Effect of Zn2+ content on the microstructure and magnetic properties of nanocrystalline Ni1−x Zn x Fe2O4 ferrite by a spraying-coprecipitation method

Nanocrystalline Ni1-xZnxFe2O4 ferrites with 0≤x≤1 were successfully prepared by a spraying-coprecipitation method.The microstructure was investigated by using XRD and TEM.Magnetic properties were measured with vibrating sample magnetometer(VSM) at room temperature.The results show that the grain size of nanocrystalline Ni1-xZnxFe2O4 ferrite calcined at 600 ℃ for 1.5 h is about 30 nm.Lattice parameter and specific saturation magnetization Ms of nanocrystalline Ni1-xZnxFe2O4 ferrite increase with the Zn2+ ions content at room temperature,and maximum Ms is 66.8 A·m2·kg-1 as the Zn2+ ions content is around 0.5,and coercivity Hc of the nanocrystalline Ni1-xZnxFe2O4 ferrite decreases with Zn2+ ions content.     

Structural evolution and stability of mechanically alloyed Fe-Ni nanocrystalline

The structural evolution and stability of Fe100-xNix(x=10, 20, 35, 50) alloys prepared by mechanical alloying were investigated through X-ray diffraction analysis and transmission electron microscopy. The intrinsic conditions of preparation determining phase stability in nanocrystalline were clarified. After being milled for 120 h, the powders of Fe90Ni10 and Fe80Ni20 consist of a single α(bcc) phase, Fe30Ni30 powders are a single γ(fcc), and for Fe65Ni35 powders there is co-existence of α and γ phases. The as-milled Fe80Ni20 powders annealed at 680 ℃ exhibits the stability of high-temperature γ phase at room temperature, which is consistent with the theoretical prediction.     

Influence of Ti^4＋ doping on hyperfine field parameters of Mg0.95Mn0.05Fe2-2xTizxO4 （0 ≤x ≤ 0.7）

The mixed spinel ferrite system Mg_0.95Mn_0.05Fe_2−2x Ti_2x O₄ (0⩽x⩽0.7) was synthesized by the conventional solid-state reaction technique. The effect of Ti⁴⁺ doping was studied by using the M?ssbauer spectroscopy measurements at room temperature. From the analysis of the M?ssbauer spectra, it is observed that s-electron density, electric field gradient (EFG), quadrupole coupling constant (QCC) and the net hyperfine magnetic fields acting on the M?ssbauer nuclei-Fe_A ³⁺ and Fe_B ³⁺ change with the increase of Ti⁴⁺ doping in Mg_0.95Mn_0.05Fe₂O₄. The hyperfine magnetic field decreases with the increase of Ti⁴⁺ doping.     

Magnetic Properties of NiCuZn Ferrite Thin Films Prepared by the Sol-gel Method

Ni0.4Cu0.2Zn0.4Fe2O4 thin films were fabricated on Si substrates by using the sol-gel method and rapid thermal annealing （RTA）, and their magnetic properties and crystalline structures were investigated. The samples calcined at and above 600 ℃ have a single-phase spinel structure and the average grain size of the sample calcined at 600 ℃ is about 20 nm. The initial permeability μi, saturation magnetization M and coercivity H of the samples increase with the increasing calcination temperature. The sample calcined at 600 ℃ exhibits an excellent soft magnetic performance, which has μi=33.97 （10 MHz）, Hc=15.62 Oe and Ms=228.877 emu/cm^3. Low-temperature annealing can enhance the magnetic properties of the samples. The work shows that using the sol-gel method in conjunction with RTA is a promising way to fabricate integrated thin-film devices.     

Synthesis and characterization of Nd doped M-type hexagonal barium ferrite ultrafine powders

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Structure and Giant Magnetoresistance in Zinc Ferrite

The tunneling structure of ZnFe3-xO4 ferrite was confirmed by high resolation electron microscopy （HREM）, non-Ohmic Ⅰ-Ⅴ curve and kinetics for α-Fe2O3 isothermal phase transformation. The Zn0.41 Fe2.59O4/ α-Fe2O3 two-phase polycrystalline has a huge tunneliug magnetorsistance （ TMR ） mainly caused by the tummeliug structure. The Zn0.41Fe2.59O4 grains are separated by insulatiug α-Fe2O3 thin layer boundaries. The pattern of nanostructure uns verified by HREM.     

Structure and infrared radiation property of Co<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites by XAFS analysis

Co_1−x Zn _x Fe₂O₄ ferrites were prepared by solid state reaction. The microstructure and performance were studied by X-ray diffraction, X-ray absorption fine-structure analysis and IRE-2 infrared radiant test. It is found that infrared radiance show a nonlinear change with x, exhibiting the infrared radiance of this material improved and the average radiance in the 8–14 μm waveband reached 0.91. The Co³⁺ and Zn²⁺ ions are found to occupy both tetrahedral and octahedral sites, and correspondingly, the fraction of Fe³⁺ ions in B-site decreases nonlinearly in ferrites. The lattice parameters are found to concern with Zn²⁺, and the activation energy deduces from crystal strain and crystal vibrate increases with content Zn²⁺. The redistribution of the Co³⁺ and Zn²⁺ ions between tetrahedral and octahedral sites is related to the providing a selective tetrahedral and octahedral sites infrared radiance of Co_1−x Zn _x Fe₂O₄ ceramics with increasing x.     

Regulation mechanism of EM parameters in natural ferrite and its application in microwave absorbing materials

1 Introduction Microwave absorbing materials (MAM) refer to a kind of materials that can be used to absorb the emitted electromagnetic (EM) energy and to minimize the wave reflected in the direction of an energy radar receiver. When the EM wave incidents into MAM, it is readily absorbed, attenuated, and changed into heat or other energy. MAM are functional materials that possess special performance for absorbing EM wave. Along with the advancement in radar and microwave technologies, MA…     

Preparation and properties of FeZrB amorphous-nanocrystalline soft magnetic alloy

Fe₆₈Zr₂₀B₁₂ amorphous alloy was prepared by mechanical alloying(MA) method and annealed at different temperatures. Microstructures and magnetic properties of Fe₆₈Zr₂₀B₁₂ alloys as-milled and annealed at 693, 843, 943 and 993 K were studied. The raw powders(Fe, Zr, B) formed b. c. c. α-Fe solid solution at early stages of MA and then transformed into amorphous alloy. Grain size(D) of Fe₆₈Zr₂₀B₁₂ alloys increases with increasing annealing temperature and keeps at nanometer level. The specific saturation magnetization(σ _s ) increases with increasing annealing temperature from 300 K to 943 K, and then decreases with annealing temperature at 993 K because of the precipitation of Fe₃B.     

Effect of sintering aid CuO-MnO2 on dielectric properties of 0.5Ba(Mg1/3Nb2/3)O3-0.5Ba(Ni1/3Nb2/3)O3 ceramics

Microstructures and microwave dielectric properties of 0.5Ba(Mg_1/3Nb_2/3)O₃-0.5Ba(Ni_1/3Nb_2/3)O₃ ceramics with x wt% CuO−x wt% MnO₂ additions (x=0.25–1) prepared by conventional solid-state route were investigated. It is found that low level-doping of CuO-MnO₂ can significantly improve the density of the specimens and their microwave dielectric properties. The relative density of 0.5Ba(Mg_1/3Nb_2/3)O₃-0.5Ba(Ni_1/3Nb_2/3)O₃ ceramics can be increased by 95% sintering at 1 330 °C due to the liquid phase effect. The second phase is not observed in ceramics with CuO-MnO₂ addition. The parameter ε _r increases with increasing sintering temperature, and Q _f is effectively promoted by CuO-MnO₂ addition. Higher CuO-MnO₂ content would make τ_f value more positive. Meanwhile, ε _r value of 30.5, Q _f value of 63 200 GHz and τ _f value of 0.5 ppm/°C were obtained for 0.5Ba(Mg_1/3Nb_2/3)O₃-0.5Ba(Ni_1/3Nb_2/3)O₃ ceramics with 0.5 wt% CuO-0.5 wt% MnO₂ addition sintered at 1 330 °C for 4 h.     

Preparation of ZrB2 Ceramics by Self-propagating High-temperature Synthesis and Hot Pressing Sintering

ZrB2 ceramics were prepared by self-propagating high-temperature synthesis（SHS） and were sintered by hot pressing（HP）.The effects of the granularities and doses of raw materials in Zr-B2O3-Mgon SHS process and product were investigated.XRD and combustion temperature curves prove that the ideal SHS reactants of Zr-B2O3-Mg are 50μm Zr powder,75μm B2O3 powder and 400μm Mg powder with 45% excessive.The particle sizes of SHS product,acid-leached product,sintered product are 2-5μm,0.5-2μm,2-10μm respectively.Chemical analysis indicates that the acid-leached product consists of ZrB2（94.59%）,ZrO2（3.87%）,and H3BO3（1.54%）,The sintered product has a relative density of 95.4%.     

Synthesis and Characterization of LiCoxMn2-xO4 Cathode Materials

LiCoxMn2.04 cathode materials for lithium ion batteries were synthesized by mechanical activation-solid state reaction at 750 ℃ for 24 h in air atmosphere, and their crystal structure, morphology, element composition and electrochemical performance were characterized with XRD, SEM, ICP-AES and charge-discharge test. The experimental results show that all samples have a single spinel structure, well formed crystal shape and uniformly particle size distribution. The lattice parameters of LiCo Mn2-xO4 decrease and the average oxidation states of manganese ions increase with an increase in Co content. Compared with pure LiMn2O4, the LiCo Mn2xO4 （x=0.03-0.12） samples show a lower special capacity, but their cycling life are improved. The capacity loss of LiCo009Mn191O4 and LiCo0.1Mn1.88O4 is only 1.85% and 0.95%, respectively, after the 20th cycle. The improvement of the cycle performance is attributed to the substitution of Co at the Mn sites in the spinel structure, which suppresses the Jahn-Teller distortion and improves the structural stability.     

Formation of bulk ferromagnetic nanostructured Fe<Subscript>40</Subscript>Ni<Subscript>40</Subscript>P<Subscript>14</Subscript>B<Subscript>6</Subscript> alloys by metastable liquid spinodal decomposition

Nanostructured Fe₄₀Ni₄₀P₁₄B₆ alloy ingots of 3–5 mm in diameter could be synthesized by a metastable liquid state spinodal decomposition method. For undercooling ΔT > 260 K, the microstructure of the undercooled specimen had exhibited liquid state spinodal decomposition in the undercooled liquid state. The microstructure could be described as two intertwining networks with small grains dispersed in them. For undercooling ΔT > 290 K, the overall microstructure of the specimen changed into a granular morphology. The average grain sizes of the small and large grains are ≅ 30 nm and ≅ 80 nm, respectively. These prepared samples are soft magnets with saturation magnetization B _s ≅ 0.744 T. Supported by the Hong Kong Research Grants Council the National Natural Science Foundation of China (Grant No. 50861007) and Xinjiang University Doctoral Research Start-up Grant (Grant No. BS050102)     

Influence on performance and structure of spinel LiMn2O4 for lithium-ion batteries by doping rare-earth Sm

The spinel LiMn₂O₄ used as cathode materials for lithium-ion batteries was synthesized by mechano-chemistry fluid activation process, and modified by doping rare-earth Sm. Thesting of X-ray diffraction, cyclic voltammograms, charge-discharge and SEM was carried out for LiMn₂O₄ cathode materials and the modified materials. The results show that the cathode materials doped rare earth Li _x Mn_2−y Sm _z O₄ (0.95⩽x⩽1.2, 0⩽y⩽0.3, 0⩽z⩽0.2) exhibit standard spinel structure, high reversibility of electrochemistry and excellent properties of charge-discharge. In EC: DMC(1 : 1)+1 mol/L LiPF₆ electrolyte with discharge capacity more than 130 mA · h/g, and its capacity is deteriorated less than 15% after 300 cycles at room temperature and less than 20% after 200 cycles at 55°C. At the same time, Crystal Field Theory was applied to explain the function and mechanism of doped rare earth element. Foundation item: Project (02JJY2081) supported by the Natural Science Foundation of Hunan Province     

Structure and stability of Li-Mn-Ni composite oxides as lithium ion sieve precursors in acidic medium

A series of spinel Li-Mn-Ni composite oxides with theoretical chemical formula of LiNixMn2-xO4 (0≤x≤1.0) were synthesized by liquid phase method. Their structure and morphology were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM),respectively. The stability of these Ni-substituted spinel oxides prepared at different temperatures was investigated in acidic medium as well. The results show that Ni can be brought into the spinel framework completely to form well-crystallized ...     

Critical driving force for martensitic transformation fcc (γ)→hcp(ε) in Fe-Mn-Si shape memory alloys

By the application of Chou's new geometry model and the available data from binary Fe-Mn, Fe-Si and Mn-Si systems, as well as SGTE DATA for lattice stability parameters of three elements from Dinsdale, the Gibbs free energy as a function of temperature of the fcc(γ) and hep(ε) phases in the Fe-Mn-Si system is reevaluated. The relationship between the Neel temperature of the γ phase and concentration of constituents in mole fraction, is fitted and verified by the experimental results. The critical driving force for the martensitic transformation fcc (γ)→ hep (ε), △ G_C~(γ→ε), defined as the free energy difference between γ and ε phases at M_s of various alloys can also be obtained with a known M_s. It is found that the driving force varies with the composition of alloys, e. g. △ G_C~(γ→ε) = - 100.99 J/mol in Fe-27.0Mn-6.0Si and △ G_C~(γ→ε) = - 122.11 J/mol in Fe-26.9Mn-3.37Si. The compositional dependence of critical driving force accorded with the expression formulated by Hsu of the     

First-principle investigation on stability of Co-doped spinel λ-Mn4-xCoxO8

The mechanism of stability of Co-doped spinel λ-MnO2 that is referred to as spinel LixMn2O4 （x=0） was studied by using the first-principle calculation method. The total energy and formation enthalpy can be decreased remarkably due to the Co substation, resulting in a more stable structure ofλ-MnxCr2-xO4. The bond order and DOS analysis were given in detail to explain the nature of stability improvement. The calculated results show that as the content of Co dopant increases, the bond order of Mn-O becomes larger and the peak of density of states around Fermi level shifts toward lower energy. The charge density distribution illustrates that the Mn-O bonding is ionic and partially covalent, and the covalent Mn-O bonding becomes stronger with the increase of Co dopant content. The results confirm that the Co-doping will enhance the stability of λ-MnO2 and hence improve the electrochemistry performance of LixMn2O4.     

球形LiMn1.5Ni0.5O4材料的嵌脱动力学

为明晰Li Mn1.5Ni0.5O4正极材料的动力学性能,采用水热辅助共沉淀法合成了尖晶石Li Mn1.5Ni0.5O4正极材料,并采用扫描电镜(SEM)、X射线粉末衍射(XRD)和电化学阻抗(EIS)研究了材料的结构和锂离子嵌脱动力学.实验结果表明:共沉淀法制备的Li Ni0.5Mn1.5O4材料颗粒呈均匀球形,且平均粒径较小,粒度分布较窄.在循环过程中,Li Ni0.5Mn1.5O4的电荷转移电阻增大,锂离子扩散系数减小,进而电子电导率和离子电导率下降.温度升高后,Li Ni0.5Mn1.5O4材料的溶液电阻变化不大,但是电荷转移电阻逐渐增大,锂离子扩散系数逐渐减小;此外,随着温度的升高,Li Ni0.5Mn1.5O4材料的溶解速度加快,从而导致SEI膜的厚度增大.Li Ni0.5Mn1.5O4材料的嵌脱锂动力学与温度和循环次数有密切关系.     

Microstructure and microwave dielectric properties of CaO-B2O3-SiO2 glass ceramics with various B2O3 contents

The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 (CBS) glass ceramics were investigated by Fourier transform infrared spectroscopy (FTIR),X-ray diffractometry (XRD) and scanning electron microscopy (SEM).The results show that the increasing amount of B2O3 causes the increase of the contents of [BO3],[BO4] and [SiO4],which deduces the increase of CaB2O4 and α-SiO2 and the decrease of CaSiO3 correspondingly.No new phase is observed throughout the...     

Low-temperature sintering and microwave dielectric properties of Li2MgTi3O8 ceramics doped with BaCu（B2O5）

The influences of BaCu(B₂O₅) (BCB) addition on sintering, microstructure and microwave dielectric properties of Li₂MgTi₃O₈ ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu(B₂O₅) addition can effectively reduce the sintering temperature to 900 °C, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of ɛ _r=24.5, Q×f =24 622 GHz, τ _f=4.2×10⁻⁶ °C⁻¹ are obtained for 1.0% BCB-doped Li₂MgTi₃O₈ ceramics sintered at 900 °C for 3 h. The BCB-doped Li₂MgTi₃O₈ ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.