Non-overlapping Small Polaron Tunneling Research Articles

Structural, Thermal, Optical, Electrical, and Dielectric Properties of Complex Lead-Free Compound: [Bi1∕2Na1∕2][Fe1∕2W1∕2]O3

Some physical properties (structural, dielectric and optical) of a complex lead-free ceramic [[Formula: see text][Formula: see text]][[Formula: see text][Formula: see text]]O3 have been thoroughly examined in different experimental conditions in this study. It was fabricated via a solid-state reaction method. The crystal structure is monoclinic, according to the detailed analysis of the X-ray diffraction pattern. Also, the functional vibrational bands can be observed in the FT-IR and Raman spectra, which support the creation of the molecular structure. Scanning electron microscope (SEM) images of the sample clearly show the effects of [Formula: see text] and [Formula: see text] incorporation in morphology, and energy dispersive X-ray spectroscopy (EDX) indicates the existence of all constituents. The non-overlapping small polaron tunneling (NSPT) and correlated barrier hopping (CBH) model conduction mechanisms are examined through Jonscher’s power law. The contribution of the grain and grain boundary to the capacitive behavior is shown by Nyquist plots. According to a leakage current analysis, the compound exhibits Ohmic and space charge limited conduction (SCLC) conduction mechanisms. Electric field polarization was used to study the ferroelectric nature. The findings of this study show that the inclusion of [Formula: see text] and [Formula: see text] is an efficient technique to improve its dielectric and optical characteristics.

Electrical conductivity and relaxation mechanisms of nanocrystalline Ba0.75Ca0.2Cs0.05TiO3

Ca and Cs doped barium titanate lead-free ceramic with the formula Ba0.75Ca0.2Cs0.05TiO3 has been prepared by the solid-state reaction method. X-ray diffraction (XRD) confirms the crystallization of the sample in a tetragonal structure with a P4mm space group. The phase purity and grain morphology were evaluated using X-ray diffraction and scanning electron microscopy (SEM). The material exhibits a primary phase of Ba0.75Ca0.2Cs0.05TiO3 with a minor secondary phase of BaO2, and the average grain size is determined to be 1.66 μm. Using non-destructive complex impedance spectroscopy (CIS), we extensively studied the electrical behavior, including complex impedance (Z*), complex modulus (M*), electrical conductivity, and relaxation mechanisms, of Ba0.75Ca0.2Cs0.05TiO3 over a wide temperature (85 K–290 K) and frequency range. The ac conductivity analysis reveals that the dominant conduction mechanism is the non-overlapping small polaron tunneling (NSPT) model. The impedance analysis indicates a single semi-circle in the real and imaginary parts, suggesting a single relaxation mechanism. Additionally, the activation energy was calculated to be approximately 0.0489 eV. These findings contribute to the understanding of the structural and electrical properties of Ba0.75Ca0.2Cs0.05TiO3, highlighting its potential applications in electronic devices such as capacitors, thermistors, and ferroelectric random access memories (FRAMs).

Development of Lead‐Free Defect Brownmillerite Perovskite Ceramic LiBiFeMnO5 Solid Solution for Electronic Devices

This article reports the fabrication (synthesis) and characterizations (structural, microstructural topographic surface, dielectric, transport, impedance, current–voltage, and resistive properties) of a complex lead‐free defect perovskite material of composition LiBiFeMnO5. A preliminary structural investigation of the X‐ray diffraction pattern using N‐TREOR09 methods shows monoclinic symmetry. The scanning electron microscopic spectrum examines the sample's microstructural topographic surface, fractal study, and roughness (using the standard ISO25178). The analysis of Maxwell–Wagner dielectric dispersion, relaxation, and transport mechanisms is investigated utilizing dielectric, impedance, and conductivity spectrum accumulated within the experimental frequency of (1 kHz–1 MHz) at different temperatures (30–500 °C). A nonoverlapping small polaron tunneling conduction mechanism and correlated barrier hopping mechanism in the material have helped to understand its conduction phenomena. The Ohmic and space–charge limited conduction mechanisms are investigated by the slope of the logarithmic electric field (E) and current density (J). The thermistor constant (β) is determined to be 1982.87. The temperature coefficient of resistance is found to be −0.00419, which may be suitable for negative temperature coefficient thermistors, sensors, and other related devices.

Enriched electron donor sites and non-overlapping small polaron tunneling electrical conduction in oxygen-deficient β-Ga2O3 thin film on p-Si (100)

Enriched electron donor sites and non-overlapping small polaron tunneling electrical conduction in oxygen-deficient β-Ga2O3 thin film on p-Si (100)

Strong magnetoelectric coupling in novel Na0.5Bi0.5TiO3–BaFe12-2xCoxTixO19 multiferroic composite

Multiferroic composites of sol-gel synthesized Sodium Bismuth Titanate (Na0.5Bi0.5TiO3) and Co–Ti substituted Barium Hexaferrite (BaFe12-2xCoxTixO19; x = 0.0, 0.5, 1.0, 1.5 and 2.0) in the ratio 3:1 was synthesized through ceramic route. Successful formation of R3c rhombohedral and P63/mmc hexagonal phases corresponding to Na0.5Bi0.5TiO3 and BaFe12-2xCoxTixO19 respectively was confirmed from the XRD and Rietveld refinement pattern. The frequency and temperature dependence of dielectric constant and loss of the composite systems exhibited typical dispersion behaviour which could be understood using the Maxwell-Wagner model. Substituted samples showed enhanced dielectric behaviour where dielectric constant was observed to increase while loss tangent decreased. Using the Universal Jonscher's Power law (JPL), conductivition mechanisms of the composite systems were studied from the ac conductivity behaviour which revealed that the x = 0.0 sample followed Non-overlapping Small Polaron Tunnelling (NSPT) model while the remaining samples followed the Correlated Barrier Hopping (CBH) model. The complex impedance and Nyquist plot analysis showed the enhancement of resistive property in the x≠0 systems. Magnetic hysteresis loop measurements were conducted, and the associated parameters were determined with the assistance of the Law of Approach to Saturation (LAS). Favourable reduction in the magnetic anisotropy was observed indicating the disturbance of magnetic spin structure in the hexaferrite phase. The P-E loops established the novel room temperature multiferroic nature of the composite systems. Significant magnetoelectric coupling was detected at room temperature in all samples, with the x = 0.5 sample exhibiting the highest value of approximately 59.81 mV/cmOe. These desirable properties suggest that the composites may find future device applications as in magnetically tunable energy harvesting devices and self-powered magnetoelectric sensors in the future.

Synthesis, Structural characterization and complex impedance analysis of a novel organic-inorganic hybrid compound based on Mercury (II) chloride

The organic-inorganic hybrid compounds are promising materials due to their electro-optical and semiconducting properties. In this study, a single crystal of (C6H16N)2[HgCl4] has been synthesized and characterized using single-crystal X-ray diffraction at room temperature, SEM/EDS and complex impedance spectroscopy. The crystal structure is centrosymmetric with the monoclinic system (P21/c space group). It consists of isolated tetrahedral anions [HgCl4]2− and protonated amines (C6H16N) +. SEM/EDS analyses proved the composition of the title compound. The frequency-dependent electrical and dielectric properties were analyses using complex impedance spectroscopy in the frequency range of 10−1 Hz – 1 MHz. The Nyquist plots (-Z’’ vs Z’) was characterized by the appearance of a single semicircle arc, indicating a non-Debye type relaxation process in the (C6H16N)2[HgCl4] material. The AC conductivity followed Jonscher law, and the variation of frequency exponent s with temperature suggested that non-overlapping small polaron tunneling (NSPT) is the dominant electrical transport mechanism. So, this work will be very beneficial to the further development of the (C6H16N)2[HgCl4] compound and its potential electrical applications.

Effect of rare earth (Ho and Er) co-substitution on the magnetic and dielectric properties of nanocrystalline cobalt ferrites

Nanocrystalline cobalt ferrites co-substituted with rare earth Ho and Er (CoFe2-2xHoxErxO4, 0 ≤x≤0.10) have been synthesized via the sol-gel method. X-ray Diffraction (XRD) confirmed the single-phase spinel structure with reduced crystallite sizes (65 nm–12 nm), micro-strain (ε) and increased lattice constant (a) with Ho–Er co-substitution. Rietveld refinement and theoretical computation revealed Ho and Er occupancy at octahedral sites and Fe and Co ions redistribution between the tetrahedral and octahedral sites. Infrared spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) supported the formation of the desired spinel structure, aggregated spherical morphology, chemical stoichiometry and elemental states. Magnetic measurements showed a systematic decrease in saturation magnetization (Ms), magnetocrystalline anisotropy (K1), coercivity (Hc) and Curie temperature (Tc) with Ho–Er co-substitution. Electron Spin Resonance (ESR) exhibited asymmetric resonance peaks, reduced resonance field (Hr), linewidth (ΔHpp) and deviation in Lande g values. Impedance spectroscopy revealed two conduction mechanisms (holes and electrons) with distinct activation energies (EaI and EaII). Modulus spectrum analysis confirmed the thermally activated sample-electrode effects and the Nyquist plots indicated the dominant contribution of the grain boundary resistance to the conduction process. A notable enhancement in the dielectric constant (ε′) was observed with Ho–Er co-substitution. The ac conductivity (σac) followed the Jonscher Power Law (JPL). The temperature-dependent frequency exponent s(T), suggests the existence of two conduction mechanisms: non-overlapping small polaron tunneling (NSPT) and correlated barrier hopping (CBH).

Temperature and frequency dependence of conductivity, density of states, and dielectric permittivity of ternary metal chalcogenide PbSnSe2 flake

The mechanically cleaved flake of ternary metal chalcogenide PbSnSe2 was transferred onto the interdigitated electrodes to form electrical contacts. The temperature dependent (180 K–250 K) electrical properties were then analyzed employing complex impedance spectroscopy from 2 kHz to 2 MHz. A detailed analysis of Nyquist plots proposed the space charge dependent behavior and negative temperature coefficient of PbSnSe2 flake. The AC conductivity followed Jonscher's power law with s-parameter value being less than unity. The values of s-parameter increased with rise in temperature suggesting the presence of non-overlapping small polaron tunneling (NSPT) in the PbSnSe2 flake. From this NSPT model, tunneling distance, hopping energy, and density of states (DOS) were estimated at temperatures from 180 K–250 K. The dielectric permittivity showed dispersion at lower frequencies and the tangent loss was also found to be directly related to temperature. A single semicircular arc in complex modulus analysis showed the dominance of bulk effect in the material.

Contribution of strong electron-phonon interaction in the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3 system

La0.8Ca0.2Mn0.5Ni0.5O3 NTC (negative thermal coefficient) thermo-sensitive material was prepared using a conventional solid-state reaction method. From the structural results, we found that the material is pure and crystallizes in the orthorhombic structure with a Pnma space group. It is found that the La0.8Ca0.2Mn0.5Ni0.5O3 ceramic can be used as an NTC thermistor compound in specific temperature sensors and attenuators. Based on Holsten's theory, detailed electrical investigations concerning the nature of the activated small polaron hopping mechanism were reported. The temperature dependence of the DC conductance was used to determine the electrical conduction processes that govern the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3. Hence, the DC mechanisms exhibit changes from the variable range hopping at very low temperatures to the non-adiabatic small polaronic hopping at T = 210 K. In the intermediate temperature range, the semiconductor behavior of La0.8Ca0.2Mn0.5Ni0.5O3 was attributed to the contribution of the tunneling transport process. At various temperatures, the conductance spectra were discussed based on Jonscher and Bruce's laws. Contributions of the overlapping-large-polaron-tunneling, the correlated barrier hopping, the quantum mechanical tunneling, and the non-overlapping small polaron tunneling mechanisms to the transport properties were observed in the dispersive region of the conductance spectra. In addition, Summerfield scaling and corrected Summerfield scaling approaches prove that the charge mobility is temperature-dependent. The positive value of the correction parameter α = 1.2 confirms the presence of interactions in the studied sample.

Structural, optical, and impedance spectroscopy of the pseudobrookite Pb0·5Ba0·5Fe2O5 synthesized by sol–gel route

Pseudobrookite of general formula Pb0·5Ba0·5Fe2O5 was synthesized by the sol–gel route. X-ray diffraction confirms the orthorhombic Pnma space group of our sample. UV–Vis absorption spectroscopy was used to characterize this material's optical properties. We used the Tauc model and absorption measurements to estimate the direct optical band gap at 3.53 eV. We also calculate the Urbach energy, the optical extinction coefficient, and the refractive index. In addition, the skin depth, optical conductivity, and Cauchy parameters were investigated in relation to the incident photon's wavelength. Electrical conductivity data flow the Jonscher's power law and show that PBFO has two different conducts; Semiconductor behavior in the temperatures region [400 K–520 K]. Then, a metallic trend was detected beyond TS-M = 520 K. The correlated barrier hopping (CBH) model is the appropriate model to describe the conduction process in low temperature range. On the other hand, the conduction is ensured by the non-overlapping small polaron tunneling (NSPT) at high temperature zone. The scaling study shows that the conductivity spectra deviate from Summerfield and Ghosh scaling. The random barrier model (RBM) is employed to correct the Summerfield approach and we note that the conductivity isotherms are combined into a single master curve. The estimated activation energies values from dc-conductivity, hopping frequency and relaxation time are very close. The behavior of dielectric parameters was examined using the Maxwell-Wagner theory of interfacial polarization. The dielectric-relaxation phenomenon is shown by the behaviors of imaginary parts of impedance (Z″) and modulus (M″). The ideal electrical equivalent circuit for simulating the Nyquist curves (i.e. Z′′(Z′)) for our pseudobrookite is (Rg + Rgb//CPEgb). Finally, the entropy (ΔS), and enthalpy (ΔH) were established as thermodynamic parameters.

Structural, morphological, optical, magnetic and impedance spectroscopic properties of Ni0·5Fe2·5O4 nanoparticles synthesized by the self-combustion method

The synthesis of Ni0·5Fe2·5O4 nanoparticles was successfully carried out by the self-combustion method using glycine as fuel. Analysis of the XRD measurements indicates the formation of a cubic spinel monophase with the space group (Fd-3m) and a nanometric crystallite size. According to the optical study, this sample shows strong absorption in the visible range with a gap energy of 3.7 eV, making it a good candidate for optoelectronic and photovoltaic applications. Complex impedance spectroscopy was carried out in the temperature range 300–480 K with the frequency varying between 40 Hz and 5 MHz. The frequency dependence of the dielectric constant was explained in terms of charge carrier transport between Fe2+ and Fe3+, while its temperature dependence indicates dielectric relaxor behavior. The scaling law shows a perfect superposition of impedance and modulus spectrum in the temperature range studied which confirms that the increase of temperature does not bring any change on the mechanism of relaxation. For the electrical properties, the conductivity study shows a semiconducting behavior with a predominance of the Non-Overlapping Small Polaron Tunneling (NSPT) model over the conduction process. The dc conductivity and jump frequency are positively correlated by the extracted activation energies. Summerfield scaling leads to the superposition of the conductance spectra into a single main curve, confirming the validity of this approach. The low value of the dielectric loss and the high value of the permittivity at room temperature and at low frequencies make this sample a potential candidate for energy storage and microwave devices. In addition, the dependence of the magnetisation on the applied magnetic field has been studied in depth by adjusting the hysteresis cycle by different laws of the saturation approach.

Synthesis, crystal structure, BFDH morphology, Hirshfeld surface analysis and electrical characterization of the new bi-(2-amino-5-methylpyridinium) hexa-chlorostannate compound

The Organic–inorganic hybrid compounds have attracted considerable attention for their scientific and technological potential according to their wide field application. In this paper, we describe the preparation of a new hybrid crystal, with the structural formula [C6H9N2]2SnCl6, of which crystallographic, BFDH morphology, Hirshfeld and complex impedance spectroscopy have been studied and analyzed. The X-ray diffraction analysis revealed that the title compound crystallized in the centrosymmetric space group P21/c of the monoclinic system. The powder XRD is used to confirm the phase purity of the sample and the crystalline nature of the powder.The [C6H9N2]2SnCl6 crystal morphologies are simulated from the Laue symmetry (2/m), and from the space group symmetry (P21/c), which highlighted the effect of the screw axe 21 and the glide plane c in reducing the Importance morphology in the constructed model considering the space group symmetry. The intermolecular interactions studied using Hirshfeld surfaces showed the important contribution of H⋯Cl/Cl⋯H intercontacts (67.1 %) in the [C6H9N2]2SnCl6 crystal packing.The analysis of real and imaginary parts impedance spectra shows that the electrical properties are heavily dependent on frequency and temperature, indicating a relaxation phenomenon and semiconductor-type behavior. The Nyquist plot (-Z″ vs Z′) showed only one semicircular arc, representing the grain effect in the electrical conduction. The obtained results were analyzed by fitting the experimental data to an equivalent circuit model R/CPE/C. The Alternating current conductivity (σAC) follows Jonscher's power law. The latter confirmed that the conduction is insured by the non-overlapping small polaron tunneling model (NSPT) model, which has been studied in depth.

Exploring dielectric and AC conduction characteristics in elemental selenium glass modified with silver halides.

In this research work, we have examined the influence of silver halide doping on the dielectric dispersion and AC conduction of elemental selenium. The in-depth investigation shows that when the dopant silver halides are incorporated, there are noticeable changes in the parent selenium's dielectric constant (ε'), dielectric loss (ε''), and AC conductivity (σ ac). When we frame the discussion of the obtained results with the relevant transport models, we found that in pure selenium and Se95(AgI)5, conduction is primarily due to polaron hopping and follows the correlated barrier hopping (CBH) model. In contrast, Se95(AgBr)5 predominantly exhibits non-overlapping small polaron tunneling (NSPT). Interestingly, Se95(AgCl)5 demonstrates both NSPT and CBH conduction mechanisms, depending on the temperature range: NSPT is dominant between 303 K and 313 K, while CBH prevails from 318 K to 338 K. Additionally, our findings revealed the presence of both the Meyer-Neldel rule (MNR) and its reverse in the prepared silver halide chalcogenide alloys. The best optimization of dielectric constant and loss is observed for silver iodide as compared to silver chloride and silver bromide. Comparison with other silver-containing chalcogenide glasses indicates the better dielectric performance of the present silver halides containing selenium.

An investigation of structural, thermal, and electrical conductivity properties for understanding transport mechanisms of CuWO4 and α-CuMoO4 compounds.

Recently, inorganic oxide components with high ionic conductivity have been widely explored due to their high stability, safety, and energy density properties. In this context, the present work focuses on the inorganic oxides CuMO4 (M = W, Mo), which have been successfully synthesized using the traditional solid-state method. They were characterized by X-ray powder diffraction, thermal analysis, and complex impedance spectroscopy. X-ray diffraction data refined via the Rietveld method indicated that these compounds are well crystallized in the triclinic system with the P1̄ space group. Besides, the electrical conductivity behavior of these materials was analyzed using the impedance spectroscopy technique in the frequency range of 100 to 106 Hz and in the temperature range of 443 K to 563 K. The absence of a phase transition observed in the calorimetric study was confirmed by the σg and ωh variations as a function of temperature. The AC conductivity was analyzed by Jonscher's power law. The outcomes of the study on charge transportation in CuMO4 (where M = W, Mo) suggest that the overlapping large polaron tunneling (OLPT) mechanism was present in CuMoO4, while the correlated barrier hopping (CBH) and the non-overlapping small polaron tunneling (NSPT) were present in CuWO4. A correlation between the crystal structure and the ionic conductivity was established and discussed. For the two title compounds, modulus analysis revealed that the charge carriers were mobile over short and long distances at low and high frequencies, respectively. The temperature variation of the M'' peak showed a thermally activated relaxation process.

Cu and Er modified barium zirconium titanate (BaZr0.05Ti0.95O3) ceramics: Composition-dependent dielectric properties

Cu2+ and Er3+ doped BaZr0.05Ti0.95O3 (BZT) ceramics were prepared using the solid-state reaction method, where amount of CuO + Er2O3 was fixed at 2 wt.% and different CuO : Er2O3 molar ratios (i.e. 1:1, 1:2, 1:3, 2:1 and 3:1) were used. The influence of Cu2+ and Er3+ doping on crystal structure and dielectric properties of the samples sintered at 1300 ?C was investigated. X-ray diffraction analysis confirmed the formation of a single-phase material and tetragonal crystal structure with P4mm symmetry. Microstructural analysis conducted with a scanning electron microscope revealed well-defined and uniformly distributed grains across the surface of the sintered samples and reduction of grain size and density with doping. The highest energy storage density of 40.51mJ/cm3 with an energy efficiency of 78.8% was obtained in the sample with CuO : Er2O3 molar ratio of 2:1. The doped BZT ceramics have high dielectric constant and significantly lower tangent loss in comparison to the undoped BZT. The dielectric data confirm the non-Debye behaviour for all the samples. Impedance spectroscopy and electrical modulus analysis indicated that conduction in the materials was influenced by both the grains and grain boundaries. The AC conductivity is described by the Jonscher?s universal power law, whereas DC conductivity follows a dependency based on the Arrhenius?s theory. The results revealed a conduction mechanism characterized by non-overlapping small Polaron tunnelling up to 340?C and a transition to correlated barrier hopping conduction above 340?C within the selected temperature range for all the samples. According to the Arrhenius fitting of DC conductivity the activation energy of the undoped BaZr0.05Ti0.95O3 sample is 0.168 eV and decrease with doping to 0.138 and 0.131 eV for the sample with lower Cu2+ contents (CuO : Er2O3 molar ratios of 1:2 and 1:3, respectively).

Morphological, structural, optical and dielectric analysis of Cs2TiBr6 perovskite nanoparticles.

In the pursuit of lead-free perovskite materials suitable for harnessing solar energy, a recent discovery has emerged regarding Cs2TiBr6. This compound has garnered attention as a prospective candidate, exhibiting favorable optical and electrical characteristics alongside exceptional resilience when subjected to environmental strains. This study details the successful synthesis of non-hazardous metal halide nanoparticles of Cs2TiBr6via the slow cooling method. Comprehensive investigations into the structural, optical, and dielectric characteristics have been undertaken. The temperature sensitivity of various electrical properties, including the dielectric constant, loss factor, electric modulus, and AC/DC conductivity, is evident in this perovskite material. This phenomenon is observed across a frequency range of 1 to 107 Hz. Furthermore, examination of the Nyquist plot highlights the distinctive contributions of both grain and grain boundaries to the overall impedance characteristics. In the high-frequency range, it is observed that the dielectric constant exhibits an upward trend as the temperature rises. Examination of the adapted Cole-Cole plot unveils that both space charge and free charge conductivity escalate with increasing temperature, while concurrently, the relaxation time experiences a reduction with the temperature's ascent. We observed an asymmetrical pattern in the electric modulus spectra at varying temperatures using a modified Kohlrausch-Williams-Watts equation. This asymmetry is consistent with the inherent non-Debye nature of perovskite materials. Additionally, as the temperature increases, we note a shift in the imaginary component of the electric modulus spectra, transitioning from a non-Debye character towards a semi-Debye nature, though it does not achieve a strictly Debye-type response. This transformation indicates the semiconducting properties of the material. We elucidate the AC conductivity behavior in Cs2TiBr6 by employing the non-overlapping small-polaron tunneling (NSPT) mechanism as the basis. The activation energy, as determined from both the modulus spectra and DC conductivity, aligns closely, providing robust evidence for the congruence between the relaxation dynamics and the conduction mechanism. In addition to these attributes, Cs2TiBr6 exhibits a substantial dielectric constant coupled with negligible dielectric loss, thus establishing its potential suitability for energy harvesting devices.

Synthesis of a scheelite barium molybdate: Structural, topological, electrical, and transport properties for negative temperature coefficient thermistor application

Preliminary structural analysis of Scheelite barium molybdate BaMoO4 (BMO) ceramic using NTREOR-09 and McMaille methods has confirmed the tetragonal symmetry with room temperature X-ray diffraction (XRD) spectrum. Further, other structural parameters like crystallite size and compressive lattice strain are found to be of 31 nm and −0.00151 respectively. The topographical study of scanning electron microscope (SEM) image confirms the polycrystalline nature with no other impurities in the sample. Detailed analysis of dielectric permittivity (εr), and loss (tanδ) supports Maxwell-Wagner and Koop's phenomena. The non-overlapping small polaron tunnelling (NSPT) and correlated barrier hopping (CBH) model have emphasis on transport mechanism. The presence of semiconducting behavior of the scheelite material at various temperatures and frequencies examined by complex impedance and modulus spectra. The value of grain resistance decreases as temperature increases demonstrating the existence of negative temperature coefficient (NTCR) behavior of the material. The increase of the value of thermistor constant (β) (67.339, 516.613, and 772.485 in the different high-temperature range) suggests an efficient application of the material for NTC-thermistor.

Dielectric behavior and impedance spectroscopy of Niobium substituted Lanthanum based orthovanadates at high temperatures

We present the detailed study of the temperature dependent dielectric properties, impedance spectroscopy and electrical conductivity of LaV1−xNbxO4 (x=0–1) samples prepared by the solid-state reaction method. The dielectric constant (ϵr′) increases (decreases) with increase in the temperature (frequency); while, the magnitude of ϵr′ remains almost invariant (order of 104 at 100 Hz and 600 °C) with x. The single phase x=0 (monoclinic-monazite, P21/n) and x=1 (monoclinic fergusonite, I2/a) samples show the lower values of loss factor [tanδ= (4–8)] as compared to the x=0–0.8 samples [tanδ= (12–18)] having mixed tetragonal and monoclinic phases, which indicates the strong correlation between the crystal structure and the dielectric properties. The real part of impedance (Z′) decreases with both temperature and frequency, and the observed weak relaxation remains almost unaltered with x. The imaginary part of impedance (Z′′) shows strong relaxation peaks shifting towards higher temperatures with frequency, which is attributed to the effect of grains, grain boundaries, and electrodes in the samples. The activation energy of the relaxation process is estimated to be 0.8–1.0 eV for the x=0–0.6 samples, and ≈1.4 eV for the x=0.8; whereas the x=1 sample shows two values (≈0.5 eV and ≈1.0 eV) in the higher and lower temperature range, respectively. Further, the change in total conductivity with the angular frequency, which found to be in the range of 10−3 to 10−5 S/m, is fitted using the Jonsher power law. The analysis suggests the overlapping large polaron tunneling (OLPT) model for all the samples, whereas the x = 1 sample exhibit a transition near 480 °C and at higher temperatures it shows non-overlapping small polaron tunneling (NSPT) and quantum mechanical tunneling (QMT). This transition is corroborated by the tangent loss curves and may be associated with the change in structure.

Studies of structural, dielectric, conductivity, leakage current mechanism, and efficiency of complex electroceramic

Bismuth ferrites are quite interesting because of their high conductivity and dielectric constant. Recent times now need innovative materials with high mechanical strength, minimal energy loss, and cost effective. The analysis of X-ray diffraction pattern/data and scanning electron micrograph provides the formation of complex bismuth ferrite containing lithium and tungsten of a composition Bi1/2Li1/2Fe1/2W1/2O3, with monoclinic symmetry. The relation between the electrical and dielectric characteristics was examined in the frequency region from 1 kHz to 1 MHz at different temperatures (25–500 °C). The electrical conductivity experiments on the compound containing lithium and tungstate produced some exciting findings. As the frequency increases, the ac resistivity showing decreasing trend with small resistance and large conductivity. With the help of non-overlapping small polaron tunneling (NSPT) and overlapping large polaron tunneling (OLPT) models, temperature-frequency dependent conduction mechanisms have been explained. When electrical characteristics are examined using impedance spectroscopy (non-Debye relaxation), the contributions of grain and grain boundaries effect in the material are observed in the material. The Ohmic and Space Charge Limited Current conduction mechanism (SCLC) were found at low and high electric field (voltage) under forward bias current-voltage situations. The energy storage efficiency of the material is 61.80 %, obtained at room temperature with an applied electric field (−3 to +3 kV/cm) at a frequency of 50 kHz from the hysteresis loop. It implies that the material is promising for pulsed power energy storage capacitors.

Structure, optical, charge transport mechanism, dielectric properties and leakage current analysis of Sm2MgMnO6 double perovskite

Structure, optical, dielectric, charge transport properties, and leakage current density of Sm2MgMnO6 prepared via auto–combustion method have been investigated in this study. The stoichiometry of the constituent elements in the prepared sample agrees with the expected values. The sintered sample exhibits a monoclinic crystal structure with space group P21/n. The crystal structure is distorted and tilted. The grains are irregular in shape and size and distributed non–uniformly. The average crystallite and grain size are 151 nm and 176.49 nm, respectively. The direct optical band gap (1.41 eV) is associated with octahedral distortion. The tangent of dielectric loss increases beyond ∼300 °C rapidly. The Havriliak–Negami formalism has been used to explain the dielectric properties. The material is relaxor ferroelectric in nature. The conduction of charge carriers follows non–overlapping small polaron tunneling (NSPT) conduction model. The ac activation energy decreases with frequency. The leakage current conduction is Ohmic in nature. The sample exhibits 1.53 × 10−6 Acm−2 leakage current density at 5.11 Vcm−1 and 150 °C, which follows the Schottky emission relation. The obtained results have been compared with the literature.