Dielectric Relaxation Mechanism Research Articles

Dielectric Relaxation Mechanism in the Phase-Transition Region of a Chiral Hybrid Perovskite and Its Piezoelectric-Energy-Harvesting Properties

Dielectric Relaxation Mechanism in the Phase-Transition Region of a Chiral Hybrid Perovskite and Its Piezoelectric-Energy-Harvesting Properties

High-temperature impedance properties of Sr1-xCaxTiO3 ceramics for lead-free capacitor applications

ABSTRACT Lead-free Sr0.6Ca0.4TiO3 ceramic was prepared by solid-state reaction route. X-ray diffraction technique showed the phase purity and identified the orthorhombic perovskite structure. Scanning Electronic Microscopy observation evidenced homogeneous morphology and dense microstructure. Electrical conduction and dielectric relaxation mechanisms at high temperature have been studied by complex impedance measurement techniques over a wide range of frequencies and temperatures, from 100 Hz to 1 MHz and from 573 K to 783 K. Fitting of impedance measurements allowed us to study grains and grain boundaries electrical characteristics and their contribution to the conduction and dielectric relaxation processes in the ceramic. Electrical conduction in grains is due to oxygen vacancy jumps for temperatures below 733 K and to polarons above 763 K. Electrical DC conductivity in grains and grain boundaries is mainly due to oxygen vacancies. Impedance measurements and relaxation time distribution function calculations show non-Debye-type relaxation effects for both grains and grain boundaries.

Variable range hopping transport and dielectric relaxation mechanism in GdCrO3 rare-earth orthochromite perovskite

The polycrystalline GdCrO3 (GCO) perovskite orthochromite was synthesized by the sol–gel auto-combustion method. The Rietveld refined X-ray diffraction (XRD) profile of GCO confirms that the orthorhombic phase crystallizes in perovskite crystal structure with space group Pbnm. The transmission electron microscopy and selected area electron diffraction divulge the polycrystalline nature of the perovskite chromite. The field emission scanning electron microscopy (FESEM) images reveal the microstructural polyhedral growth of grains separated by sharp grain boundaries. The chemical states of the ions present in the compound were investigated by X-ray photoelectron spectroscopy (XPS) studies, and the electrical pathways were identified. Complex impedance studies were carried out in the experimental frequency and temperature ranges of 40 Hz–4 MHz and 178–408 K, respectively. The equivalent circuit model (RGQG) (RGBQGB) resolves the impedance response into two contributions originating from the intra-grain and inter-granular micro-constituents of the material. The electrical conduction mechanism is based on the Mott variable range hopping model. The complex electric modulus studies demonstrate the short- and long-range mobility of the charge carriers and rule out the presence of electrode effects on the dielectric relaxation mechanism of the material. The decreasing pattern of dielectric permittivity with frequency is explained by the Maxwell–Wagner type of polarization. The frequency dependence of the loss factor exhibits the presence of thermally activated relaxation time distribution in the material.

High-Temperature Dielectric Relaxation and Electric Conduction Mechanisms in a LaCoO3-Modified Na0.5Bi0.5TiO3 System.

This research study examines the high-temperature dielectric relaxation and electric conduction mechanisms in (x)LaCoO3-(1 - x)Na0.5Bi0.5TiO3 samples, where x is 0.05, 0.10, and 0.15. The findings demonstrate that all the samples exhibit two dielectric transitions: first, a frequency-dispersive shoulder at a lower temperature (Ts) around 425-450 K, which is associated with polar nanoregions (PNRs), and second, from ferroelectric to paraelectric transition at the Curie temperature (Tc) approximately between 580 and 650 K. The impedance analysis reveals the negative temperature coefficient of resistance behavior of the specimens. The broad and asymmetric relaxation peaks obtained from modulus spectroscopy demonstrate a wide range of relaxations, suggesting non-Debye-type behavior. Furthermore, the conductivity studies provide insights into understanding the transport phenomena in the samples. The oxygen vacancies resulting from the addition of LaCoO3 into the Na0.5Bi0.5TiO3 ceramics are responsible for the relaxation and conduction processes, and the charge carrier is doubly ionized oxygen ion vacancies. All samples except for LCNBT10 at 1 kHz exhibit a negative magnetodielectric response.

Tuning electrical properties of BaTiO3 with iron modification

BaTiO3 plays an important role in advanced functional devices owing to its fascinating properties. Though it is an excellent ferroelectric material, its magnetism can be switchable via suitable modification. In this report, we have studied iron-modified BaTiO3, which has been prepared using cost-effective high-temperature solid-state reaction techniques. The Fe-modified BaTiO3 maintains its crystallinity in the tetragonal phase with P4mm space group with a slight variation of tetragonality ratio to 1.002 from 1.008 of BaTiO3 of the identical synthesis method. This is confirmed by Rietveld refinement. Field emission scanning electron microscopy (FESEM) and EDX (energy dispersive X-rays) spectrum along with an elemental mapping analysis has provided the feature of the Fe-modifed BaTiO3. Atomic force microscope (AFM) has been employed to get the detailed surface topology (2D and 3D) and surface roughness of the developed systems. This deformation caused by the incorporation of Fe significantly modifies the electrical properties of barium titanate. The ferroelectric-paraelectric phase transition temperature (Tc) of Fe-modified BaTiO3 has been diffused and shifted to 300 °C from 120 °C of pure BaTiO3, suggesting the materials for the high-temperature capacitive application. The room temperature M-H hysteresis of Fe-modified BaTiO3 indicates the ferromagnetism developed in the BaTiO3 with the introduction of Fe. The ac conductivity is in the order of 10−4 Ω−1cm−1, and its frequency response obeys Jonscher's power law. Different charge carriers are responsible for diverse conduction processes in different temperature ranges confirmed by the Arrhenius plot. Impedance spectroscopy studies reveal the existence of NTCR characteristics of the developed system. Well defined ferroelectric hysteresis loop indicates the existence of ferroelectricity in the developed system. The analysis of various electrical parameters has provided information on the material's dielectric relaxation and conduction mechanisms for possible application in functional devices.

Electrical and optical properties of a lead-free complex double perovskite BaNaFeMoO6: Photovoltaic and thermistor applications

In this communication, synthesis (solid-state reaction) and characterizations of a complex double perovskite BaNaFeMoO6 are reported. X-ray diffraction analysis (structure and lattice parameters) adopts a monoclinic structure while Raman spectroscopy provides information about the vibrational characteristics. Homogenous distribution of the grains is observed from the scanning electron microscope (SEM) whereas energy dispersive X-ray analysis (EDX) supports compositional consistency. Ultraviolet–visible (UV–vis) data provides a direct energy bandgap of 2.75 eV, which may be suitable for photovoltaic applications. The analysis of Maxwell-Wagner type of dielectric dispersion, resistance, relaxation, and transport mechanism are carried out using dielectric, impedance, modulus, and conductivity data recorded within an available range of frequency (1 kHz – 1 MHz) and temperature (25 °C – 500 °C). Both the theoretical fit of the Nyquist data using ZSIMPWIN software as well as temperature-dependent conductivity support a negative temperature coefficient of resistance (NTCR) nature. The scaling nature of modulus data supports the non-Debye type of relaxation. The obtained temperature-dependent thermistor constant (β), sensitivity factor (α), and activation energy make the prepared material suitable for thermistor-related device application. The study of polarization–electric field (P-E) loop suggests the possibility of ferroelectric nature in the reported material.

Photoluminescence, Raman and photosensitive dielectric properties of lead-free antimony-based Cs3Sb2Br9 single crystals for energy storage devices

• Cs3Sb2Br9 SCs with the trigonal crystal structure and the P 3 m 1 space group were prepared by the slow cooling method. • The temperature-dependent photoluminescence analysis shows that Cs3Sb2Br9 has a low thermal activation energy of 54.7 meV. • Temperature dependence of Raman scattering in Cs3Sb2Br9 proves that there is no structural phase transition in the range of 50-300 K. • The Debye-type process in the SCs is interpreted through the complex modulus formalism. • The M′′(ω) plots presented a reversible shift under light-on conditions. • The light-sensitive dielectric and conductivity relaxation mechanisms are studied through the modified Cole-Cole and Debye-type relaxation approaches. Recently, all-inorganic lead-free halide perovskites have drawn the researchers’ attention because of their excellent stability, lower toxicity, and good optoelectronic characteristics. This paper first investigates both temperature-dependent PL and Raman spectrum of all-inorganic antimony-based Cs 3 Sb 2 Br 9 single crystals (SCs). Secondly, the light-sensitive dielectric and conductivity comportment in Cs 3 Sb 2 Br 9 SCs by electrochemical impedance spectroscopy (EIS), which is used under both dark and light conditions by displaying these conditions in sequence. The photosensitive dielectric and conductivity comportment are studied through the modified Cole-Cole and Debye-type relaxation approaches. The dipolar relaxation behaviors, which are assisted by the reversible photo-induced trap in Cs 3 Sb 2 Br 9 SCs are interpreted by a comprehensive study of the reversible variation found in the modulus crest frequencies. The conductivity is illustrated in terms of Jonncher's s power law. The Debye-type nature of relaxation is additionally confirmed by the power factor (n) value, which is almost equal to 1. This paper presents thorough knowledge and fresh ideas of light-sensitive dielectric and conductivity relaxation processes in all inorganic lead-free perovskite SCs. This scientific research will inspire the coming pattern of the perovskite SCs-based energy storage system.

Small polaron hopping transport mechanism, dielectric relaxation and electrical conduction in NiAl2O4 electro-ceramic spinel oxide

In this study, the frequency and temperature dependent dielectric relaxation and electrical conduction mechanisms in NiAl2O4 spinel oxide ceramic have been explored in a frequency range of over a measured temperature from 163–283 K. The polycrystalline NiAl2O4 was synthesized via solid state reaction route and sintered at 1000 °C. The room temperature x-ray powder diffraction pattern confirmed the formation of NiAl2O4 spinel phase with Fd3m space group. The surface morphology of the sample was investigated by scanning electron microscopy and chemical properties by Fourier transform infrared spectroscopic analysis. Complex impedance studies revealed the presence of relaxation time distribution and charge carriers were found to be thermally activated. The Nyquist plots exhibited depressed semicircles and their fitting by an equivalent circuit model with configuration (RGCG)(RGBCGB) resolved the contributions of grains and grain-boundaries to the electrical transport properties of the material. Electrical conductivity analysis followed the Jonscher’s power law behavior and the frequency exponent suggested small polaron hopping as the governing transport mechanism in NiAl2O4 spinel oxide. Non-Debye type nature of dielectric relaxation was confirmed by the complex modulus analysis whereas dielectric constant and tangent loss analysis verified that the hopping mechanism was thermally activated.

Low-temperature dielectric relaxation mechanism and correlated barrier hopping transport in neodymium perovskite chromite

Herein, neodymium chromite (NdCrO3) has been synthesized by the sol–gel auto-combustion method. The Rietveld analysis of the X-ray diffraction pattern has shown that NdCrO3 crystalizes in the perovskite structure with orthorhombic unit cell and Pbnm space group symmetry. The electrical transport properties have been investigated by complex impedance spectroscopy over the experimental frequency and temperature ranging from 40 to 1 × 106 Hz and 158–283 K, respectively. The equivalent circuit modeling of Nyquist plots revealed the contribution of grains and grain boundaries to the charge conduction and the relaxation mechanism of NdCrO3, respectively. The AC conductivity analysis divulged the correlated barrier hopping transport mechanism in the NdCrO3. The imaginary electrical modulus spectra fitted by the Kohlrausch, Williams, and Watts function presented the non-Debye type nature of the relaxation mechanism in the material. The dielectric permittivity has exhibited the Maxwell–Wagner type polarization of the material, and the loss factor has exhibited an increasing trend with temperature.

Investigation on electrical transport and dielectric relaxation mechanism in TbCrO3 perovskite orthochromite

Herein, the TbCrO3 (TCO) chromite was synthesized by the sol-gel auto-combustion route and sintered at 900 °C. The Rietveld analysis of the room temperature powder X-ray diffraction profile confirmed the single-phase formation of the material crystallized in the orthorhombic phase of the perovskite structure with Pbnm space group symmetry. The surface morphology, the elemental composition, and the chemical states of the compound were investigated by field emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy, respectively. The electronic density of states, band structure, and electron density were analyzed by Density Functional Theory. The electrical transport and dielectric relaxation mechanism were investigated using complex impedance spectroscopy over the experimental frequency and temperature ranging from 40-1.2x106Hz and 138−273 K, respectively. Two semicircular arcs in the impedance complex plane plots were modeled to an equivalent circuit configured by RG∥QG+RGB∥QGB which were attributed to the contributions of the highly resistive grain boundaries and relatively conducting grains in the material. The electrical conductivity as a function of frequency followed Jonscher’s universal power law behavior and an increasing nature of the temperature-dependent frequency exponent suggested small polaron hopping as the electrical conduction mechanism of the material. The least capacitive response of the TCO system was investigated by the complex electrical modulus formalism and the frequency-dependent imaginary modulus spectra were modeled by the Kohlrausch–Williams–Watts function, which resolved the thermally activated peaks of bulk and interface effects to the dielectric relaxation mechanism. The dielectric constant exhibited Maxwell-Wagner interfacial polarization effects and the dielectric loss factor showed frequency dispersion at all temperatures.

Effect of transition metal and alkali oxides on structural, optical and dielectric properties in Zinc-Phosphate amorphous glassy systems

The influence of transition metal and alkali earth metal oxide on the structural, optical and dielectric properties of inorganic glasses prepared by melt quenching method, having chemical composition 0.35ZnO0.25P2O5-(0.4-x) Na2O-xV2O5 (0.05≤x≤0.25), have been studied. The Rietveld Refinement of the XRD spectra confirms the presence of Na3P8VO23 and Zn2V2O7 nanocrystallites. Raman spectroscopy has been deployed to identify and quantify the individual phases present within the glass matrix. The optical bandgap energy values, which are obtained from the UV–Vis spectra, vary with V2O5 concentration (x), and an inverse association between the optical bandgap and Urbach energy has been demonstrated. The absorbance and reflectance spectra have been investigated, and several optical parameters, such as the excitation and absorption coefficients, refraction index, polarizability, SELF and VELF functions, etc., have also been examined. The dielectric constant and dielectric loss decrease with the increase in frequency but increase with the rising temperature. The dielectric properties have been examined at various temperatures and frequencies. The analysis of the scaling property of electric modulus indicates the conductivity or dielectric relaxation mechanisms, which is temperature independent and composition-dependent. The estimated value of the exponent parameter from Bergman's function being less than unity confirms the non-Debye type relaxation process occurring within the transition metal and alkali oxide doped zinc-phosphate glass matrix.

Dielectric relaxation and charge carrier mechanism in doped Ce1-xSmxO2-δ (0 ≤ x ≤ 0.3) nanoceramics: An investigation with dielectric spectroscopy

We present herein the structural, dielectric, and ionic conduction properties of a series of doped Ce1-xSmxO2-δ (0 ≤ x ≤ 0.3) nanocrystalline ceramics. X-ray photoelectron spectroscopy studies have indicated a non-stoichiometry induced mixed Ce4+ and Ce3+ charge state, with the content of Ce3+ ions decreasing with increasing Sm concentration. Analysis of impedance data has suggested that both grains and grain boundaries contribute to the overall conductivity, but grain boundaries make the dominant contribution. Further, we have observed an enhancement in conductivity, which can be attributed to reduced grain size and increased interfaces in these nanostructured materials that lead to faster ionic diffusion across the boundaries. While our results suggest that dopant vacancy related high frequency relaxation is active in all the materials, for the sample with x = 0.2 we have found two Debye-type dipoles in the relaxation process, with an additional low frequency dipole relaxation due to long-range migration of free oxygen vacancies. This migration is responsible for high conductivity in Ce0.8Sm0.2O2-δ, making the compound an ideal candidate for applications.

Unveiling the high-temperature dielectric relaxation and conduction mechanisms in sol-gel derived LaFeO3 modified Sodium Bismuth Titanate ceramics

The lead-free NBT (Na0.5Bi0.5TiO3) ceramics doped with LaFeO3 having general chemical composition (1-x)Na0.5Bi0.5TiO3-(x)LaFeO3, where x = 0 and 0.05 (abbreviated as LFNBT0 and LFNBT5) were synthesized by sol-gel technique. These ceramics were characterized using X-Ray photoelectron spectroscopy to determine the elemental composition and chemical state of the samples whereas impedance spectroscopy was performed to investigate the electrical properties viz. dielectric constant, dielectric loss, impedance, modulus and conductivity over a wide temperature range (300–775 K) along with frequency (1 Hz - 1 MHz). XPS spectra at room temperature revealed the gradual reduction of valence states i.e., Fe3+ to Fe2+ and Ti4+ to Ti3+ resulting in the formation of oxygen vacancies in LFNBT system. A decrease in dielectric constant as well dielectric loss has been observed at room temperature i.e., from 898 to 541 and 0.75–0.25 respectively at 1 KHz frequency with the incorporation of LaFeO3 in the NBT. A phase transition from ferroelectric to para-electric phase is obtained at 583 K and 623 K for LFNBT0 and LFNBT5 respectively. The negative temperature coefficient of resistance (NTCR) behaviour is obtained from the analysis of impedance data. The Cole-Cole plots perceives the grain and grain boundary effect contribution of the materials with the non-Debye type of relaxation which is also confirmed by electric modulus data and aids in understanding of the transport phenomenon. The fitted conductivity data indicated that the conduction in the NBT system is governed by correlated barrier hopping (CBH). XPS analysis and activation energy values obtained from imaginary part of electrical impedance, modulus, and ac conductivity confirmed that the relaxation and conduction processes in LFNBT0 and LFNBT5 ceramics are attribute to the presence of oxygen vacancies.

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.

Interpretation of dielectric behavior and polaron hopping in lead-free antimony-based double perovskite.

Lately, double perovskite materials have become well-known in the commercialization area owing to their potential use in optoelectronic applications. Here, double perovskite Cs2AgSbCl6 single crystals (SCs) with cubic crystal structure and Fm3̄m space group were successfully synthesized via the slow cooling technique. This paper investigates the dielectric relaxation and charge transfer mechanism within Cs2AgSbCl6 using electrochemical impedance spectroscopy (EIS) in the 273-393 K temperature range under light. The dielectric response in Cs2AgSbCl6 has been explained by the space charge polarization and the ionic motion. The ε'(ω) study at different temperatures shows a remarkable frequency transition at which dε'/dT changes from a positive to a negative coefficient. Based on Stevels approach, the density of traps diminishes with the temperature increase, which improved conduction. However, this approach proves the polaronic conduction in Cs2AgSbCl6. 0.42 and 0.21 eV are the binding (Ep) and polaron hopping (WH) energy values, respectively. Contrary to free-charge carrier motion, polaron hopping was proposed as the principal conduction process since the ambient-temperature thermal energy was lower than Ep. Moreover, the analysis of M''(ω) and -Z''(ω) as a function of temperature shows the thermally-activated relaxation from the non-Debye to Debye type model in Cs2AgSbCl6. This scientific research offers an essential understanding of the dielectric relaxation behavior, which is required for improving dielectric switches. Also, this paper provides a deep insight into the conduction mechanism within double perovskite materials.

Structural transformation, dielectric and multiferroic properties of (Gd1-Ba )(Fe1-Ti )O3 ceramics by tuning composition

The structural transformation, ferro-paraelectric and magnetic ordering induced dielectric phase transitions, multiferroic properties, relaxation and conduction mechanisms of (Gd 1- x Ba x )(Fe 1- x Ti x )O 3 ceramics with different compositions ( x = 0.0–0.4) have systematically been investigated. The chemical route is adopted for material synthesis. Rietveld refinement reveals the structural transformation from orthorhombic to mixed phase (coexistence of orthorhombic and tetragonal phase) for x > 0.2. The analysis of the FESEM micrographs suggests a decrease in average grain size with the increase in BT in the composition. Dielectric anomalies are explained based on ferroelectric-paraelectric phase transition of BaTiO 3 , polarization induced by a spin reorientation, and antiferromagnetic ordering of GdFeO 3 . The multiferroic properties of all the samples are studied from P-E, M-H, and magneto-electric plots. The improved magnetic properties in compositions x = 0.1–0.3, make them suitable candidates for spintronic devices. The maximum magneto-electric coupling coefficient of 4.77 mV/cm‧Oe in the composition x = 0.3, makes it very much suitable for application in magnetoelectric coupling devices.

Octahedra-Tilted Control of Displacement Disorder and Dielectric Relaxation in Mn-Doped SrTiO3 Single Crystals.

Strontium titanate SrTiO3 (STO) is a canonical example of a quantum paraelectric, and its doping with manganese ions unlocks its potential as a quantum multiferroic candidate. However, to date, the specifics of incorporation of the manganese ion into the perovskite lattice and its impact on structure-property relationships are debatable questions. Herein, using high-precision X-ray diffraction of a Mn (2 atom %)-doped STO single crystal, clear fingerprints of the displacement disorder of Mn cations in the perovskite B-sublattice are observed. Moreover, near the temperature of the antiferrodistortive transition, the off-center Mn position splits in two, providing the unequal potential barrier's distribution for possible local atomic hopping. A link with this was found via analysis of the dielectric response that reveals two Arrhenius-type relaxation processes with similar activation energies (35 and 43 meV) and attempt frequencies (1 × 1011 and ∼1.6 × 1010 Hz), suggesting similar dielectric relaxation mechanisms.

Correlated barrier charge hopping and non-Debye relaxation in columbite MnNb2O6

A comprehensive study on the mechanism of ac-charge transport and dielectric relaxation in the MnNb2O6 columbite system has been reported. Thermally driven, Arrhenius-like behaviour of the ac-conductivity is predominant at temperatures above 300 K in the frequency range 50 Hz–5 MHz with activation energies lying between 0.45 and 0.38 eV. Besides, a quadratically decreasing trend in the activation energy is evident as given by: = A + Bf + Cf 2 with the constants A (0.413 eV), B (0.023 eV Hz−1) and C (−0.004 eV Hz−2). The measured data is analysed using the Double power law to explain the dispersive behaviour of electrical conductivity. These studies also provide evidence for the correlated-barrier hopping (CBH) conduction mechanism of charge carriers for temperatures in the range 173–473 K. Further, the temperature dependence of frequency exponent, s(T) displays two distinct regions both of which are associated with the CBH mechanism with slopes K−1 and K−1 in Region-I (173–300 K) and the slope K−1 with non-linear variation of s 2 in Region-II (300–473 K). However, the second region is more dominated by thermally activated Arrhenius-like behaviour. The dynamical response of complex electric modulus spectra and the corresponding analysis using Kohlrausch-Williams-Watts method reveals the presence of a non-Debye type relaxation process with decay function exponent β lying between 0.794 and 0.840. This inference of the non-Debye type relaxation process is further supported by depressed semicircles in Nyquist plots and the higher magnitude of full width half maximum (FWHM) (≈1.44 decades) of the normalized master cusp vs compared to the FWHM ( = 1.14 decades) for ideal Debye behaviour. Both short-range and long-range conductivity regions are ubiquitous in with a pronounced distribution of relaxation times (s) with temperature. This study further leads to the estimation of activation energy of charge carriers, E M = 0.44 eV which is in consonance with .

Effect of Fe ion substitution at B site of samarium cobaltite perovskites

Transition metal ion, Fe ion, doped at B site of samarium cobaltite (SmCoO3) perovskite was synthesized by solid state reaction method. The structural studies using X-ray diffraction technique confirmed perovskite structure with orthorhombic symmetry for SmCo1-xFexO3 (x = 0, 0.4, 0.6, 1.0) at room temperature. The scanning electron microscopy images show porous morphology for the synthesized samples. The vibrational band observed at 426 cm−1 in FTIR spectrum corresponds to Co–O stretching mode in cobaltite system. The DC conductivity increases with increase in temperature and was explained by the hopping model. The cole-cole plot explained the dielectric relaxation mechanism and established the negative temperature coefficient of resistance (NTCR) for the material. The relaxation frequency observed from the imaginary impedance plot is temperature dependent and obeyed Arrhenius relation. The activation energy for different composition is in the range 0.011–0.017eV. The frequency dependent conductivity spectra were explained on the basis of Jonscher's power law.

Theoretical and experimental analyses of the dynamic electroadhesion force

Electroadhesion (EA) is a polarization-induced dynamic electrostatic attraction phenomenon, including the saturation and attenuation delays of the EA force, and its repeatability under repeated application. Due to the complex polarization and dielectric relaxation mechanisms, it is pretty challenging to establish a theoretical EA model to clearly reveal the underlying polarization behind the dynamic EA force. In this paper, a theoretical model is proposed to describe the dynamic EA effect and analyze the dynamic EA characteristics by establishing the relationship between the EA force and polarization and introducing the Debye model into the polarization function. This model suggests that interfacial polarization is responsible for the dynamic behavior of EA force, which results in the saturation and attenuation delays, as well as the poor repeatability of EA force. Theoretical analysis also indicates that the application of an AC voltage can reduce the saturation and attenuation delays and enhance force repeatability by alleviating this effect, and that increasing the voltage frequency will reduce the EA force and eventually stabilize the EA force at hundreds of Hertz. Experiments show that our theoretical model can well explain the saturation and attenuation delay time scales, as well as the dependence of EA force on charging/discharging cycle and frequency. This work not only provides a theoretical tool for analyzing the dynamic EA effect but also offers potential strategies to improve EA performance.