Static magnetic properties of Co and Ru substituted Ba-Sr ferrite

M-type hexagonal ferrite powders, Ba_0.5Sr_0.5Co_xRu_xFe_(12−2x)O₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) have been synthesized by conventional ceramic method. Magnetic properties have been investigated as a function of substitution of Co and Ru ions at applied external field of 10 kOe. XRD and SEM revealed hexagonal structure for these ferrites. The Co and Ru ions substitution cause increase in saturation magnetization and rapid decrease in magnetocrystalline anisotropy at lower substitution. The magnetic parameters variation has been explained by taking into account preferential site occupancy of sublattice sites by substituted ions. Curie temperature decreases with substitution due to weakening of superexchange interaction. The obtained hysteresis parameters suggest that the proposed materials cannot be used for recording applications.     

Magnetic and processability studies on rubber ferrite composites based on natural rubber and mixed ferrite

Polycrystalline single phasic mixed ferrites belonging to the series Ni_1–x Zn _x Fe₂O₄ for various values of _x have been prepared by conventional ceramic techniques. Pre-characterized nickel zinc ferrites were then incorporated into a natural rubber matrix according to a specific recipe for various loadings. The processability and cure parameters were then determined. The magnetic properties of the ceramic filler as well as the ferrite loaded rubber ferrite composites (RFC) were evaluated and compared. A general equation for predicting the magnetic properties was also formulated. The validity of these equations were then checked and correlated with the experimental data. The coercivity of the RFCs almost resemble that of the ceramic component in the RFC. Percolation threshold is not reached for a maximum loading of 120 phr (parts per hundred rubber by weight) of the filler. These studies indicate that flexible magnets can be made with appropriate magnetic properties namely saturation magnetisation (M _s) and magnetic field strength (H _c) by a judicious choice of x and a corresponding loading. These studies also suggest that there is no possible interaction between the filler and the matrix at least at the macroscopic level. The formulated equation will aid in synthesizing RFCs with predetermined magnetic properties.     

Dielectric and tunable characteristics of Ba0.4Sr0.6TiO3-BaWO4 composite ceramics for microwave applications

Phase compositions, microstructure and microwave dielectric properties, of BaWO₄ (BW)-Ba_0.4Sr_0.6TiO₃ (BST) composite ceramics, prepared by the traditional solid-state route, were systematically characterized. Meanwhile, mechanism of dielectric tunability of those materials was discussed. Dielectric properties of the BW-BST composites at a DC bias field near the phase transition temperature could be interpreted by using Johnson's phenomenological equation. The sample with x = 0.60 exhibited a tunability of 29.5%, a dielectric permittivity of 192 and a Q value of 231 (at 2.700 GHz), which make it a promising candidate for applications in electrically tunable microwave devices.     

Modified tunable dielectric properties by addition of MgO on BaZr0.25Ti0.75O3 ceramics

Phase composition, microstructure and tunable dielectric properties of (1 − x)BaZr_0.25Ti_0.75O₃-xMgO (BZTM) composite ceramics fabricated by solid-state reaction were investigated. It was found Mg not only existed in the matrix as MgO, there was also trace amount of Mg²⁺ ions dissolved in the BZT grains, which led to Curie temperature of the BZTM composites ceramics shifting to below −100 °C. Dielectric permittivity of the BZTM composite ceramics was reduced from thousands to hundreds by manipulating the content of MgO. Johnson's phenomenological equation based on Devonshire's theory was used to describe the nonlinear dielectric permittivity of the ceramics with increasing applied DC field. With increasing content of MgO, anharmonic constant α_(T) increased monotonously. Dielectric permittivity was 672, while dielectric tunability was as high as 30.0% at 30 kV/cm and dielectric loss was around 0.0016 for the 0.6BaZr_0.25Ti_0.75O₃-0.4MgO sample at 10 kHz and room temperature.     

Investigations on structural evolution and dielectric characteristics of high performance Bi-based dielectrics

A new system of (Bi_1.5Zn_1−x/3Ti_xNb_1.5−2x/3)O₇ (0 ≤x ≤ 1.5) ceramics have been successfully developed and the dielectric properties have been systematically studied. The results showed the formation of temperature compensation dielectrics over the wide range of Ti concentrations. The incorporation of Ti⁴⁺ into the bismuth zinc niobate ceramics induce the decrease of lattice constant linear while remaining cubic pyrochlore phase. The IR spectra confirm the formation of pyrochlore structure and give information about the distribution of ions between the A and B sites. It has been found that the effect of Ti substitution on dielectric properties of sintered ceramics intensifies with a higher x. The system exhibits the novel high permittivity and low dielectric loss: the permittivity values (?_r) saturate at 160-210, and loss values remain at low values (∼1 × 10⁻⁴). The temperature dependence of permittivity is strongly dependent with the compositions. Dielectric relaxation phenomena have been observed during low temperature. New high frequency and MW materials, differed by Ti content, with temperature compensation and controllable dielectric constant of 150-210 have been developed.     

Magnetic properties of NiCuZn ferrite nanoparticles synthesized using egg-white

A new process to prepare single-phase nano-sized ferrites, Ni_0.8−xCu_0.2Zn_xFe₂O₄ with x = 0.1-0.7, was developed using egg-white precursors. TG measurement showed that, the precursors must be calcined at 550 °C. XRD patterns indicated the formation of single-phase cubic ferrites with particle size in the range 28.7-48.4 nm. TEM image gave particle size agrees well with that estimated using XRD. FT-IR spectroscopy showed the characteristic ferrite bands. Hysteresis loops measurements exhibited an increase in the saturation magnetization value (M_s) up to zinc content of 0.2 followed by unexpected decrease, which suggests the preference of Zn²⁺ ions to occupy octahedral sites. The decrease in the coercivity (H_c) with increasing zinc content is attributed to the lower magneto-crystalline anisotropy of Zn²⁺ ions compared to Ni²⁺ ions. Temperature dependence of the molar magnetic susceptibility (χ_M) suggested a ferrimagnetic behavior of the investigated samples and showed a decrease in the value of the Curie temperature (T_C) with increasing zinc.     

Structural, spectroscopic and dielectric investigations on Ba8Zn(Nb6−xSbx)O24 microwave ceramics

Ba₈Zn(Nb_6−xSb_x)O₂₄ (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 and 2.4) ceramics were prepared through the conventional solid-state route. The materials were calcined at 1250 °C and sintered in the range 1400-1425 °C. The structure of the system was analyzed by X-ray diffraction, Fourier transform infrared and Raman spectroscopic methods. The theoretical and experimental densities were calculated. The microstructure of the sintered pellets was analyzed using scanning electron microscopy. The low frequency dielectric properties were studied in the frequency range 50 Hz-2 MHz. The dielectric constant (?_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q_u) are measured in the microwave frequency region using cavity resonator method. The τ_f values of the samples reduced considerably with the increase in Sb concentration. The materials have intense emission lines in the visible region. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Could binary mixture of Nd-Ni ions control the electrical behavior of strontium-barium M-type hexaferrite nanoparticles?

Cationic substitution in M-type hexaferrites is considered to be an important tool for modification of their electrical properties. This work is part of our comprehensive study on the synthesis and characterization of Nd-Ni doped strontium-barium hexaferrite nanomaterials of nominal composition Sr_0.5Ba_0.5−xNd_xFe_12−yNi_yO₁₉ (x = 0.00-0.10; y = 0.00-1.00). Doping with this binary mixture modulates the physical and electrical properties of strontium-barium hexaferrite nanoparticles. Structural and electrical properties of the co-precipitated ferrites are investigated using state-of-the-art techniques. The results of X-ray diffraction analysis reveal that the lattice parameters and cell volume are inversely related to the dopant content. Temperature dependent DC-electrical resistivity measurements infer that resistivity of strontium-barium hexaferrites decreases from 1.8 × 10¹⁰ to 2.0 × 10⁸ Ω cm whereas the drift mobility, dielectric constant and dielectric loss tangent are directly related to the Nd-Ni content. The results of the study demonstrate a relationship between the modulation of electrical properties of substituted ferrites and nature of cations and their lattice site occupancy.     

Effect of MgWO4 content on properties of Ba0.5Sr0.5TiO3 composite ceramics for tunable microwave applications

xMgWO₄-(1 − x) Ba_0.5Sr_0.5TiO₃ (x = 0.0, 5.0, 15.0, 25.0 and 35.0 wt%) composite ceramics were prepared via solid state reaction processing. Their structural and dielectric properties were systematically characterized. A significant increase in grain size was observed with increasing MgWO₄ content, which was accompanied by obvious variations in dielectric properties of the composite ceramics. It is found that the permittivity peaks of the samples gradually shifted to low temperatures with increasing MgWO₄ content. At the same time, tunabilities of the composite ceramics decreased, but their Q values increased. The sample with 35 wt% MgWO₄ possesses a high tunability of 16.8% (∼10 kHz), a low permittivity of 65 and an appropriate Q value of 309 (∼4.303 GHz), which meet the requirements of high power and impedance matching, thus making it a promising candidate for applications as electrically tunable microwave devices.     

Evaluation of a.c. conductivity of rubber ferrite composites from dielectric measurements

The effect of frequency, composition and temperature on the a.c. electrical conductivity were studied for the ceramic, Ni_1−xZn_xFe₂O₄, as well as the filler (Ni_1−xZn_xFe₂O₄) incorporated rubber ferrite composites (RFCs). Ni_1−xZn_xFe₂O₄ (where) (bix)varies from 0 to 1 in steps of 0.2 were prepared by usual ceramic techniques. They were then incorporated into a butyl rubber matrix according to a specific recipe. The a.c. electrical conductivity (σ_a.c) calculations were carried out by using the data available from dielectric measurements and by employing a simple relationship. The a.c. conductivity values were found to be of the order of 10⁻³ S/m. Analysis of the results shows that σ_a.c. increases with increase of frequency and the change is same for both ceramic Ni_1−xZn_xFe₂O₄ and RFCs. σ_a.c increases initially with the increase of zinc content and then decreases with increase of zinc. Same behaviour is observed for RFCs too. The dependence of σ_a.c on the volume fraction of the magnetic filler was also studied and it was found that the a.c. conductivity of RFCs increases with increase of volume fraction of the magnetic filler. Temperature dependence of conductivity was studied for both ceramic and rubber ferrite composites. Conductivity shows a linear dependence with temperature in the case of ceramic samples.     

Highly aluminium doped barium and strontium ferrite nanoparticles prepared by citrate auto-combustion synthesis

Aluminium doped barium and strontium hexaferrite nanoparticles BaAl_xFe_(12−x)O₁₉ and SrAl_xFe_(12−x)O₁₉ were synthesised via a sol-gel route using citric acid to complex the ions followed by an auto-combustion reaction. This method shows promise for the synthesis of complex ferrite powders with small particle size. It was found that around half of the iron could be substituted for aluminium in the barium ferrite with structure retention, whereas strontium aluminium ferrites could be produced with any aluminium content including total substitution of the iron. All synthesised materials consisted of particles smaller than 1 μm, which is the size of a single magnetic domain, and various doping levels were achieved with the final elemental composition being within the bounds of experimental error. The materials show structural and morphological changes as they move from iron to aluminium ferrites. Such materials may be promising for imaging applications.     

Electrical conduction, dielectric behavior and magnetoelectric effect in (x)BaTiO3 + (1 − x)Ni0.94Co0.01Mn0.05Fe2O4 ME composites

Electrical and magnetoelectric properties of magnetoelectric (ME) composites containing barium titanate as electrical component and a mixed Ni-Co-Mn ferrite as the magnetic component are reported. The ME composites with a general formula (x)BaTiO₃ + (1 − x)Ni_0.94Co_0.01Mn_0.05Fe₂O₄ where x varies as 0, 0.55, 0.70, 0.85 and 1 were prepared by standard double sintering ceramic method. The presence of both the phases was confirmed by X-ray diffraction technique. The dc resistivity was measured as a function of temperature. The variation of dielectric constant (?) and loss tangent (tan δ) with frequency (100 Hz-1 MHz) and with temperature was studied. The conduction is explained on the basis of small polaron model based on ac conductivity measurements. The static value of ME conversion factor i.e. dc (ME)_H was studied as function of intensity of magnetic field. The changes were observed in dielectric properties as well as ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 610 μV/cm Oe was observed in the case of a composite containing 15 mol% ferrite phase.     

Dielectric, electrical and magnetoelectric characterization of (x)Ni0.8Zn0.2Fe2O4 + (1 − x)Pb0.93La0.07(Zr0.60Ti0.40)O3 composites

The structural, electrical, dielectric, magnetic and magnetoelectric properties of (x)Ni_0.8Zn_0.2Fe₂O₄ + (1 − x)Pb_0.93La_0.07(Zr_0.60Ti_0.40)O₃ (x = 0, 0.15, 0.30, 0.45 and 1) have been studied by means of various experimental techniques. Polycrystalline samples of this series have been prepared by the double sintering ceramic method. X-ray diffraction data analysis revealed purity of the composites. Microstructural analysis using scanning electron microscopy mode depicts the presence of two phases in contact with each other. Dielectric properties were studied at and well above room temperature. Temperature dependent variation of the dielectric constant show diffused phase transition which can be well described by fitting the Lorentz-type relation, . Observation of well-saturated ferroelectric hysteresis loop and magnetic hysteresis loop for composites indicates that ferroelectric and magnetic ordering exist simultaneously at room temperature. The static value of magneto electric voltage coefficient (α_E) has been studied as a function of magnetic field at room temperature for all the composites. The maximum value of α_E is 7.53 mV/(cm Oe) for 85% PLZT-15% NZFO composites.     

Properties of the PLZTN x/54/46 (0.4 ≤ x ≤ 1.4) ceramic system

Even though the PZT ceramic system has been thoroughly studied and modified with different additives, no numerous reports have been published focusing on the PZT double ‘soft’ modification with La³⁺ and Nb⁵⁺ (PLZTN). In this paper, we explore the structural, morphological, dielectric, ferroelectric and piezoelectric properties of the PLZTN system for different doping levels (x_La3+ = x_Nb5+ = 0.4, 0.6, 0.8, 1.0 and 1.4 at.%) synthesized by conventional powders reaction. The temperature dependence of the piezoelectric response of poled ceramic disks is also analyzed and, according to its overall features, an optimum modification is proposed in order to develop PZT-based sensors for several applications.     

Dielectric properties of (1−x)(Mg0.95Co0.05)TiO3-xCaTiO3 ceramic system at microwave frequency

The microwave dielectric properties and the microstructures of the (1−x)MgTiO₃-xCaTiO₃ ceramic system were investigated. With partial replacement of Mg by Co, dielectric properties of the (1−x)(Mg_0.95Co_0.05)TiO₃-xCaTiO₃ ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature. At 1275°C, the 0.95(Mg_0.95Co_0.05)TiO₃-0.05CaTiO₃ ceramics possesses excellent microwave dielectric properties: a dielectric constant ε_r of 20.3, a Q×f value of 107 000 ( at 7 GHz) and a τ_f value of −22.8 ppm/°C. By appropriately adjusting the x value in the (1−x)(Mg_0.95Co_0.05)TiO₃-xCaTiO₃ ceramic system, zero τ_f value can be achieved. With x=0.07, a dielectric constant ε_γ of 21.6, a Q×f value of 92 000 (at 7 GHz) and a τ_f value of −1.8 ppm/°C was obtained for 0.93(Mg_0.95Co_0.05)TiO₃-0.07CaTiO₃ ceramics sintered at 1275°C for 4 h.     

Phase evolution and dielectric properties of MgTi2O5 ceramic sintered with lithium borosilicate glass

Phase evolution, densification, and dielectric properties of MgTi₂O₅ dielectric ceramic, sintered with lithium borosilicate (LBS) glass, were studied. Reaction between LBS glass and MgTi₂O₅ was significant in forming secondary phases such as TiO₂ and (Mg,Ti)₂(BO₃)O. The glass addition was not necessarily deleterious to the dielectric properties due to the formation of TiO₂: permittivity increased and temperature coefficient of resonance frequency could be tuned to zero with the addition of LBS glass, although the inevitable glass-induced decrease of quality factor was not retarded by the formation of TiO₂. The sintered specimen with 10 wt% LBS fired at 950 °C for 2 h showed permittivity of 19.3, quality factor of 6800 GHz, and τ_f of −16 ppm/°C.     

Dielectric properties of a new ceramic system (1 − x)Mg4Nb2O9-xCaTiO3 at microwave frequency

The microstructures and the microwave dielectric properties of the (1 − x)Mg₄Nb₂O₉-xCaTiO₃ ceramic system were investigated. In order to achieve a temperature-stable material, CaTiO₃ (τ_f ∼ 800 ppm/°C) was chosen as a τ_f compensator and added to Mg₄Nb₂O₉ (τ_f ∼ −70 ppm/°C) to form a two phase system. It was confirmed by the XRD and EDX analysis. By appropriately adjusting the x-value in the (1 − x)Mg₄Nb₂O₉-xCaTiO₃ ceramic system, near-zero τ_f value can be achieved. A new microwave dielectric material, 0.5Mg₄Nb₂O₉-0.5CaTiO₃ applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ?_r ∼ 24.8, a Q × f value ∼82,000 GHz (measured at 9.1 GHz) and a τ_f value ∼−0.3 ppm/°C.     

Synthesis,electrical and dielectric characterization of cerium doped nano copper ferrites

The nanosized CuFe_2−xCe_xO₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8) ferrites doped with cerium are synthesized by chemical co-precipitation method. The synthesized materials are characterized by XRD, FTIR, TGA and SEM. XRD analysis of cerium substituted copper ferrites confirms the cubic spinel structure. The average crystallite size calculated by using Scherrer's formula ranges from 37 to 53 nm. The values of cell constant and cell volume vary with the dopant concentration. These variations can be explained in terms of their ionic radii. The DC electrical resistivity, measured by two point probe method, increases with increase in dopant concentration while it decreases with rise in temperature exhibiting semiconductor behaviour. Energy of activation of these ferrites is calculated by using Arrhenius type resistivity plots. Dielectric measurements of the synthesized compounds show exponential decrease in dielectric constant and dielectric loss factor with increase in frequency. This indicates the normal dielectric behaviour of ferrites.     

Microstructural evolution and dielectric properties of Cu-deficient and Cu-excess CaCu3Ti4O12 ceramics

The microstructural evolution and dielectric properties of CaCu_3−xTi₄O_12−x (3 − x = 2.8-3.05) ceramics were investigated. Normal grain growth behavior was observed at Cu/Ca ≤ 2.9, while abnormal grain growth was observed at Cu/Ca ≥ 2.95. A CuO-rich intergranular liquid phase at Cu/Ca ≥ 2.95 and angular grain morphology were the main reasons for abnormal grain growth. However, the abundant intergranular liquid at Cu/Ca = 3.05 significantly affected the relative dielectric permittivity and dielectric loss. The CuO composition is the key parameter that determines the microstructure and dielectric properties of CCTO ceramics.     

High frequency magnetic mechanism of Ni-substituted Co2Z hexagonal ferrite

The magnetic properties, especially the high frequency magnetic mechanism, of Ni-substituted Co₂Z hexagonal ferrite were studied. The polycrystalline Z-type hexagonal ferrite of Ba₃Ni_xCo_2−xFe₂₄O₄₁ (0 ≤ x ≤ 2) were prepared by solid-state reaction. The results indicate that Ni-substituted Co₂Z samples all exhibit typical soft magnetic character. Substitution of Ni for Co will turn the planar magnetocrystalline anisotropy of Co₂Z to uniaxial anisotropy when x ≥ 1, so that the permeability drops dramatically and domain wall resonance appears in the frequency spectra. With the rise of Ni amount or sintering temperature, domain wall resonance strengthens gradually.