Dielectric Relaxation Phenomena Research Articles

Dielectric Relaxation Phenomena in some Lead and Non-Lead Based Ferroelectric Relaxor Materials: Recent Advances

Relaxors with general formula AA'BB'O3with different cationic distributions at A/B-sites have important device applications in capacitors, piezoelectric ultrasonic transducers, electrostrictive actuators, SAW substrates, etc. The doping or compositional changes in these ceramics can control the high electromechanical characteristics. Lead zirconate titanates (PZT) - based solid solutions exhibit excellent electrochemical properties and are widely used as actuators, transducers, ceramic filters, resonators, sensors and other electronic devices, due to their excellent piezoelectric properties. Although, there has been a concerted effort to develop leadfree piezoelectric ceramics, no effective alternative to PZT has yet been found; most other materials that possess high dielectric and piezoelectric coefficients still contain lead ions. Dielectric relaxation in these materials is of fundamental importance. Recently, new relaxor ferroelectric materials (Pb (B1/3Nb2/3)O3types) have been reported by our group in which the dielectric relaxation character is different from that observed in typical lead based relaxors. In the first part of the review, relaxor characteristics, strategies to synthesize phase pure lead based relaxors and dielectric relaxation phenomena are presented. Deviation of the frequency dependent susceptibility from Curie-Weiss law is analysed both in terms of Gaussian and Lorentzian formalisms. Lead based ferroelectric relaxor materials, due to environmental, health and social reasons are not preferred in devices and attempts are being made to eliminate the lead content from these materials. Sodium bismuth titanate (Na0.5Bi0.5TiO3, abbreviated as NBT), is considered to be one of the excellent candidates for lead-free piezoelectric material. However, pure NBT piezoelectric ceramics are difficult to pole due to its relatively large coercive field and high electrical conductivity. Therefore, many solid solutions of NBT with other ceramics are proposed to improve the relevant properties. In the second part of the review, relaxor behaviour of newly developed solid solutions of NBT is discussed. Finally, the future scope of research on these advance materials is presented.

Dielectric properties and relaxation phenomena in the diffuse ferroelectric phase transition in K3Li2Nb5O15 ceramic

Structural and dielectric properties of Potassium Lithium Niobate polycrystalline ceramic K3Li2Nb5O15 (KLN), having the tetragonal tungsten bronze (TTB) – type structure are studied in the temperature interval 50−550 °C. Special emphasis is given to the diffuse phase transition occurring around 440 °C. Space charge polarization, relaxation phenomena and free charge conductivity have been elucidated using impedance spectroscopy technique. Argand plots have revealed a non Debye and polydispersive type relaxation. In paraelectric phase the Arrhenius activation energy E τ = 0.533 eV was determined. The structural and dielectric results are compared with two others TTB compounds derived from KLN family: Pb1.85K1.15Li0.15Nb5O15 (PKLN) and GdK2Nb5O15 (GKN).

Dielectric Relaxation And Conductivity Studies Of (K0.5Bi0.5)(Fe0.5Nb0.5)O3 Ceramics

The polycrystalline sample of (K0.5Bi0.5)(Fe0.5Nb0.5)O3 was synthesized by a high- temperature solid-state reaction technique. The material crystallizes in cubic structure at room temperature. The dielectric properties of the material were investigated in a temperature range from 30-200 ºC in the frequency range (102–107 Hz). Impedance data is well fitted using proper equivalent circuit composed of a parallel resistance and capacitance in series with a parallel resistance, constant phase element and a capacitance. The compound shows a typical negative temperature coefficient of resistance type (NTCR) behavior like that of semiconductors. Modulus spectroscopy and dielectric conductivity formalism were employed to study dielectric relaxation phenomena in the material. The frequency dependence of conductivity is well fitted to Jonscher’s single power law.

Dielectric Properties of the Bismuth Neodymium Titanate Pyrochlore Solid Solution

The dielectric properties of a new, cubic, pyrochlore-type solid solution Bi(1.6−1.08x)NdxTi2O(6.4−0.11x) have been studied across the compositional range 0.35 < x < 0.86. The dielectric constant (ε) of the ceramics based on the pyrochlore-type solid solution within the experimental compositional range varied from 104 to 76 at 1 MHz, whereas the dielectric losses were well below tan δ = 8 × 10−3. The temperature coefficient of the dielectric constant τk for single-phase pyrochlore samples was found to be in the range between −20 and −40 ppm/K. Below room temperature dielectric relaxation phenomena were observed for all the compositions.

An alternative dielectric model for low and high frequencies: A non-equilibrium thermodynamic approach

In this paper a model for dielectric material in the formalism of Kluitenberg's theory on dielectric relaxation phenomena is proposed. The aim of the paper is to suggest a thermodynamic model with internal variable for dielectric isotropic material; in particular, by introducing the reciprocal complex dielectric susceptibility, expressions will be proposed for the dielectric storage modulus and dielectric loss modulus in cases of low and high frequencies. Finally, an expression for the reciprocal of complex susceptibility allows us to compare the results obtained with experimental data in the case of low frequencies.

An alternative dielectric model for low and high frequencies: A non-equilibrium thermodynamic approach

In this paper a model for dielectric material in the formalism of Kluitenberg's theory on dielectric relaxation phenomena is proposed. The aim of the paper is to suggest a thermodynamic model with internal variable for dielectric isotropic material; in particular, by introducing the reciprocal complex dielectric susceptibility, expressions will be proposed for the dielectric storage modulus and dielectric loss modulus in cases of low and high frequencies. Finally, an expression for the reciprocal of complex susceptibility allows us to compare the results obtained with experimental data in the case of low frequencies.

Dielectric relaxation phenomena in lead titanate crystals

Relaxation properties of crystalline lead titanate are interpreted in terms of Maxwell-Wagner polarization.

On the compound- LiNi3/5Fe2/5VO4 for dielectric response

The LiNi3/5Fe2/5VO4 has been prepared by solution-based chemical method. An orthorhombic unit cell structure with lattice parameters a = 3.7778 A, b = 15.8244 A and c = 5.5629 A is confirmed by X-ray diffraction. Frequency dependence of dielectric constant (er) at room temperature indicates the features of dielectric material. Temperature dependence of tangent loss at some selected frequencies shows the presence of dielectric relaxation phenomena in the material. Dielectric anomalies in er at different temperatures are studied by temperature dependence of er at some selected frequencies. The variant of relaxation time with temperature follows the Vogel-Fulcher relation.

Effect of the film thickness on the impedance behavior of sol–gel Ba 0.6Sr 0.4TiO 3 thin films

Perovskite Ba 0.6Sr 0.4TiO 3 sol–gel thin films with different thicknesses are fabricated as MFM configuration to study the effect of the film thickness on the dielectric relaxation phenomenon and the ionic transport mechanism. The frequency dependent impedance, electric modulus, permittivity and AC conductivity have been investigated in this context. Z⁎ plane for all the tested samples shows two regions, corresponding to the bulk mechanism and the distribution of the grain boundaries–electrodes process. Electric modulus versus frequency plots reveal non-Debye relaxation peaks. The observed decrease in both the impedance and permittivity with the increase in film thickness is attributed to the grain size effect. The frequency dependent conductivity plots show three regions of conduction processes, i.e. low-frequency region due to DC conduction, mid-frequency region due to translational hopping motion and high-frequency region due to localized hopping and/or reorientational motion.

ナノおよびマイクロフィラーが添加されたエポキシ樹脂コンポジットにおける力学緩和と誘電緩和の相関

Effects of addition of nano-sized and micro-sized fillers into epoxy resin on its mechanical and dielectric relaxation phenomena were examined. The glass transition temperature (Tg) decreased when a small content of nanoclay modified by octadecylamine was added, but the decrease in Tg was suppressed when the nanoclay was modified by dimethyldodecylamine. On the other hand, Tg increased when an abundant amount of microsilica was added. At temperatures above Tg, both mechanical and dielectric relaxations were accelerated in samples with octadecylamine-modified nanoclay, while the acceleration did not occur in samples with nanoclay modified by dimethyldodecylamine. Both relaxations were restricted in composites with abundant microsilica. Therefore, co-addition of dimethyldodecylamine-modified nanoclay and abundant microsilica is adequate in order to make an epoxy resin composite with a high Tg and low dielectric loss. ©2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(9): 1–9, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11420

Dielectric properties of castor oil cross-linked polyurethane

A series of polyurethanes cross-linked with castor oil were synthesized and the influence of the polyurethane chemical structure on molecular relaxations in such systems was determined. Three different castor oil rates were used in the synthesis of the cross-linked polyurethane chains. These cross-linked polyurethanes were compared with a linear polyurethane which was obtained by chain extension with 1,4-butane diol. The dielectric properties and relaxation phenomena of the polyurethane were studied as a function of the hard segment structure and cross-linker content as structural variables and frequency and temperature as experimental variables. It was found that the formation of hydrogen bonds between urethane groups of physical networks may control the molecular mobility, but the chemical nature and content of the cross-links of the hard segments strongly influences the molecular relaxation. The relaxation peaks were observed in the temperature range of -65 to 60°C for polyurethane with different cross-linked segment contents, peaks which shifted to high temperature with the increase in frequency.

Electrical and Piezoelectric Studies of (Na1-xKx)1/2Bi1/2TiO3

Lead-free ceramic samples of [(Na1-xKx)1/2Bi1/2Ti O3] (NKBT) (x = 0.1, 0.15, 0.2, 0.3, 0.45) were prepared by double sintering method and the impedance measurements were carried out in the frequency range of 100 Hz–1 MHz. The Cole–Cole plot show depressed semicircular arcs with spur-like behavior indicate that the temperature dependent dielectric relaxation phenomenon associated with grain boundary conductivity. The temperature variation of grain and grain boundary resistance is found to be linear and obeys Arrhenius law. AC–activation energies, evaluated from the variation of ac-conductivity with inverse temperature plots, were found to decrease with decreasing frequencies and obey the Universal power law. The ferroelectric hysteresis measurements were carried out on poled sample at room temperature and the sample with x = 0.15 composition exhibited the highest Pr value (= 19.2μC/Cm2). The d33 measurements indicate that the sample with x = 0.2 composition has shown the maximum d33 = 85pC/N, when compared with other compositions.

Excess-electron induced polarization and magnetoelectric effect in yttrium iron garnet

Magnetoelectric (ME) properties in yttrium iron garnet $(\text{YIG}:{\text{Y}}_{3}{\text{Fe}}_{5}{\text{O}}_{12})$, including both the first-order and second-order effects, have long been under dispute. In particular, the conflict between observations of the first-order ME effect and the centrosymmetric lattice structure has remained as a puzzling issue. As a key to solve the problem, we found that YIG shows quantum ME relaxation; the dielectric relaxation process is correlated closely with the magnetic one and has characteristic features of quantum tunneling. An application of magnetic field enhances the dielectric relaxation strength (by 300% at 10 K with 0.5 T), which gives rise to the large second-order ME (magnetocapacitance) effect critically dependent on the magnetization direction. The temperature and magnetic-field dependence of dielectric relaxation strength is well described by the noninteracting transverse-field Ising model for the excess-electron or ${\text{Fe}}^{2+}$ center with the quantum tunneling and spin-orbit coupling effects. We could also spectroscopically identify such a ME ${\text{Fe}}^{2+}$ center in terms of linear dichroism under a magnetic field along the specific direction. On this basis, the fictitious first-order ME effect---the magnetic-field induced electric polarization without the presence of external electric field---as observed for the electric-field cooled sample is ascribed to the combined effect of the above large second-order ME effect and the poling induced charge accumulation. The correlation between the ME effect and the thermally stimulated depolarization current indicates that hopping electrons freeze below around 125 K and the frozen-in dipoles generate an internal electric field (i.e., an electret-like effect). Investigation of electron-compensating doping effect on dielectric relaxation phenomena gives compelling evidences that excess electrons forming ${\text{Fe}}^{2+}$ ions play a critical role in the charge accumulation as well as in the ME effect in YIG.

Dielectric relaxations and ferroelectric behaviour of even–odd polyamide PA 6,9

Thermo Stimulated Current (TSC) combined with Dynamic Dielectric Spectroscopy (DDS) have been applied to the investigation of dielectric relaxation modes of an even–odd Polyamide PA 6,9. The correlation between results obtained by both methods allows us to describe precisely the molecular mobility. At high temperature, the various dielectric relaxation phenomena are separated by applying the dielectric modulus formalism. The comparison between the activation enthalpy values obtained by DDS and TSC leads to the assignment of the so-called α mode to cooperative movements of polymeric sequences. Molecular mobility of PA 6,9 is compared with the one of PA 11. The piezoelectric activity of PA 6,9 is shown and analyzed.

A Study of Concrete Hydration and Dielectric Relaxation Mechanism Using Ground Penetrating Radar and Short-Time Fourier Transform

Ground penetrating radar (GPR) was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC) hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.

Dielectric relaxation phenomena in the compound: LiCo3/5Mn1/5Cu1/5VO4

Solution-based chemical method has been used to produce LiCo3/5Mn1/5Cu1/5VO4 ceramics. The formation of the compound is checked by X-ray diffraction analysis and it reveals an orthorhombic unit cell structure with lattice parameters of a = 9.8262 A, b = 3.0706 A, c = 14.0789 A. Field emission scanning electron micrograph indicates a polycrystalline texture of the material with grains of unequal sizes (~0.2 to 3 μm). Complex impedance spectroscopy technique is used to study the dielectric properties. Temperature dependence of dielectric constant (er) at various frequencies exhibits the dielectric anomalies in er at Tc (transition temperature) = 245, 255, 260 and 265 °C with (er)max. ~458, 311, 214 and 139 for 50, 100, 200 and 500 kHz, respectively. Frequency dependence of tangent loss at various temperatures shows the presence of dielectric relaxation in the material.

Dielectric relaxation related to single-ionized oxygen vacancies in (Pb 1− xLa x)(Zr 0.90Ti 0.10) 1− x/4 O 3 ceramics

The dielectric relaxation phenomenon has been studied in lanthanum modified lead zirconate titanate ceramics in the high temperature paraelectric phase. The high temperature dielectric response revealed an anomalous behavior, which is characterized by an increase of the real component of the dielectric permittivity with the increase of the temperature. At the same time, a similar behavior, with very high values, has been observed in the imaginary component of the dielectric permittivity, which can be associated with conduction effects related to the conductivity losses. The frequency and temperature behavior of the complex dielectric permittivity has been analyzed considering the semi-empirical complex Cole–Cole equation. The activation energy value, obtained from the Arrhenius’ dependence for the relaxation time, was found to decreases with the increase of the lanthanum concentration and has been associated with single-ionized oxygen vacancies. The short-range hopping of oxygen vacancies is discussed as the main cause of the dielectric relaxation.

An abnormal dielectric relaxation phenomenon observed in PbZr0.38Ti0.62O3 multilayers

We report an unusual dielectric relaxation phenomenon associated with dipolar defect complexes Ti3+-(Vo2−)•• observed in the PbZr0.38Ti0.62O3 multilayers. The dielectric loss aroused by the polarization of defect dipoles varies with time under ac electric fields, and its change can be controlled by an applied dc bias. This abnormally dynamic behavior of dielectric loss can be interpreted by the formation and dissociation of dipolar defect pairs Ti3+-(Vo2−)•• by injection of charged carriers. These investigations may be beneficial to getting further insight into the defect dynamics and the mechanism of ferroelectric polarization fatigue and restoration in ferroelectric materials.

Dielectric Analysis of Dynamic Fouling Behavior on Surface of Polyethersulfone Composite Ultrafiltration Membrane

A dielectric analysis model for the fouling layer on the polyethersulfone composite ultrafiltration (UF) membrane and solution system, which consists of the solution, concentration polarization layer (CPL), and cake layer, was established by virtue of the interfacial polarization and the electrostatic field theory. The effect of some important parameters, such as the depth, conductivity of CPL, and cake layer, on the dielectric spectroscopy (or dielectric relaxation properties) of the UF system was discussed by the parameter sensitivity analysis and the dielectric measurement. The simulations indicate that the CPL can be created rapidly and the cake layer formation is the dynamic balance process of growth and erosion in the process of UF. The key factor affecting on the dielectric spectrum of UF system is the electrical properties of the CPL and the cake layer. In comparison to the results of dielectric measurement, the simulations indicate that the model proposed in this work is valid and reliable to some degree for describing and explaining the dielectric relaxation phenomenon in UF system. It is very important to further understand the fouling behavior of membrane surface and optimize the controlling techniques of membrane fouling in the process of UF.

Comparative dielectric study of pentanol isomers with terahertz time-domain spectroscopy

Using terahertz (THz) time-domain spectroscopy, we have measured the complex permittivity of seven pentanol isomers (1-pentanol, 2-pentanol, 3-pentanol, 2-methly-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, and 3-methyl-2-butanol) in the frequency range of 0.2–2.5 THz at temperatures from 253 to 323 K. For all samples, the complex permittivity contains the following three components: (i) a high-frequency side of dielectric relaxation processes, (ii) a broad vibration mode around 1.5 THz, and (iii) a low-frequency side of an intermolecular stretching mode located above 2.5 THz. At low temperatures, the relaxation process moves to a low-frequency range and a peak of the broad vibration mode, which is independent of temperature, is clearly observed around 1.5 THz. Spectra in the THz region change sensitively according to the molecular structure of the pentanol isomers. We have also observed the complex permittivity in the microwave range of 1 MHz–20 GHz. The behavior of the dielectric relaxation processes below GHz region much depend on the isomers. Our experimental data demonstrate that the molecular structures of the pentanol isomers influence all the molecular dynamics ranging from dielectric relaxation phenomena, which are due to reorientational motion of the molecules, to vibration dynamics within the hydrogen-bonded network structure.