Maxwell-Wagner Polarization Research Articles

Low-frequency carrier kinetics in triple cation perovskite solar cells probed by impedance and modulus spectroscopy

Organometallic halide perovskites-based solar cells have emerged as next-generation photovoltaic technology. However, many of its intriguing optoelectronic properties at low frequency are highly debated. Here, we investigate the low-frequency carrier kinetics of the state-of-the-art triple cation perovskite Cs0.06FA0.79MA0.15Pb(I0.85Br0.15)3 solar cells using bias-dependent impedance and modulus spectroscopy under dark and illumination conditions. We observe a strong dependence of dielectric permittivity on frequency in 1 Hz to 1 MHz region with a dielectric relaxation, which is observed to follow the Maxwell-Wagner type interfacial polarization possibly originating from the grain boundary/ionic defects. Furthermore, correlating the impedance and modulus spectra reveals the localized charge carrier relaxation in this triple cation device from which we obtain a phenomenological picture of the hopping process and developing an understanding of the charge carrier kinetics in these high-efficiency perovskite photovoltaics.

Characterizing electrical breakdowns upon reoxidation atmosphere for reliable multilayer ceramic capacitors

Electrical breakdowns of multilayer ceramic capacitors (MLCCs) manifest an increase in leakage current and are characterized as a function of atmospheric reoxidation. The atmospheric reoxidation is controlled with respect to the theoretical oxygen partial pressure for the oxidation of Ni internal electrodes. The breakdowns are characterized by a Maxwell–Wagner polarization technique, which dominantly exhibits space-charge-limited and Poole–Frenkel currents for all measured samples. The threshold voltage for the transition between these two conduction modes is suggested as an index for the robustness of the grain boundary resistance of BaTiO3; therefore, the breakdown voltage. The reoxidation atmosphere, which prevents the Ni oxidation, increases the threshold voltage, dramatically enhancing the breakdown voltage and insulation resistance. Impedance spectroscopy and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy reveal that the cation distribution throughout BaTiO3 grains and grain boundaries changes during the reoxidation, including Ni cations from the internal electrodes, which affects the grain boundary resistance and determines the breakdown voltage of MLCCs with Ni internal electrodes. These observations emphasize that the reoxidation should be concurrently optimized in terms of the cation redistribution and elimination of oxygen vacancies.

120 MeV Au+9 swift heavy ion irradiation of pulsed laser deposited BaM/LSMO bilayers

In the present study, we report the structural and electrical properties of pulsed laser deposited (PLD) bilayers of BaFe12O19 (BaM) and La0.67Sr0.33MnO3 (LSMO) thin films deposited on platinized silica substrate. Structural and electrical variation arising due to irradiation of 120 MeV Au+9 ion in these bilayers were studied with different fluences. X-ray diffraction (XRD) shows co-existence of phase pure BaM and LSMO throughout the measurement range. Scanning electron micrographs reveals the influence of irradiation on grains and its density. Frequency dependent real permittivity, imaginary permittivity, tangent loss and AC conductivity are highly affected by irradiation. Well established theoretical models like Maxwell-Wagner polarization, Relaxation mechanism, Universal dielectric response and Jonscher's power law have been employed to explain irradiation induced discrepancies in electrical properties. Magnetic field dependent magnetodielectric properties have been investigated for ion beam assisted modifications in the presently studied samples.

High-temperature 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 multiferroic: Microstructure, ferroelectric properties, and Mössbauer effect

Research findings of the microstructure, dielectric, ferroelectric characteristics, and Mössbauer effect of solid solution ceramics with 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 composition in a wide temperature range are presented. The examined ceramic chip surface allows one to draw conclusions about the internal homogeneity of grains and the absence of pores inside them. It was shown that Fe3+ iron cations in the material are valence and they are found only in seven locally different states, which is associated with disorder in the solid solution structure. The Néel temperature is TN ~ 445 K. The anomalous behavior at T < 30 K becomes clear when analyzing the dielectric spectra of 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 ceramics in the range of 10 … 1000 K. It is explained by the appearance of a spin-glass state in the object. The presence of contributions to the dielectric response in ceramics at T > 300 K is revealed. It is claimed that the ferroelectric–relaxor → paraelectric phase transition caused the low-temperature contribution, and the second one is a manifestation of the Maxwell–Wagner polarization and the corresponding non-Debye type dielectric relaxation. The causes of the revealed regularities and the prospects for using the material in the thin films form are discussed.

Interfacial Charge Dynamics of XLPE/EPDM Double Layers by Simultaneous Measurement of Space Charge and Relaxation Current

Simultaneous measurement at various temperatures of space charge and relaxation current is performed on cross-linked polyethylene (XLPE)/ethylene-propylene-diene monomer (EPDM) double layers with and without silicone grease. The simultaneous measurement correlates the charge distribution and current information for the same sample and avoids discrepancy, due to the separate measurement on different samples. It is found that the polarity of interfacial charges change to the opposite with the increase in temperature in most samples, which is related to both Maxwell-Wagner polarization and enhanced charge injection and migration at higher temperatures. Bipolar charges appear in the vicinity of interface in some XLPE/EPDM double layers with silicone grease. This phenomenon can be explained by Maxwell-Wagner polarization at two interfaces of XLPE/silicone grease and EPDM/silicone grease. The addition of silicone grease decreases the conductivity of XLPE/EPDM double layers. Based on the proposed three-component exponential decay model, it is found that the interfacial charge movement affects the polarity of induced relaxation current, and the addition of silicone grease decreases the interface trap depth.

Tunable dielectric and energy storage studies in NdMnO3 based composites

Composites are a class of materials which provide a scope of tailoring properties that are not possible amongst its constituents. Magnetoelectric composite materials exhibit product property arising because of mutually connected electric and magnetic phases. The systematic and comprehensive study on structural, tunable dielectric and flexible energy storage study of NdMnO3 (ND) manganite-based composites has been reported. The phase purity is estimated X-ray diffraction studies and confirm composite formation. The dielectric studies display a step-like decrease and reveal Maxwell-Wagner polarization with relaxation processes. The effect of magnetic field on dielectric constant reveals strong variation due to modification of spatial charge distribution. The qualitative evidence of tunable energy storage studies in ND based composites is observed by measuring the ferroelectric P-E hysteresis loop in variable magnetic field and is strain originated from coupling amongst individual component phases.

Structural and AC Electrical Properties of Tantalum Disulfide Embedded Polyaniline Composites

Employing in situ chemical polymerization technique, polyaniline-tantalum disulfide (PANI/TaS2) composites in different compositions have been synthesized. Poor crystallinity of the composites has been ascertained by XRD spectra. FTIR studies confirmed that the interaction in composites occurred at interfacial level. TGA results indicated an improvement in the stability of composites. The results of field emission scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy have confirmed the incorporation of TaS2 in PANI matrix as the embedded structures. Conductivity in the composite was found to increase by one order of magnitude compared to pristine PANI, and impedance spectra revealed that the conductivity is of electronic in nature. Dielectric behavior of the composites is attributed to the Maxwell–Wagner polarization. As the observed tangent loss peaks are in the low-frequency regime (103 Hz), the present composites may be explored for designing of low or medium frequency devices. Various parameters such as power law exponent, critical frequency and relaxation time have been estimated and discussed.

CH3NH3PbI3 as a radio frequency decoupling capacitor: interplay between Maxwell–Wagner polarization and a pseudo inductive response

Frequency-dispersive impedance analysis of CH3NH3PbI3 perovskite is carried out under the external Direct current (DC) field to investigate the interplay of dielectric polarization and delocalized carrier transport. Switching of capacitance from positive to negative values is observed in the radio frequency range (42.1–42.5 MHz) for the external bias ranging from 0–4 V. The switching frequency outlined a decreasing trend with an increase in bias. Upon fitting the experimentally obtained dispersions, a bi-relaxation mechanism is unveiled. One of its constituents arises due to the typical Maxwell–Wagner interfacial polarization between the grain cores and boundaries and acts at the lower frequencies. The other one is manifested via hopping of delocalized carriers, resulting in a high frequency degenerative pseudo inductive response. The interference of these two mechanisms is manifested into an asymmetric Breit–Wigner–Fano profile of the dielectric susceptance spectra. The results are further elaborated from a theoretical point of view involving the energy band structure, electron localization function, and Mulliken charge distribution.

Influence of La2O3 doping on the characteristics of ZnO linear resistors

ZnO linear resistors have anticipated application prospect in electrical and electronic industry, but the study of La2O3 doping is still poor. In this paper, the ZnO linear resistors doped with Al2O3, MgO, SiO2 and La2O3 were prepared by the conventional solid-state sintering method, and the effects of La2O3 doping on the microstructure and comprehensive electrical properties were studied. Structural and morphological characteristics of the samples were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. The property of resistivity-frequency reveals that the samples could be applied in high-frequency electric field. The dielectric property indicates Maxwell-Wagner interfacial polarization exists in the matrixes. With La2O3 content of 1 wt%, ZnO linear resistors have the best linear performance: the grain size is relatively uniform, the resistance temperature coefficient αT is − 6.63 × 10−3/°C, and the nonlinear coefficient α is 1.09. The comprehensive analysis of the influence of La2O3 doping on the electrical properties is of important significance for preparing ZnO linear resistors with excellent electrical properties.

Electric Field and DC Breakdown Voltage of Multi-layer Dielectrics in Parallel-Plane Geometry

In this paper, the electric field, space charge and temperature distributions across a double layered dielectric are investigated under DC voltage. The dissimilarity of material properties of different layers, the effect of electric field and temperature dependent conductivity are found to play critical role in the electro-thermal problem of multi-dielectrics. At the interface, Maxwell-Wagner polarization is incorporated for electric field and interfacial charge, while temperature is considered as a continuous function of space inside the material. The current continuity equation, thermal continuity equation and Poisson's equation are simultaneously solved using numerical methods in parallel-plane electrode geometry. The electric field distribution, temperature distribution, space charge distribution and thermal breakdown limits are obtained at various boundary temperatures for different thickness proportions of layers.

Structural, thermal and dielectric studies of mixed spinel CoFe2O4

In the present work, the phase development and dielectric response of polycrystalline CoFe2O4 has been studied as a function of temperature. The CoFe2O4 was synthesized by solid state reaction technique. The thermal activation of the reactions between precursors were studied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) to optimize the calcination temperature. The structural studies performed by X-ray diffraction followed by Rietveld refinement shows that CoFe2O4 crystallize in cubic Fd-3 m, conforming to a mixed spinel structure (Co0.95Fe0.05) (Fe0.975Co0.025)2O4. The dielectric studies show a low frequency dispersion, predominantly associated with the Maxwell-Wagner polarization. The real part of ac conductivity, σ' shows a change of ~ 4 orders in magnitude and follows the modified Jonscher’s law. The derived values of σdc, comply with Arrhenius behavior with the activation energy of ~ 0.382 eV. The values of exponents range from 0 to 1, indicating the conductivity in measured range is dominated by hopping of charge carriers.

Polyaniline-fly ash nanocomposites synthesized via emulsion polymerization: Physicochemical, thermal and dielectric properties

The polyaniline (PANI)/nano-fly ash composites were synthesized by Inverted emulsion polymerization technique. The FTIR spectrum of PANI/nano-fly ash composite (50/50) shows the vibrational bands due to N–Hstretching (2165 cm−1), quinoid (1517 cm−1) and benzenoid ring stretching (1354 cm−1), etc. The UV–Visible absorption shows an absorption peak at 267 and 374 nm for PANI/nano-fly ash composite. Raman spectrum of composite shows peaks at 1635, 1339, 1179, 829, 569, 414 and 200 cm−1. The conductivity of pure polyaniline was decreased as a result of the addition of nano fly ash. X-ray diffraction of the composite shows two crystalline peaks at 20.9° and 26.2° (2Θ). The stability of pure PANI is enhanced by the incorporation of nano -fly ash. The coating of polyaniline on nano-fly ash has been confirmed by FESEM pictures. The AC conductivity was explained using the hopping model. The dielectric constant decreases as the frequency increases, it was explained by using Maxwell–Wagner polarization theory.

High electrical conductivity at room temperature of MnCo2O4 cobaltite spinel prepared by sol–gel method

The cobaltite spinel MnCo2O4 nanopowder was prepared by the sol–gel method. X-ray diffraction shows the pure compound that crystallized in the cubic structure with the Fd $$\stackrel{-}{3}$$ m space group. The infrared spectrum (IR) revealed two absorption peaks that can be attributed to Mn–O and Co–O vibrations in the octahedral and tetrahedral sites, respectively. The electrical and dielectric studies were characterized by impedance spectroscopy (IS) at different frequencies (40–106Hz) and temperatures (200–440K). As a matter of fact, the DC conductivity exhibits a semiconductor behavior. It is worth mentioning that the conductivity of our investigated cobaltite spinel was found to be σ = 6.10−3 Sm−1 at room temperature. These results allowed this material to be a good candidate for potential application as an anode material (fuel cell). The AC conductivity obeys the Jonscher's law at low temperatures T 340K. Moreover, the dielectric result shows the permittivity (e '≈ 103) which is due to the contribution of the Maxwell–Wagner polarization.

Dielectric Response and Structural Analysis of (A3+, Nb5+) Cosubstituted CaCu3Ti4O12 Ceramics (A: Al and Bi).

CaCu3Ti4-x((A0.05Nb0.05))xO12 ceramics (A: Al and Bi; x = 0, 0.3) were synthesized by high-energy mechanical ball milling and reactive sintering at 1050 °C in air. Rietveld refinement of XRD data revealed the pure and (Al3+, Nb5+) cosubstituted ceramics contained a minor CuO secondary phase with a mole fraction of about 3.2% and 6.9%, respectively, along with a CaCu3Ti4O12 (CCTO)-like cubic structure. In addition, (Bi3+, Nb5+) cosubstituted ceramics had a pyrochlore (Ca2(Ti, Nb)2O7) secondary phase of about 18%. While the (Al3+, Nb5+) cosubstituted CCTO showed the highest relative permittivity (ε’ = 3.9 × 104), pure CCTO showed the lowest dielectric loss (tanδ = 0.023) at 1 kHz and 300 K. Impedance-spectroscopy (IS) measurements showed an electrically heterogeneous structure for the studied ceramics, where a semiconducting grain was surrounded by highly resistive grain boundary. The giant relative permittivity of the ceramics was attributed to the Maxwell–Wagner polarization effect at the blocking grain boundaries and domain boundaries. The higher tanδ of the cosubstituted samples was correlated with their lower grain boundary’s resistivity, as confirmed by IS analysis. Modulus-spectrum analysis revealed two relaxation processes for the pure and (Bi3+, Nb5+) cosubstituted CCTO samples. Dissimilar behavior was observed for the (Al3+, Nb5+) cosubstituted CCTO, where three relaxation mechanisms were observed and attributed to the grain, domain-boundary, and grain-boundary responses.

Influence of Bismuth Ferrite on Dielectric and Ferroelectric Properties of Strontium Iron Niobate Lead-Free Ceramics

Effects of BiFeO3 (BFO) on the properties of strontium iron niobate, Sr(Fe0.5Nb0.5)O3 ceramics were investigated and synthesized using a conventional solid-state reaction method. X-ray diffraction analysis revealed that all ceramics exhibited a single perovskite structure with orthorhombic symmetry. The x = 0.05 ceramic showed a very high dielectric constant (εr > 40,680 at 1 kHz). By using a complex impedance analysis technique, bulk, grain boundary, and electrode responses were found to affect the dielectric behavior which could be related to the Maxwell–Wagner polarization mechanism. Furthermore, ferroelectric behavior was also found to improve for a higher amount of BFO content.

Green Synthesis of Ba1−Sr TiO3 ceramic nanopowders by sol-gel combustion method using lemon juice as a fuel: Tailoring of Microstructure, ferroelectric, dielectric and electrical properties

Abstract This article represents a simple, economic and low-temperature green combustion synthesis of Ba1−xSrxTiO3 (BST) ceramic nanopowders for composition x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 with lemon juice as a firing agent. The fabricated nanopowders were characterized by TGA/DSC, XRD, FTIR, FESEM, TEM etc. analytical techniques. XRD analysis reveals the formation of single-phasic tetragonal perovskite structure with no impurity phases for x = 0.0 to 0.2 samples. However, cubic phase was appeared for x = 0.4 to 1.0 samples. FTIR spectroscopic study evidenced the formation of perovskite structure by demonstrating a noticeable band in between 400 and 750 cm−1. The Scherrer and Williamson-Hall (W–H) analysis was utilized to evaluate the crystallite size. TEM study showed that, spherical shaped and uniform nanocrystalline powders (23–28 nm) were fruitfully synthesized. The saturation electric polarization (Ps), remanence polarization (Pr) and coercive field (Ec) decreases with increase in Sr2+ content expected to be dependent on the creation of oxygen vacancies and occurrence of cubic polymorphs by doping of Sr2+ ions. The ideal ferroelectric characteristics were obtained Ps = 5.6661 μC/cm2 and Ec = 2.1242 kV for pristine BaTiO3 sample. Dielectric constant (e’) was obtained at room temperature as a function of frequency, which shows exponential decay with the increase of frequency. The Maxwell-Wagner polarization and dipole polarization were existing in the Sr2+-substituted BaTiO3 nanopowders and were responsible for the obtained dielectric properties. The variation of DC-electrical resistivity (log ρ) versus temperature (300 K–833 K) was observed to be decreased with increasing temperature and Sr2+ substitution; demonstrating that an electrical energy transfer was a thermally stimulated procedure. The Sr2+-substitution has brought an overall enhancement in dielectric and electrical properties. However, the ferroelectric characteristics are weakened, which is primarily attributed to a considerable variation in the micro-structure of the solid.

Colossal relative permittivity and low dielectric loss in BaFe0.5Nb0.5O3 ceramics prepared by spark plasma sintering

BaFe0.5Nb0.5O3 (BFN) ceramics has been prepared using a rapid process where the powder was synthesised using mechanical milling of the components then consolidated by spark plasma sintering (SPS) for 5 min at 1100 °C. X-ray diffraction results confirmed the pure cubic phase of the prepared SPS BFN ceramic. The average grain size as measured by SEM analysis was ~300 nm. Complex impedance measurements revealed giant dielectric constant (ε′ ~ 2.3 × 104) and low dielectric loss (tanδ ~ 0.48) for the SPS BFN ceramic at room temperature and 1 kHz. Two thermally activated relaxation peaks were observed in the spectra of imaginary part of modulus (M″). These relaxations were attributed to the Debye-like relaxation process in grains (at high frequency and low temperature) and non-Debye Maxwell-Wagner (M-W) polarization effect at grain-boundary (at low frequency and high temperature).

Conduction Mechanism and Dielectric Properties of Polycrystalline La0.53Ca0.47Mn0.5Cr0.5O3

The electric conductivity and dielectric properties of polycrystalline La0.53Ca0.47Mn0.5Cr0.5O3 are studied with impedance spectroscopy techniques over a wide range of frequencies and temperatures from 100 to 1 MHz and 100 and to 400 K, respectively. The material exhibits a semiconductor behavior in the whole temperature range, characterized by a change in the slope at a specific temperature with a saturation at ~ 360 K. At low temperature, the conduction mechanism is governed by distributed trap localized charge carrier states described by a variable-range hopping model. At high temperature, the conduction mechanism is thermally activated by a small polaron hopping process. At low frequencies, the high dielectric constants of the material decrease rapidly with frequency and increase with temperature due to the free charges accumulated at the electrode-sample interface (interfacial Maxwell–Wagner polarization). These high dielectric constants can be interpreted by the existence of grain boundaries. Additionally, the Nyquist plots are presented by two depressed not centered semicircles on the real axis, indicating non-Debye behavior for the material. The resistance of the grain boundaries is larger than the resistance of the grains, confirming that the grain boundaries govern the conductivity in La0.53Ca0.47Mn0.5Cr0.5O3. Finally, the modulus analysis indicates a transition of carrier mobility from the long range in the low-frequency region to the short range in the high-frequency region.

Phase states, microstructure and dielectric characteristics of solid solutions (1 – x)NaNbO3 – xCa2Nb2O7 and (1 – x)NaNbO3 – xSr2Nb2O7

Ceramics of binary systems solid solutions (1 – x)NaNbO3 – xCa2Nb2O7 and (1 – x)NaNbO3 – xSr2Nb2O7 with non-isostructural extreme components were prepared by the solid-phase reactions technique with the following sintering using conventional ceramic technology. It was found that ceramics with x ≤ 0.2 have a perovskite structure. Layered type of structure predominates in the concentration range 0.2 <x ≤ 1. Phase diagrams of both systems at room temperature have been determined in the perovskite area. It was shown that this area contains two concentration regions with the different crystal structures and the morphotropic phase boundary between them. Microstructure and dielectric characteristics of selected solid solutions were investigated. The influence of technological regulations, such as mechanical activation and variation of sintering temperatures, on the formation of the microstructure and dielectric characteristics was studied for the individually selected concentrations (x = 0.1 and x = 0.25). Dielectric characteristics of ceramics revealed the presence of the Maxwell-Wagner polarization and its corresponding relaxation in the solid solutions (1 – x)NaNbO3 – xCa2Nb2O7 at x > 0.20.

Dielectric and impedance spectroscopy of Nd2CoIrO6 double perovskite

Polycrystalline Nd2CoIrO6 double perovskite crystallizes in monoclinic crystal structure with P21/n space group. The average grain size of powder sample is 400–500 nm. The dielectric, impedance and ac conductivity of the sample were studied in the temperature range 5–300 K and in the frequency range 20 Hz–2 MHz. Dielectric constant reveals a step like increase from low temperature value of ∼5 to colossal value of ∼104 at high temperature. High value of dielectric constant is associated with Maxwell–Wagner polarization due to large grain boundary capacitance. Cations (Co2+ and Ir4+) disorder leads to variable range hopping conduction of electrons in grain and grain boundary regions. Distribution of grain size induces distribution of relaxation time as confirmed from depressed semicircles in Nyquist plots. Frequency dependent conductivity follows universal power law behavior.