while the character of the dielectric dispersion remains the same in both sides of the transition. Upon increasing of x, the dielectric dispersion transforms from the behaviour characteristic to relaxor ferroelectrics into the behaviour resembling dipolar glass. Problems, arising from introducing of the concept of freezing, described by the Vogel-Fulcher law, are discussed.

Enhanced dielectric permittivity and relaxor behavior in thermally annealed P(VDF-TrFE) copolymer films

Modification of relaxor behavior and large enhancement in dielectric permittivity are demonstrated in a P(VDF-TrFE) ferroelectric polymer film by thermal annealing treatment. For coexisting normal ferroelectric and relaxor behavior in P(VDF-TrFE) (molar ratio: 45:55) films, the relative contribution from the relaxor component is increased when annealed at high temperature and subsequently quenched. A relative peak permittivity of ε′ ∼ 100 is obtained for an annealing temperature of T = 90 °C, which is one of the highest reported so far among poly(vinylidene fluoride) copolymer and terpolymer films. Based on x-ray diffraction analysis, we attribute the changes in dielectric properties to a decrease in crystallite domain size and a consequent increase in the crystalline-amorphous interfacial area.

Systematical study of multi-walled carbon nanotube nanofluids based disposed transformer oil

In this paper, the electrical, dielectric, Raman and small angle X-ray scattering (SAXS) structure behavior of disposed transformer oil in the presence of multi-walled carbon nanotube (MWCNT) were systematically tested to verify their versatility for preparing better alternative transformer oil in future. MWCNT nanofluids are prepared using a two-step method with concentrations ranging from 0.00 to 0.02 g/L. The test results reveal that 0.005 g/L concentration possesses the most optimum performance based on the electrical (AC breakdown and lightning impulse) and dielectric (permittivity, dissipation factor and resistivity) behavior. According to the trend of AC breakdown strength and lightning impulse pattern, there were 212.58% and 40.01% enhancement indicated for 0.005 g/L concentration compared to the disposed transformer oil. The presence of MWCNT also yielding to the decrement of dissipation factor, increased on permittivity and resistivity behavior of disposed transformer oil which reflected to the performance of electrical properties. Furthermore, it is found that these features correlated to the structural properties as systematically verify by Raman and SAXS analysis study.

Jahn-Teller assisted polaronic electron hopping in LiCuNb3O9

The role of A-sited elements in double perovskite colossal dielectric LiCuNb3O9 has been analyzed by replacing the Cu ions with Li ions. Structural analysis revealed the presence of Jahn-Teller effect because of the Cu ions. Two thermally activated relaxations have been observed: the lower temperature one has been assigned to be a polaronic relaxation following Mott variable-range-hopping mechanism. Impedance analysis and humidity sensitive test proved that the higher temperature one is a Maxwell-Wagner relaxation. Our work highlights that the polaronic hopping is responsible for the colossal dielectric permittivity behavior of LiCuNb3O9.

Origin of ultrahigh thermal stability on dielectric permittivity and dipole glass-like behavior of 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3 based ceramics

The 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3 (BCT-BMT) and 5 mol% Si doped 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3 (BCST-BMT) ceramics with a pseudo-cubic crystal structure were prepared. Both as-prepared and O2 annealing ceramics (BCT-BMT-O2 and BCST-BMT-O2) exhibit a typical re-entrant dipole-glass-like relaxor behavior and excellent thermal stability of dielectric permittivity above Tm. A statistical model was employed to describe the temperature dependence of dielectric permittivity, which reveals the origin of the special dielectric properties. The large dielectric permittivity is attributed to the weakly interacting polar nanoregions (PNRs) associated with complex ionic substitution of both the A-site and B-site. The ultrahigh thermal stability is related to the thermal distribution of active dipoles. The Si doped BCT-BMT ceramic shows that the capacitance variation are lower than ± 5 % (1209 ± 60) in a wide temperature range from 437 K to 796 K with a low dielectric loss (tanδ < 0.025) from 443 K to 714 K, indicating a promising material for use in high-temperature capacitors.

Impedance spectroscopy and conduction mechanism of ferroelectric rich [formula omitted] magnetoelectric composite

In the present work, structural and dielectric properties of 0.7PbZr0.52Ti0.48O3−0.3CoFe2O4 composite prepared by a mixed oxides route were explored. X-ray diffraction analyses confirmed the formation of distinct CoFe2O4 and PbZr0.52Ti0.48O3 phases in the prepared composite. Temperature dependent dielectric permittivity behavior displayed three distinct peaks: a frequency independent peak at high temperature (T = 663K) is identified as structural phase transition of PbZr0.52Ti0.48O3 and two thermally activated frequency dependent peaks which showed a Debye- and relaxor-like behaviors at low and intermediate temperatures, respectively. The mechanism for these relaxations is elucidated on the basis of conduction associated with the single- and doubly-ionized oxygen vacancies. Impedance spectroscopy analysis was used to estimate the activation energy (Ea) of constituent phases and we found that Pb(Zr0.52Ti0.48)O3 phase has a dominant role (i.e., EPZT>ECFO) in describing the relaxation/conduction mechanism of prepared composite. Moreover, the values of Ea calculated from the dielectric, impedance and conductivity data were found to be comparable which clearly indicate that the relaxation and conduction processes in the prepared composite are related to same origin.

Permittivity experimental determination as a frequency function

Objective: To determine the behavior of dielectric permittivity of class II ceramic capacitor in function of frequency up to 10MHz.&#x0D; Context: in telecommunications and high frequency circuits is necessary to take into account the diminishing of permittivity on dielectrics of ceramic capacitors with the frequency growth, two quantitative methods are proposed to determine this behavior.&#x0D; Method: First, the impedance meter bridge FLUKE PM5306 was used in the frequency range from 10^2 Hz to 10^5 Hz; and second, a novel low-cost electronic circuit for the frequency range between 10^4 Hz to 10^7.&#x0D; Results: The results from the circuit were validated using the impedance meter bridge RLC FLUKE PM 6306. The measure of the complex capacitance from three capacitors and their loss tangent were obtained.&#x0D; Conclusions: The capacitance decreasing with the increment of the frequency was observed in the impedance meter bridge and the implemented circuit, finding a convergence between both methods in the common frequency region.