Polyaniline/LiNi0.5La0.08Fe1.92O4 Nanocomposite: A Study of Dielectric and Electric Modulus Spectroscopy

Polyaniline(PANI)/LiNi_0.5La_0.08Fe_1.92O₄ nanocomposite was synthesized by an in situ polymerization of aniline in the presence of LiNi_0.5La_0.08Fe_1.92O₄ nanoparticles. The dielectric properties of a PANI/LiNi_0.5La_0.08Fe_1.92O₄ (10 wt% weight ratio of LiNi_0.5La_0.08Fe_1.92O₄ to aniline monomer) nanocomposite were investigated in the frequency range of 10⁶–10⁹ Hz. The dielectric constant (?′) and dielectric loss (?″) were frequency dependent, having relatively high values at low frequency and decreasing with increasing frequency. The values of ?′ and ?″ of PANI/LiNi_0.5La_0.08Fe_1.92O₄ nanocomposite were found to be lower than those of the pristine PANI. Electric modulus analysis was carried out to understand the electrical relaxation process.     

In situ synthesis and characterization of LiNi0.5La0.08Fe1.92O4-polyaniline core-shell nanocomposites

Core-shell-structured LiNi_0.5La_0.08Fe_1.92O₄-polyaniline (PANI) nanocomposites with magnetic behavior were synthesized by in situ polymerization of aniline in the presence of LiNi_0.5La_0.08Fe_1.92O₄ nanoparticles. The structure, morphology and magnetic properties of samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-vis absorption, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) technique. The results of spectroanalysis indicated that there was interaction between PANI chains and ferrite particles. TEM study showed that LiNi_0.5La_0.08Fe_1.92O₄-PANI nanocomposites presented a core-shell structure with a magnetic core of 30-50 nm diameter and an amorphous shell of 10-20 nm thickness. The nanocomposites under applied magnetic field exhibited the hysteresis loops of the ferromagnetic nature. The saturation magnetization and coercivity of nanocomposites decreased with decreasing content of LiNi_0.5La_0.08Fe_1.92O₄. The polymerization mechanism and bonding interaction in the nanocomposites have been discussed.     

Microwave absorption behavior of a polyaniline magnetic composite in the X-band

The development of nanosized materials is a subject of considerable interest both for understanding of the fundamental properties of magnetic materials for new technological applications. Polyaniline, composites Fe₃O₄/(PANI) with conducting, magnetic and electromagnetic properties with different amounts of Fe₃O₄ were successfully prepared. The samples were structurally characterized by scanning electron microscopy (SEM), X-ray diffraction and transmission electron microscopy (TEM) and magnetically, with a superconducting quantum interference device (SQUID) magnetometer. In order to explore microwave-absorbing properties in X-band, the composite nanoparticles were mixed with an epoxy resin to be converted into a microwave-absorbing composite. Microwave behavior with different Fe₃O₄/(PANI)-epoxy resin ratio was studied using a microwave vector network analyzer (VNA) in the range 7.5 to 13 GHz. For a constant thickness of 1.5 mm, absorption increases with the magnetite contents in the composites and in the oriented samples by the application of a magnetic field.     

Synthesis and Characterization of La‐Doped Fe3O4‐Polyaniline Magnetic Response Nanocomposites

Lanathum (La)‐doped Fe₃O₄ magnetic nanoparticles were prepared in aqueous solution at room temperature, then La‐doped Fe₃O₄‐polyaniline (PANI) nanocomposites containing a dispersion of La‐doped Fe₃O₄ nanoparticles were synthesized via in‐situ polymerization of aniline monomer. The structure and properties of the synthesized samples were characterized with X‐ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectrometry (ICPAES), and a vibrating sample magnetometer (VSM). The resulting particles of La‐doped Fe₃O₄ and La‐doped Fe₃O₄‐PANI were almost spherical with diameters ranging from 15 to 25 nm and 25 to 85 nm, respectively. The La‐doped Fe₃O₄‐PANI composite presented core‐shell structures; polyaniline covered the La‐doped Fe₃O₄ completely. The specific saturation magnetization of La‐doped Fe₃O₄‐PANI depended on the starting material of La‐doped Fe₃O_4. It increased with increasing amounts of La and Fe₃O₄ content.     

Preparation of superparamagnetic Fe3O4/PMMA nano composites and their magnetorheological characteristics

Fe₃O₄/PMMA composite particles were fabricated by a simple one-pot hydrothermal method. The magnetic measurement showed that the composite particles displayed a higher saturated magnetization and superparamagnetic property. The rheological properties of the magnetorheological fluids (MRFs) based on Fe₃O₄/PMMA particles were measured on a rotational rheometer with a magnetic field generator. It was found that the MRFs exhibited better MR effect and sendimentary stability than the similar materials.     

Fabrication and magnetic properties of Ni0.50.5Zn0.5Fe2O4 nanofibres by electrospinning

NiZn ferrite/polyvinylpyrrolidone composite fibres were prepared by sol–gel assisted electrospinning.Ni0.5Zn0.5Fe2O4 nanofibres with a pure cubic spinel structure were obtained subsequently by calcination of the composite fibres at high temperatures.This paper investigates the thermal decomposition process,structures and morphologies of the electrospun composite fibres and the calcined Ni0.5Zn0.5Fe2O4 nanofibres at different temperatures by thermogravimetric and differential thermal analysis,x-ray diffraction,Fourier transform infrared spectroscopy and field emission scanning electron microscopy.The magnetic behaviour of the resultant nanofibres was studied by a vibrating sample magnetometer.It is found that the grain sizes of the nanofibres increase significantly and the nanofibre morphology gradually transforms from a porous structure to a necklace-like nanostructure with the increase of calcination temperature.The Ni0.5Zn0.5Fe2O4 nanofibres obtained at 1000 C for 2 h are characterized by a necklace-like morphology and diameters of 100–200 nm.The saturation magnetization of the random Ni0.5Zn0.5Fe2O4 nanofibres increases from 46.5 to 90.2 emu/g when the calcination temperature increases from 450 to 1000 C.The coercivity reaches a maximum value of 11.0 kA/m at a calcination temperature of 600 C.Due to the shape anisotropy,the aligned Ni0.5Zn0.5Fe2O4 nanofibres exhibit an obvious magnetic anisotropy and the ease magnetizing direction is parallel to the nanofibre axis.     

Studies of the electrochemical properties and thermal stability of LiNi1/3Co1/3Mn1/3O2/LiFePO4 composite cathodes for lithium ion batteries

A series of LiNi_1/3Co_1/3Mn_1/3O₂/LiFePO₄ composite cathodes with the LiFePO₄ mass content ranging from 10 to 30 wt% were prepared by ball milling in order to combine the merits of layered LiNi_1/3Co_1/3Mn_1/3O₂ and olivine LiFePO₄. The structure and morphology of the samples were characterized by X-ray diffraction and scanning electron microscope. The composite cathodes exhibited improved electrochemical performance compared with pristine LiNi_1/3Co_1/3Mn_1/3O₂. Among all the composite cathodes, the one with 20 wt% of LiFePO₄ showed the best electrochemical performance in terms of discharge capacity, cycle stability, and rate capability. Electrochemical impedance spectroscopy showed that mixing of LiFePO₄ in LiNi_1/3Co_1/3Mn_1/3O₂ decreased the internal resistance of the electrode, retarded the formation of SEI film, and facilitated the charge transfer reaction. Differential scanning calorimetry showed that the composite cathode had better thermal stability than pristine LiNi_1/3Co_1/3Mn_1/3O₂.     

Mössbauer study of a Fe3O4/PMMA nanocomposite synthesized by sonochemistry

Magnetite nanoparticles of 10 nm average size were synthesized by ultrasonic waves from the chemical reaction and precipitation of ferrous and ferric iron chloride (FeCl₃ · 6H₂O y FeCl₂ · 4H₂O) in a basic medium. The formation and the incorporation of the magnetite in PMMA were followed by XRD and Mössbauer Spectroscopy. These magnetite nanoparticles were subsequently incorporated into the polymer by ultrasonic waves in order to obtain the final sample of 5 % weight Fe₃O₄ into the polymethylmethacrylate (PMMA). Both samples Fe₃O₄ nanoparticles and 5 % Fe₃O₄/PMMA nanocomposite, were studied by Mössbauer spectroscopy in the temperature range of 300 K–77 K. In the case of room temperature, the Mössbauer spectrum of the Fe₃O₄ nanoparticles sample was fitted with two magnetic histograms, one corresponding to the tetrahedral sites (Fe^3?+?) and the other to the octahedral sites (Fe^3?+? and Fe^2?+?), while the 5 % Fe₃O₄/PMMA sample was fitted with two histograms as before and a singlet subspectrum related to a superparamagnetic behavior, caused by the dispersion of the nanoparticles into the polymer. The 77 K Mössabuer spectra for both samples were fitted with five magnetic subspectra similar to the bulk magnetite and for the 5 % Fe₃O₄/PMMA sample it was needed to add also a superparamagnetic singlet. Additionally, a study of the Verwey transition has been done and it was observed a different behavior compared with that of bulk magnetite.     

A high-voltage lithium-ion battery prepared using a Sn-decorated reduced graphene oxide anode and a LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

This paper describes the preparation and characterization of a high-voltage lithium-ion battery based on Sn-decorated reduced graphene oxide and LiNi_0.5Mn_1.5O₄ as the anode and cathode active materials, respectively. The Sn-decorated reduced graphene oxide is prepared using a microwave-assisted hydrothermal synthesis method followed by reduction at high temperature of a mixture of (C₆H₅)₂SnCl₂ and graphene oxide. The so-obtained anode material is characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and electron diffraction spectroscopy. The LiNi_0.5Mn_1.5O₄ is a commercially available product. The two materials are used to prepare composite electrodes, and their electrochemical properties are investigated by galvanostatic charge/discharge cycles at various current densities in lithium cells. The electrodes are then used to assemble a high-voltage lithium-ion cell, and the cell is tested to evaluate its performance as a function of discharge rate and cycle number.     

Synthesis and electrochemistry of LiNi0.6Fe0.3−xMg0.1+xO2 (x=0, 0.5 and 1.0) materials for lithium-ion batteries

Lithium nickel oxide cathodes doped with Fe and Mg was synthesized by the solid state reaction method at 800 °C. Structural investigation of these materials was performed using XRD and EDAX. The electrochemical behavior was studied using galvanostatic charge/discharge in order to investigate the performance of LiNi_0.6Fe_0.3Mg_0.1O₂, LiNi_0.6Fe_0.25Mg_0.15O₂ and LiNi_0.6Fe_0.2Mg_0.2O₂ materials. It is shown that LiNi_0.6Fe_0.3Mg_0.1O₂ produced about 96 m Ah/g of discharge capacity. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

One‐Dimensional Magnetic Composite of Polypyrrole‐Containing Carbon Nanotubes/Ni0.75Zn0.25Fe2O4

A novel one‐dimensional electromagnetic nanocomposite of polypyrrole (PPY) containing carbon nanotubes (CNTs)/Ni_0.75Zn_0.25Fe₂O₄ was synthesized by an in‐situ polymerization method. The composite was characterized by x‐ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared. The XRD results confirmed that PPY, CNTs, and Ni_0.75Zn_0.25Fe₂O₄ coexisted in the composite. The TEM and HRTEM results indicated that PPY coated the surface of the CNTs/Ni_0.75Zn_0.25Fe₂O₄ with a thickness of 15–30 nm. The lattice spacings, according to the first main peak of the CNTs, Ni_0.75Zn_0.25Fe₂O₄, and PPY, was about 0.34 nm, 0.25 nm, and 0.42 nm, respectively. The FTIR result also indicated that the PPY formed in the composite. A test of magnetic properties indicated that the composite was ferromagnetic with the saturated magnetization of 12.86 electromagnetic units (emu)/g, and the coercive of 127.18 Oersted (Oe).     

Effect of carbon coating process on the structure and electrochemical performance of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>2</Subscript> used as cathode in Li-ion batteries

LiNi_0.5Mn_0.5O₂ powder was synthesized by a coprecipitation method. LiOH.H₂O and coprecipitated [(Ni_0.5Mn_0.5)C₂O₄] precursors were mixed carefully together and then calcined at 900°C. Surface modified cathode materials were obtained by coating LiNi_0.5Mn_0.5O₂ with a thin layer of amorphous carbon using table sugar and starch as carbon source. Both parent and carbon-coated samples have the characteristic layered structure of LiNi_0.5Mn_0.5O₂ as estimated from X-ray diffractometry measurements. Transmission electron microscope showed the presence of C layer around the prepared particles. TGA analysis emphasized and confirmed the presence of C coating around LiNi_0.5Mn_0.5O₂. It is obvious that the carbon coating appears to be beneficial for the electrochemical performance of the LiNi_0.5Mn_0.5O₂. A capacity of about 150 mAh/g is delivered in the voltage range 2.5–4.5 V at current density C/15 for carbon coated LiNi_0.5Mn_0.5O₂ in comparison with about 165 mAh/g obtained for carbon free LiNi_0.5Mn_0.5O₂ at the same current density and voltage window. About 92% and 82% capacity retention was obtained at 50th cycle for coated LiNi_0.5Mn_0.5O₂ using sucrose and starch, respectively; whereas, 75% was retained after only 30th cycle for carbon free LiNi_0.5Mn_0.5O₂. This improvement is mainly attributed to the presence of thin layer of carbon layer that encapsulate the nanoparticles and improve the conductivity and the electrochemical performance of LiNi_0.5Mn_0.5O₂.     

Structure and insertion properties of disordered and ordered LiNi0.5Mn1.5O4 spinels prepared by wet chemistry

We present the synthesis, characterization, and electrode behavior of LiNi_0.5Mn_1.5O₄ spinels prepared by the wet-chemical method via citrate precursors. The phase evolution was studied as a function of nickel substitution and upon intercalation and deintercalation of Li ions. Characterization methods include X-ray diffraction, SEM, Raman, Fourier transform infrared, superconducting quantum interference device, and electron spin resonance. The crystal chemistry of LiNi_0.5Mn_1.5O₄ appears to be strongly dependent on the growth conditions. Both normal-like cubic spinel [Fd3m space group (SG)] and ordered spinel (P4 ₁ 32 SG) structures have been formed using different synthesis routes. Raman scattering and infrared features indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Ni, Mn)-O bonds. Scanning electron microscopy (SEM) micrographs show that the particle size of the LiNi_0.5Mn_1.5O₄ powders ranges in the submicronic domain with a narrow grain-size distribution. The substitution of the 3d⁸ metal for Mn in LiNi_0.5Mn_1.5O₄ oxides is beneficial for its charge–discharge cycling performance. For a cut-off voltage of 3.5–4.9 V, the electrochemical capacity of the Li//LiNi_0.5Mn_1.5O₄ cell is ca. 133 mAh/g during the first discharge. Differences and similarities between LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ oxides are discussed.     

Electrical characterization of nylon-6 composite nanofibers

The electrical characteristics of nylon-6 nanofibers incorporated with TiO₂ and Fe₃O₄ nanoparticles were investigated. The resultant nanofibers exhibited good incorporation of nanoparticles. The impregnated TiO₂ and Fe₃O₄ nanoparticles into the nylon-6 nanofibers were confirmed by high resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray (EDX) spectroscopy studies. The electrical conductivity of the nylon-6 incorporated with TiO₂ and Fe₃O₄ composite nanofibers were higher than that of the pristine nylon-6 nanofibers. The impregnation of TiO₂ and Fe₃O₄ nanoparticles significantly enhanced the electrical property of the composite nanofibers. These polymeric/nanoparticles composite nanofibers structure may open a new direction for future organic electronics.     

Solvothermal one-step synthesis of MWCNTs/Ni0.5Zn0.5Fe2O4 magnetic composites

A magnetic multi-walled carbon nanotubes-based (MWCNTs-based) composite, MWCNTs/Ni_0.5Zn_0.5Fe₂O₄, was synthesized via a facile solvothermal approach. The composites were characterized by X-ray diffraction analysis, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and vibrating sample magnetometry. The results confirmed that MWCNTs and Ni_0.5Zn_0.5Fe₂O₄ coexisted in the composites. The TEM and HRTEM results showed a thick layer of Ni_0.5Zn_0.5Fe₂O₄ was intimately connected to the surface of MWCNTs. The saturation magnetization value of the composites was 45.8 emu/g. Furthermore, the probable synthesis mechanism of the magnetic composites was also investigated based on the experimental results.     

Characterisation of the reduction properties of La0.5Sr0.5Fe0.5Co0.5O3

We report here on the characterisation by temperature programmed reduction, ⁵⁷Fe Mössbauer spectroscopy and X-ray absorption spectroscopy of the phases resulting from treatment of the perovskite-related material La_0.5Sr_0.5Fe_0.5Co_0.5O₃ in a flowing 90% hydrogen/10% nitrogen atmosphere. The results show that treatment of La_0.5Sr_0.5Fe_0.5Co_0.5O₃ (which contains approximately 50% Fe⁴⁺ and 50% Fe³⁺) in the flowing 90% hydrogen/10% nitrogen atmosphere at 600°C does not result in the reduction of any of the constituent elements of the material and that the perovskite structure is still retained. The Mössbauer spectrum recorded following heating in the gaseous reducing environment at 1,000°C shows the presence of metallic iron, an Fe³⁺-containing phase with parameters compatible with the presence of SrLaFeO₄ which has a K₂NiF₄-type structure, and a paramagnetic Fe³⁺ phase. The X-ray absorption spectroscopy results show the presence of metallic cobalt. The Mössbauer spectrum recorded following heating at 1,200°C continues to show the Fe³⁺-containing components plus a larger contribution from metallic iron. The X-ray absorption spectroscopy results show the presence of metallic cobalt, SrLaFeO₄, La₂O₃ and SrO.     

Recent developments in the doping of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material for 5 V lithium-ion batteries

LiMn₂O₄ has been considered a promising cathode material for lithium-ion batteries in electric vehicles. However, there are still a number of problems of severe capacity fading before any materials modifications. Among all doped LiMn₂O₄, spinel LiNi_0.5Mn_1.5O₄ material is seen as a potential cathode material for use in electric vehicles and energy storage systems in the future because of its high working potential (4.7 V), high energy density (the energy density of LiNi_0.5Mn_1.5O₄ is 20% higher than that of LiCoO₂), acceptable stability, and good cycling performance. In the presented paper, the structure and electrochemical performance of doped LiNi_0.5Mn_1.5O₄ are reviewed. The rate capability, rate performance and cyclic life of various doped LiNi_0.5Mn_1.5O₄ materials are described. This review also focuses on the present status of doped LiNi_0.5Mn_1.5O₄, then on its near future developments.     

Synthesis of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> nano/microspheres with adjustable hollow structures for lithium-ion battery

High-voltage spinel LiNi_0.5Mn_1.5O₄ nano/microspheres with adjustable hollow structures have been fabricated based on the Kirkendall effect. The main characteristic is that the wall thickness of the hollow structure as well as the cavity size of the hollow structure can be adjusted by the different ratio of mixed precipitation agents. Especially, the diagrammatic sketch for the formation process of various LiNi_0.5Mn_1.5O₄ materials with adjustable hollow structures is discussed. Besides, the results of electrochemical performance test show that LiNi_0.5Mn_1.5O₄ obtained from 10:1 Na₂CO₃/NaOH (in mole) ratio is worth looking forward to, owing to its special hierarchical nano/microsphere and moderate hollow structures.     

Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ spinels： A first-principles study

<正>Structural and magnetic properties of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.5O_4-δ are investigated using densityfunctional theory calculations.Results indicate that nonstoichiometric LiNi_0.5Mn_1.5O_4-δ and stoichiometric LiNi_0.5Mn_1.5O₄ exhibit two different structures,i.e.,the face-centred cubic（Fd-3m） and primitive,or simple,cubic （P4₃32） space groups,respectively.It is found that the magnetic ground state of LiNi_0.5Mn_1.5O₄（P4₃32 and Fd-3m） is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the[110]direction whereas they are antiferromagnetic with respect to each other.We demonstrate that it is the presence of an O-vacancy in LiNi_0.5Mn_1.5O_4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi_0.5Mn_1.5O₄ with the P4₃32 space group.     

The role of matching thickness on the wideband electromagnetic wave suppresser using single layer doped barium ferrite

The effect of Mg²⁺, Co²⁺and Ti⁴⁺ substitution on microwave absorption has been studied for BaMg_0.5Co_0.5Ti_1.0Fe₁₀O₁₉ ferrite-acrylic resin composite in frequency range from 13 to 20 GHz. X-ray diffraction (XRD), scanning electron microscopy (SEM), vector network analysis and vibrating sample magnetometry (VSM) were employed to analyze structure, electromagnetic and microwave absorption properties of prepared ferrite. The obtained results of reflectivity demonstrate that by varying matching thickness along with weight percentage of ferrite to acrylic resin, the bandwidth coupled with reflection loss values of prepared composites can be easily tuned. Based on microwave measurement on reflectivity, it is found that BaMg_0.5Co_0.5Ti_1.0Fe₁₀O₁₉ is a good candidate for wideband electromagnetic compatibility and other practical applications at high frequency.