Activation Energy Of Dielectric Relaxation Research Articles

Electrical and dielectric characteristics of molybdenum dioxide nanoparticles for high-performance electrocatalysis

As an attempt to improve the catalytic processes in different electrochemical systems, molybdenum dioxide nanoparticles were prepared using the hydrothermal method, and their electrical and dielectric properties were investigated. The nanoparticles were polycrystalline with an orthorhombic structure. AC electrical transport properties of the pressed disc were conducted over a temperature range of 303–423 K and a frequency range of 42–5 × 106 Hz. The AC conductivity follows Jonscher's universal dynamic law, and it has been determined that correlated barrier hopping (CBH) is the primary conduction mechanism. The maximum barrier height (WM) was found to be 0.92 eV. The low activation energy showed that hopping conduction is the dominant mechanism of transporting current. The dielectric parameters were analyzed using both complex permittivity and complex electric modulus, with a focus on how they vary with temperature and frequency. At relatively high temperatures and low frequencies, the dielectric parameters showed a high-frequency dependence. The dielectric modulus showed that relaxation peaks move towards lower frequency when temperature increases. The dielectric relaxation activation energy, Δ Eω was determined to be 0.31 eV.

Tunable optical, electro-optical and dielectric properties of eco-friendly graphene quantum dots-nematic liquid crystal composites

ABSTRACT The changes in physical properties obtained by dispersing hydrophilic carboxylated graphene quantum dots (GQDs, <10 nm), which are non-toxic, biocompatible, and eco-friendly, into a room-temperature nematic liquid crystal, 5CB (4-pentyl-4ˈ- biphenylcarbonitrile) are described. Nematic–isotropic transition temperatures, polarising microscopy, electro-optic, photoluminescence, and dielectric investigations are reported for two composites having concentrations of GQDs of 0.25 and 1.0 wt.% in 5CB and compared to pristine 5CB. At the lower concentration (0.25%) of GQDs there is an enhancement in the order parameter by 5.49%, the birefringence by 1.28%, and the activation energy for dielectric relaxation by 4.4% compared to pure 5CB. However, at the higher concentration (1%), aggregation of GQDs occurs. This is apparent in optical textures and resulted in the deterioration of optical and electrical properties compared to 5CB. The photoluminescence spectrum of both concentrations of GQDs are centred at the same wavelength; however, the 1% GQD-5CB mixture exhibits significant quenching and may be suitable for some optical devices. Overall, our results support that, in addition to promoting sustainable, heavy-metal-free, and environmentally safe technologies, a low concentration of GQDs in LCs produces composites that have superior electrical and optical properties; thus, making them suitable for a variety of photonics and display applications.

Influence of confined phase transition on dielectric relaxation characteristics of thermochromic epoxy insulating materials

The dielectric relaxation characteristic and mechanism of thermochromic microcapsule-epoxy insulating material are investigated. The results show that thermochromic microcapsule-epoxy insulating material exhibits non-monotonic dielectric relaxation characteristic, namely the dielectric relaxation time gradually increases with the temperature rising in a range of about 58–66 ℃, which cannot be depicted by the conventional Arrhenius equation or Vogel-Fulcher-Tammann equation. It is proposed that the non-monotonic dielectric relaxation characteristic is derived from the free volume variation induced by the confined phase transition in microcapsule. With the increase of temperature, the solid-liquid phase transition occurs in the limited space of microcapsule, reducing the free volume inside the microcapsule, which could restrict the reorientation of dipole with the external electric field and lead to the increase of dielectric relaxation time. The non-monotonic dielectric relaxation characteristic of thermochromic epoxy specimen is fitted based on the confined dielectric relaxation model, obtaining the activation energy of dielectric relaxation. The relaxation activation energy values of thermochromic epoxy insulating materials with different microcapsule content are of the same order of magnitude, indicating that the non-monotonic dielectric relaxations occur inside the thermochromic microcapsule, verifying the role of confined phase transition in the non-monotonic dielectric relaxation characteristic.

Modulation of electric and magnetic ordering in GdFeO3 orthoferrites system by Ce-doping

In the present attempt, orthoferrites system GdFeO3 (GFO) is modified by partially substituting Gd by Ce and its influence on structure, electric and magnetic orderings of GFO are systematically explored. The doped-GFO systems with various compositions Gd1-xCexFeO3 (GCFO; x = 0 ≤ x ≤ 0.1 with 0.02 interval) are developed by using sol-gel combustion route. The Rietveld refinements of the XRD data confirm orthorhombic phase with Pbnm space group of all compositions. The substitutional effect of Gd by Ce in GFO is found to reduce Dielectric constant and to enhance dissipation factor. Both these effect is associated with change in hybridization between O-2p states and Fe-3d due to change in Fe–O bond length by dopant effect. The dielectric relaxation are revealed using impedance loss spectra and electric modulus formalism in the frequency range 1 Hz to 1 MHz and in the temperature rage 200–450 °C and relaxation time is found to decrease with doping level and temperature. The net resistivity of GFO is reduced with increase in conductivity by around two orders by Ce-doping. The frequency dependence of conductivity follows the power law. The activation energy for dielectric relaxation in GCFO is varying between 0.3 and 0.5 eV at grain boundaries; while 0.25–0.4 eV on grain, indicate the conduction mechanism on grain boundaries is attributed by oxygen vacancies defect and grains by polaron hopping. The magnetization study displays doping of Ce modifies the M-H hysteresis loop and gives canted antiferromagnetic behavior in GFO. The remnant magnetization and coercivity is suddenly jumped by two order in GCFO system. The significant enhancement in electric and magnetic orderings is achieved by Ce addition in GFO.

Solid-State NMR and Impedance Spectroscopy Study of Spin Dynamics in Proton-Conducting Polymers: An Application of Anisotropic Relaxing Model

The 1H–13C cross-polarization (CP) kinetics in poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) was studied under moderate (10 kHz) magic-angle spinning (MAS). To elucidate the role of adsorbed water in spin diffusion and proton conductivity, PMETAC was degassed under vacuum. The CP MAS results were processed by applying the anisotropic Naito and McDowell spin dynamics model, which includes the complete scheme of the rotating frame spin–lattice relaxation pathways. Some earlier studied proton-conducting and nonconducting polymers were added to the analysis in order to prove the capability of the used approach and to get more general conclusions. The spin-diffusion rate constant, which describes the damping of the coherences, was found to be strongly depending on the dipolar I–S coupling constant (DIS). The spin diffusion, associated with the incoherent thermal equilibration with the bath, was found to be most probably independent of DIS. It was deduced that the drying scarcely influences the spin-diffusion rates; however, it significantly (1 order of magnitude) reduces the rotating frame spin–lattice relaxation times. The drying causes the polymer hardening that reflects the changes of the local order parameters. The impedance spectroscopy was applied to study proton conductivity. The activation energies for dielectric relaxation and proton conductivity were determined, and the vehicle-type conductivity mechanism was accepted. The spin-diffusion processes occur on the microsecond scale and are one order faster than the dielectric relaxation. The possibility to determine the proton location in the H-bonded structures in powders using CP MAS technique is discussed.

Effects of ultralow concentration MXene (nano-Ti3C2Tx) on the electric and physical properties of ternary polyvinyl alcohol composites

High-dielectric-constant (high-κ) fillers are embedded in polymer materials to improve the dielectric constant of polymer and form high-κ composites for the latest generation of energy storage devices. However, the addition of high-κ fillers will introduce interface polarization and cause space charge accumulations that will increase dielectric loss and reduce breakdown strength. Herein introduces a conductive MXene(nano-Ti3C2Tx) with high surface area to remarkably suppress space charge in polyvinyl alcohol (PVA) matrix. A ternary PVA composite with high dielectric constant and low dielectric loss is formed by doping with ultralow concentration MXene and soluble ferroelectric [Hdabco]ClO4 (TEDA.C) via solution mixing. The space charge suppression capability of MXene sharply reduces the dielectric loss of 1M@1788PVA and 5M@1788PVA (PVA with 0.0001 wt.% and 0.0005 wt.% MXene) at low frequency (0.1−10 Hz). By comparing the activation energy of dielectric relaxation (Ea) and breakdown strength (BDS) under AC electric field between pure PVA and PVA composites, ultralow concentration MXene declines the Ea of 1M@1788PVA and 5M@1788PVA by 26.8 % and 60.9 %, and effectively improves the BDS of 1M@1788PVA and 1M5T@1788PVA (PVA with 0.0001 wt.% MXene and 4.7 wt.% TEDA.C) by 3%. The addition of ultralow concentration MXene and TEDA.C bring 5M5T@1788PVA(PVA with 0.0005 wt.% MXene and 4.7 wt.% TEDA.C) highest discharged energy density(17.32 J/cm3)which is 1.53 times of that of 1788PVA.

Enhanced electrical properties of La1.9Nd0.1Ti2O7 ceramics

La2−xNdxTi2O7 (LNTO) ceramics with enhanced electrical properties have been prepared by traditional solid-state reaction method. The LNTO ceramics maintain a pure monoclinic phase at x ≤ 0.1. At x > 0.1, an orthorhombic phase Nd0.95TiO3 appears. Impedance spectra indicates that the substitution of La3+ ions by Nd3+ ions at A sites generates defects, resulting in the enhanced distortions of TiO6 octahedrons. The dielectric relaxation activation energy for these defects is 1.2 eV in temperature range T ≥ 650 ℃. The conductance activation energies are 0.3 eV and 1.0 eV for impure ions/thermions and defects/oxygen vacancies, respectively. The contributions of impure ions/thermions and defects/oxygen vacancies have been distinguished through the analysis of both normalized imaginary impedance Z″ and electrical modulus M″. Their impedance relaxation activation energies in normalized Z″ spectra are 1.3 eV and 0.8 eV, respectively. An enhanced piezoelectric coefficient (d33 = 2.8 pC/N) appears in La1.9Nd0.1Ti2O7 (LNTO-0.1) ceramics.

THERMAL AND AC ELECTRICAL PROPERTIES OF THIN FILMS PREPARED FROM n-BUTYL METHACRYLATE BY A CAPACITIVELY COUPLED PLASMA REACTOR

Plasma-polymerized thin films of n-butyl methacrylate (PPnBMA) have been deposited on to glass substrate in an aluminium/PPnBMA/aluminium configuration by a capacitively coupled glow discharge reactor. The field emission scanning electron microscope and atomic force microscope images of PPnBMA thin films showed a flat, uniform and continuous surface. With increasing deposition time the root mean square roughness of the PPnBMA thin films increases. The differential thermal analysis and thermogravimetric analysis demonstrated that PPnBMA was thermally stable up to about 476 and 500[Formula: see text]K in air and N2 environments, respectively. The alternating current (AC) electrical conductivity ([Formula: see text]) and dielectric properties of the PPnBMA thin films of thickness 120[Formula: see text]nm were investigated in the frequency region from 102–106[Formula: see text]Hz at various temperatures. It was found that the mechanism dependable for the conduction process in PPnBMA is hopping. The trend of dielectric constant ascends with ascending temperature and descends with frequency. The dielectric loss tangent is seen to increase with frequency and attains a maximum loss peak at around 105[Formula: see text]Hz and above this frequency it decreases. The plot of relaxation time against the reciprocal of absolute temperature for PPnBMA thin film yields the activation energy for dielectric relaxation at 0.05[Formula: see text]eV. Cole–Cole plot exhibits little distorted semicircle which also indicates nearly Debye type relaxation process in this film.

Dielectric properties of modified montmorillonites suspensions in polydimethylsiloxane

ABSTRACTThe dielectric characteristics of various modified montmorillonites suspensions in polydimethylsiloxane were investigated. Such materials are promising candidates as electrorheological fluids. The effect of small water content and temperature change in the dielectric spectra of suspensions was studied. The electrical conductivity of suspensions rises with filler concentration. Conductivity also increases with frequency for all samples by 5–6 orders of magnitude. The frequency dependence of permittivity changes significantly with temperature and strongly depends on the type of modifier. The positions of relaxation transitions peaks observed in dielectric loss curves substantially depend on the type of filler and water content. Dielectric loss peaks shift to higher frequencies with temperature. Relaxation mechanism is related to filler and described by capacitor model. Based on X‐ray data a model of relaxation transitions is proposed. Also, the activation energy of dielectric relaxation is estimated. The activation energy is independent of filler concentration but is determined by the structural features of fillers in polymer medium. The prospects of dielectric spectroscopy for analyzing the layered nanosilicates structure in polymer solution are demonstrated. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46614.

High-temperature dielectric and impedance spectroscopy of Ca2NaNb3O10 ceramic

Ca2NaNb3O10 ceramic was prepared by solid state reaction. The XRD patterns show that Ca2NaNb3O10 ceramic has an orthorhombic phase. The dielectric and impedance spectroscopy of the sample was investigated which shows dielectric permittivity and the dielectric loss peaks shift to high temperature with increasing frequency. According to the analysis of Cole–Cole and impedance–frequency spectroscopy, non-Debye relaxation process exists in the sample. The activation energy of dielectric relaxation and conduction are estimated to be 1.41 and 1.23 eV.

Effect of isovalent lanthanide cations compensation for volatilized A-site bismuth in Aurivillius ferroelectric bismuth titanate

Bismuth titanate ferroelectric ceramics (BiT) compensated(doped) by 3 mol% of Bi3+ or Ln3+ (BiT–Bi, BiT–Ln; Ln = La, Nd, Sm) were synthesized by conventional solid-state reaction, then the effects of compensation towards the lattice structure as well as the ferroelectric properties were studied. Rietveld refinement of the structure confirmed the pure Aurivillius phase with space group B2cb in all the constituents, however the trace amount of Bi2O3 and Ln2O3 could also act as sintering aids during sintering. The 6s 2 lone pair electrons of Bi3+ in perovskites localize into a lobe shape and the lobes major axis prefer to align along the a-axis, resulting the Bi3+ in perovskites showing a smaller effective radius compared with Ln3+ and causing higher lattice distortion. In addition, the paraelectric–ferroelectric phase transition temperature (Curie temperature, T c ), piezoelectric coefficient (d 33), spontaneous polarization (P s ), a.c. conductivity [σ(ω)] and activation energy of dielectric relaxation (E a ) increase with decreasing A-site cation radius. Furthermore, ferroelectric polarization and electromechanical properties of the BiT–Bi were enhanced dramatically due to the oxygen vacancies suppression by the compensation, which was confirmed by electric modulus approach.

Aliovalent Ba2+ doping: A way to reduce oxygen vacancy in multiferroic BiFeO3

This paper demonstrates the impact of Ba2+ substitution on the structural, dielectric relaxation and AC conductivity properties of Bi1−xBaxFeO3(0≤x≤0.25) ceramics. Ba doping incorporates rhombohedral to tetragonal structural transformation in perovskite BFO. XPS data shows change in oxygen vacancy concentration with Ba doping and it also suggests that schoimetry of the doped compounds is not maintained by creating mix valance state of Fe. Reduction in oxygen vacancy (OVs) in the doped samples is explained by Kroger–Vink notation. Arrhenius plot shows activation energy for dielectric relaxation of the doped samples lies between ~1.16 and 1.44eV. AC conductivity of material decreases as Ba ion substitution increases in the parent compound. Electrical conductivity is attributed to the correlated barrier hopping (CBH) motion of the oxygen vacancies in the samples. Coulombic potential barrier (WM) height, calculated from Elliott model for CBH motion of charge carriers shows correlation with the activation energy of AC conductivity at low temperature. Activation energy value obtained from the impedance measurements of the samples implies short range migration of oxygen vacancies dominates the frequency dependent conductivity while the frequency independent part of conductivity is the result of long range migration of oxygen vacancies.

Structure, photoluminescence and electrical properties of BaBi3.5Eu0.5Ti4O15 ceramics

Aurivillius phase BaBi3.5Eu0.5Ti4O15 (BBET) ceramics were synthesized using a solid state reaction method. X-ray diffraction analysis confirmed that the compound is a four-layer Aurivillius oxide with tetragonal space group I4/mmm and Raman spectrum indicated that Eu3+ ions occupy the A site. It was observed that the average grain size is 0.5–2.5μm by the scanning electron microscope. The photoluminescence spectra showed that the intense emission bands centered at about 593 and 615nm are due to the transitions of 5D0→7F1 and 5D0→7F2 of Eu3+ ions respectively. The temperature of dielectric constant maximum, the room temperature dielectric constant and loss at 1MHz are 373°C, 222 and 0.013, respectively. The activation energy of dielectric relaxation was estimated to be 1.17eV, which could be attributed to the thermal motion of oxygen vacancies. The BBET ceramics had a remnant polarization (2Pr) of 0.75μC/cm2 at room temperature. The results suggest that BBET ceramics can be considered as a promising multifunctional optoelectronic material.

Evaluation of the intrinsic magneto-dielectric coupling in LaMn0.5Co0.5O3 single crystals

The magneto-dielectric coupling in (l00) oriented LaMn0.5Co0.5O3 single crystals has been investigated using temperature, frequency, and magnetic field dependent dielectric response. Electronic transport data divulges that polaronic hopping arises due to Emin-Holstein adiabatic small polarons. Spin realignment through external magnetic field favors faster polaronic hopping by lowering activation energy for dielectric relaxation. Finally, positive magneto-dielectricity and magnetoloss under increasing magnetic field at high frequency of the exciting ac field confirms intrinsic magneto-dielectric effect in disordered ferromagnetic-insulator LaMn0.5Co0.5O3. This study also emphasizes the need to use single crystals as well as the frequencies higher than the corresponding inverse relaxation time.

Synthesis, characterization, and dielectric properties of Y2NiMnO6 ceramics prepared by a simple thermal decomposition route

In attempt to search for an improved material preparation technique, Y2NiMnO6 dielectric material is prepared by a one-step thermal decomposition route where a solution of stoichiometric mixtures of metal acetates is directly heated. Structural characterization by X-ray diffraction and electron diffraction shows that the samples were successfully prepared at relatively low temperature comparing to a standard solid state synthesis. Results from several techniques including thermal analysis, electron microscopy, and X-ray absorption are used to investigate compound formation. It is revealed that metal acetates decompose at 300–350 °C resulting in mixture of several metal oxide intermediates which continue to react to form the desired product. Y2NiMnO6 nanoparticles are first obtained at 800 °C. Later, these nanoparticles agglomerate and grow at higher temperature and/or longer heating time to give larger particle size and more crystallinity. Although the starting reagent contains Mn in 2+ oxidation state, X-ray absorption near edge structure analysis indicates that the obtained Y2NiMnO6 contain Mn and Ni in 4+/3+ and 2+ oxidation states, respectively. Ceramic sample shows large dielectric constant of about 6,000–7,000 at 30–120 °C at 1 kHz. Dielectric constant and dielectric response of the sample are consistent with those reported in other works where different synthetic techniques were used. The activation energy of dielectric relaxation is similar to the energy required to transfer electrons between Ni2+ and Mn4+, thus the observed large dielectric constant is intrinsically related to electronic ferroelectricity due to charge ordering of Ni2+ and Mn4+.

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.

Frequency and temperature dependent dielectric and conductivity behavior of 0.95(K 0.5Na 0.5)NbO 3–0.05BaTiO 3 ceramic

Dielectric and conductivity measurements were carried out on the 0.95(K 0.5Na 0.5)NbO 3–0.05BaTiO 3 (KNN–5BT) ceramic both as a function of temperature (∼350–850 K) and frequency (40 Hz to 100 MHz). A high-temperature dielectric relaxation above Curie temperature (∼590 K) was observed and analyzed with the Cole–Cole function. Frequency dependent conductivity was analyzed with an augmented Jonscher relation and exhibited a universal conductivity behavior. The activation energy of dielectric relaxation was estimated to be 1.09 eV. It could be attributed to the thermal motion of double ionized oxygen vacancy or to the formation of defect dipoles between the acceptor ion and charge compensating oxygen vacancies. The mechanism for both the high-temperature dielectric relaxation and the frequency dependent conductivity was proposed based on a possible mode of incorporation of Ba 2+ and Ti 4+ ions into the KNN lattice sites.

Structure and dielectric relaxation of double-perovskite La2CuTiO6 ceramics

Dielectric properties of La2CuTiO6 ceramics were investigated in a broad frequency and temperature range. There is only one dielectric relaxation in the curve of temperature dependence of dielectric properties for La2CuTiO6 ceramics. This dielectric relaxation is a thermal activated process. The bulk and grain boundary resistances can be obtained from results of the least-mean-square fitting on impedance spectra. The conduction mechanism of the present ceramics is also a thermal activated process. The activation energy of dielectric relaxation is almost same as that of electrical conductivity and this indicates the closely correlation between the dielectric relaxation and electrical conductivity. The dielectric relaxation in the present ceramics should be attributed to the mixed-valent structure (Cu+/Cu2+ and Ti3+/Ti4+), which is induced from the oxygen vacancy.

Impedance studies on high energy Li 3+ irradiated PZT thin films

The ferroelectric Pb(Zr 0.48Ti 0.52)O 3 (PZT) thin films prepared by the pulsed laser deposition technique were studied for their response to high energy lithium ion irradiation through impedance spectroscopy. The Debye peaks, observed in the impedance and modulus plots of irradiated films, shifts towards higher frequencies compared to those of unirradiated films. This is equivalent to the trend observed with increase in temperature in the unirradiated films due to the dielectric relaxation. The irradiated films showed a decrease in the grain resistance compared to the unirradiated films. The activation energy of dielectric relaxation increases from 1.25 eV of unirradiated film to 1.62 eV of irradiated film. The observed modifications in the irradiated film were ascribed to the modifications in the grain structure due to the high value of electronic energy loss.

Size Effect of Al2O3 Nanowires on the Molecular Relaxation in Epoxy Composites

AbstractThe size effect of Al2O3 nanowires on the molecular relaxation of an epoxy system was investigated by means of DSC and dielectric relaxation spectroscopy. Tg and activation energy of dielectric relaxation decreased with the incorporation of the nanowires. To explain the observed results, a coarse‐grained confined‐region structure model is proposed, and on the basis of this model, the change in molecular motion arising from the nanowires could be understood. The variations of thermal stability and water absorption for the nanocomposites were also discussed. These original experimental results should be helpful in scientific research and nanocomposite applications.magnified image