Lithium Zinc Ferrite Research Articles

Effect of Bismuth Oxide on the Structure, Electrical Resistance and Magnetization of Lithium Zinc Ferrite

The structural, electrical, and magnetic properties of lithium zinc ferrite prepared by ceramic technology have been studied. The composition of lithium zinc ferrite is Li0.4Fe2.4Zn0.2O4 with 1 and 2 wt % bismuth oxide. The addition of Bi2O3 prior to sintering of the samples has been shown to affect the structural, electrical, and magnetic properties of the ferrite. A significant increase in density from 4.47 to 4.65 g/cm3 and a decrease in porosity from 4.8 to 2.3% have been observed when the concentration of bismuth oxide has been increased to 2 wt %. The Bi2O3-containing samples have higher specific electrical resistivity compared to that of the additive-free lithium zinc ferrite. The introduction of bismuth oxide has reduced the specific saturation magnetization from 70.55 to 54.76 G cm3/g. The Curie temperature has not changed significantly. An optimal combination of macroscopic properties of ferrite has been found at 1 wt % Bi2O3 concentration.

Effect of Bismuth Oxide on the Structure, Electrical Resistance, and Magnetization of Lithium Zinc Ferrite

Effect of Bismuth Oxide on the Structure, Electrical Resistance, and Magnetization of Lithium Zinc Ferrite

Investigation and treatment of carbon pollution in LiZn ferrite ceramics prepared by spark plasma sintering

In this study, lithium–zinc ferrite (LZF) ceramics were prepared by spark plasma sintering. Problem of carbon pollution was effectively resolved by annealing decarburization, formation of BN-coated carbon paper, and formation of protective layer of different metal foils (Ti, Mo, W, and Ta). The effects of carbon pollution and different protective layers on microstructure and dielectric and magnetic properties of LZF ceramics were studied comprehensively. Results reveal that annealing decarburization and BN-coated carbon paper could significantly improve resistance and saturation magnetization (Ms) of LZF, while real part of dielectric constant (ε′) and dielectric loss (tanδ) were significantly reduced. X-ray diffraction patterns indicate that all selected protective layers can provide good spinel-phase LZF ceramics. The utilization of metallic foil as protective layer can effectively reduce carburization, improve the resistance of LZF ceramics, and reduce ε′ and tanδ values. X-ray photoemission spectroscopy and Raman spectroscopy results reveal that cations with the highest valence state replace Fe3+ at B-site. The use of metal foil protective layer leads to the infiltration of metal ions into LZF lattice, leading to the increase in the lattice constant and decrease in the Ms value. This study deepens the understanding of carburization during SPS, providing a reference scheme for future applications.

Structural, optical, electrical and magnetic properties of lithium zinc ferrite – Silica nanocomposites

Lithium zinc ferrite - silica nanocomposites; with a formula [Li0.5−x/2ZnxFe2.5−x/2O4]30%[SiO2]70%, have been synthesized using ultrasonic assisted sol-gel auto combustion method. Thrust of the study is to investigate effect of zinc substitution in lithium ferrite (dispersed in silica matrix) on structural, optical, electrical and magnetic properties. X-ray diffraction (XRD), UV Visible (UV-Vis), Transmission Electron Microscopy (TEM), Complex Impedance Spectroscopy (CIS) and Vibrating Sample Magnetometry (VSM) have been employed to investigate the samples. XRD patterns confirm the phase purity and revealed that incorporation of Zn2+ at Li+ sites expand the unit cell dimensions from 8.3281 Å to 8.4398 Å, strain and crystallite size escalates from 0.29 to 1.42 and 18.28–27.50 nm respectively. Results from TEM and XRD match well indicating least agglomeration. Optical bandgap and refractive index show a significant effect on increasing zinc content. The impedance (Z) is found to reduce with increase in Zn2+ and may be attributed to enhancement in crystal boundaries. Dielectric properties were explored using cole-cole theoretical fitting of permittivity (ε), universal dielectric response (UDR) model, Koop’s theory and Maxwell–Wagner (M-W) mechanism. Complex electrical modulus (M*) formulation has been employed to explore the transport mechanism. Cole-cole plots in M* reveal that all the samples, except x = 0.50, show relaxation originating from grain boundaries whereas x = 0.50 sample shows contributions from both, grain and grain boundaries. Equivalent circuits have been derived using M* spectrum and are presented with circuit parameters. Frequency dependent AC conductivity (σac) curves have been fitted successfully using Jonscher’s power law; σac for a typical sample x = 0.50 was fitted using double power law. All samples have η ≤ 1, confirming correlated barrier hopping (CBH) mechanism of conductivity. Present system exhibits lower dc conductivity due to highly resistive silica in the samples. Magnetic properties have been studied using Vibrating Sample Magnetometry (VSM). Zn2+ substitution has a significant impact on magnetization due to migration of cations.

Microstructure and magnetization study of Li and Li–Zn ferrites synthesized by an electron beam

Lithium ferrites are widely used in high frequency electronic devices. The present work reports structural and magnetization analysis of lithium (Li0.5Fe2.5O4) and lithium-zinc (Li0.4Fe2.4Zn0.2O4) ferrites synthesized by electron beam heating (RT) of powdered and compacted samples. The synthesis was carried out at 600 and 750 °C for up to 120 min using 2.4 MeV electron beam generated by an ILU-6 pulsed electron accelerator. The characteristics of the samples synthesized by RT were compared with the ones of samples obtained by traditional thermal heating under the same temperature and time conditions. From XRD and thermomagnetometric analyses, α-Li0.5Fe2.5O4 ordered spinel phase and Li0.5(1−x)Fe2.5−0.5xZnxO4 ferrite phase with different zinc substitution were formed from Fe2O3/Li2CO3 and Fe2O3/Li2CO3/ZnO reagents, respectively. RT synthesis significantly increases the rate of interaction between the initial powders and, as a consequence, the rate of ferrite phase formation. In this case, lithium-containing ferrites can be successfully achieved from compacted powders at 750 °C, which is lower than the temperature of synthesis in conventional thermal heating. The average crystallite sizes calculated from the XRD and BET analyses were 114 nm for Li, 120 nm for Li–Zn ferrites and 142 for Li, 150 nm for Li–Zn, respectively. The specific saturation magnetization and Curie temperature were estimated and are 60 emu/g for Li, 70 emu/g for Li–Zn ferrites and 632 °C for Li, 492 °C for Li–Zn ferrites, respectively. The data obtained in this work are of considerable interest for the creation of a technology for producing ferrites at low synthesis temperatures.

A sintering strategy for lithium zinc ferrite with a high saturation magnetization and low ferromagnetic resonance line-width

Based on the activation energy and diffusion kinetics theory of grain growth, Li0.42Zn0.28Ti0.1Fe2.2O4 ceramics with a low ferromagnetic resonance line-width (ΔH) and high saturation magnetization (Ms) were synthesized by adopting LTCC (low-temperature cofired ceramics) technology. The critical sintering temperature of ferrite synthesis was reduced to 925 °C due to activation energy reduction and the liquid phase sintering mechanism of Bi2O3. The sintering agent B2O3 further improved the grain size, homogeneity, density and properties. EDS and XRD refinement showed that Bi3+ and B3+ ions did not enter lattices, but Ti4+ ions entered lattices and replaced part of the Fe3+ ions, leading to the lattice expansion. Finally, homogeneous and compact Li0.42Zn0.28Ti0.1Fe2.2O4 ferrite with Ms up to 354.6 kA/m and ΔH as low as 184.2 Oe was synthesized at temperatures as low as 925 °C by adding an appropriate content of Bi2O3 and B2O3. In the present study, the exploration and practice of reducing the sintering temperature and improving the material properties based on sintering agents is a beneficial supplement and improvement to the wider application of the LTCC technique.

Study of XRD, dielectric properties and DC electrical conductivity of Li-Zn-Al ferrite synthesized by sol–gel combustion method

A series of nanocrystalline aluminum (Al3+) doped Lithium-Zinc ferrites (LZA) having general chemical formula Li0.5(1- x )Zn x Fe2.5- y Al y -0.5 x O4 with x = 0.1 and y = 0.2 (S1C1), 0.4 (S1C2), 0.6 (S1C3) and 0.8 (S1C4) were synthesized by citrate sol-gel combustion method. The structural characterizations of the samples were carried out by X-Ray Diffraction (XRD) studies. Morphological investigations were performed using Scanning Electron and Transmission Electron Microscopies. XRD analysis confirmed the formation of single phase of the reported samples. All the samples crystallized in spinel cubic crystal structure with Fd-3m (227) space group. Crystallite size was estimated in the range of 19 nm to 21 nm using Scherrer formula. The variation of D.C. electrical conductivity as a function of temperature of as-prepared samples revealed the semiconducting nature. The dielectric constant (ε'), dielectric loss factor (ε") and the dielectric loss tangent (tan δ) were studied in the frequency range of 1 KHz to 1 MHz at room temperature by using LCR Meter. The values of dielectric constant, dielectric loss factor and dielectric loss tangent were found to decrease with addition of Al3+ content as well as with the increase in the frequency. The observed dielectric dispersion at lower frequency is attributed to Maxwell-Wagner type of interfacial polarization due to hopping of charge between Fe+2 and Fe+3. High value of resistivity (≈106 Ω-cm) and low value of dielectric constant and dielectric loss are the prime achievements of the present research work which make these investigated nanoferrites useful for the microwave devices.

Effect of cooling medium on the preparation and microwave absorption properties in low frequency for LiZn ferrites hollow microspheres

The lack of research on low-frequency absorbing materials working at frequencies lower than 8 GHz makes it difficult to meet the military needs of the large wavelength electromagnetic shielding. In this study, crystalline and amorphous lithium zinc ferrites hollow microspheres (LiZn FHMs) were prepared by self-reactive quenching technology, based on Fe+Zn+Fe2O3 +O2 +Li2CO3 reactive system, using distilled water and 15 wt% NaCl solution as cooling medium, respectively. Effect of cooling medium on the formation mechanism and microwave absorption properties in low frequency range for two kinds of LiZn FHMs was studied. The results show that LiZn FHMs surface with distilled water as cooling medium has polygonal crystal structure. While the surface of LiZn FHMs is smooth by using 15 wt% NaCl solution, and XRD patterns prove that LiZn FHMs are of amorphous structures. When the cooling medium is changed from distilled water to NaCl solution, the magnetic loss of amorphous LiZn FHMs changes from double loss mechanism (natural resonance and eddy current loss) to a single loss mechanism (natural resonance). Compared with crystalline materials, the emergence of "rheology unit" and the change of magnetic loss mechanism are the main reasons for the improvement of microwave absorption properties in low frequencies. When the thickness of the amorphous sample is equal to 2 mm, the minimum reflectivity is −29.8 dB, and the corresponding frequency is 7.1 GHz. The absorption frequency band below −10 dB is 5.3–10.3 GHz, and its bandwidth is 5 GHz. This effectively meets the low frequency new absorbent "thin, light, wide and strong" demand, and it could be promising in the application of invisible coatings on the weapon equipments. The survival performances of weapon equipments in the complex electromagnetic field are expected to be improved.

Исследование намагниченности и температуры Кюри LiZn-феррита, синтезированного электронно-пучковым методом нагрева из механоактивированных реагентов

In this work, the magnetization of Li0.4Fe2.4Zn0.2O4 lithium-zinc ferrite, synthesized by electron-beam heating of a mechanically activated mixture of Fe2O3-Li2CO3-ZnO initial reagents, was studied by measuring the specific saturation magnetization and the Curie temperature. Mechanical activation of the initial reagents was carried out at different times using a planetary mill and a steel set. The grinding rotation speed was 1290 and 2220 rpm. To heat the samples during the synthesis, an ILU-6 pulsed accelerator with an electron energy of 2.4 MeV was used. The synthesis temperatures were 600 and 750 °C, the synthesis time did not exceed 120 minutes. It was established that preliminary grinding of samples at 2220 rpm followed by electron beam heating at 750 °C for 120 minutes leads to the formation of the main amount of ferrite with the desired chemical formula. This is confirmed by the data on the specific saturation magnetization of 80 emu/g and the nominal value of the Curie temperature of 500 °C. The use of this mode allows to significantly reduce the ferrite synthesis temperature in comparison with traditional ceramic technology.

Dilatometric and kinetic analysis of sintering Li–Zn ferrite ceramics from milled reagents

The impact of mechanical milling of the mixture of Fe2O3–Li2CO3–ZnO reagents on thermal sintering of lithium–zinc ferrites of Li0.4Fe2.4Zn0.2O4 composition was studied using X-ray diffraction, dilatometric and kinetic analyses. The dilatometric analysis showed that mechanical pre-activation of the mixture of the initial reagents in a planetary mill reduces the initial shrinkage point and accelerates compaction of ferrite-pressed samples during sintering, which ultimately increases the density of the finished ferrite ceramics. The sintering of lithium–zinc ferrite from a non-milled mixture proceeds in two steps. At the first stage, the samples show linear expansion, and at ~ 720 °C, a sharp shrinkage occurs. The data obtained from milled samples indicate that shrinkage starts at lower temperatures and is in the range of 370–400 °C. This result allows simultaneous synthesis and sintering of lithium–zinc ferrite through one-stage heating of pressed samples to the sintering point. The resulting lithium–zinc ferrite ceramics exhibits high density, specific magnetization and Curie temperature. The kinetic analysis of ferrite compaction was performed, and kinetic parameters and the model to describe this process were found.

Solid-Phase Formation of Li-Zn Ferrite under High-Energy Impact

The effect of complex high-energy action, including mechanical milling of Li2CO3-Fe2O3-ZnO initial reagents mixture and its consistent heating by the pulsed electron beam on solid-phase synthesis was studied by X-ray powder diffraction and thermal analyses. The initial mixture Li2CO3-Fe2O3-ZnO corresponds to the ferrite with stoichiometric formula: Li0.5(1–x)ZnxFe2.5–0.5xО4, where х = 0.2. The same studies were carried out with thermal heating in a laboratory furnace for detection the effect of radiation on the formation of phase composition lithium-zinc ferrite. Initial mixture was milled in AGO-2S planetary ball mill with a milling speed of 2220 rpm for 60 min. Radiation-thermal synthesis of the milled mixture was carried out by the pulsed electron accelerator (ILU-6) at 600°C and 750°C. The maximum time of the isothermal stage was 60 minutes. According to the X-ray powder diffraction and thermogravimetric analysis, it was found that the complex high-energy action leads to decrease a temperature and time of obtaining lithium-zinc ferrite homogeneous in phase composition. The proposed high-energy regimes allow to synthesized lithium-zinc ferrites at 600 °C for 60 minutes, which is much lower compared to conventional ceramic technology.

Synthesis of lithium zinc ceramics with a high saturation magnetization and a low ferromagnetic resonance line-width via two-step sintering strategy using low temperature co-fired ceramic technology

Abstract Lithium zinc ferrite (Li0·435Zn0·26Mn0·06Ti0.1BiyFe2.155-yO4) with a high saturation magnetization (Ms) and a low ferromagnetic resonance line-width ( Δ H ) was successfully synthesized by Low Temperature Co-Fired Ceramic (LTCC) technology using a two-step sintering strategy. In the pre-sintering stage, the optimal amount of active agent (Bi2O3) was added to LiZnMnTi ferrite to reduce reaction activation energy and promote grain growth at low temperature. SEM revealed that active agent effectively reduced critical sintering temperature to 920 °C and promoted grain growth at low temperature. During the final sintering process, various amount of V2O5 additive was added to make up the defect of asymmetrical grain growth caused by imbalances between grain growth and boundary diffusion from the influence of Bi2O3. It not only further promoted grain growth, but also greatly improved grain uniformity, reduced defects and increased material density. Finally, LiZnMnTi ferrite with a high Ms (353 kA/m), a low Δ H (182Oe), and a large average grain size (∼8 μm) was successfully synthesized by adding an optimal amount of V2O5 (0.6 wt%).

Effect of Rare Earth Doping on Electrochemical Properties of Fe<sub>2</sub>O<sub>3</sub> Nanoparticle for Supercapacitor

Fe2O3 nanoparticle was prepared by a hydrothermal method, and the influence of rare earth elements (Y3+, Nd3+ and La3+) on the electrochemical performance was studied. The crystal structure and microstructure of the synthesized lithium zinc ferrite were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM). The results show that the powder is well crystallized and the particles are mostly irregular.The electrochemical property was characterized via cyclic voltammetry (CV) and constant current charge-discharge method. The capacitance of the Fe2O3 nanoparticle is 258.3 F/g, 342.7 F/g after doping Y3+ ,337.1 F/g after doping Nd3+and 331.2 F/g after doping La3 +. The results show that the rare earth elements (Y3+, Nd3+ and La3+) after the specific capacitance has increased, more suitable for super capacitor materials.

Investigation of grain boundary diffusion and grain growth of lithium zinc ferrites with low activation energy

AbstractActivation energy and diffusion kinetics are important factors for grain growth and densification. Here, Bi2O3 was introduced into Li0.43Zn0.27Ti0.13Fe2.17O4 ferrite ceramics via a presintered process to lower the reaction activation energy and to achieve low temperature sintering. Interestingly, Bi3+ ions entered the lattice and substituted for Fe3+ in the B‐site (i.e., a pure LiZn spinel ferrite). Also, SEM image results show that Bi2O3‐substituted LiZn ferrite ceramics have low critical temperature for grain growth (920°C), which is very advantageous for LTCC technology. This indicates that Bi2O3 is an excellent dopant for ceramics. Furthermore, to promote normal grain growth of the ceramics at low temperatures, different volumes of V2O5 additive were added at the final sintering stage. Results indicate that an optimal volume of V2O5 additive promotes grain growth (with no abnormal grains) and enhances magnetic performances of the ceramics at low sintering temperature. Finally, adding the optimal volume of V2O5 additive resulted in a homogeneous and compact LiZnTiBi ferrite ceramic with larger grains (average size of ~8 μm), high 4πMs (~4100 gauss), and low ΔH (~190 Oe) obtained (at 900°C). Moreover, the doping method reported in this study also provides a reference for other low temperature sintered ceramics.

Microstructure and reactivity of Fe2O3-Li2CO3-ZnO ferrite system ball-milled in a planetary mill

In this work, the microstructure of mechanically activated Fe2O3-Li2CO3-ZnO mixture for the lithium-zinc ferrites production was studied using the Brüner, Emmett, Teller and laser diffraction methods as well as X-ray diffraction and scanning electron microscopy analyses. The reactivity of reagent mixture was investigated by thermogravimetric and calorimetric analyses. The ball milling was performed in a AGO-2S high energy planetary ball mill with a vial rotation speed of 2220 rpm using steel grinding balls. The milling times were 0, 5, 15, 30 or 60 min. It was shown that the composition of mixture changes during the ball milling, which consists in decreasing the α-Fe2O3 concentration and increasing the Fe3O4 spinel phase, while the Li2CO3 and ZnO concentrations remain unchanged. It was found that the milling leads to decrease in the average particle size of the reagents and simultaneously formation of large size agglomerates with denser structure and well-interlinked particles. It was established that observed changes in microstructure and phase composition lead to an increase in the reactivity of the Fe2O3-Li2CO3-ZnO system and the acceleration of the chemical reaction between reagents.

X-ray Diffraction and Magnetic Investigations of Lithium-Zinc Ferrites Synthesized by Electron Beam Heating

Li0.5(1−x )ZnxFe2.5−0.5x O4 ferrites (x = 0.2; 0.4) were produced by thermal and radiation-thermal (RT) synthesis from Li2CO3-Fe2O3-ZnO powder mixtures and then studied using x-ray diffraction (XRD) and saturation magnetization analysis. The RT synthesis was carried out by 2.4 MeV electron beam heating of samples from the first batch at the temperatures of 600°C, 700°C, 750°C and isothermal exposure time of 0 min, 10 min, 20 min, 30 min, 60 min, and 120 min. For comparative analysis, thermal heating of samples from the second batch was performed in a resistance laboratory furnace using the same time and temperature regimes. XRD analysis of samples showed the formation of lithium-zinc ferrites with greater homogeneous phase composition at lower values of temperature and time during RT synthesis compared to the samples obtained by thermal heating. Also, RT-synthesized ferrites are characterized by significantly higher values of saturation magnetization at all time and temperature regimes. It was established that a regime of RT synthesis at 750°C–30 min provides the formation of lithium-zinc ferrites with a high degree of final phase composition.

Synthesis of Highly Uniform and Compact Lithium Zinc Ferrite Ceramics via an Efficient Low Temperature Approach.

LiZn ferrite ceramics with high saturation magnetization (4πMs) and low ferromagnetic resonance line widths (ΔH) represent a very critical class of material for microwave ferrite devices. Many existing approaches emphasize promotion of the grain growth (average size is 10-50 μm) of ferrite ceramics to improve the gyromagnetic properties at relatively low sintering temperatures. This paper describes a new strategy for obtaining uniform and compact LiZn ferrite ceramics (average grains size is ∼2 μm) with enhanced magnetic performance by suppressing grain growth in great detail. The LiZn ferrites with a formula of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 were prepared by solid reaction routes with two new sintering strategies. Interestingly, results show that uniform, compact, and pure spinel ferrite ceramics were synthesized at a low temperature (∼850 °C) without obvious grain growth. We also find that a fast second sintering treatment (FSST) can further improve their gyromagnetic properties, such as higher 4πMs and lower ΔH. The two new strategies are facile and efficient for densification of LiZn ferrite ceramics via suppressing grain growth at low temperatures. The sintering strategy reported in this study also provides a referential experience for other ceramics, such as soft magnetism ferrite ceramics or dielectric ceramics.

Influence of reagents mixture density on the radiation-thermal synthesis of lithium-zinc ferrites

Influence of Li2CO3-ZnO-Fe2O3 powder reagents mixture density on the synthesis efficiency of lithium-zinc ferrites in the conditions of thermal heating or pulsed electron beam heating was studied by X-Ray diffraction and magnetization analysis. The results showed that the including a compaction of powder reagents mixture in ferrite synthesis leads to an increase in concentration of the spinel phase and decrease in initial components content in lithium-substituted ferrites synthesized by thermal or radiation-thermal heating.

Magnetic properties of lithium zinc ferrites synthesized by microwave sintered method

In this paper, a series of polycrystalline ferrite samples were prepared with the composition of Zn0.1Li0.525-xTi0.15MgxFe2.225-0.5xO4 (LiZn) (x=0, 0.05, 0.10, 0.15 and 0.20) using both microwave sintering (MS) and conventional sintering (CS) technologies, respectively. The sintering time and temperature were 22 hours and 1000°C for the CS process, and 2 hours and 880°C for the MS process. Experiments showed that the MS treated LiZn ferrites exhibited more excellent magnetic properties and denser, more uniform micro-structures comparing with the ones treated by CS method. For the LiZn ferrite (x=0.1) sintered at 880°C using MS, the saturation magnetic induction (Bs) is 242.3 mT, the coercive force (Hc) is 135 A/m, the square ratio (Br/Bs) is 0.87 and the ferromagnetic resonance line-width (Δ H) is 143.2 Oe. These results represented very good properties for an X-band phase shifter material and indicated that the MS method is a potentially important technique for fabricating low temperature co-fired ceramics (LTCC).

NMR study of domain wall pinning in a magnetically ordered material

The use of nuclear magnetic resonance in the form of spin echo in combination with magnetic field pulses applied to a magnetically ordered material sample offers a convenient tool for studying characteristics of the centers of domain-wall pinning. Possibilities of this method have been demonstrated in experiments with lithium–zinc ferrite.