Temperature Dependence Of Dielectric Permittivity Research Articles

Structural and ferroelectric phase evolution in [KNbO3]1−x[BaNi1/2Nb1/2O3−δ]x (x=0,0.1)

The phase transition evolution for ${[{\mathrm{KNbO}}_{3}]}_{1\ensuremath{-}x}{[{\mathrm{BaNi}}_{1/2}{\mathrm{Nb}}_{1/2}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}]}_{x}\phantom{\rule{0.16em}{0ex}}(x=0,0.1)$ is determined via complementary dielectric permittivity and Raman-scattering measurements. Raman scattering by optical phonons over the range of 100--$1000{\mathrm{cm}}^{\ensuremath{-}1}$ for 83 K $lTl873$ K reveals six discernible zone-center optical phonon modes. Mode behaviors are observed through structural and ferroelectric phases in the solid solution $x=0.1$ and compared with those for end member $x=0$ and with the results of temperature-dependent dielectric permittivity. Rigorous peak fitting analyses of spectra collected from the solid solution and end member indicate structural and ferroelectric phase transition temperatures that are close to those for the ${\mathrm{KNbO}}_{3}$ end member despite the inclusion of 5 atomic % of ferroelectrically inactive Ni cations. Density functional theory calculations were performed in the solid solution and end member using both cation displacement and Berry phase-based methods. Differences in the electronic and polar properties between the solid solution and the end member highlights local and nonlocal characteristics, which are discussed in relation to the experimental data.

Dielectric and ferroelectric properties of Ba0.87Ca0.10La0.03Ti1-xSnxO3 lead-free ceramics

Ba0.87Ca0.10La0.03Ti1-xSnxO3 (BCLTS) piezoelectric lead-free ceramics were fabricated by conventional solid-state sintering process at 1480 °C. The effects of Sn4+ substitution on microstructure and electrical properties of the ceramics were researched. All samples show a pure perovskite structure with no secondary phase, and the coexistence of orthorhombic phase and tetragonal phase in the composition range of x = 0.06–0.10 is identified in the XRD pattern. Average grain size decreases with the increase of Sn content in the BCLTS samples. The BCLTS ceramics exhibit excellent piezoelectric properties and ferroelectric properties with d33 = 501pC/N and kp = 45.6% at x = 0.10, and Pr = 9.87 μC/cm2 at x = 0.06. The analysis on the temperature dependence of dielectric permittivity approved the diffuse relaxor ferroelectric feature for all the BCLTS samples.

High-temperature dielectrics based on (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xNaNbO3 system

The microstructure, phase structure, ferroelectric and dielectric properties of (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xNaNbO3 (BNT-BT-xNN) ceramics were investigated as candidates for high-temperature capacitors with a working temperature far beyond 200 °C. The decreased polar rhombohedral phase shown in XRD and the weakened macroscopical polarization in P-E test indicate that NN addition can dilute the mutual coupling of polar nanoregions (PNRs), which is very conducive to flattening the curves of temperature dependent dielectric permittivity at the expense of a small reduction in dielectric permittivity values. Among all manufactured samples, those with composition of x = 0.10 showed a high permittivity of more than 2700 (1 kHz) and energy storage density of 0.61 J/cm3 (7 kV/mm) at 150 °C with a ΔC/C150°C varying no more than 15% in a wide temperature range of 54°C–318 °C. All of these exhibit wonderful temperature stable dielectric properties and indicated the promising future of BNT-BT-xNN system as high-temperature ceramic capacitors.

Baric transformations of anomalies of dielectric permeability of CuСr<sub>0,5</sub>In<sub>0,5</sub>P<sub>2</sub>S<sub>6</sub> layered crystals

Purpose: The investigation of the nature of the dipole glass state in ferroelectrics has become one of the most interesting and important areas in solid state physics in recent years. Layered crystals of solid solutions based on CuCrP 2 S 6 and compounds are very convenient materials for studying the effects of relaxation dynamics caused by dipole disordering. With the change of the chemical composition of solid solutions, we can observe a transformation from dipole ordering with a long-range order, (a ferroelectric CuInP 2 S 6 in and an anti-ferroelectric in CuCrP 2 S 6 ) to a state of dipole glass with a relaxation behavior caused by the freezing of ferroactive ions in the crystal lattice. Based on the investigations of dielectric spectroscopy (10 mHz-3 GHz) in mixed Cu(In x Cr 1-x )P 2 S 6 crystals, it was found that the phase changing point between the ferroelectric phase and the dipole glass phase lies between x=0.5 and 0.7 , and the corresponding point between the state of the dipole glass and the anti-ferroelectric phase is between x=0.4 and 0.2. The main aim of this study is to investigate the effect of high hydrostatic pressure on the temperature dependences of dielectric properties of CuСr 0,5 In 0,5 P 2 S 6 crystals, in which the state of dipole glass occurs at atmosphere pressure according to the phase x , T -diagram . Methods: Studied CuСr 0,5 In 0,5 P 2 S 6 crystals were grown by the gas transport reaction method. For the dielectric measurement polished plate like crystals were used. All measurements were performed in a direction perpendicular to the layers. The complex dielectric permittivity e∗ was measured using an HP4262A capacitance bridge at the frequency 1 MHz. All measurements have been performed on cooling and heating mode with a temperature rate 0.5 K/min. Silver paste has been used for contacting. Hydrostatic pressure was applied a high-pressure chamber, its value being controlled within ±1MPa. Scanning electron microscopy (SEM) studies combined with energy dispersive X-ray spectroscopy (EDX) were performed using a SEM JEOL 7000F microscope. Results: Studies of a complex dielectric permittivity e* of CuСr 0,5 In 0,5 P 2 S 6 crystals with different values of hydrostatic pressure were performed in a wide temperature range 77 K 300MPa, two anomalies of the real part of the dielectric constant are revealed. One, at lower temperatures. corresponds to the transition to the state of a dipole glass, the other-at higher temperatures, is a ferroelectric phase transition induced by hydrostatic pressure. The Value of the baric temperature shift of the ferroelectric phase transition for CuСr 0,5 In 0,5 P 2 S 6 crystals induced by high hydrostatic pressure d Tc /d p =0,18 K/MPa is close to the similar value of d Tc /d p =0,21 K/MPa and d Tc /d p =0,29 K/MPa for crystals CuInP 2 S 6 and CuСr 0,3 In 0,7 P 2 S 6 , respectively. Conclusions: Based on the studies of temperature dependences of dielectric permittivity of layered crystals at high hydrostatic pressure, the baric behavior of the temperatures of the anomalies of dielectric permittivity of crystals CuСr 0,5 In 0,5 P 2 S 6 is established. Hydrostatic pressure induces the appearance of an anomaly of dielectric constant, which corresponds to a ferroelectric phase transition. p , T phase diagram of these crystalls was built, and pressure coefficients for the phase transition temperature shift were determined. The phase transition temperature in crystals CuСr 0,5 In 0,5 P 2 S 6 determined by extrapolation of the baric dependence of the temperature of the ferroelectric phase transition to atmospheric pressure is equal to T c =162K. The phase x , T diagram of Cu(In x Cr 1-x )P 2 S 6 solid solutions was built. The concentration shift of the temperature of the ferroelectric phase transition for solid solutions of Cu(In x Cr 1-x )P 2 S 6 can be well described by the equation Т с ( х )=314,6-3,5× х +0,009× х 2 ( х, mol.%)

Microstructural design and properties of PMNT crystal-embedded barium calcium zirconate titanate ceramics

Abstract In this study, BCZT-0.02Bi ceramics embedded with PMNT single crystals in the amount of 1, 3 and 5 wt% were prepared. The ceramics were sintered in the temperature range of 1100–1200 °C for 2 h. All the samples were characterized in terms of microstructure, and dielectric and ferroelectric properties. The microstructural characterization revealed good interfaces between PMNT single crystals and BCZT-0.02Bi grains. The addition of PMNT single crystals was found to increase the dielectric constant of the ceramics. The temperature dependences of dielectric permittivity and ferroelectric hysteresis loops also indicated an increase in relaxor behavior with increasing PMNT content. The important factors related to the relaxor behavior in this material system were discussed in detail. The BCZT-0.02Bi-xPMNT ceramic composites with exceptionally large dielectric constant with very low loss and linear P-E behavior may be used as a viable replacement for lead-based materials in electromechanical actuators and sensors and in frequency-tunable capacitors.

Relaxor Ferroelectric-Like Behavior in Barium Titanate-Doped Glass via Formation of Polar Clusters

Glass lead free sample of composition 10BaTiO3–60V2O5–30B2O3 in mol% was prepared by conventional melt quenching technique. The as-prepared sample shows relaxor ferroelectric-like behavior which is a novel phenomenon in the field of glass science. XRD and DSC were used to emphasize the glassy nature of the present sample. Diffraction spots from clusters are clearly observed using HRTEM, which is presumably from polar clusters (PCs). The sample shows a broad and diffuse peak in the temperature dependence of dielectric permittivity ɛ` (T) and tangent loss, the temperature of which increases with increasing measuring frequency, denoting the typical relaxor behavior. The existence of distorted BaTiO3 PCs embedded in the glass matrix is responsible for the appearance of this behavior. The present glass sample shows energy storage density of about 0.11 J/cm3 at room temperature and 0.44 J/cm3 at 120 °C, which is reasonably good for bulk polar material. The results obtained in this work could lay the basis for the development of lead free materials to meet the energy storage and Eco-friendly applications.

Broadband dielectric spectroscopy of Pb-based relaxor ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 with intermediate random fields

This work is devoted to the investigation of the broad band dielectric spectra of 0.83PbMg1/3Nb2/3O3-0.17PbTiO3 (PMN-17PT) single crystals which have intermediate random fields. The necessity to understand the impact of random fields for the phase transition in heterogeneous perovskite oxides is of central importance. The thorough studies of dielectric properties revealed that the structural phase transition in PMN-17PT has a very complex dynamics. The temperature dependences of dielectric permittivity show that this material has features characteristic of polar nano regions and order-disorder phase transition dynamics. We speculate that this is the fingerprint of the phase transition in such heterogeneous perovskite oxides.

Dielectric and ferroelectric properties of Ba0.97-xCaxLa0.03Ti0.9Sn0.1O3 lead-free ceramics

Abstract The Ba 0.97-x Ca x La 0.03 Ti 0.90 Sn 0.10 O 3 (x = 0.02–0.10) lead-free piezoelectric ceramics were fabricated via conventional solid-state sintering process at 1480 °C. The effects of Ca 2+ ions substitution on microstructure and electrical properties of the ceramics were researched. Ca 2+ ions substitute for A-site Ba 2+ ions to enter the unit cell maintaining the perovskite structure of th solid solution and the orthorhombic phase and tetragonal phase coexist in the composition with x = 0.04 to 0.10. SEM images confirmed the inhibiting effect of Ca ions on the grain growth process of the Ba 0.97-x Ca x La 0.03 Ti 0.90 Sn 0.10 O 3 ceramics. Uniformly distributed microstructures with high relative densities above 94.71% were developed with the further addition of Ca 2+ ions. Main piezoelectric parameters were optimized at x = 0.04 with a high piezoelectric coefficient (d 33 = 541 pC/N), a planar electromechanical coupling factor (k p = 45.7%), The analysis on the temperature dependence of dielectric permittivity approved the existence of the mixed ferroelectric-relaxor features in all the BCLST samples. The remnant polarization (Pr) reaches an extreme value of 7.81 μC/cm 2 at x = 0.08.

Dielectric properties and phase p,T –diagram of CuBiP<sub>2</sub>Se<sub>6</sub> layered crystals

Purpose: CuBiP 2 Se 6 layered crystals exhibit a temperature-dependent antiferroelectric ordering of the Cu + and Bi 3+ ions in the lattice. The temperature dependence of the static dielectric permittivity reveals the first-order ’’displacive’’ antiferroelectric phase transition at Tc=136 K At thys time no literature data on the effect of hydrostatic pressure on the dielectric properties and antiferroelectric phase crystals CuBiP 2 Se 6 . The aim of this paper is to investigate the p,T-phase diagram CuBiP 2 Se 6 layered crystals via broadband dielectric measurement. Methods: Studied CuBiP 2 Se 6 crystals were grown by the gas transport reaction method. For the dielectric measuremen polished platelike crystals were used. All measurements were performed in a direction perpendicular to the layers. The complex dielectric permittivity e∗ was measured using an HP4262A capacitance bridge at the frequency 1 MHz. All measurements have been performed on cooling and heating mode with a temperature rate 0.5 K/min. Silver paste has been used for contacting. Hydrostatic pressure was applied a high-pressure chamber, its value being controlled within ±1MPa. Results: Studies of complex dielectric permittivity e∗ of CuBiP 2 Se 6 crystals with different values hydrostatic pressure in a wide temperature range 77 K <T <400K and pressure of 0 MPa <p <600 MPa were performed. In the temperature range 120K <T <200K for CuBiP 2 Se 6 crystals the law of Curie-Weiss.In the paraelectric phase and antiferroelectric phase Curie-Weiss constant and Curie-Weiss temperature respectively are: , та , . Тhe coefficient , та , for the paraelectric phase and antiferroelectric phase respectively. The transition temperature linearly decreases with increasing pressure with the ratio of -0,049 K/MPa. Conclusions: Based on the studies of temperature dependences of dielectric permittivity of CuBiP 2 Se 6 layered crystals at high hydrostatic pressure, a p,T phase diagram was built, and pressure coefficients for the phase transition temperature shift were determined. Hydrostatic pressure shifts beginning superionic temperature ion transport in the low temperatures region.

Composition dependence of physical properties in Pr0.7Ca0.3Mn1−xNixO3

We have prepared orthorhombic Pr0.7Ca0.3Mn1−xNixO3 ceramics by conventional solid-state reaction. Then, we have studied their electrical, magnetic and magnetocaloric properties. From electrical conductivity study, it is found that Ni-doped PrCaMnO3 systems exhibit a semiconductor behavior. In conductance versus temperature curves, a specific saturation region appears for x = 0, 0.02 and 0.05. Such behavior seems to appear at high temperature (T > 300 K) for x = 0.1. The evolution of such behavior with nickel content is attributed to the variation of the density of trapped charge and to the capture efficiency of charge traps. It is also found that electrical transport is governed by thermally activated hopping process. The activation energy of such process is sensitive to the nickel concentration. It increases from Ehop = 35 meV for x = 0 to Ehop = 128 meV for x = 0.1. The temperature dependence of dielectric permittivity is characterized by the appearance of dielectric transition and it is described by the Curie-Weiss law. The transition temperature Td does not change for small Ni content (Td = 145 K for x = 0.02 and 0.05), but it increases for x = 0.1 (Td = 155 K). Impedance study indicates the presence of a non-Debye relaxation phenomenon in the investigated materials and approves the applied role of the grain boundary in electrical transport process. The magnetic measurements reveal that an x increase in Pr0.7Ca0.3Mn1−xNixO3 enhances the ferromagnetic-paramagnetic transition temperature. Based on the isothermal curves we have calculated the magnetic-entropy which persistently increases with the increase of magnetic field. The magnetic-entropy has been also deduced from the Landau theory. Satisfactory agreement between the theoretical curves and the experimental dependencies has been found.

Structure and dielectric properties at phase transition of Na1/2Bi1/2TiO3-BaTiO3 solid solutions

ABSTRACTPhase coexistence region is studied by x-ray diffraction for Na1/2Bi1/2TiO3-BaTiO3 solid solutions in the tetragonal phase side from the morphotropic phase boundary. The first order ferroelectric phase transition, determined from a jump in the temperature dependence of dielectric permittivity, is located inside the coexistence region of cubic and tetragonal phases and is below the temperature, where tetragonality disappears. At low BaTiO3 concentrations phase transition into ferroelectric state at cooling is slowly approached in time and is smeared over large temperature range. Rietveld method, applied for more precise evaluation of phase content, reveals large local deformations inside the ferroelectric phase.

Duplex structure in K0.5Na0.5NbO3-SrZrO3 ceramics with temperature-stable dielectric properties

Temperature-stable dielectric properties have been developed in the 0.86K0.5Na0.5NbO3-0.14SrZrO3 solid solution system. High dielectric permittivity (ε′=2310) with low loss sustained in a broad temperature range (−55–201°C), which was close to that of the commercial BaTiO3-based high-temperature capacitors. Transmission electron microscopy with energy dispersive X-ray analysis directly revealed that submicron grains exhibited duplex core-shell structure. The outer shell region was similar to the target composition, whilst a slightly poor content of Sr and Zr presented in the core region. Based on Lichtenecker’s effective dielectric function analysis along with Lorentz fit of the temperature dependence of dielectric permittivity, a plausible mechanism explaining the temperature-stable dielectric response in present work was suggested. These results offer an opportunity to achieve the X8R specification high-temperature capacitors in K0.5Na0.5NbO3 based materials.

Raman and dielectric spectroscopic analysis of magnetic phase transition in Y(Fe0.5Cr0.5)O3 multiferroic ceramics

Here, we report the Raman and dielectric spectroscopic studies as a function of temperature of orthorhombically distorted Y(Fe0.5Cr0.5)O3 (YFC) ceramics, measured from 80 to 300K. The dc-magnetization measurements under field cooled (FC)-zero field cooled (ZFC) protocol indicate a small onset of magnetic ordering at TN∼270K. The field dependent magnetization plot recorded at 50K, 150K and 200K show a clear opening in hysteresis loops. The linear dependence of magnetization plot at high field without any saturation of magnetization indicates the coexistence of weak ferromagnetic (WFM) component within the canting antiferromagnetic (CAFM) matrix. Temperature evolution of Raman line-shape parameter of B2g(4) phonon mode clearly exhibits an anomalous behavior of phonon shift near TN∼270K, indicating the spin-phonon coupling in the ceramics. From the temperature dependent dielectric permittivity (ε(T)) study, two dielectric relaxation peaks are detected below 200K and above 250K. The appearance of former relaxation peak is responsible for polaronic conduction mechanism, while the later one is associated with magnetic phase transition which might be relevant to the presence of magnetoelectric coupling in YFC ceramics. The observed P-E hysteresis loops at room temperature indicate weak ferroelectric nature of the ceramics.

Optimized piezoelectric and structural properties of (Bi,Na)TiO3–(Bi,K)TiO3 ceramics for energy harvester applications

We investigated (1−x)(Bi,Na)TiO3–x(Bi,K)TiO3 (x=0, 0.14, 0.16, 0.18, 0.20, and 0.22) compositions of lead-free piezoelectric ceramics for potential energy harvester applications. Composition and sintering temperature of (1−x)(Bi,Na)TiO3–x(Bi,K)TiO3 were varied to extract the optimized processing temperature with each composition. We compared and analyzed sintering temperature-dependent surface morphologies and electrical properties. Maximum piezoelectric charge constant of 180pC/N were obtained from the 0.8(Bi,Na)TiO3–0.2(Bi,K)TiO3composition at the sintering temperature of 1180°C. Temperature dependent dielectric permittivity was measured to know the phase transition. We corresponded two different anomaly peaks, observed at 84 and 290°C, as the rhombohedral-tetragonal and tetragonal-cubic phase transitions, respectively. Due to these phase transitions, different shapes of polarization-electric field loops (P-E loops) were measured and compared. Finally, output power of 42.39nW/cm2 were obtained for the (1−x)(Bi,Na)TiO3–x(Bi,K)TiO3 lead free piezoelectric ceramics.

Phase transitions in Na0.5Bi0.5TiO3-(Sr0.7Bi0.2)TiO3-PbTiO3 solid solutions

ABSTRACTIncreasing of Sr0.7Bi0.2TiO3 concentration in Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions causes increasing of Bi/Na relation and vacancies in the A-site of perovskite structure. In temperature dependence of dielectric permittivity, such a change of composition is reflected by transforming of the frequency-dependent shoulder into a maximum characteristic for relaxor ferroelectrics and diminishing of the frequency-independent maximum characteristic for Na0.5Bi0.5TiO3. Here changes in behavior of dielectric permittivity and polarization are studied if PbTiO3 is added in a certain concentration range of Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions. Changes of the characteristic temperatures as a function of PbTiO3 concentration are determined. Behavior of the electrocaloric effect is compared with the results obtained for Na0.5Bi0.5TiO3-SrTiO3-PbTiO3.

Structural characterization, vibrational spectroscopy accomplished with DFT calculation, thermal and dielectric behaviors in a new organic-inorganic tertrapropylammonium aquapentachlorostannate dihydrate compound

In this work a novel compound tertrapropylammonium aquapentachlorostannate dihydrate was synthesized and characterized by; single crystal X-ray diffraction, vibrational spectroscopy, differential scanning calorimetric and dielectric measurement. The crystal structure refinement at room temperature reveled that this later belongs to the monoclinic compound with P121/c1 space group with the following unit cell parameters a = 8.2699(3) Å, b = 12.4665(4) Å, c = 22.3341(7) Å and β = 92.94(0)°. The crystal arrangement can be described by stacked organic-inorganic layers in the c direction with two independent water molecules placed between each two layers. The detailed interpretations of the vibrational properties of the studied compound were performed using density functional theory (DFT) with the B3LYP/LanL2DZ basis set, and has enabled us to make the detailed assignments by comparative study of the experimental and calculated Raman and IR spectra. The differential scanning calorimetry (DSC) measurement disclosed two anomalies in the temperature range 356–376 (T1) K and at 393 K (T2) characterized by the dehydration of the sample and probably a reconstruction of a new structure after T2 transition. The temperature dependences of dielectric permittivity show a relaxation process around T2 anomaly indicating the occurrence of the disorder at high temperature. The dependence of the exponent m(T) on temperature, extracted from the straight lines of log(ε″) with log (ω), suggests that the correlated barrier hopping is the appropriate model for the conduction mechanism.

High energy density dielectrics in lead-free Bi0.5Na0.5TiO3–NaNbO3–Ba(Zr0.2Ti0.8)O3 ternary system with wide operating temperature

The 0.6Bi0.5Na0.5TiO3–(0.4 − x)NaNbO3–xBa(Zr0.2Ti0.8)O3 (BNT–NN–BZT) ceramics were developed for application as high energy density capacitor by conventional solid-state reaction method, and their structure, dielectric and ferroelectric properties were investigated in detail. When BZT was introduced into the system, the crystal structure changed from tetragonal to pseudocubic. Temperature dependent dielectric permittivity showed a broad maximum in these pseudocubic ceramics, exhibitting distinct relaxor feature. The relaxor behavior was evaluated by modified Curie–Weiss and confirmed to be enhanced with increasing BZT content. Benefited from the relaxor feature, its dielectric constant and dielectric temperature stability were largely improved. The remanent polarization (Pr) and coercive electric field (Ec) decreased with high BZT content and the maximum polarization (Pm) improved as shown in ferroelectric hysteresis loops (P–E loops). The energy storage property was also improved with increasing BZT, the optimized energy storage property was obtained in x = 0.20 sample with W = 1.69 J/cm3 at 17.5 kV/mm, which was superior to many other ferroelectric relaxors, indicating that BNT–NN–BZT ceramics were promising candidates for temperature stable energy storage applications.

Study of physical properties of cobalt substituted Pr0.7Ca0.3MnO3 ceramics

An investigation on single phase semiconducting polycrystalline Pr0.7Ca0.3MnO3 and Pr0.7Ca0.3MnCo0.1O3 crystallized in the orthorhombic system with Pnma space group is reported. We found that σDC increases when introducing Co for T<110K but for T>110K, it decreases. Also, the contribution of hopping process in conduction mechanism was in agreement with the Jonscher law and Mott theory. Capacitance was extensively dependent on temperature and frequency. A dielectric transition was observed at T=150K for the doped compound. The temperature dependence of dielectric permittivity is well described by Curie–Weiss law. The parameter of deviation from Curie–Weiss behavior to modified Curie–Weiss law is found to be ΔTm=30K. The substitution of Mn by Co was found to destroy the charge order state observed in the parent compound and to induce a ferromagnetic phase at low temperature. The cobalt-substituted sample exhibits a maximum value of magnetic entropy change |∆Smax|=3.2Jkg−1K−1and a large relative cooling power with a maximum value of 301J/kg under an applied field of 5T. Technically, these large values make the prepared material very promising for magnetic refrigeration.

Lead-free Relaxor Ferroelectrics for Electrocaloric Cooling

In this work, we consider electrocaloric (EC) device operation at high electric fields E above the temperature Tm of the maximum dielectric permittivity. Here, the EC response is determined by the temperature dependence of dielectric permittivity while dielectric losses are comparably low. We discuss materials selection and EC device concepts. An upper bound of the EC effect - independent on phase transition - is proposed which is based on the maximum energy density storable in a dielectric. Relaxors promising for EC applications are discussed.

Complex dielectric and impedance behavior of magnetoelectric Fe2TiO5

We have investigated the complex dielectric and impedance properties of magnetoelectric compound Fe2TiO5 (FTO) as a function of temperature (T) and frequency (f) to understand the grain (G) and grain boundary (Gb) contributions to its dielectric response. The temperature and frequency dependent dielectric permittivity (ε′) data shows a sharp increase in permittivity above 200 K accompanied with a frequency dependent peak in tanδ. At T < 175 K, only G contribution dominates even at lower frequency (∼100 Hz), but for T ≥ 175 K, the Gb contribution starts appearing at low frequency. The value of critical frequency distinguishing these two contributions increases with increasing temperature. The observed non-Debye dielectric relaxation follows thermally activated process and is attributed to polaron hopping. Further the frequency dependence of ac conductivity follows the Jonscher's power-law. The temperature dependency of critical exponent ‘s’ shows that the correlated barrier hopping model is appropriate to explain the conductivity mechanism of FTO in the studied temperature regime.