Dielectric behaviour of erbium substituted Mn-Zn ferrites

Dielectric properties such as dielectric constant (ε′) and dielectric loss tangent (tan□δ) of mixed Mn-Zn-Er ferrites having the compositional formula Mn_0.58Zn_0.37Fe_2.05−xEr_x0₄ (where itx = 0.2, 0.4, 0.6, 0.8 and 1.0) were measured at room temperature in the frequency range 1–13 MHz using a HP 4192A impedance analyser. Plots of dielectric constant (ε′) vs frequency show a normal dielectric behaviour of spinel ferrites. The frequency dependence of dielectric loss tangent (tan δ) was found to be abnormal, giving a peak at certain frequency for all mixed Mn-Zn-Er ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. Plots of dielectric constant vs temperature have shown a transition near the Curie temperature for all the samples of Mn-Zn-Er ferrites. However, Mn_0.58Zn_0.37Er_1.0Fe_1.05O₄ does not show a transition. On the basis of these results an explanation for the dielectric mechanism in Mn-Zn-Er ferrites is suggested.     

Structural, microstructural and dielectric studies of tin-doped barium niobate perovskite

Monophasic oxides of the type Ba(Nb_1-x Sn _x ) O₃ (0 ≤ x ≤ 1) have been synthesized by solid-state reaction method. All these compounds are found to have tetragonal structure except x = 1. The cell parameters and their variation with composition x have been determined. The X-ray density is found to increase gradually with increase of dopant concentration. Tolerance factor and volume of unit cell was found to be almost constant for all the compositions. Scanning electron microscopy showed the presence of grains of approximately 1 μm in size. Dielectric measurements in the frequency range 100 Hz to 1 MHz and in the temperature range from − 100°C to 500°C has been carried out to determine the dielectric parameters. A strong frequency dependence of both dielectric constant (ɛ′) and dielectric loss (D) is observed in the frequency range 100 Hz to 100 kHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. Dielectric loss showed a typical behaviour in the temperature and frequency range studied.     

Dielectric behaviour of MgFe2O4 prepared from chemically beneficiated iron ore rejects

Chemically beneficiated high silica/alumina iron ore rejects (27–76% Fe₂O₃) were used to synthesize iron oxides of purity 96–98% with SiO₂/Al₂O₃ ratio reduced to 0.03. The major impurities on chemical beneficiations were Al, Si, and Mn in the range 2–3%. A 99.73% purity Fe₂O₃ was also prepared by solvent extraction method using methyl isobutyl ketone (MIBK) from the acid extracts of the ore rejects. The magnesium ferrite, MgFe₂O₄, prepared from these synthetic iron oxides showed high resistivity of ∼ 10⁸ ohm cm. All ferrites showed saturation magnetization, 4πM_s, in the narrow range of 900–1200 Gauss and the Curie temperature,T, _cof all these fell within a small limit of 670 ± 30 K. All ferrites had low dielectric constants (ε′), 12–15, and low dielectric loss, tan δ, which decreased with the increase in frequency indicating a normal dielectric dispersion found in ferrites. The presence of insignificant amount of polarizable Fe²⁺ ions can be attributed to their high resistances and low dielectric constants. Impurities inherent in the samples had no marked influence on the electrical properties of the ferrites prepared from the iron ore rejects, suggesting the possibility of formation of ferrite of constant composition, MgFe₂O₄, of low magnetic and dielectric losses at lower temperatures of 1000°C by ceramic technique.     

Laser induced structural and transport properties change in Cu–Zn ferrites

The samples were prepared from analar oxides (BDH) using the standard double sintering ceramic technique. X-ray diffraction (XRD) was carried out to assure the formation of the sample in single spinel phase. The effect of Q-switched Nd:YAG laser irradiation with wavelength of 1064 nm on the electrical properties of the prepared samples Cu_{1 − x} Zn _x Fe₂O₄ (0.1 ≤ x ≤ 0.6) was discussed. The temperature dependence of the polarization and a.c. conductivity was studied in the range (300 K ≤ T ≤ 700 K) at different applied frequencies (10 kHz ≤ f ≤ 4 MHz). The activation energies were calculated at different temperature regions for the unirradiated and irradiated samples. Their values indicate the semi-conducting like behaviour of the sample. Comparison between the ac electrical conductivity, dielectric constant, dielectric loss, for unirradiated and irradiated samples with different Zn concentrations (0.1 ≤ x ≤ 0.6) was performed. Seebeck voltage measurements showed that, the n and p-type conduction act in cooperation with each other. The change in a.c. conductivity is attributed to the creation of lattice vacancies after laser irradiation. The decrease of the a.c. conductivity and the dielectric constant after laser irradiation with 18000 shots may be due to formation of traps, which decrease the number of carriers. The lattice mismatch in the grain boundaries causes a planar array of localized states, being able to capture free carriers. The accumulated charge constitutes an electrostatic barrier impeding carriers from free motion. Thus, it is possible to optimize the conductivity of this type of ferrite material to be used in technological applications at room temperature.     

Structural and dielectric properties of nanocrystalline Nd<Superscript>3+</Superscript> substituted nickel–zinc ferrites

Ferrite samples with general formula Ni_1−xZn_xNd_yFe_2−yO₄ (x = 0, 0.2, 0.4, 0.6, 0.8 and 1; y = 0.01, 0.02 and 0.03) were synthesized by oxalate co-precipitation technique. The X-ray diffraction study confirms the formation of single-phase cubic spinel structure. The lattice constant of the samples increases with increase in zinc content and obeys Vegard’s law. On Nd³⁺ substitution lattice constant of the samples slightly increases except zinc ferrite. The frequency dependence of the dielectric constant, dielectric loss and AC conductivity of the samples were determined in the frequency range from 20 Hz to 1 MHz at room temperature. The experimental results reveal that the dielectric constant and dielectric loss decreases where as AC electrical conductivity increases with increase in frequency. The dielectric loss increases with increase in zinc content whereas it decreases with increase in Nd³⁺ content. There is no appreciable change in permittivity of the samples with increase in Nd³⁺ content. Permeability of all the samples increases with increase in Nd³⁺ content. Because of lower dielectric loss, Nd³⁺ substituted Ni–Zn ferrites are useful in electronic devices.     

Crystal structure and magnetic properties of high-coercivity Sr1 ? xPrxFe12 ? xZnxO19 solid solutions

Sr_1−x Pr _x Fe_{12 − x} Zn _x O₁₉ ferrites with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by solid-state reactions between praseodymium, iron, and zinc oxides and strontium carbonate in air at 1470 K. According to X-ray diffraction results, the samples with x ≤ 0.2 were single-phase and those with 0.3 ≤ x ≤ 0.5 contained, in addition to the magnetoplumbite phase, small amounts of α-Fe₂O₃, ZnFe₂O₄, and PrFeO₃. The mixed-phase samples further fired twice at 1470 K for 4 and 2 h contained no impurity phases at x = 0.3 and contained only α-Fe₂O₃ at x = 0.4 and 0.5. In the composition range 0 ≤ x ≤ 0.3, the a and c cell parameters, unit-cell volume V, and X-ray density ρ_x of the magnetoplumbite phase vary linearly according to the relations a(?) = 5.8869 − 0.0162x, c(?) = 23.027 + 0.449 x, V(?³)= 691.10 + 9.65x, and ρ_x(g/cm³) = 5.102 + 0.230 x. The highest degree of combined heterovalent substitution of Pr³⁺ for Sr²⁺ and Zn²⁺ for Fe³⁺ in the SrFe₁₂O₁₉ ferrite (formation of Sr_1−x Pr _x Fe_{12 − x} Zn _x O₁₉ solid solutions) at 1470 K is x = 0.32−0.36. The saturation magnetization per formula unit (n _s) of the x = 0.1 ferrite exceeds that of SrFe₁₂O₁₉ by 1.7% at 6 K and by 15.2% at 308 K. The 308-K n _s and coercive force (_σ H _c) of the x = 0.2 ferrite exceed those of SrFe₁₂O₁₉ by 7.6 and 8.5%, respectively.     

An investigation on electrical properties of microwave treated natural ilmenite (FeTiO3)

It has been observed that microwaves of 2.45 GHz heat dielectric materials. On subjecting natural ilmenite to microwave irradiation, the mineral is observed to heat, with a surface temperature in proportion to the irradiation time. With irradiation times from 40 to 240 seconds (increased in steps of 40 sec), the surface temperature measured on the samples were between 280 and 520 K. Electrical measurements made on the samples before and after irradiation show that the electrical properties are modified by the microwave irradiation. The real conductivity (σ′), dielectric constant (ɛ′) and the dielectric loss (ɛ″) plotted against frequency generally showed universal dielectric behaviour [1 and references therein] similar to that observed in other systems studied in the literature but using conventional heating techniques. Plots of σ′, ɛ′ and ɛ″ against the surface temperature of the sample showed frequency independent peaks around 460 K. The experimental dielectric loss (ɛ″) results fit a peak function of the form:

The effect of Al-substitution on structure and electrical properties of Mn-Ni-Zn ferrites

X-ray diffraction, Infra-red spectroscopy and scanning electron microscopy have been used to investigate the Mn_0.5Ni_0.1Zn_0.4Al_xFe_{2 − x}O₄ system (0 ≤ x ≤ 0.15 in steps of 0.025). The analysis of IR spectra indicates the distribution of Al-ions between both A and B-sites. The electrical resistivity and thermoelectric power as a function of temperature and Al-content have been investigated. It is observed that the resistivity increases with increasing the Al-content. It is also found that the temperature variation of resistivity exhibits two breaks, each break is associated with a change in the activation energy. Measurement of the thermoelectric power reveals n-type conduction for all samples. The activation energies of all samples in the paramagnetic region are found to be greater than those in the ferrimagnetic region. The results are explained on the basis of the formation of spin polarons in the paramagnetic region.     

Anomalous electrical properties of nanocrystalline Ni–Zn ferrite

Nanocrystalline powders of Ni–Zn ferrite (NZFO) having the chemical formula Ni _x Zn_1−x Fe₂O₄, where x varies as 1, 0.8, 0.6, 0.4, 0.2, and 0, were synthesized by chemical co-precipitation technique. The samples synthesized were characterized by X-ray diffraction (XRD) technique at several stages. As prepared samples at room temperature show absence of Bragg peak indicating that there was no crystalline phase formation of ferrite. The XRD pattern of the samples sintered at 400 °C clearly showed the characteristic Bragg peaks of spinel cubic structure. XRD patterns were further analyzed to calculate the lattice constant, porosity, and jump length of charge carriers. Electrical dc resistivity measurements were carried out with respect to temperature using two probe method. NZFO samples showed abnormal electrical behavior at room temperature. Also abnormal electrical behavior with increase in temperature in the range 600–800 K was observed. Variation of dielectric constant and loss tangent with frequency were studied at room temperature. The electrical and dielectric behavior of the Ni–Zn samples is discussed in the light of literature.     

Magnetic and dielectric properties of the M-type barium strontium hexaferrite (Ba x Sr1−x Fe12O19) in the RF and microwave (MW) frequency range

This paper presents results for the dielectric permittivity (ε′), dielectric loss (tg δ _E) dielectric permeability (μ′) and magnetic loss (tg δ _M) in the radio-frequency and microwave frequency range of Ba _x Sr_1−x Fe₁₂O₁₉ hexaferrite (0 ≤ x ≤ 1). The samples were prepared by a new route of the ceramic method. The magnetic permeability (μ′) and magnetic loss (tg δ _M) measurements in the range 100 MHz to 1.5 GHz, reveals that 1.32 ≤ μ′ ≤ 1.68 for the permeability of BFO100 (BaFe₁₂O₁₉) and 1.16 < μ′ ≤ 1.88 for SFO100 (SrFe₁₂O₁₉) in the range of studied frequencies. The BFO100 sample presented lower loss (tg δ _M = 4.10⁻³ at 1.5 GHz). The permittivity of BFO100 and SFO100 in 1.5 GHz are, respectively 8.18 and 8.19, and in the 1 MHz are, respectively 52.04 and 19.09. The samples presented coercive field in the range of 3–5 kOe and remanence magnetization in the range of 33–36 emu/g. The subjects of paper were study the dielectric and magnetic properties of the barium and strontium hexaferrite, in view of applications as a material for permanent magnets, high density magnetic recording and microwave devices.     

Electrical and dielectric properties of nano crystalline Ni–Co spinel ferrites

Nanocrystalline samples of Ni_xCo₁–_xFe₂O₄, where x = 1, 0.8, 0.6, 0.4, 0.2 and 0, were synthesized by chemical co-precipitation method. The spinel cubic phase formation of Ni–Co ferrite samples was confirmed by X-ray diffraction (XRD) data analysis. All the Bragg lines observed in XRD pattern belong to cubic spinel structure of ferrite. Scanning Electron Microscopy (SEM) technique was used to study the surface morphology of the Ni–Co ferrite samples. Nanocrystalline size of Ni–Co ferrite series was observed in SEM images. Pellets of Ni–Co ferrite were used to study the electrical and dielectric properties. The resistivity measurements were carried out on the samples in the temperature range 300–900 K. Ferrimagnetic to paramagnetic transition temperature (T_c) for all samples was noted from resistivity data. The activation energy below and above T_c was calculated. The dielectric constant (ɛ′) measurements with increasing temperature show two peaks in the temperature range of measurements for all samples under investigation. The peaks observed show frequency and compositional dependences as a function of temperature. Electrical and dielectric properties of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples show unusual behavior in temperature range of 500–750 K. To our knowledge, nobody has discussed such anomalies for nanocrystalline Ni_xCo₁–_xFe₂O₄ at high temperature. Here, we discuss the mechanism responsible for electrical and dielectric behavior of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples.     

Cadmium substituted (Bi1.5ZnNb1.5)O7 dielectric ceramics

The effects of small amounts of Cd substitution for Zn in the low loss dielectric material Bi_1.5ZnNb_1.5O₇ are reported. Solid solution of (Bi_1.5Zn_0.5-x Cd _x )(Zn_0.5Nb_1.5)O₇ was formed in the present ceramics for x < 0.1, and β-Bi₂O₃ secondary phase appeared at x = 0.3. For x = 0.5, another phase Bi_1.6Cd_0.4O_2.8 appeared gradually with increasing x. With increasing x, the dielectric constant increased firstly and reached their maximums 168 at 1 MHz, then decreased after x > 0.2. High-ɛ dielectric ceramics with low dielectric loss were created at the composition x = 0.2: ɛ = 168, and α_ɛ = − 554 ppm/° at 1 MHz.     

Microstructure and dielectric properties of BaTiO3-based X7R ceramics

The relationship between the microstructures and dielectric properties of BaTiO₃-based X7R ceramics has been investigated at different calcination temperatures. The XRD and SEM results show that calcinations of BaTiO₃ raw powders increase the grain size and stabilize the tetragonality (c/a ratio) of the ceramics. The grain growth caused by the calcination prevents the doped ions from diffusing into the interior of the grains, and then increases the volume fraction of the tetragonal phased core. This process greatly increases the dielectric constant by improving the ferroelectricity. As a result, the relaxation mechanism of the domain reorientation generates high loss tangent. The BaTiO₃ ceramics with X7R specifications were prepared at the calcination temperature of 1200 °C and the sintering temperature of 1240 °C, whose dielectric properties were ɛ _r ≥ 4500, Δɛ _r/ɛ _r25 ≤ ± 10%(−55∼125 °C), tanδ ≤ 0.012(25 °C), respectively.     

Dielectric properties of the system Ca1 −x La x Ti1 −x Co x O3

Dielectric behaviour of samples of the system Ca_{1 −x} La _x Ti_{1 −x} Co _x O₃ withx ⩽ 0·20 has been studied in the temperature range 300–525 K as a function of frequency. The strong dispersion ofɛ andD observed in these materials indicate the significant contribution of interfacial polarisation to the observed dielectric properties. The interfacial polarisation arises due to the presence of microscopic chemical heterogeneities arising out of the slow diffusion-controlled solid state sintering process used for their preparation.     

Influence of copper substitution on magnetic and electrical properties of MgCuZn ferrite prepared by microwave sintering method

Polycrystalline MgCuZn ferrites with chemical formula Mg_0.50-xCu_xZn_0.50Fe₂O₄ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were prepared by microwave sintering method. These powders were calcined, compacted and sintered at 950 °C for 30 min. Structural, microstructural and elemental analyses were carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. The sintered ferrite was characterized for initial permeability, dielectric constant and dielectric loss tangent and ac conductivity measurements. The temperature variation of the initial permeability of these samples was carried out from 30 °C to 200 °C. The dielectric constant, dielectric loss tangent and ac conductivity have been measured in the frequency range of 100 Hz to 1 MHz. Initial permeability and dielectric constant were found to increase and dielectric loss decreased with Cu substitution for Mg, up to x = 0.20. The ferrite powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency.     

Frequency effect on the electrical and dielectric properties of (TlGaS2) 1 ? x(TlInSe2)x (x = 0.005, 0.02) single crystals

The electrical properties (loss tangent (tanδ), real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity, and ac conductivity across the layers (σ_ac)) of (TlGaS₂)_{1 − x} (TlInSe₂) _x (x = 0.005, 0.02) layered single crystals have been studied in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. Almost throughout the frequency range studied, their ac conductivity follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level. The Fermi-level density of states (N _F ), the spread of their energies, the mean hop time τ and distance R, and the concentration of deep traps determining the ac conductivity of the crystals (N _t ) have been estimated. With increasing x in (TlGaS₂)_{1 − x} (TlInSe₂) _x , N _F and N _t increase, while τ and R decrease.     

Synthesis, Structural, Electrical, Magnetic Curie Temperature and Y–K Angle Studies of Mn–Cu–Ni Mixed Spinel Nanoferrites

Nanoferrites of composition Mn_0.50Cu_0.5−x Ni _x Fe₂O₄ (0.00≤x≤0.50) are prepared by chemical coprecipitation method. The prepared nano-ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), two probe resistivity apparatus, and vibrating sample magnetometer (VSM) to study the compositional, structural, morphological, electrical, and magnetic properties with varying concentration (x) in the composition of the prepared nanoferrites. XRD confirmed formation of single phase spinel ferrite with crystalline size in the range of 16–29 nm. The lattice parameter (a) decreases with a decrease of Cu concentration. Further information about the structure and morphology of the nanoferrites was obtained from SEM and results are in good agreement with XRD. FTIR gives information about distribution of cations and anions by confirming the presence of high and low frequency bands due to tetrahedral and octahedral sites, respectively. The electric properties were measured and analyzed by using homemade two probe resistivity apparatus showing semiconducting behavior of synthesized ferrites. The magnetic hysteresis curves clearly indicate the soft nature of the prepared samples. Various magnetic parameters such as saturation magnetization (M _s), and remanence (M _r) are calculated from the hysteresis loops and observed compositional dependent. Saturation magnetization and magnetic moment increase with Ni content. This is due to the existence of localized canted spin. Coercivity and M _s decreases while Y–K angles increase with Cu²⁺ content. The Ni²⁺ addition improves the magnetic properties. Curie temperature decreases with increase in Cu contents.     

Influence of Zr doping on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Pure and Zr-substituted CaCu₃(Ti_1−x Zr _x )₄O₁₂ (x = 0, 0.01, 0.02, 0.03) ceramics were prepared by the Pechini method. X-ray powder diffraction analysis indicated the formation of single-phase compound, and all the diffraction peaks were completely indexed by the body-centered cubic perovskite-related structure. The effects of Zr⁴⁺ ion substituting partially Ti⁴⁺ ion on the dielectric properties were investigated in frequency range between 100 Hz and 1 GHz. The low frequency (f ≤ 10⁵ Hz) dielectric constant decreases with Zr substitution and the high frequency (f ≥ 10⁷ Hz) dielectric constant is unchanged. Interestingly, a low-frequency relaxation was observed at room temperature through Zr substitution. The observed dielectric properties in Zr-substituted samples were discussed using the internal barrier layer capacitor model. A corresponding equivalent circuit was adopted to explain the dielectric dispersion. The characteristic frequency of low-frequency relaxation rises due to the decrease of the resistivity of grain boundary with Zr substitution, which is likely responsible for the large low-frequency response at room temperature.     

The effect of Ti<Superscript>4+</Superscript> ions and gamma radiation on the structure and electrical properties of Mg ferrite

Ferrite samples of the general formula Mg_1+x Ti _x Er _y Fe_2−2x−y O₄; 0.1 ≤ x ≤ 0.9, y = 0.025 were prepared using the standard ceramic method. The final sintering temperature was 1,200 °C with heating rate 4 °C/min during 100 h. X-ray diffraction analysis was carried out to assure the formation of the spinel structure. The effect of Ti⁴⁺ ion concentration on the structural and the electrical properties of the investigated samples is studied. It change the iron ion concentration from 2 to 2−2x thereby decreasing the number of ferrous ions on octahedral sites, with a consequent decrease the dielectric constant. The most important result of γ-irradiation on the electrical properties is the change of ratio on the octahedral site leading to increase the conductivity as well as the dielectric constant. The variation of the thermoelectric power with a temperature is performed, the common feature of all compositions is the fluctuation of Seebeck coefficient between positive and negative over the whole range of temperature. This indicates that the charge carriers are electrons and holes, depending on both the temperature range and the additive in the ferrite samples.     

Structural and Magnetic Properties of Nanocrystalline Mg–Co Ferrites

Mg?CCo nano crystalline ferrites having the general formula Mg_1?x Co _x Fe₂O₄ (x=0, 0.05, 0.1, 0.15, 0.2, 0.25) were prepared by the sol?Cgel method. X-ray powder diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR) were carried out to investigate the structural properties of the samples. X-ray powder diffraction patterns indicated the formation of a spinel structure of the prepared compounds. Fourier Transform Infrared (FTIR) spectroscopy of the samples confirmed the XRD results. The crystallite size, lattice parameters and porosity of samples were calculated by XRD data analysis as a function of cobalt concentration. The dielectric constant (?? _r ), dielectric loss tangent (tan???) and ac electrical conductivity (?? _ac) of nanocrystalline Mg?CCo ferrites were investigated as a function of frequency and Co concentration. The frequency dependence of ?? _r , tan??? and ?? _ac is in accordance with the Maxwell?CWagner model. The effect of Co doping on dielectric and electric properties was explained on the basis of cations distribution in the crystal structure. The saturation magnetization M_S, remanent magnetization M_r and coercivity H_C of all samples were explained as a function of cobalt concentration on the basis of Néel??s two-lattice model.