Koops Phenomenological Theory Research Articles

High frequency enhancement of dielectric constant, crystal structure analysis, and magnetic properties of Pr3+- Zn2+ substituted Co2Y-type barium hexagonal ferrites

The effect of Pr3+-Zn2+ doping on the magnetic and dielectric properties of Co2Y-type barium hexaferrites with the chemical composition Ba2Co2Fe12-x-yPrxZnyO22 (x = 0.00, 0.10, 0.20, and y = 0.00, 0.15, 0.25), was investigated in this study. The prepared Pr3+-Zn2+ substituted Co2Y-type barium hexaferrites were calcined for 5 h at 1100 °C in a digital heating chamber. The XRD analysis confirms the presence of a crystalline phase in the undoped Co2Y-type barium hexaferrite samples, with a space group identified as R-3m. Characteristic absorption bands of Co2Y-type barium hexaferrites were observed at 540 and 422 cm−1 due to the asymmetric stretching vibration of Fe3+ and O2− at both, octahedral and as well as tetrahedral crystallographic sites. The magnetic interaction between the particles causes slight agglomeration. Dielectric and impedance spectroscopy were performed using Koop's phenomenological theory and the Maxwell-Wagner two-layer dielectric relaxation model. The ε′ was found to decrease with an increase in applied frequency due to the space-charge polarization phenomenon. The rise in ε′ at higher frequencies enhances the material's suitability for high-frequency applications. The magnetic parameters were extracted from the M − H hysteresis loop, and it was observed that they were affected by the site preferences of Pr3+ and Zn2+. The prepared Y-type hexaferrite's optimized magnetic parameters make it a good option for magnetic memory applications.

Detailed investigation of the structural and electrical properties of ZnO/Fe3O4 nanocomposites

The nanocomposites with the formula (1-x)ZnO+xFe3O4 (x = 0, 0.01, 0.03, 0.05, 0.7 and 0.09) were prepared using the sonomechanical method, while the pristine ZnO and Fe3O4 were prepared using the co-precipitation technique. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and a high-resolution broadband impedance analyzer were used to examine the structural, microstructure, and dielectric properties of the investigated samples. XRD analysis assures the wurtzite hexagonal structure of ZnO for all nanocomposite samples. The FTIR showed the existence of a functional group of ZnO and Fe3O4. The ac conductivity, dielectric constant (ε′), dielectric loss (ε′), electric modulus, impedance, and Nyquist plot were studied as a function of frequency and at different temperatures. The results show that the small concentration of Fe3O4 affects the ac conductivity and dielectric properties. The Koops phenomenological theory and the Maxwell-Wagner interfacial model were used to analyze the observed dielectric dispersion. The analysis of modulus and impedance results indicated the existence of non-Debye relaxation and the involvement of both grains and grain borders in polarization. The impedance study reveals that just one semicircle is observed in all samples, indicating that the influence of grain boundaries is more significant than the contribution of grains.

Influence of Nb2O5 Additive on Elastic and Dielectric Properties of NiCuZn Ferrites

The influence of Nb2O5 additive on elastic and dielectric properties of NiZnCu ferrite is reported. The longitudinal and shear wave velocities were measured by ultrasonic pulse transmission method. The elastic constants increased as the Nb2O5 contents increased. The dielectric parameters such as dielectric constant (ɛ′) and dielectric loss tangents as a function of frequency and Nb2O5 additive composition for all samples at room temperature. The variations in the dielectric constant (ɛ′) and dielectric loss tangents values were explained using Maxwell–Wagner interfacial polarization according to Koops phenomenological theory. AC conductivity was increased with an increase in the frequency. A reduction in AC conductivity with Nb2O5 additive is reported.

Ferromagnetism and dielectric properties in Zn0.95−xNdxTM0.05O (TM=Co, Fe) nanocrystals: Collective role of grain boundaries and oxygen vacancies

Herein, Zn0.95−xNdxTM0.05O (TM = Co, Fe) (x = 2%, 6%) nanocrystals with spherical shape, wurtzite-like hexagonal structure, and average crystallite size of 35 nm were prepared by sol-gel method, those exhibit ferromagnetic (FM) behavior at room temperature. X-ray photoelectron spectroscopy (XPS) results confirmed the successful incorporation of dopants ions such as Nd3+ and Co2+/Fe2+ into the host ZnO lattice. Size-strain analysis based on the Williamson-Hall plot was performed to evaluate the crystallite size and lattice strain. High-resolution transmission electron microscope characterization shows that the fine nanocrystals are separated by grain boundaries (GBs). The calculated specific grain boundary area (SGB) of 60 × 106m2m-3 in the co-doped samples is above the threshold value of 5.3 × 107 m2m-3. The UV–Visible analysis shows that the energy band gap decreases with increasing Nd3+ concentration. The photoluminescence spectra (PL) show a broad emission band in the visible region corresponding to the various structural defects and oxygen vacancies in the prepared nanocrystals responsible for the activation of bound magnetic polarons (BMPs). Fitting the experimental magnetization data with the BMP model based on the Langevin function shows that the density of magnetic polarons (1020cm−3) in the doped samples is equal to the typical percolation threshold. The dielectric constant and dielectric loss was observed to increase at lower frequency due to the presence of GBs and oxygen vacancies, and this behavior was explained based on Koop's phenomenological theory. Based on these results, it was demonstrated that the FM response and the dielectric properties in studied samples are strongly associated with GBs and oxygen vacancies.

Electrical and Magnetoelectric Properties of Particulate Composites and Laminated Trilayered Thick‐Film Composites

Hydraulic pressing and screen printing methods are used to create particulate magnetoelectric composites and laminated trilayered thick‐film composites. X‐ray diffraction studies reveal the presence of cubic spinel and tetragonal perovskite structures for individual powders of ferrite CuFe2O4 and ferroelectric‐phase PbZr0.58Ti0.42O3. The dielectric constant of particulate composites decreases with increasing frequency around 1 MHz and beyond that frequency, a saturation state is attained. However, for laminated films, the dielectric constant decreases up to 1 MHz and then increases. The maximum dielectric constant at low frequency for particulate CuFe2O4/PZT composites is around 72.2, whereas for laminated CuFe2O4/PZT/CuFe2O4 composites it is 4.97 and for PZT/CuFe2O4/PZT composites is 5.24. Loss tangent exhibits the same trend as dielectric constant with frequency, which is explained by space charge polarization and is consistent with Koop's phenomenological theory. The dielectric constant's variation with temperature describes the contribution of electric dipoles to polarization and both composites exhibit absorption peaks. The semiconducting nature of both particulate and laminated composites can be seen in the DC resistivity graph with frequency and as frequency increases, DC resistivity decreases for both composites, which is explained by the small polaron‐hopping phenomenon. The magnetoelectric coupling effect for particulate composites (44 mV Oe−1cm−1) is also found to be small when compared to laminated trilayered composites (CuFe2O4/PZT/CuFe2O4—105 mV Oe−1cm−1 and PZT/CuFe2O4/PZT—68 mV Oe−1cm−1).

Enhanced electrical and magnetic functionality of Ni-Zn-co-doped CoFe2O4 rGO nanocomposites.

Enhancement in electrical and magnetic functionalities of rGO CoFe2O4 and Co0.7Zn0.3Fe1.7Ni0.3O4 nanocomposites was identified compared to their spinel-type metal oxides. Moreover, changes in morphology that occurred during the formation of the composites were fabricated via a simple in situ hydrothermal route. Electron microscopic investigations confirmed that the microspheres of the metal oxides were constructed by porous nanolamellae comprising nanoparticles interconnected to form highly stable porous microspheres. Conversely, in rGO-CoFe2O4 and rGO-Co0.7Zn0.3Fe1.7Ni0.3O4 composites, distorted spinel-type metal oxide spheres on rGO sheets were observed. Frequency-dependent conductivity increased with an increase in temperature, obeying Jonscher's power law and Koop's phenomenological theory. The resistance of ferrites decreased from ∼1.4 MΩ to 30 KΩ for their respective rGO-based nanocomposites. The hysteresis curves of all the compounds showed them to be isotropic, soft ferrimagnetic in nature. Furthermore, a 30-50% enhancement in the values of magnetic parameters of the ferrites occurred when they were interfaced with rGO sheets. This enhancement was probably due to the interfacial interaction of rGO with ferrites. Such enhancement may afford an advancement in the potential applications of these nanocomposites.

Synthesis and Characterization of Rare Earth Doped Ferrite / Polyethylene Oxide Nanocomposites

Nano-sized Li0.5Ni0.48Tb0.02Dy0.1Fe1.9O4 spinel ferrite nanoparticles were synthesized employing the micro-emulsion synthesis method. Polyethylene oxide was prepared through in-situ polymerization route. The ferrite-polymer nanocomposites have been synthesized by combining Li0.5Ni0.48Tb0.02Dy0.1Fe1.9O4 ferrite with polyethylene oxide polymer. Spectral, structural, morphological, and dielectric properties of the prepared nano-ferrite powders as well as nanocomposites were investigated by “X-ray diffraction analysis” (XRD), “scanning electron microscopy” (SEM), “Fourier transform infrared spectroscopy” (FTIR) and dielectric measurements. XRD analysis confirmed the synthesis of single-phase spinel structure only. The dielectric parameter was augmented with an increase of ferrite amount. FTIR spectra confirmed the existence of interactions between polyethylene oxide and ferrite particles. SEM study revealed that the nanocomposites comprised core/shell structure and inhomogeneous distribution of grain size. The dielectric parameters such as “real part of dielectric constant” (?), “imaginary part of dielectric constant” (?"), “tan loss”, “AC conductivity” and “quality factor” were investigated in the required range of frequency; that is, 1 MHz – 3 GHz. The peaking behavior has been observed for real (??) and “imaginary (???) parts of dielectric constant” and “dielectric loss” (tan?). “The peaking behavior” was detected beyond 1.5 GHz. A decrease in “the dielectric constants” and “dielectric loss” was found to with the increasing frequency. Dielectric parameters have been well elucidated by explaining “Debye-type relaxation model” in agreement with two layer “Koop's phenomenological theory”. The present investigated samples might have potential applications in high frequency.

Enhanced performance of magnetoelectric voltage coefficient in giant magnetostrictive (Ni0.7Mg0.3Fe2O4)/piezoelectric (BaZr0.2Ti0.8O3) composites

The non-toxic lead-free multiferroic composite samples Ni0.7Mg0.3Fe2O4/BaZr0.2Ti0.8O3 were synthesized by using standard double sintering ceramic method. The composite samples are found to exhibit dielectric response, which might be associated with Maxwell-Wagner type interfacial polarization and Koop's phenomenological theory. The variation of DC conductivity with respect to temperature revealed the conduction of electrons i.e. due to the small polarons hopping mechanism. The synthesized ME composite samples show a representative magnetic hysteresis (M − H) loop type behaviour at room temperature. In a previous report, the response of ME voltage coefficient 4.262 mVcm-1.Oe was determined for (30%) Ni0.8Mg0.2Fe2O4 + (70%) BaZr0.2Ti0.8O3 composites at 5.0 kOe applied DC magnetic field. But in this report, we improved the ME voltage coefficient for the composition 50% (Ni0.7Mg0.3Fe2O4) + 50% (BaZr0.2Ti0.8O3) which is a lead-free ME composite with the massive ME voltage coefficient of 8.562 mV/cm.Oe was achieved. Hence, the estimated results can provide experimental guidance for the optimal design of high-performance magnetoelectric devices and render better support for the technological development in the field of magnetoelectricity.

Structural, electrical and gas sensing functionality of fabricated Co1-xZnxFe2-xNixO4 (x= 0.0,0.3) nanoparticles

This article reports for the first time the structural, electrical, and gas sensing functionality of novel composition of spinel-type porous Co0.7Zn0.3Fe1.7Ni0.3O4 microspheres fabricated through a simple hydrothermal route. The structural, morphological, and elemental properties of the materials are characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) along with selected area electron diffraction pattern. XRD and XPS data reveal a pure phase spinel-type cubic crystal formation. Electron microscopic investigations confirm that the microspheres are devloped by the porous nano-lamellae made up of nanoparticles that are interconnected in a manner to form highly stable porous microspheres. AC impedance spectroscopy is utilized to analyse the electrical conductivity at different temperatures which disclose extrinsic semiconductor behaviour. The DC conductivity derived activation energy of the sample is found to be 0.76 eV. The frequency dependent conductivity of the compound obeyed Jonscher's power law and Koop's phenomenological theory. The sensing properties of the Zn and Ni doped ferrite were investigated for different gases and it demonstrates the promising sensing behaviour towards butane gas.

Microstructure Analysis, Optical, and Electrical Transport Properties of NiAl2O4/Al2O3 Nanocomposite Powder

The microstructure characterization, optical properties, electrical transport, and dielectric properties of the thermally stable NiAl2O4/Al2O3 nanocomposite powder sample synthesized by the mechanochemical‐assisted solid‐state reaction from the equimolar mixture of NiO and Al2O3 powders are reported. Rietveld refinement, selected‐area electron diffraction pattern, and Fourier‐transform infrared spectrum analyses confirm the formation of a NiAl2O4 spinel phase with a minor Al2O3 phase in the as‐synthesized powder. Transmission electron microscope images reveal the particle size of the powder sample, ≈26 nm. Raman spectrum reveals the presence of NiAl2O4 normal spinel as a major phase in the sample. The temperature and frequency dependence of the dielectric constants of the NiAl2O4/Al2O3 nanocomposite are explained by Koop's phenomenological theory. The electric modulus approach is used to analyze the electrical transport and dielectric relaxation of NiAl2O4/Al2O3 at different temperatures. The electric modulus plot with elevated temperature shows a dielectric loss peak and reflects interesting information on the grains and grain boundaries of the material with varying temperatures.

Molten Salt Flux Synthesis, Structure determination, Optical, Impedance and Modulus Spectroscopy Characterization of perovskite compound

The chemical Molten Salt Flux process was used for the synthesis of Ba0.97La0.02Ti1-xNb4x/5O3 polycrystalline sample (well-known as BLTi0.93Nb0.056). Doping with Niobium caused significant alterations in the physical properties of BLT ceramic. The XRD analysis revealed that Nb introduction forms a pure perovskite phase and crystallize in the P4/mmm-tetragonal symmetry. The average crystallite size was proven to decrease with the increase in Nb concentration. TEM image showed the formation of particles, where the average grain size decreased with Nb doping. The Nb incorporation into the BLT host lattice was also confirmed by the optical band gap (Eg) value. The optical properties were strongly influenced by Nb doping. The dielectric parameters were subsequently investigated as a function of frequency and d.c bias voltage. The observed dielectric dispersion was interpreted on the basis of Maxwell-Wagner interfacial model and Koop's phenomenological theory. Overall, Nyquist plot shows both bulk and grain boundary effect. The electrical relaxation process occurring in the material has been found to be d.c bias voltage dependent. Modulus analysis has established the possibility of hopping mechanism for electrical transport processes in the system.

Impedance spectroscopy analysis of SnS chalcogenide semiconductors

Tin Sulfide (SnS) semiconductors have captivated attention in recent years as a low-cost photovoltaic material alternative. Tin Sulfide (SnS) was successfully synthesized using a wet-chemical method, yielding a cubic phase that was later annealed at 500 °C to produce an orthorhombic phase. The ac conductivity mechanism and dielectric properties of SnS with cubic and orthorhombic phases were investigated in this paper.Dielectric constant (ε) and ac conductivity (σac) were measured in frequencies in the rangeof 40 Hz to 20 MHz at room temperature. The dielectric constant and dielectric loss tangent decrease as frequency increases. The increase in frequency-dependent ac conductivity is explained by the correlated barrier hopping (CBH) model. In addition, Nyquist (Cole-Cole) plots of cubic and orthorhombic phases revealed a distinct difference in Nature. Koop's Phenomenological theory helps to explain the variation of dielectric properties.

Synthesis, Characterization, and Dielectric Study of Titania Supported ZnFe2O4

AbstractThe nanocomposites of TiO2 loaded ZnFe2O4powders are synthesized using wet chemical process. The synthesized powder is characterized by using XRD, TEM, and VSM. In the XRD patterns of sintered composite samples, no peaks other than TiO2 and ZnFe2O4 are observed. Nanosized two different layers such as cubic zinc ferrite and TiO2are confirmed by transmission electron microscopy technique. The dielectric properties are measured in the frequency range of 20 Hz–1 MHz. The frequency variation of dielectric properties is understood with the help of Maxwell–Wagner type of interfacial polarization, which is in agreement with Koop's phenomenological theory. Dielectric permittivity data reveals dielectric permittivity decreases with frequency and increases with TiO2 composition. The dielectric constant (ϵ′) is decreased continuously with increased frequency for all the samples at room temperature revealing normal dielectric behavior of ferrites. Magnetic properties are also measured on all the composite samples at room temperature. The saturation magnetization (Ms) of the samples decreases with an increase of TiO2content in ZnFe2O4.

Dynamical response of localized electron hopping and dipole relaxation in Cu1 − x Zn x Fe2O4 magnetoceramics

We report a detailed study on the dynamical response of localized electron hopping and dipole relaxation in bulk polycrystals of Zn diluted Cuprospinel (Cu1 − x Zn x Fe2O4). The variations in the dielectric dispersion and ac-resistivity (ρ ac ) were analyzed over a wide temperature (77 K ≤T ≤ 823 K) and frequency (20 Hz ≤ f ≤ 20 MHz) window for a critical composition x c = 0.4. The variation of R (f, T) followed the Maxwell–Wagner type polarization mechanism in-line with the Koops phenomenological theory. Our analysis of ρ ac (T, f) provide strong evidence to the Mott’s variable range hopping of charge transport between the localized states at low temperatures, however, thermally-activated Arrhenius like behaviour was noticed at high temperatures with E A = 656 meV for x c = 0.4. Moreover, electric modulus spectroscopic studies (M *(f, T)) reveals two distinct types of relaxation phenomena: (i) the short-range oscillations of the charge carriers within the potential well of grains and (ii) the long-range movement of charge carriers across the grain boundaries. The depressed semi-circles of the Nyquist plots and lower values of non-exponential parameter extracted from M *(f, T) suggest the non-Debye type relaxation process present in the system with a widespread distribution of relaxation times. The frequency exponent (s(x, T)) study of Jonscher’s power law reveals that the ac-conductivity follows small-polaron tunnelling followed by the correlated-barrier-hopping mechanism for 0.1. However, for x ≥ x c reorientational hopping mechanism is predominant, except for 400 K, where thermally activated Arrhenius-type conduction of charge carriers is prevalent in this spinel system. Furthermore, the tetragonally (I41/amd) distorted systems (x ≤ 0.05) exhibit less activation energy (E A − VRH ) values as compared to those of cubic-spinel symmetry (Fd-3m) which saturates at 130 meV for 0.1 ≤ x ≤ 0.6. Compositional dependent tunability of the above discussed parameters may open a constructive approach to design low energy-loss and high-resistive electromagnetic elements for microwave devices which is the key significance of the present study.

Structural and impedance spectroscopy study of Mn1.5Y1.5CSr1.5Ba1.5 antiperovskite

The experimental study on temperature and frequency dependent impedance spectroscopy study of an antiperovskite is being reported for the first time in this work as until now only the theoretical studies on dielectric behavior of various antiperovskites have been reported. Additionally, the effect of the presence of alkaline earth metals at A-site on the physical properties of an antiperovskite has been investigated for the first time. The structural and impedance characteristics of Mn1.5Y1.5CSr1.5Ba1.5 antiperovskite, synthesized by mixed oxide method, have been reported in this work. X-Ray Diffraction (XRD) analysis of this antiperovskite indexes it in a cubic crystal system with Ia3‾ space group. The impedance spectroscopy study reveals that the persistent rise in the magnitude of relative dielectric constant (εr) and dielectric loss (tan δ), with increasing temperature, is due to thermally activated charge carriers which results in the surge in conductivity of the sample. The dielectric dispersion in this antiperovskite is ascribed to Maxwell–Wagner form of interfacial polarization that is explained on the basis of Koop's phenomenological theory. The complex impedance analysis signifies a non-Debye relaxation process for this compound.

Doping Effect and Microstructure Behavior of Rare-Earth Element Cerium (Ce+3) in Barium Hexaferrite (BaCexFe12-xO19) Nanoparticles

Cerium substituted BaM hexaferrites BaCexFe12-xO19 (x = 0.0, 0.25, 0.5, 0.75, and 1.0) nano crystallites were synthesized via Sol-gel method. The x-ray diffraction (XRD) patterns were analyzed by Rietveld refinement which confirms the formation of hexagonal structure. The crystalline size was calculated by Debye Scherrer method, W–H method and SSP method. The lattice constant ? found to decrease, this was due to the octahedral site replacing a large radius of Ce3+ ion with a smaller radius Fe3+ ion, While the lattice constant c found increase. The x-ray density observed increases with increasing Ce3+ concentration. Fourier transform infrared spectroscopy (FTIR) confirmed the two frequency bands n1 tetrahedral site and n2 octahedral site in a range between 400–620 cm-1. Impedance analyzer was used to investigate the dielectric properties in a range of 1 MHz – 3 GHz following Maxwell Wagner model. Dielectric constant showed decreasing trend while dielectric loss showed dispersive behavior by increasing frequency and same was that with tangent loss, such behavior was due to Koop's phenomenological theory. AC conductivity exhibits a plane behavior in a low frequency, while dispersive in high frequency. Such behavior was due to grain effect at high frequency. Impedance showed continuous action at high frequency, which is attributed to the release of space charges. The real and imaginary modulus showed variation by increasing frequency, which was due to the occurrence of relaxation phenomenon. As per dielectric research, these ferrites can be utilized in high frequency devices, microwave technologies, and semiconductor devices.

Influence of bismuth doping on structural, electrical and dielectric properties of Ni–Zn nanoferrites

Bismuth doped Ni–Zn ferrites of the composition Ni0.5Zn0.5BixFe2-xO4 with (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.1) have been synthesized by a citrate precursor method. Bismuth was doped to tailor the properties of Ni–Zn spinel ferrite. X-Ray Diffraction (XRD) data was used to calculate lattice parameter, density, porosity and hopping length values which revealed that all annealed bismuth doped nickel zinc nanoferrites display a single phase cubic spinel structures. Average crystallite size was found to be in the range of 15–28 nm. Williamson-Hall method was used to deduce the average lattice strain experienced by the nanocrystalline. A tensile strain was observed with an increase in the bismuth concentration from x = 0.00 to x = 0.04 which leads to an expansion of lattice while a compressive lattice strain was observed for the concentration x = 0.06 due to contraction of the lattice. Fourier Transform Infra Red (FTIR) peaks confirmed the appearance of absorption bands at a wave number 405 cm−1 and at a wave number 580 cm−1 confirming tetrahedral and octahedral modes of vibrations respectively. I–V characteristics at 4 V voltage were studied at room temperature. A highly resistive behaviour of the samples of the order of 1010 Ω-cm was observed making these materials suitable for high frequency applications. The investigations on real part, imaginary part of dielectric constant and dielectric loss tangent were carried out in the frequency range 10 kHz to 10 MHz at room temperature. Dielectric behaviour showed that with an increase in concentration of bismuth, the value of real part of dielectric constant increases from 5.161 to 11.162 at 104 Hz frequency and the value of dielectric loss tangent decreases from 0.79 to 0.33. AC conductivity of all the samples was found to increase with an increase in frequency which is explained on the basis of Koop's Phenomenological theory.

Fabrication of Cerium Doped Nickel-Cobalt Ferrite by Co-Precipitation Method

In the modern world researchers caught the attraction towards spinal ferrites. The current work is based on spinel ferrites having formula Ni0.5Co0.5CexFe2-xO4 where (x = 0.0, 0.05, 0.1, 0.15, 0.2) Prepared by co-precipitation method. The confirmation of spinal ferrite structure was done through XRD analysis. The crystallite size was found to be in the range of 8 to 11 nm. Lattice perimeter is observe to obey the increasing trend due to replacement of larger ionic radii of cerium with smaller ionic radii of iron. Koop's phenomenological theory, Maxwell–Wagner interfacial polarization and Vegard’s law is used to explain the behavior of lattice constant. The electrical properties of prepared ferrites were revealed by impedance analyzer. Various parameters like real and imaginary parts of dialectic constant, impedance and modulus was determined. In the frequency range of 1 to 3 GHz the detailed electrical inspection was done. During the electrode polarization the effect of grains on the increasing substitution of cerium was analyzed through real and imaginary parts of electrical modulus M' and M". In the frequency range of 3 GHz the value of M' is 2.1934 × 10-1 to 2.6581 × 10-1 and the value of M" is from 4.67 × 10-3 to 3.538 × 10-3. AC conductivity spectra shows a non-Debye relaxation behavior and it dependents of conductivity on frequency. The observed dielectric constant, dialectic loss and tangent loss are found to be decreasing with the increase in frequency. The investigation shows that real and imaginary impedance Z' and Z" was found to be decreasing on lower frequencies and on higher frequencies all the curves merge with each other. The value of Z' and Z" at 3GHz frequency is in the range of 8.02 × 10-3 to 0.6073 and 3.7641 × 101 to 4.5617 ×101 respectively. Increase in frequency increases the AC conductivity. The applications of prepared nanoparticles are suggested in high frequency devices because of the splendid dielectric properties of these particles.

Investigation of the conduction mechanism, high dielectric constant, and non-Debye-type relaxor in La0.67Ba0.25Ca0.08MnO3 manganite

The conduction mechanism and electric properties of La0.67Ba0.25Ca0.08MnO3 (LBCM) were analyzed depending on temperature and frequency. The frequency dependence of electrical conduction plot was explained by the jump relaxation model. The electrical conduction process was based on both theoretical conduction models assigned to the Correlated Barrier Hopping and Non-overlapping Small Polaron Tunneling mechanism. The impedance plot studies reveal that the relaxation is a non-Debye poly-dispersive pattern in the LBCM. This compound has excellent dielectric properties such as the dielectric permittivity exceeding 105 at room temperature, i.e., colossal permittivity, and is one of the highest values recorded for ceramic capacitors. Thus, evolution of dielectric permittivity, described in terms of spatial charge polarization based on Koop's phenomenological theory and Maxwell–Wagner's (M– W) model and high dielectric response, has been driven by barrier layers into the grain boundaries and blended structures of Mn3+/Mn4+. The relaxation processes were examined with modulus, impedance formalism, and electrical conductivity. In the thermal analysis, the relaxations mechanism are related oxygen vacancies.

Electrical conductivity improvement of Fe doped ZnO nanopowders

The chemical co-precipitation process was used for the synthesis of Fe-doped ZnO nanopowders (ZnO:Fe) with varying doping concentrations from 0% to 10 %. Doping with iron caused significant alterations in the physical properties of ZnO nanopowders. The XRD analysis revealed that Fe introduction forms a secondary phase of spinel ZnFe2O4 for doping concentration higher than 1%. The average crystallite size was proven to decrease with the increase in Fe concentration. SEM images showed the formation of spherical nanoparticles, where the average grain size decreased with doping. The Fe incorporation into the ZnO host lattice was also confirmed by FTIR and Raman spectroscopy. The optical properties were strongly influenced by Fe doping. The dielectric parameters were subsequently investigated as a function of frequency and composition. The observed dielectric dispersion was interpreted on the basis of Maxwell-Wagner interfacial model and Koops phenomenological theory. Overall, Fe doping improved the electrical conductivity of ZnO nanopowders.