Maxwell-Wagner Research Articles

Space charge dynamics in epoxy resin impregnated crepe paper multilayer under voltage polarity reversal

In this paper, the temporal space charge dynamics under both temperature and voltage polarity reversal of an epoxy resin impregnated crepe paper are characterized by pulsed electroacoustic method. It is found that the space charge injection and the interfacial traps located between the epoxy and paper plays an important role in determining the space charge dynamics. The results reveal that below 353 K, the calculated interfacial charge density is consistent with the Maxwell-Wagner (MW) model, while above 353 K, it is smaller than the measured value. The time constant during charging is much smaller than that predicted by the MW model and the space charge injection showed polarity effect, which leads to the interfacial charge densities under polarity poling voltage not being equal. It is proposed that the interfacial traps and space charge injection should be responsible for the observed space charge dynamics.

Structural, morphological and dielectric investigations on NiO/CuO/ZnO combined semiconductor metal oxide structures based ternary nanocomposites

NiO/CuO/ZnO combined semiconductor metal oxide structures based ternary nanocomposites were synthesized in 2:1:1, 1:2:1 and 1:1:2 molar ratios using a simple and combined co-precipitation - hydrothermal method without utilizing any fuels, capping agents or surfactants. The structural, bonding, band gaps and morphological behaviour of the synthesized ternary nanocomposites were investigated using x-ray diffraction, Fourier transform infrared spectroscopy, UV-Diffuse reflectance spectroscopy and atomic force microscopic measurements. The dielectric properties recorded for these combined semiconductor metal oxide structures are valid with Maxwell-Wagner (M-W) model which is based on the dielectric nature in conducting grains layered with poorly conducting grain boundaries. The higher values of dielectric constant were observed for the ternary nanocomposite ratio 1:2:1 and the reduction in the values of dielectric constant of other ternary nanocomposite ratios (1:1:2 and 2:1:1) at lower frequencies is due to the fact the grain boundaries are preferably occupied by more Cu2+ ions than Ni2+ and Zn2+ ions. This kind of attempt in investigating the physical insights of combined semiconductor metal oxide structures is needed for the development of novel semiconducting devices.

Effect of temperature and frequency on electrical properties of composite multiferroic of lead titanate and strontium hexaferrite (PbTiO3 – SrFe12O19)

The work describes the use of dielectric and ac complex impedance and modulus spectroscopy techniques to obtain the electrical parameters like electrical conductivity and activation energy of composite multiferroic having composition (x) PbTiO3 – (1-x) SrFe12O19; where x = 0.10, 0.30, 0.50 in the frequency range 10–1000 KHz over a temperature range of 30–550 °C. The coexistence of low dielectric constant region with high dielectric constant region results in Maxwell – Wagner (M-W) polarization in the composite. Complex impedance and modulus spectroscopic analysis indicated the presence of non-Debye type dielectric relaxation in the composites. The grain (Rg) and space charge polarization resistance (RSCP) decreases with increase in temperature providing convincing evidence that the electrical properties of composite are temperature as well as microstructure dependent. The ac conductivity of composite calculated from dielectric loss and it shows an increase with increasing temperature suggesting semiconductor behavior. The hopping rate and concentration of charge carriers was calculated using Almond and West formalism based on Jonscher's universal power law. The activation energy of the ion migration and conduction was determined from temperature dependence of the hopping rate and dc conductivity respectively. For all compositions, the activation energy of dc conductivity is greater than that of hopping; i.e., Ea > Em. The increase in drift mobility represents enhanced mobility of the charge carriers due to thermal activation.

Analysis of Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors with Bi-Layer Gate Dielectric Stacks Using Maxwell-Wagner Instability Model

Aluminium oxide (Al2O3) and hafnium oxide (HfO2) have been grown, using atomic layer deposition (ALD), as single and bi-layer gate dielectric films. Electrical and structural characterisation indicates that the material properties depend on layer thickness and growth order, when deposited as bi-layers. Charge trapping at the interface between the bi-layer stacks results from the Maxwell-Wagner (MW) instability, which states a difference of conductivities at the dielectric-dielectric interface with respect to the bulk dielectric films. Hence a build-up of this interface charge compensates for the condition that the current densities of individual dielectric films match that of the overall stack. This causes electrical instabilities in stack behaviour. Bottom-gate amorphous indium-gallium-zinc-oxide thin-film transistors are fabricated with these gate oxides, single and bi-layer stacks, with low VTH and gate leakage current to understand this instability. By empirically adopting ideal MOSFET equations and single gate dielectric film behaviour as a reference, this MW instability in bi-layer gate dielectric stacks has been accounted for in amorphous indium-gallium-zinc-oxide thin-film transistor transfer characteristics with a good fit in both above threshold and sub-threshold regimes.

Analysis of Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors with Bi-Layer Gate Dielectric Stacks Using Maxwell-Wagner Instability Model

Aluminium oxide (Al2O3) and hafnium oxide (HfO2) have been grown, using atomic layer deposition (ALD), as single and bi-layer gate dielectric films. Electrical and structural characterisation indicates that the material properties depend on layer thickness and growth order, when deposited as bi-layers. Charge trapping at the interface between the bi-layer stacks results from the Maxwell-Wagner (MW) instability, which states a difference of conductivities at the dielectric-dielectric interface with respect to the bulk dielectric films. Hence a build-up of this interface charge compensates for the condition that the current densities of individual dielectric films match that of the overall stack. This causes electrical instabilities in stack behaviour. Bottom-gate amorphous indium-gallium-zinc-oxide thin-film transistors are fabricated with these gate oxides, single and bi-layer stacks, with low VTH and gate leakage current to understand this instability. By empirically adopting ideal MOSFET equations and single gate dielectric film behaviour as a reference, this MW instability in bi-layer gate dielectric stacks has been accounted for in amorphous indium-gallium-zinc-oxide thin-film transistor transfer characteristics with a good fit in both above threshold and sub-threshold regimes.

Substitution‐induced near phase transition with Maxwell–Wagner polarization in SrBi2(Nb1−xAx)2O9 ceramics [A = W, Mo and x = 0, 0.025

AbstractThe synthesis, micro‐structure, spectroscopic, and dielectric properties of [with AW, Mo and , 0.025] ceramics were systematically studied. A relative density of 98% was obtained for all the samples using a two‐step solid state sintering process. XRD images showed that a single phase layered perovskite structure of (SBN) was formed. The orthorhombic structure with phase group was found up to ∼2.5 at.% substitution of W and Mo into the SBN matrix. SEM revealed the rod‐like grain structure similar to the Maxwell–Wagner (MW) parallel plate capacitor model in SBN ceramic, whereas smaller heterogeneous grain structure was observed in W and Mo donor doped ceramics. The initial high value of real and imaginary part of relative permittivity also indicated the presence of interfacial MW relaxation in the SBN ceramics. The experimental data fit well to the theoretical data obtained from MW polarization model in SBN ceramics. The possible origin of the difference of the properties present in the doped sample has been explained based on grain size, orientation, and modification done in the ceramic matrices.

Low temperature sintered giant dielectric permittivity CaCu3Ti4O12 sol-gel synthesized nanoparticle capacitors

This paper reports on synthesis of polycrystalline complex perovskite CaCu3Ti4O[Formula: see text] (as CCTO) ceramic powders prepared by a sol–gel auto combustion method at different sintering temperatures and sintering times, respectively. The effect of sintering time on the structure, morphology, dielectric and electrical properties of CCTO ceramics is investigated. Tuning the electrical properties via different sintering times is demonstrated for ceramic samples. X-ray diffraction (XRD) studies confirm perovskite-like structure at room temperature. Abnormal grain growth is observed for ceramic samples. Giant dielectric permittivity was realized for CCTO ceramics. High dielectric permittivity was attributed to the internal barrier layer capacitance (IBLC) model associated with the Maxwell–Wagner (MW) polarization mechanism.

Dielectric relaxation and Maxwell-Wagner interface polarization in Nb2O5 doped 0.65BiFeO3–0.35BaTiO3 ceramics

Electrical characterizations of Nb2O5 doped 0.65BiFeO3–0.35BaTiO3 (0.65BF–0.35BT) ceramic were carried out over broad temperature and frequency ranges through dielectric spectroscopy, impedance spectroscopy, and ac conductivity measurements. The dielectric constant and loss tangent are drastically reduced with introducing Nb2O5 into the 0.65BF–0.35BT system. Two dielectric anomalies are detected in the temperature regions of 100 °C ≤ T ≤ 280 °C and 350 °C ≤ T ≤ 480 °C, and the Curie temperature (TC) was confirmed in higher temperature region. A dielectric relaxation with large dielectric constants was detected near the TC. This dielectric relaxation becomes even stronger with the gradual increase in the Nb2O5 content. Impedance spectroscopy results clearly show the contributions of grains and grain boundaries in the frequency range of 100 Hz ≤ f ≤ 1 MHz, and the relaxation processes for grains and grain boundaries are non-Debye-type. The grain boundaries are more resistive than that of the grains, revealing the inhomogeneity in samples. The experimental results are well fitted based on a Maxwell-Wagner (MW) interfacial polarization model below 100 kHz, and the MW interfacial polarization effect becomes more and more obvious with the increase in the Nb2O5 content. The increase in dielectric constant is possibly related to space charge polarization, which is caused by charges accumulated at the interface between the grain and grain boundaries. Frequency dependence of the ac conductivity confirms the MW interfacial polarization effect below 100 kHz.

Effects of LaNiO3 interlayer on the microstructures and electrical properties of Ba0.9Sr0.1Ti0.99Mn0.01O3 multilayer

The aim of this work was to investigate the effects of low-resistivity interlayer on the physical properties of periodic Ba0.9Sr0.1Ti0.99Mn0.01O3 (BSTM) multilayers prepared by a chemical solution deposition method. A LaNiO3 (LNO) layer was inserted into the periodic BSTM multilayer artificially to form a sandwiched configuration of BSTM/LNO/BSTM. The capacitances at low frequencies (<100 kHz) of the sandwiched multilayer are significantly enhanced compared to that of the pure BSTM multilayer. The space charge accumulated at the LNO layer was proposed to explain the enhancement based on Maxwell-Wagner (M-W) model. However, LNO interlayer leads to an increase in the leakage current. A non-Ohmic conduction region is observed for BSTM/LNO/BSTM multilayer when the electric field exceeds 100 kV/cm. The results offer a new approach to achieve dielectric films with high dielectric constant.

Dielectric properties and defect mechanisms of (1-x)Ba(Fe0.5Nb0.5)O3 -xBiYbO3 ceramics

(1-x)Ba(Fe0.5Nb0.5)O3 -xBiYbO3 (BFN-xBY) ceramics were prepared by a conventional solid-state reaction method. The dielectric properties and relaxation behavior of BFN-xBY ceramics were analyzed according to dielectric and impedance spectroscopy. Dielectric permittivity of the ceramics increases with increasing temperature below 500 K then remains unchanged up to 700 K, while corresponding loss factor decreases with the increase of temperature below 500 K then increase slowly. Defect compensation mechanism of this system was analyzed in detail. The giant dielectric behavior of the ceramics arises from the internal barrier layer capacitor (IBLC) effect. Polarization effect at insulating grain boundaries between semiconducting grains accompanied by a strong Maxwell-Wagner (MW) relaxation mode. The characteristic of grain boundaries was revealed using impedance spectroscope and the universal dielectric response law.

Conduction and Dielectric Relaxation Mechanisms in Athabasca Oil Sands with Application to Electrical Heating

Six oil sands with increasing water and clay content were investigated for their electrical relaxation mechanisms using broadband dielectric spectroscopy with frequency (1 Hz to 1 MHz) and temperature (20–200 °C) to identify suitable operational strategies for electrical heating. Oil sands having least water and clay content showed a conduction relaxation mechanism following Jonscher’s law due to Maxwell–Wagner (MW) polarizations at bound water interfaces between bitumen and silica grains. MW polarizations due to free water interfaces between 1 kHz and 1 MHz were observed for oil sands having pendular connected water channels between sand grains. Poor oil sands with water entrapped in fine clusters had a dominant dc conduction mechanism. Additionally, all oil sands displayed dipole relaxations due to bitumen molecules between 100 kHz and 1 MHz. Electrical properties increased as temperatures were increased from 20 to 120 °C, whereas a further increase from 120 to 200 °C resulted in reduction of these prop...

Space charge behavior in oil gap and impregnated pressboard combined system under HVDC stresses

The reliability of oil-pressboard insulation system used in high voltage direct current (HVDC) convertor transformers can be affected by the presence of space charge. In this paper, the space charge behaviors in a 0.5 mm thick oil film combined with a 1mm thick impregnated pressboard have been investigated by the pulsed electroacoustic (PEA) technique under 12 kV/mm and 20 kV/mm at room temperature for both short term and long time tests. Two types of oil with different aging status were used for comparison. The results show that a charge peak is quickly formed at the interface between oil and pressboard with the same polarity as the electrode at the oil film side. However, the dynamics of the interfacial charges are very different for fresh oil and aged oil samples. The maximum electric field occurs in the middle of the pressboard, which is significantly enhanced in the aged oil samples. Compared with the Maxwell-Wagner (MW) polarization, more space charges are formed in the insulation system. It needs much longer time to reach steady state, depending on the status of the oil. The interfacial and bulk effects result in a significant electric field enhancement in the middle of pressboard, especially in aged oil samples.

Impedance Spectroscopy Simulation of Homogeneous and Heterogeneous Systems

The influences of direct current (DC) conductance and heterogeneous microstructure on the dielectric properties of homogeneous and heterogeneous systems are discussed in detail by impedance spectroscopy simulation. It is revealed that an apparent pseudo polarization, induced by DC conductance, exists in every phase in impedance spectroscopy and that the exact mechanism of Maxwell-Wagner (MW) polarization is the pseudo polarization. At the same time, a convenient method is provided to separate one phase from others and to distinguish intrinsic polarization from MW polarization. The results of this paper lay the foundation of fine representation of dielectric properties by dielectric spectrometer.

Graphene Oxide Papers Simultaneously Doped with Mg(2+) and Cl(-) for Exceptional Mechanical, Electrical, and Dielectric Properties.

This paper reports simultaneous modification of graphene oxide (GO) papers by functionalization with MgCl2. The Mg(2+) ions enhance both the interlayer cross-links and lateral bridging between the edges of adjacent GO sheets by forming Mg-O bonds. The improved load transfer between the GO sheets gives rise to a maximum of 200 and 400% increases in Young's modulus and tensile strength of GO papers. The intercalation of chlorine between the GO layers alters the properties of GO papers in two ways by forming ionic Cl(-) and covalent C-Cl bonds. The p-doping effect arising from Cl contributes to large enhancements in electrical conductivities of GO papers, with a remarkable 2500-fold surge in the through-thickness direction. The layered structure and the anisotropic electrical conductivities of reduced GO papers naturally create numerous nanocapacitors that lead to charge accumulation based on the Maxwell-Wagner (MW) polarization. The combined effect of much promoted dipolar polarizations due to Mg-O, C-Cl, and Cl(-) species results in an exceptionally high dielectric constant greater than 60 000 and a dielectric loss of 3 at 1 kHz by doping with 2 mM MgCl2. The excellent mechanical and electrical properties along with unique dielectric performance shown by the modified GO and rGO papers open new avenues for niche applications, such as electromagnetic interference shielding materials.

Low temperature magneto-dielectric measurements on BiFeO3 lightly substituted by cobalt

Dielectric and magnetodielectric measurements are done on BiFe1−xCoxO3: x = 0, 0.01, and 0.02 in the temperature range 70–300 K and up to magnetic field 1.3 T. The dielectric data are well described by Haverliak–Negami expression plus an additional term for the Maxwell Wagner (MW) type relaxations, whose contribution is dominant near room temperature. The parameters obtained from the fitting of data using the above mentioned expression, suggest slowing down of relaxation and approach towards ideal Debye type relaxations, as the temperature is lowered. The dielectric relaxations obey polaronic variable range hopping model with distinct activation energies (Ea) in the extrinsic (6.67T3/4 meV) and intrinsic (2.88T3/4 meV) regions for the parent sample (x = 0), and thus a distinct transition from extrinsic to intrinsic behavior is seen at 215 K while lowering the temperature. This distinct transition is missing for Co substituted samples probably due to the extrinsic region values of Ea (3.42T3/4 meV and 2.42T3/4 meV for x = 0.01 and 0.02, respectively) comparable to that of the intrinsic region (see x = 0). The magnetodielectric measurement shows positive magnetodielectricity (MD) in the intrinsic region (T &amp;lt; 215 K for x = 0) and negative MD in the extrinsic region (T &amp;gt; 215 K for x = 0). The extrinsic region is found to be dominated by MW and magnetoresistance effects, whereas MD in intrinsic regions is due to the spin reorientation transitions. The Co substitution is found to increase the extrinsic and non-Debye contributions to dielectricity, which becomes so large that no spin reorientation transitions are seen in x = 0.02 sample. The pyroelectric active region in x = 0 is found to be dominated by the diffusive behavior having contribution of the form ω−0.5.

Analysis of Carrier Transport of Organic Devices by Using Nonlinear Optical Polarization

In this review, we discuss the Maxwell-Wagner (MW) effect model analysis of organic devices and time-resolved optical second harmonic generation (TR-EFISHG) measurement that is available for directly probing carrier motion in organic semiconductor devices. Using these, we show that organic field effect transistor as well organic double-layer device operation is analyzed well, and we can make clear the mechanism of these organic devices' operation. Finally, we conclude that the dielectric physics approach using the MW model analysis and the TR-EFISHG experiment is useful to study carrier transport mechanism of organic devices.

Preparation of modified polymer blend and electrical performance

In this study, a modified binary polymer blend made up of polycarbonate and polystyrene blend has been prepared by loading of aluminum oxide (Al2O3) as a dopant. The role of alumina with polymer blend system was addressed in view of interfacing criteria. The filler concentration of modified blend was taken as 5, 10, and 15%. The morphological, thermal, and electrical properties were characterized by various techniques. Optical microscopy confirms the homogenous dispersion of Al2O3 in blend. The presence of alumina was detected by subatomic level using atomic force microscope (both two and three dimensional approach). The differential scanning calorimetric thermographs demonstrate decreasing softing point as function of alumina loading. The dielectric properties such as dielectric constant, loss, and electrical modulus were studied under DC bias. The effect of DC bias exhibits significant changes at low amount of Al2O3. The dielectric polarization supports Maxwell Wagner (MW) theory due to low frequency response. 15% Al2O3 gives the highest dielectric constant (ε′) value (3.5 × 105) at 10 Hz. The polymer modified blend with Al2O3 may be used as a one of the best dielectric medium.

Conduction mechanism, impedance spectroscopic investigation and dielectric behavior of La0.5Ca0.5-xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 0.2).

This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La0.5Ca0.5-xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 0.2). Transport measurements indicate that all the samples have a semiconductor-like behavior. The metal-semiconductor transition is not observed across the whole temperature range explored [80 K-700 K]. At a specific temperature, a saturation region was marked in the σ (T) curves. We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content. Two hopping models were applied to study the conduction mechanism. We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity. Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width. From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes. Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves. Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials. It is noteworthy that relaxation species such as defects may be responsible for electrical conduction. The dielectric behavior of La0.5Ca0.5-xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (ε'') and tg δ plots versus frequency demonstrate a relaxation peak. The Debye-like relaxation is explained by Maxwell-Wagner (MW) polarization. Experimental results are found to be in good agreement with the Smit and Wijn theory.

Origin of magnetocapacitance in chemically homogeneous and inhomogeneous ferrites.

The present work mainly focuses on the magnetodielectric (MD) effect in polycrystalline Ni0.9-yCuyZn0.1Fe1.98O3.97 (y = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ferrite synthesized by a solid-state reaction method. Sintered samples showed the formation of CuO-rich grain boundary segregation for y≥ 0.2. The appearance of segregation made the present material chemically inhomogeneous and electrically heterogeneous. A negative MD response was observed in homogeneous ferrite for y = 0 and 0.1 due to lattice distortion (an intrinsic effect), whereas a positive MD response occurs in chemically inhomogeneous segregated ferrite (y≥ 0.2) due the collective effects of Maxwell-Wagner (MW) polarization with intrinsic magnetoresistance (an extrinsic effect).

Protein dynamics in a broad frequency range: Dielectric spectroscopy studies

We present detailed dielectric spectroscopy studies of dynamics in two hydrated proteins, lysozyme and myoglobin. We emphasize the importance of explicit account for possible Maxwell–Wagner (MW) polarization effects in protein powder samples. Combining our data with earlier literature results, we demonstrate the existence of three major relaxation processes in globular proteins. To understand the mechanisms of these relaxations we involve literature data on neutron scattering, simulations and NMR studies. The faster process is ascribed to coupled protein–hydration water motions and has relaxation time ~10–50ps at room temperature. The intermediate process is ~102–103 times slower than the faster process and might be strongly affected by MW polarizations. Based on the analysis of data obtained by different experimental techniques and simulations, we ascribe this process to large scale domain-like motions of proteins. The slowest observed process is ~106–107 times slower than the faster process and has anomalously large dielectric amplitude Δε~102–104. The microscopic nature of this process is not clear, but it seems to be related to the glass transition of hydrated proteins. The presented results suggest a general classification of the relaxation processes in hydrated proteins.