Preparation of spinel ferrite NiFe2O4 fibres by organic gel-thermal decomposition process

Functional spinel ferrite fibers are attractive for high-tech applications. The spinel NiFe₂O₄ fibres have been successfully prepared by the organic gel-thermal decomposition process from raw materials of Ni, Fe nitrate salts and citric acid. The gel spinning performance was a major factor for preparation of uniform gel fibrous precursors. The gel spinnability was related to the citrate-metal complex structure and linear-type structural molecules [(C₆H₆O₇)₄NiFe₂]_n for the gel precursor was possibly formed during the complexation reaction between the citric acid and metal ions at pH 5. The composition, structure of the gel precursors and products derived from thermal decomposition of these precursors were characterized by FTIR, XRD, and SEM. The thermal decomposition process of the gel precursors was investigated by TG-DSC. The prepared spinel NiFe₂O₄ fibres having grain sizes of 60–70 nm were featured with diameters of about 1 μm, and aspect ratios up to 10⁶ (length/diameter).     

Analysis of the role of M-type hexaferrite-based materials in electromagnetic interference shielding

M-type hexaferrite has attracted much attention for its large magneto-crystalline anisotropic energy, exceptionally good chemical stability, corrosion resistance, high Curie temperature, and high coercivity. In this review paper, our goal is to examine the microwave absorption properties and related studies of M-type hexaferrite-based materials. The microwave absorption properties of hexaferrite-based materials in the S, X, and Ku-band are discussed with their corresponding reflection losses. Complementarity between magnetic loss and dielectric loss is found to have a great impact on the proper absorption of microwaves. The mechanisms corresponding to the microwave absorption in different morphologies and structural adaptations of hexaferrite have been elaborated in the article. The ongoing trends and future perspectives of these materials are also outlined.     

Infrared and structural studies of Mg1-xZnxFe2O4 ferrites

Compositions of polycrystalline Mg-Zn mixed ferrites with the general formula Mg_1−xZn_xFe₂O₄ (0≤x≤1) were prepared by the standard double sintering ceramic method. The structural properties of these ferrites have been investigated using X-ray diffraction and infrared absorption spectroscopy. The lattice parameter, particle size, bonds length, force constants, density, porosity, shrinkage and cation distribution of these samples have been estimated and compared with those predicted theoretically. Most of these values were found to increase with increasing Zn content. The energy dispersive (EDS) analysis confirmed the proposed sample composition. The scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs showed aggregates of stacked crystallites of about 200-800 nm in diameter. Far infrared absorption spectra showed two significant absorption bands. The wave number of the first band, ν₁, decreases with increasing Zn content, while the band, ν₂ shifts linearly towards higher wave numbers with Zn contents, over the whole composition range. The room temperature electrical resistivity was found to decrease as Zn-content increases. Values of the vacancy model parameters showed that the packing factors P_a and P_b decrease, the fulfillment coefficient, α, remains almost constant and the vacancy parameter, β, strongly increases with increasing Zn content in the sample. The small values of P_a, P_b, α and the strong increase of the vacancy parameter, β, indicate the presence of cation or anion vacancies and the partial participation of the Zn²⁺ vacancies in the improvement of the electrical conductivity in the Mg-Zn ferrites.     

Electrochemical performance and large positive–negative magnetodielectric coupling in iron chromite spinels

Spinel ferrites with remarkable electrochemical performance and magnetodielectric (MD) coupling are promising candidates for energy storage and spintronic devices. This study focuses on structural phases, dielectric and magnetic polarization along with magnetodielectric (MD) coupling and electrochemical response of Fe-Cr spinels. Low cost sol–gel method is used to synthesize iron chromite nanopowders. Iron to chromium (Fe/Cr) ratio is varied in the range of 0.2–0.65 (with interval of 0.05). XRD patterns confirm the formation of phase pure FeCr₂O₄ at Fe/Cr ratios of 0.45, 0.6 & 0.65. Amorphous behavior is observed at Fe/Cr ratios of 0.2, 0.25, 0.5 & 0.55. Mixed phases are observed at 0.3, 0.35 & 0.4 Fe/Cr ratios. Formation of pure spinel phase at Fe/Cr ratio of 0.45 results in high saturation magnetization of 9.2 emu/g. High grain boundary resistance (189.62kΩ) and high dielectric constant (～83.38 at log f = 5.0) along with low tangent loss (0.00423 at log f = 5) are observed at Fe/Cr ratio of 0.45. Magneto dielectric studies confirm positive magneto dielectric constant (MDC) of synthesized nanopowders at 0.45, 0.6 & 0.65 Fe/Cr ratios. Cyclic voltammetry is performed at constant potential window. Oxidation/reduction process leads to the pseudo-capacitive response of the material. The cyclic voltammetry curves show specific capacitance of 156 Fg^?1, 144 Fg^?1 and 152 Fg^?1 at scan rate of 25 mV/s at Fe/Cr ratios of 0.45, 0.6 & 0.65 of FeCr₂O₄ nanopowders, respectively. The galvanostatic charging/discharging behavior shows capacitive behavior of FeCr₂O₄ nanopowders. The electrochemical results suggest that synthesized nanopowders have potential for energy storage system.     

Green synthesis,characterization and anti-cancer capability of Co0.5Ni0.5Nd0.02Fe1.98O4 nanocomposites

In this study, Co_0.5Ni_0.5Nd_0.02Fe_1.98O₄ nanoparticles CoNiNd (NPs) were synthesized by combustion method linked with biosynthesis with and without different plant extracts such as Lavender, Ginger, Flax-Seed, Lemon Juice, Tragacanth Gum, and Dates Fruit. Co_0.5Ni_0.5Nd_0.02Fe_1.98O₄ nanoparticles (NPs) with plant extracts (CoNiNd plant extracts) were analyzed by XRD, TEM and SEM methods. The structure of Co-Ni spinel ferrite was confirmed by XRD and the shape and the size of nanoparticles were examined via SEM and TEM and the size was found between 17 and 25 nm. The anti-cancer activity of NPs on cancer cells such as human colorectal carcinoma (HCT-116) and human cervical cells (Hela) were investigated. The cytotoxicity of was examined by MTT assay and followed by measuring the inhibitory concentration (IC₅₀) values after 48 h treatments. The cell viability assay confirmed a decrease in the cancer cell viability post NPs treatments and showed dose-dependent inhibitory action. The treatments of CoNiNd (NPs) and CoNiNd plant extracts via Lavender plant extract showed most profound inhibitory action on both cancer cells than extracts other plant extracts. The IC₅₀ values were for HCT-116 cells were found to be in range of 15.75–42.55 µg/mL and 13.44 to 35.65 µg/mL for HeLa cells. In contrast, the treatment of CoNiNd (NPs) and CoNiNd plant extracts showed inhibitory action but the percentage of inhibition was higher in HEK-293 cells. Our results showed that CoNiNd (NPs) and CoNiNd plant extracts possess potential application in the colon and cervical cancer treatments and we recommend molecular analysis of NPs mediated cancer cell death for future applications.     

Magnetism at spinel thin film interfaces probed through soft X-ray spectroscopy techniques

Magnetic order and coupling at the interfaces of highly spin polarized Fe₃O₄ heterostructures have been determined by surface sensitive and element specific soft X-ray spectroscopy and spectro-microscopy techniques. At ambient temperature, the interface between paramagnetic CoCr₂O₄ or MnCr₂O₄ and ferrimagnetic Fe₃O₄ isostructural bilayers exhibits long range magnetic order of Co, Mn and Cr cations which cannot be explained in terms of the formation of interfacial MnFe₂O₄ or CoFe₂O₄. Instead, the ferrimagnetism is induced by the adjacent Fe₃O₄ layer and is the result of the stabilization of a spinel phase not achievable in bulk form. Magnetism at the interface region is observable up to 500 K, far beyond the chromite bulk Curie temperature of 50-95 K.     

Synthesis and electrochemical properties of nonstoichiometric LiAlxMn2−xO4−δ as cathode materials for rechargeable lithium ion battery

Nonstoichiometric spinel oxides, LiAl_xMn_2−xO_4−δ (x=0.1,0.2), were synthesized under controlled partial pressure of oxygen, and their elecrochemical performances were investigated. As an Al content increases, solubility limit of the oxygen nonstoichiometry, δ, increased, while partial molar enthalpy of the formation of oxygen nonstoichiometry decreased.Cycle performance of LiAl_xMn_2−xO₄ showed significant improvement comparing with that of LiMn₂O₄ cathode. However, the decrease of theoretical capacity was accompanied with Al doping. Nonstoichiometric LiAl_xMn_2−xO_4−δ showed the increase in capacity with keeping good cycle performances as well as stoichiometric LiAl_xMn_2−xO₄. Although the introduction of oxygen nonstoichiometry leads to the increase of Mn³⁺ which is known as Jahn-Teller ion, DSC curves for LiAl_xMn_2−xO_4−δ showed no exothermic peak due to phase transition arising from Jahn-Teller distortion around room temperature.     

Synthesis and electrochemical properties of chemically substituted LiMn2O4 prepared by a solution-based gel method

Lithium manganese oxide, LiMn(2)O(4), and its substituted samples LiM(0.05)Mn(1.95)O(4) (M=Al, Co, and Zn) were first prepared by a cost-saving and effective new solution-based gel method using a mixture of acetate and ethanol as the chelating agent. The physical properties of the synthesized samples were investigated by thermogravimetry/differential thermal analysis, X-ray diffraction, and scanning electronic microscopy. The as-prepared powders were used as positive materials for a lithium-ion battery, whose charge/discharge properties and cycle performance were examined. The results revealed that all the substituted samples had better cycle performance than pure LiMn(2)O(4). Among these synthesized materials, the LiCo(0.05)Mn(1.95)O(4) sample had the best cycle performance. After 30 cycles, its capacity loss was only 3%. Therefore, cyclic voltammetry and electrochemical impedance spectroscopy were employed to characterize the reactions of Li ion insertion into and extraction from LiCo(0.05)Mn(1.95)O(4) electrodes.     

电解液组成对尖晶石LiMn_2O_4中锂离子嵌脱过程的影响

运用电化学阻抗谱(EIS)研究了尖晶石LiMn2O4正极在1mol·L-1LiPF6-EC(碳酸乙烯酯)∶DEC(碳酸二乙酯)∶DMC(碳酸二甲酯),1mol·L-1LiPF6-EC∶DEC∶EMC(碳酸甲乙酯)和1mol·L-1LiPF6-EC∶DMC三种不同电解液中,-20-20℃范围内的阻抗谱特征随温度的变化.研究结果表明,温度强烈影响尖晶石LiMn2O4正极的阻抗谱特征,而电解液组成对尖晶石LiMn2O4正极阻抗谱特征的影响较小,但电解液组成对锂离子在尖晶石LiMn2O4正极中嵌入脱出过程相关动力学参数影响较大.测得尖晶石LiMn2O4正极在上述三种电解液中,锂离子迁移通过固体电解质相界面(SEI)膜的离子跳跃能垒平均值分别为7.60、16.40和18.40kJ·mol-1;电子电导率的热激活化能平均值分别为44.77、35.47和68.06kJ·mol-1;嵌入反应活化能平均值分别为52.19、46.19和69.86kJ·mol-1.     

尖晶石LiMn2O4锂充放电池的电化学研究

本文报导尖晶石型ＬｉＭｎ２Ｏ４化合物的制备方法，用循环伏安法和交流阻抗技术研究了Ｌｉ／有机电解液／ＬｉＭｎ２Ｏ４电池的电化学行为，用分形理论首次考察和进一步讨论电极材料的阻抗行为随锂离子嵌入或脱嵌电极时的变化。