Dielectric Loss Peak Research Articles

Preparation and electric properties of BiFeO3 film by electrophoretic deposition

BiFeO3 (BFO) films were synthesized by electrophoretic deposition process (EPD) using suspensions containing BFO powders. The BFO powders were prepared by sol–gel method and the effects of calcining temperature and additive on phase composition, particle size and size distribution of BFO powders have been systematically investigated. It is found that the BFO powders prepared with citric acid as chelating agent and calcined at 600°C is single phase and have smaller particle size and narrow size distribution. And the well-dispersed and stable suspensions containing BFO particles were obtained by adjusting the pH value to 6.5. Single phase BFO films were deposited by EPD. The SEM micrographs show there are some pores in the BFO films and the grain size of films is in the range of 250–400nm. The dielectric constant of BFO films decreases with the increase of frequency and there is a peak of dielectric loss when frequency is about 10kHz. Moreover, the electric field and frequency dependences of ferroelectric properties in BFO films have been investigated.

Dielectric relaxation in ionic liquids: Role of ion-ion and ion-dipole interactions, and effects of heterogeneity

A semi-molecular theory for studying the dielectric relaxation (DR) dynamics in ionic liquids (ILs) has been developed here. The theory predicts triphasic relaxation of the generalized orientational correlation function in the collective limit. Relaxation process involves contributions from dipole-dipole, ion-dipole, and ion-ion interactions. While the dipole-dipole and ion-ion interactions dictate the predicted three relaxation time constants, the relaxation amplitudes are determined by dipole-dipole, ion-dipole, and ion-ion interactions. The ion-ion interaction produces a time constant in the range of 5-1000μs which parallels with the conductivity dominated dielectric loss peak observed in broadband dielectric measurements of ILs. Analytical expressions for two time constants originating from dipolar interactions in ILs match exactly with those derived earlier for dipolar solvents. The theory explores relations among single particle rotational time, collective rotational time, and DR time for ILs. Use of molecular volume for the rotating dipolar ion of a given IL leads to a predicted DR time constant much larger than the slowest DR time constant measured in experiments. In contrast, similar consideration for dipolar liquids produces semi-quantitative agreement between theory and experiments. This difference between ILs and common dipolar solvents has been understood in terms of extremely low effective rotational volume of dipolar ion, argued to arise from medium heterogeneity. Effective rotational volumes predicted by the present theory for ILs are in general agreement with estimates from experimental DR data and simulation results. Calculations at higher temperatures predict faster relaxation time constants reducing the difference between theory and experiments.

A study of the structure and dielectric properties for high-valence compensation of Bi3+ ion-doped Ba(FeTa)0.5O3 ceramics

The higher valence compensation of the Ba1−xBix(FeTa)0.5O3 (x=0–0.1) system is obtained via a solid-state reaction. The characteristics, including phase formation, microstructure and dielectric properties, are also investigated. In the complex perovskite oxides Ba1−xBix(FeTa)0.5O3 system, the dielectric constant increases when the Bi3+ ion concentration increases, because there is an increase in valence compensation dipoles. The dielectric constant Ba0.94Bi0.06(FeTa)0.5O3 ceramics sintered at 1250°C are about 8×104–105, with a low dissipation factor at temperatures between 273 and 458K and a frequency of 1kHz. The temperature-dependent dielectric constant and loss curves, measured in the temperature range, 273–458K, and at a frequency of 1kHz, indicate that the samples exhibit typical relaxor behavior over a broad temperature range. Complex impedance spectroscopy shows the presence of barrier layers in bi-phase ceramics, which indicates that the orientation and space charge polarization are dominant for Ba1−xBix(FeTa)0.5O3 dielectric behavior. The frequency dependence of the dielectric loss peak obeys an Arrhenius law, with an activation energy of 0.24eV, and the relaxation time is 10−9s.

Ca-Doping of BiFeO3: The Role of Strain in Determining Coupling between Ferroelectric Displacements, Magnetic Moments, Octahedral Tilting, and Oxygen-Vacancy Ordering.

Elastic and anelastic properties of a member of the BiFeO3–CaFeO2.5 perovskite solid solution (BCFO), which is known to have multiple instabilities, have been investigated by resonant ultrasound spectroscopy. This phase, with 64% Bi and 36% Ca on the A site, is antiferromagnetic (TN ∼650 K) and has an ordered arrangement of oxygen vacancies with tetragonal lattice geometry. The inverse mechanical quality factor, Q–1, has a maximum near 100 K, correlating closely with a peak in dielectric loss, reported previously, consistent with a loss mechanism that involves the movement of oxygen vacancies accompanied by local lattice distortion. At higher temperature, there is a further acoustic loss peak that is correlated with complex impedance anomalies. There is no clear relationship to the magnetic transition, and the observations are interpreted as relating to ionic conductivity. A small stiffening, scaling with the square of the magnetic order parameter below TN, indicates that the main coupling with strain is biquadratic, confirming that conventional coupling of magnetic order with symmetry-breaking shear strains is weak in BCFO. Data from the literature for BCFO indicates that local strain fields are likely to be responsible for suppressing the spin cycloid present in BiFeO3.

AC electrical conductivity and dielectric studies on evaporated nanostructured InSe thin films

• Nanostructured InSe thin films were prepared by thermal evaporation technique. • The results of AC conductivity were reasonably interpreted in terms of CBH model. • The dielectric relaxation was studied by applying the dielectric modulus formulism. Nanostructured InSe thin films were prepared by thermal evaporation technique under a vacuum of 10 −4 Pa. The AC electrical conductivity and dielectric properties of the prepared films have been investigated in the frequency range from 100 Hz to 5 MHz and in the temperature range 293–393 K. The frequency dependence of σ ( ω ) follows the Jonscher’s universal dynamic law with the relation σ ( ω ) = σ dc + A ω s , where s is the frequency exponent. It is found that s has value ⩽1 and decreases with increasing temperature suggesting a hopping conduction mechanism. It is found also that ln σ ac ( ω ) increases linearly with the reciprocal of the absolute temperature. This suggested that the AC conductivity is thermally activated process with AC activation energy decreased with increasing frequency. In spite of the absence of the dielectric loss peaks, application of the dielectric modulus formalism gives a simple method for evaluating the dielectric relaxation time and the activation energy of the dielectric relaxation.

On the Anomalous Magnetic Behavior and the Multiferroic Properties in BiMn2O5

Sealed-tube synthesis of BiMn2O5 materials and their physical properties have rationally been reinvestigated depending on the reactants. The aim of the study was to characterize its potential multiferroic properties and to investigate the anomalous magnetic properties in relation to the expected ferroelectric properties. Rietveld refinement of the room temperature X-ray diffraction data shows the stability of the crystallographic structure with a Mn(3+)/Mn(4+) ratio far from 1 because of bismuth and oxygen deficiencies despite the sealed-tube synthesis. Our detailed magnetic susceptibility and specific heat data analysis unambiguously support an intrinsic anomalous magnetic behavior in relation to the establishment of a magnetic short-range ordering far from the Néel temperature. Around room temperature, oxygen vacancies are responsible for supporting the dielectric loss peak measured, and, interestingly, the so-called T*, which was underlined in relation to an anomalous phonon shift (García-Flores, A. F.; et al. Phys. Rev. B 2006, 73, 104411), is not a characteristic temperature in relation to the multiferroic properties because no ferroelectric transition was detected.

Origin of giant permittivity and high-temperature dielectric anomaly behavior in Na0.5Y0.5Cu3Ti4O12 ceramics

Na0.5Y0.5Cu3Ti4O12 ceramics prepared by the conventional solid-state reaction method under various sintering conditions were found to exhibit a giant dielectric constant over 10 000 around room temperature. Two electrical responses were observed in the combined modulus and impedance plots, indicating the presence of Maxwell-Wagner relaxation. The contributions of semiconducting grains and insulating grain boundaries (corresponding to high-frequency and low-frequency electrical response, respectively) played important roles in the dielectric properties of Na0.5Y0.5Cu3Ti4O12 ceramics. The correlations between grain boundaries resistance and low frequency dielectric loss, grains resistance and the position of dielectric loss peak were addressed. Mixed-valent structures of Cu2+/Cu3+ and Ti3+/Ti4+ had been determined using X-ray photoelectron spectroscopy. Electron hopping between Cu2+ and Cu3+ and electron transport in Ti3+–O–Ti4+ paths were proposed as the origin of the semiconducting nature of Na0.5Y0.5Cu3Ti4O12 ceramics. In particular, high-temperature dielectric anomaly behavior was investigated in detail. A dielectric peak exhibiting relaxor-like behavior was observed around 200 °C, which was linked with the formation of oxygen vacancies. Based on the electric modulus results, this behavior was explored in the light of the defect formation and explained in terms of a competition process depending on the combinational contribution to polarization between n- and p-type carriers rather than a relaxation process.

An impedance spectroscopy study of the rotation and reorientation of water molecules in hydrated graphite oxide

Graphite oxide (GO) has been prepared by the modified Hummers method and hydrated to different concentrations. Samples were then characterized by nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, and gas adsorption. The results confirmed the existence of water molecules at two types of sites, namely the two-dimensional space between GO layers as well as inter-grain voids. Detailed impedance spectroscopic measurements have been performed to study the rotation and reorientation dynamics of confined water. Two dielectric loss peaks were observed in hydrated GO and attributed to relaxational motions of water molecules. The peak at the higher temperature arises from the rotation of intercalated molecules along the axis of their hydrogen bonds to hydroxyl radicals on the graphite oxide layers. The peak at lower temperature corresponds to the relaxation of inter-grain species, a relaxation that seems to deviate from Arrhenius behavior at higher temperatures.

Dielectric Tunability, Dielectric Relaxation, and Impedance Spectroscopic Studies on (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 Lead‐Free Ceramics

Dielectric and impedance spectroscopies were employed to study the electrical behavior of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (abbr. BCTZ) lead‐free ceramic. The dielectric properties versus dc bias electric field experiment revealed high dielectric tunability (> 65%) as well as figure of merit (> 27) at 10 kHz and room temperature. At elevated temperature range, a dielectric loss peak was observed and verified to be correlate of oxygen vacancy relaxation. The impedance spectra studies indicate that the ceramic is a mixed ionic conductor of p‐type nature at the paraelectric phase and, the grain and total conductivity at 600°C reaches 6.0 × 10−5 and 2.0 × 10−5 S/cm, respectively.

Direct observation of domain wall motion and novel dielectric loss in 0.23Pb(In1/2Nb1/2)O3–0.42Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 crystals

Domain wall motion was directly observed at temperatures near to the monoclinic-to-tetragonal phase transition temperature (TM–T) in [001]-oriented 0.23Pb(In1/2Nb1/2)O3–0.42Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.23PIN–0.42PMN–0.35PT) single crystals using a polarizing light microscope, and evident 90° and 180° domain switches were observed near the Curie temperature (TC). Two dielectric loss anomalies were observed at temperatures near TM–T in the [001]-oriented PIN–PMN–PT single crystals, while an additional dielectric loss peak was found at temperatures a few degrees below TC, which was associated with domain wall motion. Based on the domain structure observations, a domain switching mechanism was proposed to explain the novel dielectric loss peak at several degrees below TC.

Dielectric constant and induced dipole moment of edible oils subjected to conventional heating

The frequency dependence of dielectric constant, dielectric loss factor and conductivity are studied for five edible oils in the frequency range 100 kHz to 13 MHz at different temperatures using frequency domain spectroscopy. The dielectric constant is found similar for all the samples and in agreement with the previous reports. The dielectric loss is low (<0.01) except for the virgin olive oil with value of 0.05. Dielectric loss peak frequency is at 4 MHz for corn oil and around 5.2 MHz for the others. At this frequency conductivity is of the order of 10-7-10-9 S/cm, and decreases with temperature following the behavior of the dielectric losses. Refractive index, molar and orientation polarization are calculated for all types of oils using novel theory proposed by N. M. Putintsev and D. N. Putintsev [1]. Data show that the orientation polarization contributes to the observed dielectric constant at low temperatures and frequencies. This indicates that the edible oils are not pure nonpolar dielectrics. Induced dipole moments of oils are calculated for 400 kHz and 10 MHz at 300 K and 318 K. The results are discussed and correlated as a function of temperature and frequency to establish their relationship.

Dielectric and electric properties of plasticized PEO‐AgCF3SO3‐SiO2 nanocomposite polymer electrolyte system

AbstractThe effect of plasticizer poly(ethylene glycol) (PEG) on dielectric and electrical properties of an ionically conducting polymer nanocomposite electrolyte PEO: AgCF3SO3: SiO2: PEG has been investigated. The variation of relative dielectric constant and tangent loss peak with frequency have been discussed. The ionic and polymer segmental motions have been analyzed by electrical modulus and dielectric permittivity. The electrical modulus formalism is used to study the ionic relaxation process in these composites in terms of conductivity relaxation time. On addition of plasticizer, the modulus peak shifts toward higher frequency side suggesting the speeding up of the relaxation time. The frequency dependence of AC conductivity follows the universal power law. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Dielectric properties of strontium iron holmium niobate ceramics

Strontium iron holmium niobate (Sr(Fe1−xHox)0.5Nb0.5O3) ceramics were synthesized via a solid-state reaction technique. The undoped ceramic showed an orthorhombic phase, but it transformed to a pseudocubic phase for higher Ho concentrations. A low solubility limit of Ho in SFN caused a formation of second phase for the x=0.15 ceramic. Dielectric behavior of undoped ceramic exhibited high dielectric constant over a wide temperature range. However, the doping shifted this region to a higher temperature. The doping also shifted the peak of dielectric loss to a higher temperature. Activation energy of dielectric relaxation increased with increasing Ho concentration. In addition, complex impedance analysis was applied to determine the behaviors of grain boundary and grain after doping.

Temperature-dependent dielectric characterisation and molecular interaction behaviour in binary mixtures of dimethylacetamide with ethylene glycol and dimethylsulphoxide

Dielectric relaxation measurements on binary mixtures of dimethylacetamide with ethylene glycol and dimethylsulphoxide have been carried out at 11 concentrations using time domain reflectometry technique at 10°C, 20°C, 30°C and 40°C over the frequency range from 10 MHz to 10 GHz. For all the mixtures, only one dielectric loss peak is observed in this frequency range. The relaxation in these mixtures can be described by a single relaxation time using the Debye model. A systematic variation is observed in dielectric constant and relaxation time. Excess permittivity, excess inverse relaxation time, Kirkwood correlation factor and thermodynamic parameters such as enthalpy of activation and Gibbs free energy of activation have been determined, to confirm the formation of hydrogen-bonded homogeneous and heterogeneous cooperative domains, the dynamics of solute–solvent interaction and the hindrance to molecular rotation in the hydrogen-bonded glass forming ethylene glycol–dimethylacetamide and dimethylsulphoxide–dimethylacetamide system.

Investigation of dielectric relaxation behavior of electrospun titanium dioxide nanofibers using temperature dependent impedance spectroscopy

The electrospinning method has been utilized in the fabrication of titanium dioxide nanofibers (TNFs) with an average diameter of ∼50nm and length of ∼100μm. Effect of temperature on the dielectric relaxation behavior of the fabricated nanofibers have been studied using AC impedance spectroscopy. The morphological, structural and compositional aspects as well as the optical properties of the TNFs have been investigated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX) and ultraviolet–visible (UV–vis) absorption spectrum. The permittivity behavior of the device at the frequency below 102Hz shows the relaxation contribution along with the electrode polarization. Dielectric loss peak in loss tangent also confirms the presence of relaxing dipoles in TNFs. The AC conductance as a function of frequency confirms the semiconducting nature of TNFs and obeys Jonscher's power law except a small deviation in the low frequency region. DC conductivity increases with increase in temperature.

Dielectric Relaxation in Ethylene Glycol - Dimethyl Sulfoxide Mixtures as a Function of Composition and Temperature

Using time domain reflectometry, the complex dielectric spectra between 10 MHz to 20 GHz has been mea- sured in the whole composition range at 10, 20, 30 and 40 o C for the binary mixtures of ethylene glycol and dimethyl sul- foxide. For all the mixtures, only one dielectric loss peak was observed in this frequency range. The relaxation in these mixtures can be described by a single relaxation time using the Debye model. A systematic variation is observed in dielectric constant (e0) and relaxation time (τ). The excess permittivity (e E ), excess inverse relaxation time (1/τ) E , Kirkwood correlation factor (g) and thermodynamic parameters viz. enthalpy of activation (∆H) and Gibbs free energy of activation (∆G) have been determined, to confirm the formation of hydrogen bonded homogeneous and heterogeneous cooperative domains, the dynam- ics of solute - solute interaction and the hindrance to molecular rotation in the hydrogen bonded glass forming ethylene glycol - dimethyl sulphoxide system.

Magnetic and dielectric properties of Aurivillius phase Bi6Fe2Ti3O18 and the doped compounds

The magnetic and dielectric properties of Bi6Fe2Ti3O18, Bi6FeCoTi3O18, and Bi5LaFeCoTi3O18 are investigated. The room-temperature ferromagnetism is observed in the samples Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 compared with the paramagnetic behavior in Bi6Fe2Ti3O18 at room temperature. The ferromagnetism in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 can be ascribed to spin canting of the Fe-based and Co-based sublattices via the antisymmetric Dzyaloshinskii-Moriya interaction. The frequency-dependent behavior of the dielectric loss peak in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 manifests itself a thermally activated relaxation process. The rather large activation energy (2.62 ± 0.11 eV for Bi6FeCoTi3O18 and 1.97 ± 0.07 eV for Bi5LaFeCoTi3O18) implies that the relaxation process is not due to the thermal motion of oxygen vacancies inside ceramics.

Effects of raw natural gas on the aging of high-voltage electrical machine mainwall insulation

The total recovery of natural gas from subsea wells can be significantly increased with a compressor installed near the wellheads. The compressor is powered by a high-speed induction motor integrated in the same casing. The process gas flows through the motor and acts as a cooling medium. The insulation system of the motor is in direct contact with the gas and must be resistant to it. The gas mixture contains hydrocarbons, water, and monoethylene glycol. The effects of the gas mixture and its individual components on the properties of a high-voltage machine mainwall insulation consisting of mica, glass, and epoxy are obtained by experimental tests with raw natural gas at accelerated conditions. The tests at high pressures and temperatures indicate that heavy hydrocarbon compounds cause similar effects to plasticizers inside the bisphenol A epoxy resin, but such compounds do not penetrate easily into epoxy novolac resin. The plasticizing effect is seen as increased weight and volume, decreased mechanical strength and E-modulus, and reduced glass transition temperature. The polymers did not decompose chemically. The mainwall insulation is vulnerable to delamination, which is initiated by the detachment of glass strains and epoxy resin. Water causes dielectric loss peak at very low frequencies, while the heavy hydrocarbons produce a loss peak in higher frequency range.

AC measurements of spray-deposited CdS:In thin films

Indium doped cadmium sulfide thin films (CdS:In) were produced by the spray pyrolysis technique on glass substrates. AC measurements were used to investigate the electrical properties of the films depending on Brick-layer model for polycrystalline materials. The measurements were performed at room temperature in the dark and room light in the frequency range from 20 Hz to 1 MHz using coplanar indium electrodes. The data were analyzed by using Bode plots for the impedance Z and dielectric loss tanδ with frequency f. It is found that the impedance has no dependence on frequency in the low frequency region but has 1/f dependence in the high frequency region. One dielectric loss peak is obtained, which means the presence of a single relaxation time, and hence the films are modeled by just one RC circuit which represents the grains. This means that there is just one conduction mechanism that is responsible for the conduction in the bulk, due to electronic transport through the grains. Real values of the impedance in the low frequency region and relaxation times for treated and as-deposited films were estimated.

Electrical conductivity and dielectric relaxation of bulk iron (III) chloride tetraphenylporphyrin

The electrical conductivity and dielectric properties of bulk iron (III) chloride tetraphenylporphyrin, FeTPPCl, has been investigated in the frequency range from 40Hz to 5MHz and in the temperature range of 298–373K. The frequency dependence of σ(ω, T) follows the Jonscher's universal dynamic law. The temperature behaviour of the frequency exponents shows that the correlated barrier hopping (CBH) model is well adapted to FeTPPCl semiconductor material. The conductivity in the direct regime, σdc, is described by the variable range hopping (VRH). In spite of the absence of the dielectric loss peaks, application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation.