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Hard–soft CoFe2O4/Ni0.3CuxZnyFe2O4 (x, y ≤ 0.5) spinel ferrite nanofibers (H/S CFO/CuZnFO SFNFs) were synthesized via electro-spin. The main aim of this study is to investigate effect of co-substitution of transition metals of Cu and Zn on the dielectric features of H/S CFO/NiFO SFNFs. The microstructure and morphology of all products were studied by XRD, SEM along with EDX, TEM and HR-TEM. The dielectric features of all products were evaluated as a function of frequency, F (1 MHz–3 GHz), and temperature, T (20–120 °C). The T-dependent AC and DC conductivity of all products improved with T, in agreement with the semiconductor behavior. While AC conductivity revealed two regions as F-dependent and F-independent, DC conductivities exhibited Arrhenius-type behavior above and below the transition T. Thermally stimulated charge transfer model produced activation energies before and after transition T ranging between Ea = 78 and 297 meV, which is consistent with AC and DC conductivities. The dielectric loss, dielectric constant and dielectric loss tangent of all nanofibers decreased with the increase in F at all T. The Cole–Cole plots were used to analyze the effect of grain and grain boundary on conduction mechanism, and they displayed mainly only one incomplete semicircle signifying non-Debye behavior and domination of grain boundaries to the conduction mechanism. The dielectric parameters of all samples vary significantly with compositional ratio. The dielectric behaviors of H/S CFO/CuZnFO SFNFs are correlated with the conduction mechanisms based on grain-to-grain boundaries, clarified by Koop's model. [ABSTRACT FROM AUTHOR]

In this study, we have synthesized unique Mn0.5Zn0.5ErxYxFe1.8-2xO4 (x ≤ 0.1) SFNPs via ultrasonication (sonochemical) approach. Electrical and dielectric features of Mn0.5Zn0.5ErxYxFe1.8-2xO4 SFNPs were inspected comprehensively using impedance spectroscopy up to 3.0 MHz from 20 to 120 °C for a various substitution ratio of Er3+ and Y3+ ions. The fundamental electrical and dielectric parameters which are AC/DC conductivity, activation energy, dielectric loss, dielectric constant, and tangent loss were studied in the determined frequency and temperature ranges. The experimental results showed that ac conductivity obeys the power law equation and the value of n changes considerably with the co-substitution of Er3+ and Y3+ ions in various ratios, however, exhibiting some dependencies over a given temperature range. The DC conductivity and activation energy curves show a significant variation with temperature and co-substitutional ratios of Er3+ and Y3+ ions. The conduction mechanisms can essentially be assigned to the grain–grain boundaries. Therefore, frequency-dependent dielectric properties of Mn0.5Zn0.5ErxYxFe1.8-2xO4 SFNPs can be described by means of the Koop's model. It is revealed that conductivity and dielectric properties of Mn0.5Zn0.5ErxYxFe1.8-2xO4 SFNPs are adjustable with co-substitutional ratios of Er3+ and Y3+ ions. [ABSTRACT FROM AUTHOR]

Single-phase SrGdxFe12−xO19 (x = 0.00–0.05) nanosized M-type hexagonal ferrites (NHFs) were prepared via citrate sol–gel route. The formation of Gd substituted Sr-hexaferrites has been confirmed by XRD, SEM, TEM and EDX for all substitutions. The X-ray powder patterns revealed the hexagonal crystal structure of all products. The electrical and dielectric properties of SrGdxFe12−xO19 NHFs were investigated extensively with an impedance spectroscopy up to 3.0 MHz from 20 to 120 °C. Both electrical and dielectric components including ac/dc conductivity, dielectric constant, dielectric loss and lossy tangent were evaluated for measurement temperatures up to 120 °C. It has been indicated that ac conductivity generally complies with power law rules, mainly dependent on Gd3+-ion substitution ratios. The impedance analysis showed that due to the influence of various Gd3+-ion substitution ratios in the NHFs, the conduction mechanisms can mainly be attributed to the grain-grain boundaries. The dielectric constant of SrGdxFe12−xO19 NHFs owns a normal dielectric distribution with the frequency, largely due to varying substitution ratios. In other words, the variation of Gd3+-ion substitution can be used to modify the conduction mechanism of NHFs. Therefore, the observed change in dielectric properties as a function of frequency can be clarified on a phenomenological basis by Koop's model of the electrical conduction mechanism in most composite ferrites. [ABSTRACT FROM AUTHOR]

In this study, a series of SrGa0.02Fe11.98O19-Zn0.5Ni0.5Fe2O4 hard/soft nanocomposites (SrGaFeO-ZnNiFeO H/S NCs) were synthesized via a single-pot (citrate sol–gel) approach by applying different calcination temperatures. The electrical and dielectric properties of the SrGaFeO-ZnNiFeO H/S NCs based on the calcination temperatures in between 800 and 1100 °C were systematically investigated with an impedance analyzer of up to 3.0 MHz frequency and within 20 and 120 °C temperature range. Both electrical and dielectric parameters, such as ac/dc conductivity, dielectric loss, dielectric constant, and tangent loss, were measured for a given calcination temperature. It has been found that AC conductivity generally conforms the power law rules, largely dependent on calcination temperatures. Impedance analysis has observed that the conduction mechanisms of SrGaFeO-ZnNiFeO H/S NCs at various calcination temperatures are mainly attributable to grain–grain boundaries. The dielectric constant of SrGaFeO-ZnNiFeO H/S NCs shows normal dielectric distribution with frequency, largely dependent on calcination temperatures. Ultimately, the observed change in dielectric properties with frequency can be attributed to the conduction mechanism in most compound ferrites, which can be phenomenologically explained by Koop's model. [ABSTRACT FROM AUTHOR]

(BaTiO3–SrTiO3)/(WO3)x ceramics with x = 0 up to 5% were synthesized using solid-state reaction via high-energy ballf milling technique. Various characterization techniques were used including X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform-infrared spectroscopy (FT-IR), and UV–visible diffuse reflectance (DR) spectrophotometer. Structural analysis via XRD indicates the formation of two separate phases of SrTiO3 (STO) and BaTiO3 (BTO) having both cubic structures. The presence of BaWO4 as impurity was detected for higher concentration. SEM observations show a reduction in the average grains size with increasing WO3 addition. In comparison with free-added ceramic, the optical band gap energy (Eg) shows a slight increase with WO3 addition. Contextual investigations on the electrical and dielectric properties of various WO3 added to BTO–STO ceramics have been used to evaluate conductivity (σ ), dielectric constant and loss ( ε r ′ and ε r ″ ), and dissipation factor ( t a n δ ) against both frequency and dc bias voltages. Generally, both σ and ε r ″ correspond to the tendency of the power law to frequency. However, dc bias has been noticed to be lesser affecting the conduction mechanisms, which has a small variation for various WO3 addition ratios. In addition, the dissipation factor was found to be highly dependent on both the addition ratio and the frequency as well as dc bias applied. [ABSTRACT FROM AUTHOR]

Ce and Y substituted SrFe12O19 (x = 0.4 and 0.5) nanohexaferrites have been synthesised by sol-gel auto-combustion. The pure hexagonal SrFe12O19 phase was confirmed by XRD, FE-SEM and HR-TEM. The ac conductivity and dielectric properties of Ce and Y substituted Sr:Fe12O19 nanohexaferrites were studied by using complex impedance technique. Dielectric properties such as dielectric constant, dielectric loss, dielectric tangent loss, as well as ac conductivity are measured at various bias potentials in a varying frequency range from 10 Hz to 10 MHz. The frequency dependency of the ac conductivity could be evaluated by a power exponent law at higher frequencies, which is a characteristic mechanism for electrical charge transport by tunnelling processes with which it is more dispersive at lower frequencies. The conduction mechanisms were also investigated at various dc bias potentials, mainly being an indicative of hopping type conduction. So, the dielectric dispersion behaviour can be well elucidated in terms of Maxwell-Wagner polarization in accordance with the Koop's phenomenological theory. Utilizing an electrical equivalent circuit model, impedance studies were carried out in a specific frequency domain to characterize all the contributions of the dielectric response between the grains and grain boundaries to the dielectric parameters. [ABSTRACT FROM AUTHOR]

This study reported the effect of Eu substitutions on the conductivity and dielectric properties of Y3−xEuxAl5O12 (0.0 ≤ x ≤ 0.1), YAG:xEu3+. All products were fabricated by solid state route. The formation of YAG was approved through X-ray diffraction powder diffraction and high-resolution transmission electron microscope. It was found that the lattice parameters are increasing with increase the substitution content due to the difference in ionic radii between Y3+ and Eu3+. Electrical and dielectric properties of YAG (Y3Al5O12) and YAG:xEu3+ ceramics were investigated extensively for a variety of concentrations (0.00 ≤ x ≤ 0.1) of the substitutional Eu3+ ion from the 4f lanthanide group. The temperature dependence of dielectric loss, dielectric constant, loss tangent and ac/dc conductivity were examined up to 5.0 MHz to understand the electrical and dielectric properties for both doped and undoped YAG ceramics. The experimental results revealed that Eu3+ ion substitutions (especially x = 0.05) in YAG ceramics meaningfully influence the lossy mechanisms, conductivity and dielectric constant which is probably due to the contribution to the conduction mechanism of the 4f-Eu and 3d-Al ions. So, this can be incorporated at the exceptional sites of both Oh (octahedral) and Td (tetrahedral) symmetries in YAG: xEu3+ ceramics. [ABSTRACT FROM AUTHOR]

The Nb3+ ion substituted Sr hexaferrites (SrNbxFe12−xO19 (x = 0.00–0.08) hexaferrites (HFs)) were fabricated via a citrate-assisted sol-gel approach. X-ray powder diffractometer analysis affirmed the pureness of all products. The crystallite sizes of the products which were estimated from Scherrer equation were in the 36–40 nm range. The chemical component of the samples was proved by Energy-dispersive X-ray spectroscopy (EDX) and Elemental mapping. The hexagonal morphology of all products was confirmed by Field Emission Scanning Electron Microscopy (FE-SEM). The electrical conduction mechanisms and dielectric properties of a variety of Nb3+ions-substituted SrNbxFe12−xO19 HFs were investigated by a complex impedance system. Dielectric parameters such as conductivity, dielectric constant, dielectric loss, dielectric tangent loss and complex modulus, were studied at temperatures up to 120 °C in a frequency range varying from 1.0 Hz to 3.0 MHz for several Nb ratios. The frequency dependence of the conductivity was found to comply with the power law with diverse exponents at all frequencies studied here. Subsequently, incremental tendencies in dc conductivity with temperature indicate that the substituted Sr-HFs leads to a semiconductor-semimetal like behavior. This could be attributable to a feature of conduction mechanism which is based on the tunneling processes. Additionally, the dielectric dispersion pattern was also explained by Maxwell–Wagner polarization in accordance with the Koop's phenomenological theory. [ABSTRACT FROM AUTHOR]