Ferrite Ceramics Research Articles

Control of dielectric properties in bismuth ferrite multiferroic by compacting pressure

Single-phase lanthanum-modified bismuth ferrite multiferroic ceramics have been synthesized by the rapid liquid-phase sintering (RLS) method. Phase composition, crystal structure, microstructure and dielectric properties of the Bi0·9La0·1FeO3 multiferroic have been studied using TG/DTA, XRD, SEM, capacitive and composite dielectric resonator methods. It has been established that the optimal conditions for formation of a perovskite Bi0·9La0·1FeO3 structure are 850 °C after 5 min in air. It has been found that the compacting pressure of the initial mixture of precursors from 90 to 1090 MPa can change the dielectric constant by ~25% in the low-frequency range and by ~80% in the microwave range up to complete elimination of the elastic polarization mechanism. The use of the RLS method under various compacting pressures opens additional possibilities for creating multifunctional multiferroics with controlled magnetoelectric coupling.

Determination of the surface tension coefficient of ferrites 600NN upon sintering

The manufacturing process of ferrite production consists in a chain of structural and phase transformations resulted in formation of ferrite ceramics from disperse systems (their solid phase is represented by metal oxides). The forces of surface tension play a crucial role at all stages of the technological process. A decrease in surface tension forces during grinding due to the use of surfactants (surface active substances) leads to better disaggregation of the components (both original and ferritized). The use of surfactants reduces interparticle friction and provides manufacturing of more dense workpieces at the stage of pressing. Microadditives promote faster formation of contact isthmuses. The goal of the study is to develop a method for determining the surface tension coefficient of 600NN ferrite material during sintering. The proposed approach is based on measurements of the shrinkage of various fragments of a vertically sintered ferrite rod, which are used to determine the values of the coefficient. It is shown that the surface tension coefficient of the studied ferrite material during sintering was σ = 65.2 ± 13.0 N/m with a confidence probability of 95%. The results obtained can be used to study the effect of the sintering temperature, the size of sintered particles, the amount and quality of alloying additives on the forces of surface tension. Moreover, the data can be used in the study of the relationship between the value of the surface tension coefficient and the parameters of the microstructure.

Four-fold multifunctional properties in self-organized layered ferrite

Four different functional properties at room temperature were found in Ba12Fe28Ti15O84 quaternary ferrite ceramics: a thermoelectric character with a prominent Seebeck coefficient of -400 μV/K, a strong ferrimagnetic character and weak magnetoresistivity, non-linear dielectric character (tunability) and ferro/piezoelectric response. The complex crystalline structure with a naturally occurring self-organized layered structure was mapped by High Resolution Transmission Electron Microscopy. A n-type conduction was found for optimized samples, consistent with the negative Seebeck coefficient. The presence of magnetic domains with a lateral size ranging from few hundreds of nanometers, up to few microns, extended over several grains indicates a strong intergranular magnetic interaction. Local ferroelectric switching as revealed by piezoresponse force microscopy showed a relatively weak effective piezoelectric coefficient with a remnant value of 0.5 p.m./V and a clockwise cycling direction, which was attributed to an effective negative piezoelectric coefficient. The switching behavior was described as originating from the material’s nanoscale layered complexity, with a strong anisotropy of its dielectric and ferro/piezoelectric local properties.

Structural, magnetic and dielectric properties of (Li1+, Al3+) co-doped Ni0.5Zn0.5Fe2O4 ferrite ceramics prepared by the sol-gel auto-combustion method

(Li1+, Al3+) co-doped Ni0.5Zn0.5Fe2O4 ferrites, Ni0.5-xZn0.5-xLixAlxFe2O4 (x = 0.000, 0.025, 0.050 and 0.100), were synthesized by the sol-gel auto-combustion method. X-ray diffraction (XRD), field emission scanning electronic microscope (FESEM), vibrating sample magnetometer (VSM) and LCR meter were used to investigate the structural, magnetic and dielectric properties. Results of XRD and SEM indicate that both doping amount and calcination temperature play significant roles in crystal structure and grain growth. Also, it can be observed that the saturation magnetization and the coercivity change in a noticeable manner. The Ni0.475Zn0.475Li0.025Al0.025Fe2O4 ferrite sintered at 1200 °C has a relatively low coercivity value (62.93 Oe) and the largest saturation magnetization (110.95 emu/g). Besides, dielectric behavior is also improved by Li1+ and Al3+ co-doping.

Bi3+ doping-adjusted microstructure, magnetic, and dielectric properties of nickel zinc ferrite ceramics for high frequency LTCC antennas

Miniaturization, high frequency capability, low loss, and matching impedance play critical roles in new generation antennas. Although ferrite ceramics show a great potential as antenna substrate materials, some challenges still remain associated with their application to high performance antennas. In this work, we synthesized Bi3+-substituted NiCuZn ferrite to adjust the microstructure, magnetic, and dielectric properties at low sintering temperatures. It is shown that Bi3+ substitution not only enhances grain growth and compactness of NiCuZn ferrite at low sintering temperatures, but also effectively tailors the permeability, permittivity, and loss factor. In particular, NiCuZn ferrite doped with 0.025 wt%, of Bi2O3 possesses excellent performance with high permeability (~29.1), high n factor (~22.76), appropriate matching impedance (Z factor = 1.28), and low loss tangents (tanδμ = 0.00853, tanδε = 1.22683 × 10-4). In addition, the dielectric loss is significantly reduced and becomes as low as magnetic loss at high frequencies; the typical tanδε reduces to 1.94 × 10-6, and tanδε/ε´ is greatly decreases to 0.137 × 10-6 at 50 MHz. Thus, Bi3+-adjusted NiCuZn ferrites open up new opportunities for applications in high-frequency LTCC antennas.

Protective and Suppressing Electromagnetic Interference Properties of Epoxy Coatings Containing Nano-Sized NiZn Ferrites

Nano-crystalline ferrites with the chemical formula NixZn(1-x)Fe2O4, where x=0, 0.2, 0.4, 0.6, 0.8, 1.0, were synthesized using a co-precipitation method. The obtained ferrites were investigated by X-ray diffraction (XRD). The corrosion inhibiting behavior of nano-sized ferrites was tested using carbon steel samples and 10% aqueous ferrite extracts. Results were compared with previous data obtained for micro-sized ceramic ferrites. Nanoparticles show more favourable properties regarding inhibiting corrosion processes on steel. 2mm thick epoxy coatings on steel containing 10% vol. of nano-sized ferrites has been investigated as a microwave absorber. The microwave reflectivity of the coating was measured within the range from 6.5 to 15 GHz. Both the nano- and micro-sized ferrites included in the coatings exhibited different reflection loss spectra. The greatest attenuation on a level of 8-16 dB was observed. The nano-ferrite-filled epoxy coating exhibited a higher minimum reflection frequency in comparison with the micro-ferrite-filled coating. A frequency shift of 1-2 GHz was observed.

Effects of Bi2O3–MnO2 additives on tunable microstructure and magnetic properties of low temperature co-fired NiCuZn ferrite ceramics

The development of miniaturized high frequency ferrite ceramics is attracting widely interest for next generation MLCI (multi-layer chip inductors). However, there exist short comings in the microstructure adversely affecting magnetic properties. In this study, 0.5 wt% MnO2-x wt% Bi2O3 (x = 0.1, 0.5, 1.0, 1.5, 2.0, and 3.0) were introduced into NiCuZn ferrites to adjust the microstructure at low temperatures. Also, the microstructure changes and high frequency magnetic properties of NiCuZn ferrites were investigated via controlling the addition of MnO2–Bi2O3 and sintering temperatures. SEM results indicated that quantitative MnO2 can suppress abnormal grain growth when optimized amount of Bi2O3 was added. In addition, various amounts of Bi2O3 were added to adjust the magnetic properties by controlling grain growth. Results revealed that 0.5 wt% MnO2-1.5 wt% Bi2O3 composite addition is a critical point to enhance the homogeneity of the samples. Also, interestingly, the dominant contribution to dynamic magnetization mechanism changes from spin rotation to domain wall motion when the content of Bi2O3 is greater than 1.0 wt%. Finally, fine microstructure of NiCuZn ferrites with high permeability (μ′ ≈ 291), high saturation magnetization (Ms ≈ 58.83 emu/g), high saturation flux density (Bs ≈ 290.04), high Q factor (~ 75) and enhanced cutoff frequency (~ 60 MHz) can be obtained sintered at 925 °C. Thus, this work may provide new guidance for developing RF frequency LTCC NiCuZn ferrite ceramics.

Permeability spectra of planar M‐type barium hexaferrites with high Snoek’s product by two‐step sintering

AbstractHigh‐frequency ferrite ceramics exhibiting high permeability and low magnetic loss have been recently attracting more and more attention owing to the rapid development of modern communication technologies. It is known that the magnetic performance of ferrites is strongly associated with the morphology of their polycrystalline structure. In this work, we focus on the control of grain growth and densification process for planar Co‐Ti doped M‐type barium hexaferrites, BaCoxTixFe12‐xO19, by one‐step sintering (OSS) and two‐step sintering (TSS) techniques. Experimental results indicate that a uniform and fine‐grained microstructure is achieved by the TSS method. More importantly, the ferrites prepared by TSS demonstrate high permeability (µ' = 18‐20), low magnetic loss (tan δm = 0.1‐0.3), and high Snoek's product (>25 GHz) in the frequency range of 100‐400 MHz. By fitting experimental data, we have determined that low magnetic loss is derived from the small damping coefficient of spin rotation in terms of Kittel's theory. Therefore, the TSS technique provides an effective and efficient approach to prepare planar BaM hexaferrite materials for ultra‐high frequency (UHF) communication devices requiring low loss and high Snoek's product.

Synthesis and characterization of BaFe12O19-CoFe2O4 ferrite composite for high-frequency antenna application

Recently, ferrite composite ceramics have received much attention for high-frequency device applications as the composite has both dielectric and magnetic properties, good chemical stability, and high electrical resistivity. M-type hexagonal ferrite BaFe12O19 (BaM) and cubic spinel ferrite CoFe2O4 (CoF) composites; (BaM)1−x(CoF)x (x = 0.0, 0.25, 0.50, 0.75, and 1.0) were successfully synthesized by co-precipitation method. X-ray diffraction (XRD) analysis confirmed the formation of pure-phase BaM ferrite at 800 °C and CoF ferrite at 600 °C, respectively. The XRD analysis of composite ferrite showed the presence of both BaM and CoF ferrite phases in the composite. The composites were sintered at 1100 °C/4 h. The composite with x = 0.25 composition showed the most compact microstructure structure and higher bulk density compared to other composites. The composite (with x = 0.25) also showed the highest permittivity (~ 15), permeability (~ 13), and antenna miniaturization factor (~ 14) at 500 MHz due to mainly better densification. The permeability of composite was almost stable up to about 500 MHz. The coercivity was lowest in the composite with x = 0.25 composition indicating a change of hard magnetic behavior of BaM ferrite into a soft magnetic character after composite formation, which may be due to the formation of enlarged grain of BaM in the composite.

Lanthanum Ferrite Ceramic Powders: Synthesis, Characterization and Electrochemical Detection Application.

The perovskite-type lanthanum ferrite, LaFeO3, has been prepared by thermal decomposition of in situ obtained lanthanum ferrioxalate compound precursor, LaFe(C2O4)3·3H2O. The oxalate precursor was synthesized through the redox reaction between 1,2-ethanediol and nitrate ion and characterized by chemical analysis, infrared spectroscopy, and thermal analysis. LaFeO3 obtained after the calcination of the precursor for at least 550–800 °C/1 h have been investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). A boron-doped diamond electrode (BDD) modified with LaFeO3 ceramic powders at 550 °C (LaFeO3/BDD) by simple immersion was characterized by cyclic voltammetry and tested for the voltammetric and amperometric detection of capecitabine (CCB), which is a cytostatic drug considered as an emerging pollutant in water. The modified electrode exhibited a complex electrochemical behaviour by several redox systems in direct relation to the electrode potential range. The results obtained by cyclic voltammetry (CV), differential-pulsed voltammetry (DPV), and multiple-pulsed amperometry proved the electrocatalytic effect to capecitabine oxidation and reduction and allowed its electrochemical detection in alkaline aqueous solution.

Technological scheme for lithium-substituted ferrite production under complex high-energy impact

The paper presents technological schemes developed for synthesis of lithium-zinc ferrite powders and sintering of ferrite ceramics, including mechanical activation of the initial mixtures of reagents in a planetary ball mill and subsequent radiation-thermal heating of powders by pulsed or continuous electron beams. Their structural and electromagnetic properties, such as density, porosity, average grain size, Curie temperature, saturation magnetization, initial magnetic permeability, and electrical resistivity, are studied. The technological scheme developed for synthesis of lithium-substituted ferrites using complex effects can be used to produce ferrite powders of homogeneous phase composition with high saturation magnetization at a significantly lower temperature and synthesis time without preliminary compaction of samples. The technological scheme for sintering ferrite ceramics through single-stage radiation-thermal heating of press samples from mechanically activated reagents increases the sample density by ~5%, initial magnetic permeability by ~10%, and electrical resistivity by (2.5–3) times, decreases porosity by ~60% and reduces the duration of ferrite production as compared to that of the two-stage production of ferrite ceramics.

Mechanistic insights into the sol-gel synthesis of complex (quaternary) Co–Mn–Zn-spinel ferrites: An annealing dependent study

Synthesis conditions, cation distribution at tetrahedral and octahedral sites and their stability play very important roles in controlling phase-purity and physicochemical properties of spinel ferrite compounds. In this work, an attempt is made to understand how the progress of phase-formation and the structural and magnetic properties are influenced by the annealing temperature and nature of cations used in the synthesis of quaternary spinel ferrite ceramics. A series of Co0.8-xMn0.2ZnxFe2O4 (x = 0, 0.2, 0.4, 0.6 and 0.8) (CMZF) spinel ferrite samples were synthesized by citric acid assisted sol-gel technique followed by annealing at 400, 600 and 800 °C. To compare the progress of phase formation/stability of the cations, simple (binary) spinel ferrite reference samples, such as CoFe2O4, MnFe2O4 and ZnFe2O4, were also synthesized by the same technique and are calcined at the same conditions. In case of CoFe2O4, all the samples have single phase spinel structure, but a transformation from an inverse spinel-type to nearly normal spinel ferrite-type cation distribution is observed with increasing annealing temperature. The as-prepared MnFe2O4 sample and that annealed at 400 °C show formation of single phase spinel ferrite, while those annealed at 600 and 800 °C decomposes completely into Mn2O3, α-Fe2O3 and amorphous-FeO phases. In contrast, for ZnFe2O4 samples, a transformation from the ZnO and α-Fe2O3 phases (present in the as-prepared and up to 600 °C annealed samples) to pure ZnFe2O4–phase occurs only at/above 800 °C. Interestingly, our results show that the progress of the phase formation behavior of the CMZF samples can be predominantly considered as a combination of the behavior and energetics typically exhibited by the individual (simple) ferrite systems. Overall, our work provides the necessary impetus for achieving the phase purity and required physicochemical properties of complex ferrite systems by choosing the cations suitably, based on their nature and annealing behavior.

Ga-substituted Mg-Cd ceramic composites for improving the miniaturization and wideband characteristics of high-frequency antennas

Mg0·8Cd0·2Fe1.9Ga0.1O4 ceramic ferrites were synthesized using a solid-state reaction method at 900, 915, 930 and 945 °C. Crystallization analysis indicated that the change in temperature resulted in obvious changes in the microstructure. SEM images indicated that the grain size increased from 0.8 to 1.8 μm. Elevated saturation magnetization (Ms ≈ 26 emu/g) and reduced coercivity (Hc ≈ 53 Oe) indicated the excellent soft-magnetic behavior of the ceramics. The real part of the permeability correspondingly increased (29–51), and the real part of permittivity showed a slight fluctuation (20–25) with an increase in the temperature. Consequently, an upward bandwidth ratio (BWR ≈ 0.2, 915 °C) and matching characteristic impedance were obtained over a wide frequency range of 1–100 MHz. Additionally, with the low magnetic (tanδμ ~10−2) and dielectric (tanδε ~ 10−4-10−3) tangent values, the proposed materials can act as potential agents for enhancing the bandwidth and miniaturization of antennas operating at high frequencies.

Structural and magnetic properties of lithium-substituted ferrite ceramics sintered by continuous electron beam heating

In the present work, the structural and magnetic properties of lithium-zinc ferrite ceramics of Li0.4Fe2.4Zn0.2O4 composition, obtained using a complex high-energy impact including the mechanical activation of Fe2O3-Li2CO3-ZnO reagent mixture in planetary mill and radiation-thermal (RT) heating by continuous electron beam, were studied. The samples were divided into two batches: 1) with preliminary thermal synthesis; 2) without preliminary synthesis. All samples were studied by X-ray diffraction (XRD), electron microscopy (SEM) and thermal analysis (TG/DTG) techniques. It was established that the high density and low porosity of lithium-zinc ferrite ceramics can be received by using radiation-thermal heating. The samples are characterized by high values of specific magnetization and Curie temperature. Preliminary mechanical activation of the initial reagent mixture allows not only to accelerate the synthesis of ferrite materials, but also to combine the technological stages of synthesis and sintering in single stage of radiation-thermal processing.

Effect of compressive mechanical stress on the magnetic properties of LiTiZn ferrite ceramics

In the article, it was experimentally determined that compressive mechanical stress affects the parameters of the temperature dependence of the initial permeability. LiTiZn ferrite ceramics were sintered at 1010 °C for 2 h in air. The experimental curves were mathematically processed using the phenomenological expression to describe the initial magnetic permeability according to the Smith-Wijn model. It is shown that the change in the shape of the experimental curves correlates with the calculated data of the increase in the demagnetizing factor with an increase in mechanical stress. It is hypothesized that the change in the shape of the temperature curves is due to the magnetoelastic effect and the temperature dependence of the magnetostriction constant. Also, it was found that mechanical stress does not affect the X-ray microstructural parameters, including the true physical broadening of the reflexes. At the same time, the growth of mechanical stress to the maximum possible level for such type of ferrite ceramics leads to an increase in the coercive force by 10%. The character of the impact of mechanical stress on the shape of the temperature dependence curve of the initial permeability differs from the effect of non-magnetic Al2O3 additives. Thus the character of the change in the shape of the temperature dependence curve of the initial permeability allows monitoring nonmagnetic phases or mechanical stress in a LiTiZn ferrite ceramics production.

Enhanced magnetic properties of low temperature sintered LiZnTi ferrite ceramic synthesized through adjusting microstructure

The regulation strategy of microstructure, either through promoting grain growth or by improving compactness, is highly effective to improve magnetic properties of low temperature sintered ferrite ceramics. Until now, many studies emphasized grain growth, which often leads to deterioration in uniformity. In this work, a dense Bi2O3-substituted LiZnTi (Li0.43Zn0.27Ti0.13Fe2.167Bi0.003O4) ferrite with enhanced magnetic properties was obtained, using LBSCA (Li2O–B2O3–SiO2–CaO–Al2O3) additives (x wt.%, x = 0.00–0.40). Interestingly, SEM images revealed that the appropriate LBSCA glass not only can promote grain growth and enhance compactness of the Bi2O3-modified LiZnTi ferrite, but also can suppress abnormal grain by facilitating grain boundary diffusion. Moreover, the relationships between microstructural changes and magnetic properties of the LiZnTi ferrite have been discussed in detail. Finally, a compact LiZnTi ferrite with high saturation flux density (Bs = 319.2 mT), low coercivity (Hc = 213 A/m) and high saturation magnetization (σs = 69.5 emu/g) were synthesized when the 0.10 wt% LBSCA glasses were added and sintering temperature was ∼900 °C. Meanwhile, the ferrite samples modified with 0.20 wt% LBSCA glasses have uniform and compact grain (∼3.0 μm). Such a sintering strategy is expected to be a referential experience for other advanced ceramics.

Preparation of Ti3C2Tx/NiZn Ferrite Hybrids with Improved Electromagnetic Properties.

Ti3C2Tx/NiZn ferrite composites were synthesized using a co-precipitation hydrothermal method, and further consolidated using electric current field-assisted sintering technology. Nano NiZn ferrites were inserted into the Ti3C2Tx interlayers with uniform coverage on their surfaces. The incorporation of MXenes promoted the sintering kinetics of the NiZn ferrite ceramics. The electrical conductivity increased by six orders of magnitude compared to pure NiZn ferrite ceramics at room temperature. The present work provides a potential way to develop a large family of dense MXenes/ferrite multiphase ceramics. The multiphase ceramics could be potentially used for the on-beam-line higher-order mode load in advanced particle accelerators.

Enhanced magnetic and dielectric properties of NiFe2O4 ferrite ceramics co-substituted by (Li1+, Zn2+ and La3+)

(Li1+, Zn2+ and La3+) co-substituted NiFe2O4 ferrite ceramics (Ni0.8-xZnxLi0.1La0.1Fe2O4, x = 0.0, 0.2, 0.4, 0.6, 0.8) were prepared by the sol-gel auto-combustion method. The structural properties were investigated by X-ray diffraction and field emission scanning electronic microscope techniques. Vibrating sample magnetometer and LCR meter were used to probe magnetic and dielectric properties. A relatively high value of saturation magnetization (105.94 emu/g) can be achieved in Ni0.4Zn0.4Li0.1La0.1Fe2O4 sample sintered at 1100 °C. In addition, the soft magnetic properties are also enhanced due to a reduced coercivity value. Also, dielectric behavior is improved and all the results show that co-substitution with Li1+, Zn2+ and La3+ ions as well as modulation via Zn2+ ions has a great impact on the properties of Ni ferrites.

Synthesis of Yttrium and Cobalt Doped Bismuth Ferrite Nanoparticles for Electrical and Magnetic Properties

A series of Yttrium (Y) and Cobalt (Co) co-doped bismuth ferrite (BFO) ceramics (Bi1-xYxFe1-yCoyO3) were fabricated by sol-gel method. The precursors used are [Bi(NO3)3.5H2O], [Fe(NO3)3.9H2O], [Y(NO3)3.6H2O] and [Co(NO3)2.6H2O]. X-ray diffraction (XRD) pattern confirms the formation of the pure phase bismuth ferrite (BFO) after annealing at 600 C for 2 hrs. The chemical bonding between Fe-O and Bi-O were identified by Fourier Transform Infrared Spectroscopy (FTIR) analysis. The electric polarization, magnetic properties and dielectric properties of the doped samples were enhanced with increasing content of Y and Co.

Enhanced Electrical and Magnetic Properties of Samarium (Sm) Doped Multiferroic Bismuth Ferrite (BFO) Ceramics

Samarium (Sm) doped modified bismuth ferrite samples Bi1-xSmxFeO3 (x = 0, 0.02, 0.05, 0.08, 0.1) were prepared by sol-gel technique. A detailed study on the electrical and magnetic properties of the samples was analyzed. X-ray diffraction patterns confirm the formation of the pure phase rhombohedral structure of bismuth ferrite. The dielectric constant (ε) and loss tangent (tan δ) show the large frequency dispersion at low frequency. AC conductivity was enhanced with Sm substitution of Bi sites. The enhancement in the ferroelectric properties was delineated by Polarization-Electric field (P-E) loops. Sm substitution of Bi improves the saturation magnetization and magneto-dielectric coefficients.