Dielectric Relaxation Mechanism Research Articles

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.

Colossal permittivity and low dielectric loss in (Li, Nb) co-doped SrTiO3 ceramics with high frequency and temperature stability

Sr(Li1/4Nb3/4)xTi(1-x)O3 (0.000 ≤ x ≤ 0.04) (STLN) ceramics were synthesized via a solid-state reaction under a flowing nitrogen atmosphere. Co-doping with Li+ and Nb5+ considerably enhanced the dielectric properties of SrTiO3 ceramics. These dielectric properties increased with the co-doping concentration x up to x = 0.012 and decreased for higher x. The STLN ceramic with x = 0.012 exhibited a colossal permittivity of εr = 17,300 (1 kHz) and an ultralow dielectric loss of tanδ = 0.017 (1 kHz), with excellent frequency (20–106 Hz) and temperature (room temperature to 450 °C) stabilities. Their dielectric relaxation mechanisms and point-defect structures were also investigated. With an excessive increase in x, the formation of point defects is inhibited, resulting in the deterioration of the dielectric properties of the STLN ceramics. Further studies showed that acceptor doping Li+ and N2 atmosphere sintering provided a large number of oxygen vacancies. These oxygen vacancies contribute to the formation of some defect dipoles and defect-dipole clusters (TiTi′−VO••−TiTi′, NbTI•−TiTi′) related to oxygen vacancies. These defect dipoles and defect-dipole clusters restrict non-localized electrons, leading to electron-pinning. Consequently, the sample exhibits colossal permittivity and low dielectric loss. In addition, a high grain boundary resistance also contributes to the reduced dielectric loss.

Temperature-activated dielectric relaxation in lead-free halide perovskite single crystals

Lead-free metal-halide perovskites have recently appeared as a promising candidate in optoelectronics and photovoltaics because of their non-toxicity, stability, and unique photophysical properties. Much scientific research has been done on optoelectronic characteristics and photovoltaic applications of lead-free perovskites, but the dielectric characteristics and insight into the relaxation phenomenon remain elusive. Here, we study the dielectric relaxation and conduction mechanism in the single crystalline (SC) A3Bi2X9 (A = MA+/FA+) perovskite using temperature-dependent electrochemical impedance spectroscopy in correlation with the modulus spectroscopy. With increasing temperature, the peak of −Z″(ω) shifts toward a high-frequency regime which specifies the thermally dependent relaxation mechanism in both crystals. The activation energy was estimated as 381 meV for MA3Bi2I9 (MBI) crystal and 410 meV for the FA3Bi2I9 (FBI) crystal suggesting hopping of mobile ions between lattice sites. The connected orientational polarization with the thermal motion of molecules leads to the enhancement in the dielectric constant (ϵ′) with temperature. The ϵ″(ω) in these crystals shows the significant ionic conductivity with a typical 1/fγ type characteristics (in the low-frequency regime) where γ is found to be in the range of 0.93–1.0 for MBI crystal and 0.88–0.98 for FBI crystal. The correlated imaginary part of impedance (−Z″) and modulus (M″) demonstrate the temperature-activated delocalized relaxation (non-Debye toward the Debye type) in these crystals. Stevels model suggests that the contribution of traps reduces with temperature rise and therefore conductivity enhances. Our study provides a comprehensive analysis and in-depth knowledge about the dielectric and conductivity relaxation mechanism in these lead-free perovskite SCs, which will help to implement efficient energy storage devices using these materials.

Study of the dielectric relaxation mechanisms in KNbO3-based electro-ceramics

Electro-ceramics based on the KNbO3 ferroelectric system were synthesized from the solid-state reaction sintering method. In particular, the electrical properties have been investigated at room temperature in the (1−x)KNbO3−xBaNi1/2Nb1/2O3−δ (KBNN) solid-solution. The dielectric relaxation mechanisms have been analyzed as a function of the oxygen vacancy (δ) concentration and the frequency dispersion of the complex dielectric permittivity was analyzed in a wide frequency range. The obtained results were discussed within the framework of the current models reported in the literature for the dielectric relaxation processes.

Effect of clay/nepheline tailing ratio on the dielectric relaxation and conduction mechanism of the conventional ceramic

The dielectric relaxation and conduction mechanism of 40 wt% nepheline tailing and 60 wt% clay-based ceramic, i.e., the 40/60 ceramic, have been investigated over wide ranges of frequency and temperature, using a broadband dielectric spectrometer (BDS) and then compared with the data recently reported for the 50/50 ceramic. Both 40/60 and 50/50 ceramics were fabricated by grinding the raw materials to be very fine, wet homogenously mixing, drying and finally firing at 1200 °C. Their crystalline phases identified by X-ray diffraction were quartz, hematite, cristobalite, and albite. The 40/60 ceramic of lower glassy phase (nepheline tailing) content displays lower crystallinity than the 50/50 ceramic. Its conduction activation energies (Eac) show values between 0.12 and 0.32 eV, corresponding to the activation energy of oxygen vacancies (Vo++ ~ 0.22 eV). As oxygen vacancies migrate at relatively low operating voltages, the fabricated ceramics would be promising in manufacturing the random access memory (RAM), taking into consideration that the 50/50 ceramic is more useful than the 40/60 ceramic. As a result, nepheline tailing or the glassy phase component may generate more oxygen vacancies and thus enhance the ceramic electrical properties. Finally, the conduction mechanism of both ceramics is described via the correlated barrier hopping (CBH) model.

Exploring the High Frequencies AC Conductivity Response in Disordered Materials by Using the Damped Harmonic Oscillator

The AC conductivity response of disordered materials follows a universal power law of the form σ′(ω)∝ωn at the low frequency regime, with the power exponent values in the range 0 < n < 1. At the high frequency regime, in many experimental data of different disordered materials, superlinear values of the power exponent n were observed. The observed superlinear values of the power exponent are usually within 1<n<2, but in some cases values n>2 were detected. The present work is based on the definitions of electromagnetic theory as well as the Havriliak–Negami equation and the damped harmonic oscillator equation, which are widely used for the description of dielectric relaxation mechanisms and vibration modes in the THz frequency region, respectively. This work focuses mainly on investigating the parameters that affect the power exponent and the range of possible n values.

Structural, dielectric, electrical and optical properties of a double perovskite: BaNaFeWO6 for some device applications

In this paper, the synthesis (by solid-state reaction route) and characterization (structural, microstructural, electrical, and optical properties) of the BaNaFeWO6 lead-free double perovskite are reported. Room temperature structural analysis suggests that the material crystallizes in monoclinic crystal symmetry with average crystallite size and lattice strain of 55 nm and 0.023% respectively. The incorporation of the Na/Fe at both sites (Ba and W) of BaWO4 is confirmed from the room temperature Raman study. A study of microstructural and compositional characteristics of the sample by using scanning electron microscopy (SEM) and EDAX (energy dispersive analysis X-ray) has provided the quality (uniform and compactness) of the sample. The detailed studies of the frequency and temperature dependence of dielectric, impedance, and conductivity properties of the material suggest the presence of high dielectric dispersion, non-Debye conduction, and relaxation mechanism in it. The semiconducting nature is confirmed by the decreasing resistance or radius of semicircular arcs in both impedance analysis and Nyquist plots. This nature is also well supported by fitted parameters evaluated using ZSIMPWIN software. The temperature dependence of resistance provides a good stability factor, sensitivity factor, and thermistor constant, which may be useful for applications in the fields of the thermistor-related devices. The field-dependent polarization (P-E) hysteresis loop suggests the possibility of ferroelectricity in the sample. The sample has an energy bandgap of 2.72 eV deduced from its UV–visible spectrum, which may be useful for some applications in optoelectronic devices

Dielectric, structural and mechanical properties of thermally aged biaxially oriented polymeric substrates for flexible electronics

Two materials, polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), which are often used as flexible substrates for electronics, were exposed to accelerated thermal aging at temperatures of 190 °C and 210 °C for 5000 and 2000 h, respectively. Changes in their thermal, dielectric, and mechanical properties were investigated. The results revealed that dielectric losses increase slower for PET than for PEN at lower aging temperatures. In contrast, at higher aging temperatures, similar behavior was observed for both materials. During aging, the dissipation factors of PET and PEN increased by one order of magnitude over those of the original states. The dielectric frequency-temperature characteristics obtained by broadband dielectric spectroscopy (BDS) shifted and indicated changes in the individual dielectric relaxation mechanisms (i.e., α, β, β*). Discoloration induced by thermal aging and quantified by ultraviolet–visible spectroscopy by the peak at 453 nm was detected primarily in the spectrum of PEN. The mechanical tensile strength of PET deteriorated considerably (10 times) after only a few hundred hours, whereas PEN was stable after even longer exposure times. It was found that all of the changes mentioned above are primarily related to the change in the crystalline-to-amorphous phase ratio, as demonstrated by differential scanning calorimetry (DSC) and supported by density measurements.

Dielectric properties, polarization process, and charge transport in granular (FeCoZr)x(Pb(ZrTi)O3)(100−x) nanocomposites near the percolation threshold

This paper presents the research of dielectric properties of (FeCoZr)x(Pb(ZrTi)O3)(100−x) granular metal–dielectric nanocomposites below the percolation threshold. Tested materials have been prepared by using the ion beam sputtering technique in the atmosphere of argon and oxygen. The impedance spectroscopy method has been used to investigate the polarization processes and dielectric relaxation mechanism in the granular nanocomposites. AC measurements in the frequency region of 50 Hz to 1 MHz and measuring temperature range of 81–293 K have been performed. Interfacial, in the low frequency region, and dipolar, in intermediate and high frequency regions, types of polarization processes were observed. The interfacial relaxation process testifies to charge accumulation at the interfaces (grain boundaries) between conductive nanoparticles surrounding an insulative matrix, as well as the space charge region around the contact area between the measurement probes and tested sample. Dipolar polarization corresponds to electric dipole formation after applying to the material an external electric field. The conduction mechanism in the tested material is considered to be hopping carrier exchange and takes place between metallic phase nanograins. It corresponds to the exponential frequency dependence of conductivity. The relaxation mechanism in the (FeCoZr)x(Pb(ZrTi)O3)(100−x) layer has been estimated as a near-Debye process with relaxation time distribution. The nanocomposite exhibits dielectric type and capacitive characteristics in the whole measuring frequency range.

Dielectric relaxation and conduction mechanism of NaMgPO4 compound

The polycrystalline NaMgPO4 ceramic, synthesized via a high-temperature solid-state reaction route, has been characterized by using different experimental procedures. The X-ray powder diffraction confirmed the phase formation of the synthesized compound in the orthorhombic phase. It assumed an olivine-type structure made up of corners linked between tetrahedral PO4 and octahedral NaO6 and MgO6 groups. Infrared and Raman spectroscopies confirmed the presence of PO[Formula: see text] groups. Local structure and chemical bonding between MgO6 octahedral and PO[Formula: see text] tetrahedral groups investigated by diffusion Raman is the feature in the phase transition at [Formula: see text] 693 K. The temperature dependences of the real [Formula: see text] and imaginary [Formula: see text] parts of dielectric permittivity show a distribution of relaxation times. From Nyquist plots, the presence of grain and grain boundary effect in the material is noticed. The impedance spectroscopy measurement showed a non-Debye-type process. From the impedance data, the determined grain resistance reduces with increment of temperature showing negative temperature coefficient of resistance (NTCR)-type nature of the material which also confirmed from conductivity analysis. The temperature dependence of [Formula: see text] reveals an Arrhenius-type behavior with two activation energies, 0.98 eV in region I and 0.67 eV in region II. Studied sample’s conduction is assured by Na[Formula: see text] ions’ hopping in tunnels and its mechanism was discussed.