Magnesium doping in hierarchical ZnO nanostructures and studies on optical properties

Magnesium doping in hierarchical zinc oxide nanostructures has been carried out using an aqueous method. The XRD results confirmed the hexagonal wurtzite structure for the magnesium doped zinc oxide nanoparticles. On doping with Mg²⁺, there is a change in morphology of the hierarchical nanostructures to nanorods. The optical absorption and photoluminescence properties of the nanostructures depend on the magnesium doping level. A blue shift of the band gap absorption and the near band edge emission is observed on Mg doping.     

A comparative study of the microstructures and optical properties of Cu- and Ag-doped ZnO thin films

Cu- and Ag-doped ZnO films were deposited by direct current co-reactive magnetron sputtering technique. The microstructure, the chemical states of the oxygen, zinc, copper and silver and the optical properties in doped ZnO films were investigated by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Visible spectroscopy. XRD analysis revealed that both of Cu- and Ag-doped ZnO films consist of single phase ZnO with zincite structure while the doping elements had an evident effect on the (0 0 2) preferential orientation. The XPS spectra showed that the chemical states of oxygen were different in Cu- and Ag-doped ZnO thin films, which may lead to the shift of the band gap as can be observed in the transmittance and absorption spectra. Meanwhile, the widths of band tails of ZnO films became larger after Cu and Ag doping.     

Enhanced reflection loss and permittivity of self assembled Mg-Co-Zr substituted barium ferrite dot array on carbon nanotube

In this research work, magnetic multi-walled carbon nanotube (MWCNTs) nanocomposites have been created by the assembly of Mg-Co-Zr substituted barium ferrite film onto the surface of MWCNTs. Microwave absorption of the MWCNTs/doped barium ferrite nanocomposites is evidently enhanced compared to that of pure MWCNTs and substituted ferrites. The maximum reflection loss increased significantly with an increase in volume percentage of MWCNTs. Reflection loss evaluations indicated that nanocomposites display a great potential application as thinner and lighter wide-band electromagnetic wave absorbers.     

X-ray fine structure study and bonding in some ferrites

Extended X-ray absorption fine structure (EXAFS) of the iron K edges in copper, cobalt, zinc and manganese ferrites is studied and the EXAFS parameter α of the Lytle, Sayers and Stern's theory is shown to be a measure of fractional covalency. The linear relationship between metal to oxygen (iron to oxygen) distance and the parameter α leads us to conclude that the copper ferrite is the most covalent among the four ferrites studied in the present investigation.     

Structural, magnetic and electrical properties of NiCuZn ferrites prepared by microwave sintering method suitable for MLCI applications

Polycrystalline NiCuZn soft ferrites with stoichiometric iron were prepared by a novel microwave sintering method. The powders were calcined, compacted and sintered at 950 °C for 30 min in a microwave sintering furnace. X-ray diffraction patterns confirm the formation of single phase cubic spinel structure. The grain size was estimated using SEM micrographs. The lattice constant is found to increase with increase in zinc concentration. The sintered ferrites have been investigated for their physical, magnetic and electrical properties such as bulk density, X-ray density, porosity, anisotropy constant, initial permeability, saturation magnetization, DC resistivity, dielectric constant and dielectric loss as a function of zinc concentration. Permeability, saturation magnetization, dielectric constant and dielectric loss were found to increase while DC resistivity was found to decrease with the replacement of Zn with Ni. The present series of ferrites are found to posses properties that are suitable for the core materials in multilayer chip inductors.     

X-ray spectroscopic investigation of some spinel structures

K-absorption edges of cations in the manganites of magnesium, nickel, copper, zinc and cadmium and ferrite samples of composition, Mg_1?x Mn_x Fe₂O₄ (x=0, 0·25, 0·50, 0·75, 1·0), have been recorded employing a 40 cm curved mica crystal spectrograph of transmission type. It is observed that the absorption edges for the specimen shift towards the shorter wavelength side of the metal edge position. Shifts of both the absorption edges and the main absorptoin peaks for ferrites and manganites have been compared with compounds in which the oxidation state of the cation is well known. It is found that the manganese ions in these ferrites and manganites exist in valence states two and three respectively while iron in the ferrite samples is present in oxidation state three. An attempt has been made to interpret the observed absorption edge features in the light of neutron and X-ray diffraction studies on the same ferrite and manganite samples.     

Effects of Mg and Zn on the surface of doped melt-derived glass for biomaterials applications

Bioactive glasses in the system SiO₂-CaO-Na₂O-P₂O₅ were synthesized pure and doped with magnesium or zinc by melt-derived method. The bioactivity was studied during in vitro assays: the ability of hydroxycarbonate apatite (HCA) layer to form on the glass surface was examined after contact with simulated body fluid (SBF). The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were performed before and after immersion in vitro assays. The SBF solutions were also analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES).Introduction of magnesium and zinc as trace element induces several modifications on the observed phenomena at the glass surface and in SBF solution after immersion of the samples. The chemical durability of the glasses, the formation of the silica-rich layer and the crystallization of the HCA layer were affected, but not present the same modifications as the introduced doping element.     

Electromagnetic and microwave absorbing properties of Co2Z-type hexaferrites doped with La

Z-type ferrites doped with La³⁺, Ba_3−xLa_xCo₂Fe₂₄O₄₁ (x=0.00-0.30), were prepared by sol-gel method. The effect of the substitution La³⁺ rare-earth ions for Ba²⁺ ions on the microstructure, complex permeability, permittivity and microwave absorption of the samples was investigated. The results show that the major phase of the ferrites changed to Z-phase when sintering temperature was 1250 °C for 5 h. With the increase of the substitution ratio of La³⁺ ions from 0.0 to 0.3, the lattice parameters a and c increased gradually, which resulted in the change of the particle shape and size. The data of magnetism showed that the addition of La³⁺ ions make the ferrite a better soft magnetic material due to increase of magnetization (σ_s) and decrease of coercivity (H_c). The La³⁺ ions doped in the ferrite not only improved complex permeability and complex permittivity, but also microwave absorbency.     

Fabrication and electromagnetic properties of flake ferrite particles based on diatomite

Hexagonal ferrite BaZn_1.1Co_0.9Fe₁₆O₂₇ coated surfaces of diatomite flakes of low density were synthesized by a sol-gel method. The phase structures, morphologies, particle size and chemical compositions of the composites were characterized by X-ray diffraction, scanning electron microscope and energy dispersive X-ray spectroscopy. The results show that hexagonal ferrite coated diatomite flakes can be achieved, and that the coating consisted of BaZn_1.1Co_0.9Fe₁₆O₂₇ nanoparticles. The vibranting sample magnetometer results reveal that the flake ferrite particles have static magnetic properties. The complex permeability and permittivity of the composites were measured in the frequency range of 1-18 GHz. The microwave absorption properties of these ferrite particles are discussed. The results indicate that the flake ferrites have the potential to be used as a lightweight broad band microwave absorber.     

Electromagnetic properties and microwave absorption of W-type hexagonal ferrites doped with La

W-type barium hexaferrites with compositions of Ba₁Co_0.9Zn_1.1Fe₁₆O₂₇ and Ba_0.8La_0.2Co_0.9Zn_1.1Fe₁₆O₂₇ were synthesized by the sol-gel method. The electromagnetic properties and microwave absorption behavior of these two ferrites were studied in the 2-18 GHz frequency range. The microstructure and morphology of the ferrites were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The complex permittivity spectra, the complex permeability spectra and microwave reflection loss were measured by a microwave vector network analyzer. The XRD patterns show that the main phase of the Co₂W ferrite forms without other intermediate phases when calcined at 1200 °C. The SEM images indicate that flake-like hexagonal crystals distribute uniformly in the materials. Both the magnetic and dielectric losses are significantly enhanced by partial substitution of La³⁺ for Ba²⁺ in the W-type barium hexaferrites. The microwave absorption property of the La³⁺ doping W-type hexaferrite sample is enhanced with the bandwidth below −10 dB around 8 GHz and the peak value of reflection loss about −39.6 dB at the layer thickness of 2 mm.     

Doping effect of Y ions on the microstructural and electromagnetic properties of Mn-Zn ferrites

Mn-Zn ferrites doped with different contents of Y³⁺ ions were prepared by conventional two-step synthesis method. The microstructure and electromagnetic properties of the as-prepared Mn-Zn ferrites were investigated. It was found that all the samples consisted of ferrite phases of typical spinel cubic structure, and when Y³⁺ ion content was upto 1.5 mol%, yttriumirongarnet (Y₃Fe₅O₁₂) phase with garnet structure was detected. With increasing doping content of Y³⁺ ions, the lattice constant and grain size increased, and after an increase to its maximum value, the sample apparent and relative densities dropped down. Through the analysis of magnetic properties, it was revealed that the saturation magnetization, and both the real and imaginary parts of permeability of the as-prepared samples raised with increasing doping content of Y³⁺ ions but decreased with more Y³⁺ ions, while their coercivity showed an opposite change trend; and the Curie temperature increased monotonously. The measurement of dielectric properties indicated that the dielectric constant of the doped Mn-Zn ferrites presented a rise with increasing Y³⁺ ion content, and dropped down gradually when more Y³⁺ ions were doped, while the dielectric loss tangent would decrease with Y³⁺ content upto 1.5 mol%, but after that, it increased.     

Doped lithium nickel cobalt mixed oxides for the positive electrode in lithium ion batteries

Phase pure aluminium and magnesium doped lithium nickel cobalt mixed oxides Li(Ni,Co_0.1–0.2M_≤0.05)O₂ (M=Al, Mg) were synthesised in laboratory by a synthesis procedure adopted from H.C. Stark. Structural parameters were determined by Rietveld analysis of x-ray diffraction spectra. Electrochemical characterisation took place in three-electrode teflon cells and coin-type cells versus lithium metal. Thermal stability of cathodes without electrolyte was measured by DSC. For aluminium and magnesium doped lithium nickel cobalt mixed oxides Li(Ni,Co_0.1–0.2M_≤0.05)O₂ (M=Al, Mg) the layered structure is stabilised by both aluminium and magnesium. The lithium nickel disorder is decreased by cobalt and is nearly unaffected by aluminium. According to the Rietveld refinements, magnesium seems to reduce the lithium nickel disorder strongly, even though refinements are not totally reliable in this case. Initial capacity and reversibility in the first cycle are nearly unaffected by aluminium, but strongly inferred by magnesium. Both, aluminium and magnesium doping increase the cycling stability of lithium nickel cobalt mixed oxides. Increased thermal stability of charged electrodes without electrolyte by aluminium and magnesium doping seems to be due to limited delithiation. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001.     

Ni-Mg,Mg-Mn和Ni-Zn三种铁氧体在3厘米波段的法拉第旋转及衰耗

Faraday rotation and loss characteristics at 9200 me and at room temperature of Ni-Mg, Mg-Mn and Ni-Zn ferrite rods and disks placed in a circular waveguide are measured as a function of applied longitudinal DC magnetic field.Of particular interest are the results obtained with a new type of Ni-Mg ferrites, since very little data on Ni-Mg ferrites have been published in the literature. In this paper sufficient data are given on Faraday rotation and loss characteristics of a complete range of nickel-magnesium ferrites with composition varying from pure nickel to pure magnesium. Experimental results at 9200 me indicate that for the sintering temperature of 1300℃, the best composition range for nickel-magnesium ferrites would be Ni_0.7Mg_0.3Fe₂O₄-Ni_0.8Mg_0.2Fe₂O₄. In future, nickel-magnesium ferrites, due to their very low loss, may find practical applications in the microwave field.Comparison information as to the relative merits of these three useful microwave ferrites are given in the form of curves and tables, and their results are discussed in some detail.This paper also gives a summary of the linear theory on Faraday rotation of a linearly polarized wave propagating in ferrite-loaded waveguide which is longitudinally magnetized.     

Study of gamma ray energy absorption and exposure buildup factors for ferrites by geometric progression fitting method

The gamma ray energy absorption and exposure buildup factors (EABF and EBF) were calculated for ferrites such as cobalt ferrite (CoFe₂O₄), zinc ferrite (ZnFe₂O₄), nickel ferrite (NiFe₂O₄) and magnesium ferrite (MgFe₂O₄) using five parametric geometric progression (G-P fitting) formula in the energy range 0.015–15.00?MeV up to the penetration depth 40 mean free path (mfp). The obtained data of absorption and exposure buildup factors have been studied as a function of incident photon energy and penetration depth. The obtained EABF and EBF data are useful for radiation dosimetry and radiation therapy.     

非磁性微球掺杂对纳米磁流体场诱导双折射特性的影响

利用二氧化硅和聚苯乙烯非磁性微球掺入铁氧体纯磁流体中,制得了复合磁流体.定性地研究了复合磁流体在外磁场作用下的双折射与非磁性微球的种类、掺杂浓度以及纯磁流体自身浓度的关系.研究表明,不同浓度的纯磁流体掺杂等量的聚苯乙烯微球对其双折射随磁场的变化趋势影响不同|同一浓度的纯磁流体掺杂不同种类的非磁性微球,对其双折射的影响也不同|掺杂等量但不同比例的两种非磁性混合微球所形成的复合磁流体中,其中一种非磁性微球对其双折射的影响起主导作用,使得该复合磁流体双折射随磁场的变化趋势与起主导作用的非磁性微球单独掺杂时相似.     

Photoelectric properties of pure and aluminium doped CdS films

Photoelectric properties of pure and Al doped vacuum deposited CdS films have been studied to explore the possibility of their application in photoactivated liquid crystal light valves. The effect of heat treatment in oxygen atmosphere, rate of deposition and the extent of Al doping, etc. on the resistivity, photo-response spectral characteristics, rise and decay time of photo-current, etc. have been investigated. It has been found that in contrast to pure CdS films, the properties of Al-doped films significantly depend on both the rate of deposition and the extent of Al doping. The dark resistivity in all cases was found to increase with heat treatment in oxygen. Unlike pure CdS films, Al doped films show photo-conductivity which is enhanced by heat treatment. Al doped films deposited at higher rates show better photo response even at lower light levels. At various light levels the rise and decay time of Al-doped films were found to be fairly constant and lower than that for pure CdS films. All these properties have been explained in terms of the presence of trapping levels due to doping. These trapping levels are also indicated by TSC, optical absorption and EPR studies.     

BaCO3 mediated modifications in structural and magnetic properties of natural nanoferrites

Preparing M-type barium hexaferrite and improving the magnetic response of natural ferrites by incorporating barium carbonate (BaCO₃) is ever-demanding. Series of barium carbonate doped ferrites with composition (100−x)Fe₃O₄·xBaCO₃ (x=0, 10, 20, 30 wt%) are prepared through solid state reaction method and sintered gradually at temperatures of 800 and 1000 °C. Nanoparticles of natural ferrite and commercial BaCO₃ are used as raw materials. Impacts of BaCO3 on structural and magnetic properties of these synthesized ferrites are inspected. The obtained ferrites are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) at room temperature. Uniform barium hexaferrite particles in terms of both morphology and size are not achieved. The average crystallite size of BaFe₁₂O₁₉ is observed to be within 30–600 nm. The sintering process results phase transformation from Fe₃O₄ (magnetite) to α-Fe₂O₃ (hematite) and the formation of hexagonal barium ferrite crystals. The occurrence of barium crystal is found to enhance with the increase of BaCO₃ concentrations up to 20 wt% and suddenly drop at 30 wt%. Saturation and remanent magnetization of the doped ferrites are significantly augmented up to 16.37 and 8.92 emu g⁻¹, respectively compared to their pure counterpart. Furthermore, the coercivity field is slightly decreased as BaCO₃ concentrations are increased. BaCO₃ mediated improvements in the magnetic response of natural ferrites are demonstrated.     

Effect of sintering temperature on structural and magnetic properties of NiCuZn and MgCuZn ferrites

The low temperature microwave sintered NiCuZn and MgCuZn ferrites with compositions Ni_0.35Cu_0.05Zn_0.60Fe₂O₄ and Mg_0.35Cu_0.05Zn_0.60Fe₂O₄ were synthesized by conventional mixed oxide method. NiCuZn and MgCuZn ferrite samples obtained showed better sintered densities at 950 and 900 °C, respectively. The scanning electron micrographs of both the ferrite samples appear to be very much similar. The magnitude of initial permeability of MgCuZn ferrite samples is found to be obviously higher than those of NiCuZn ferrite samples at all sintering temperatures. This is mainly due to the fact that MgCuZn ferrite has smaller magnetocrystalline anisotropy constant and magnetostrictive constant. NiCuZn ferrites have higher saturation magnetization than MgCuZn ferrites, which is due to the higher magnetic moment of NiCuZn ferrites. Our results indicate that the microwave sintering method seems to be a potential technique in the MLCI technology.     

Anomalous magnetic behaviour of zinc and chromium ferrites without any hyperfine splitting

Two groups of ferrite namely zinc ferrite and chromium ferrite were synthesized by citrate precursor route in the size range of 8 to 35 nm. We have studied the structural and magnetic behaviour of these ferrites using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mössbauer spectroscopic techniques. Our studies show that the nanocrystalline ferrites interact with the hand magnet strongly and give large magnetization in the VSM measurement. The maximum magnetization in the samples sensitively depends on the particle size of synthesized ferrites. We observed as large as 28 Am²/kg of magnetization in the zinc ferrite nanoparticles while that in chromium ferrite is around 11 Am²/kg. In spite of the large magnetization in the zinc ferrite nanoparticles we did not observe any hyperfine splitting even down to 12 K of temperature. Similar behaviour is also observed for chromium ferrite down to 16 K.     

Magnetic resonance study of Ce and Gd doped NiFe2O4 nanoparticles

Present work is a study of temperature dependent electron paramagnetic resonance spectra of Ce and Gd doped nickel ferrite nanoparticles. The samples, synthesised by chemical route were characterised by X-ray diffractometer, electron paramagnetic resonance spectroscopy (EPR) and vibrating sample magnetometer (VSM). The average crystallite size of pure nickel ferrite is ∼64 nm and for Gd and Ce doped samples it is ∼20 nm and ∼14 nm, respectively. The EPR spectra were recorded from 120 to 300 K. Doping with Gd and Ce reduces the line width and g-value in comparison to that of pure nickel ferrite. Ce doped samples have the lowest values of both these parameters at room temperature. This indicates that Ce doped samples show lowest loss and is suitable for high frequency devices. EPR spin numbers are reduced while the spin relaxation time is increased after doping with rare earth ions. Gd doped samples have higher values of relaxation time and lower spin numbers in comparison to that of Ce doped samples. VSM results show that the magnetisation and coercivity are reduced after doping with both Ce and Gd rare earth ions.