Preparation and magnetic properties of Ni–Zr doped barium strontium hexaferrite

M-type Hexaferrites B_0.5Sr_0.5Fe_12−2x Ni _x Zr _x O₁₉ were synthesized and investigated. The XRD patterns show single phase of the magnetoplumbite barium strontium ferrite and no other phases were present. The samples exhibit well defined crystallization; all of them are hexagonal platelet grains. As the substitution level increased from x = 0.2 to 0.8 mol%, the grains are agglomerated and the average diameter increased. This suggests that Ni–Zr substitution increases the grain size, as observed in the FE-SEM micrographs. The results of magnetic measurement revealed that M_s of barium strontium hexaferrite increased when the value of x increased from 0 to 0.4 mol% and then decreased with the increasing Ni–Zr content. The H_c decreases remarkably with increasing Ni and Zr ions content. Hard magnetic material is converted into soft magnetic material when the substitution level is increased from 0.2 to 0.8 mol%. In particular, Ba_0.5Sr_0.5Fe_12−2x Ni _x Zr _x O₁₉ with x = 0.2, 0.4, 0.6, 0.8 mol% has suitable magnetic characteristics with particle size small enough for high-density magnetic recording applications.     

Effect of heat treatment on structural and magnetic properties of Li–Ni ferrite prepared via sol–gel auto-combustion method

Journal of Materials Science: Materials in Electronics - Nanocrystalline Li0.35Ni0.3Fe2.35O4 ferrites were prepared at different annealing temperatures by sol–gel auto-combustion method. The...     

Preparation and excellent microwave absorption properties of silver/strontium ferrite/graphite nanosheet composites via sol–gel method

In this experiment, excellent microwave absorption properties of Ag/SrFe₁₂O₁₉/NanoG were prepared via a two-step reaction. First, the SrFe₁₂O₁₉ was deposited on the surface of NanoG by sol–gel method. Then, the Ag/SrFe₁₂O₁₉/NanoG was perpared via electroless plating. The obtained ternary composites were analyzed by SEM, XRD, VSM and a vector network analyzer. The results indicated that the NanoG is covered by SrFe₁₂O₁₉ and SrFe₁₂O₁₉/NanoG is completely wrapped by silver layer. Ag/SrFe₁₂O₁₉/NanoG’s conductivity and Ms are 2.2 S/cm and 15.4 emu/g, respectively. Measurement of the vector network analyzer suggests that the microwave absorbing properties of Ag/SrFe₁₂O₁₉/NanoG are better than those of NanoG and SrFe₁₂O₁₉/NanoG. Its maximum reflection loss value can reach ?29 dB at 10.9 GHz when the thickness is 2.0 mm, and it’s the best match thickness of the composites in the X band.     

Effect of annealing temperature on electrical and nano-structural properties of sol–gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol–gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 °C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 °C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I–V) and capacitance versus voltage (C–V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tanδ) were increased with increase of annealing temperature.     

Magnetic properties of Ni–Co doped barium strontium hexaferrite

A series of Ni–Co substituted barium strontium hexaferrite materials, Ba_0.5Sr_0.5Ni _x Co _x Fe_12–2x O₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8 mol%) was synthesized by the sol–gel method. X-ray diffraction analysis has shown that the Ni–Co substitutions maintain in a single hexagonal magnetoplumbite phase. The room temperature magnetic properties and the cation site preferences of Ni–Co substituted ferrite were investigated by VSM. Substitutions led to decrease in coercivity while saturation magnetization remains the almost same. It indicates that the saturation magnetization (52.81–59.8 Am²/kg) and coercivity (69.83–804.97 Oe) of barium strontium hexaferrite samples can be varied over a very wide range by an appropriate amount of Ni–Co doping contents.     

Phase and microstructural development in alumina sol–gel coatings on CoCr alloy

Phase transformation of -Al₂O₃ to -Al₂O₃ in alumina sol gel coatings on biomedical CoCr alloy was studied as function of heat treatment temperature and time. Transformation in unseeded coatings was significant only above 1200 °C. Addition of -Al₂O₃ seed particles having an average size of approximately 40 nm lowered the phase transformation temperature to around 800 °C. These particles were considered to act as heterogeneous nucleation sites for epitaxial growth of the -Al₂O₃ phase. The kinetics and activation energy (420 kJ/mol) for the phase transformation in the seeded coatings were similar to those reported for seeded monolithic alumina gels indicating that the transformation mechanism is the same in the two material configurations. Avrami growth parameters indicated that the mechanism was diffusion controlled and invariant over the temperature range studied but that growth was possibly constrained by the finite size of the seed particles and/or coating thickness. The phase transformation occurred by the growth of -Al₂O₃ grains at the expense of the precursor fine-grained -Al₂O₃ matrix and near-complete transformation coincided with physical impingement of the growing grains. The grain size at impingement was 100 nm which agreed well with that predicted from the theoretical linear spacing of seed particles in the initial sol.     

Effect of Fe on the sintering and thermal properties of Mo–Cu composites

Effects of Fe on the sintering and thermal properties of Mo–Cu composites have been investigated. Mo–Cu–xFe composites are fabricated by powder metallurgy techniques with addition of various Fe contents ranging from 0.4 wt% to 2.2 wt%. The thermal properties and action mechanism of Fe to Mo–Cu composites are discussed. Results have indicated that the coefficient of thermal expansion (CTE) and thermal conductivity (TC) of Mo–Cu composites are greatly affected by the addition of Fe contents. It has also been observed that the fabricated composite powders with Fe additions exhibit high sinterability. Also, the inclusion of Fe can active the sintering course in shorter times and decline the sintering temperature thus also improving the physical properties of composites. Furthermore, it is also concluded that the utilization of steel kettle and steel balls for milling the Mo–Cu powders is also beneficial to improve the physical and thermal properties of Mo–Cu alloy.     

Effect of Zn doping on structure and ferroelectric properties of PST thin films prepared by sol–gel method

(Pb _y Sr_1−y )Zn _x Ti_1−x O_3−x thin films were prepared on ITO/glass substrate by sol–gel process using dip-coating method. The phase structure, morphology and ferroelectric property of the thin film were studied. All the thin films show the typical perovskite phase structure. Both the crystallinity and c/a ratio of the perovskite phase increases initially and then decreases gradually with doping Zn in the thin film. Ferroelectric properties of the Zn-doped PST thin films, including ferroelectric hysteresis-loop, remnant polarization and coercive force, decrease gradually with increasing Zn. And the effect of Zn on ferroelectric properties is more obvious in PST thin film with high content of Pb than that with low Pb although the high lead thin film exhibits high intrinsic ferroelectric properties.     

Effect of temperature on dielectric and electrical properties of Co–Zr doped barium hexaferrites prepared by sol–gel method

In the present research, temperature dependence of dielectric properties of cobalt–zirconium substituted barium hexaferrites, fabricated using citric acid sol gel method, has been reported. The dielectric constant, loss tangent and A.C. conductivity were investigated on the circular pellets in temperature range 30–350 °C and frequency range 10 kHz–1 MHz using impedance analyzer. This paper also presents impedance (Z*) and electric modulus (M*) analysis of all the samples. The single semi-circular arcs, observed in impedance Nyquist plots, suggest the dominance of grain boundaries in the conduction process. Dielectric constant and dielectric loss tangent show very small variation up to 200–250 °C temperature and abrupt increase afterwards up to 350 °C. Thus, these ferrites can be successfully implemented in the practical applications like capacitors, microwave devices etc. up to 250 °C, without any significant change in properties.     

Effect of Gd substitution on structural and magnetic properties of Zn–Cu–Cr ferrites prepared by novel rheological technique

Abstract

A novel rheological technique was developed to synthesise Gd substituted Zn–Cu–Cr ferrites, Zn_0·6Cu_0·4Cr_0·5Gd_xFe_1·5?xO₄ (x=0·00, 0·02, 0·04, 0·06, 0·08) powders. The effects of the Gd substitution on the structural and magnetic properties of the as prepared Zn–Cu–Cr ferrites were investigated. The microstructure, morphology and magnetic properties of the materials were characterised by X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. It was shown that the as prepared materials exhibited the single phase spinel structure. The lattice parameters increased while the crystallite sizes decreased with increasing Gd content. The magnetic properties of the as prepared materials were strongly affected by Gd content. The saturation magnetisation decreased, while coercivity increased with increasing Gd content.     

On the sol–gel synthesis and characterization of strontium ferrite ceramic material

A simple oxalate based sol–gel process has been described to produce a highly stable anion deficient strontium ferrite for separation of oxygen from air. The method involves metal nitrates and oxalic acid precursors with ethanol and water as solvents, gel formation, digestion for 4 h, drying at 150 °C for 24 h, and finally decomposition at 800 °C in air. The resulting material (i) exhibits a single perovskite-type cubic (SrFeO_3?ξ; ξ ～ 0.13) phase with a_o = 3.862 ± 0.002 Å, (ii) contains both the Fe⁴⁺ and Fe³⁺ species in 2.8:1 ratio, (iii) undergoes Fe⁴⁺ → Fe³⁺ reduction upon heating at 650 °C in rare gas ambient and transition to an orthorhombic phase with a ～ a_o√2, b ～ 4a_o, c ～ a_o√2, which reverts back to cubic phase with oxygen uptake at elevated temperatures, and (iv) acts as filter for air with excellent oxygen permeation, typical flux density value being 2.45 ml/cm² min at 1000 °C.     

Effect of solution pH on the surface morphology of sol–gel derived silica gel

We have examined the effect of solution acidity on the textural characteristics of silica gels prepared by sol–gel synthesis using tetraethyl orthosilicate (TEOS) as a silica precursor and cetyltrimethylammonium bromide (CTAB) as a template. Using IR spectroscopy, we have studied micellar TEOS solutions and the synthesized silica gel samples. The results demonstrate that, in an alkaline medium in a water–ethanol solution, SiO₂ experiences short-range ordering on the surface of micelles formed by CTAB molecules, whereas in an acid medium the process is not influenced by the presence of CTAB. Nitrogen porosimetry and electron microscopy data indicate that the silica gel obtained at pH 2 is microporous, with an average pore size of 2 nm. In an alkaline medium at pH 10, we obtained mesoporous SiO₂ (18 nm) with a narrow pore size distribution and a specific surface area of 110 m²/g.     

Preparation and magnetic properties of electrospun CuO/NiO bimetallic nanofibers via sol–gel electrospinning

We report the fabrication and magnetic properties of the CuO/NiO bimetallic composite nanofibers prepared by sol–gel electrospinning and followed by calcination. The added precursors (copper nitrate trihydrate (CuNT) and nickel chloride hexahydrate (NiCH)) significantly influenced the fiber formation and its morphologies during electrospinning. The magnetic properties were investigated by Vibrating Sample Magnetometer and Electron Spin Resonance (ESR) curves. After calcination for the production of the metallic nanofibers, the fiber morphologies were dramatically changed depending on the added amounts of precursors ranging from 2.5 to 7.5 wt%. From the magnetic hysteresis loop (M-H curve) and ESR analysis of the calcined electrospun CuO/NiO bimetallic nanofibers, it was found that the magnetization of the calcined electrospun CuO/NiO bimetallic nanofibers with various weight ratio of CuNT:NiCH = 9:1, 1:1, and 1:9 at an applied magnetic field of 10 kOe was 0.480, 0.402, and 0.337 emu/g, respectively, indicating that the calcined electrospun CuO/NiO bimetallic nanofibers have magnetic properties.     

Effect of substrate type, dopant and thermal treatment on physicochemical properties of TiO2–SnO2 sol–gel films

Thin nanocrystalline TiO₂–SnO₂ films (0–50 mol% SnO₂) were prepared on quartz and stainless steel substrates by sol–gel coating method. The obtained films were investigated by XRD, Raman spectroscopy and XPS. The size of the nanocrystallites was determined by XRD–LB measurements. We ascertained that the increase of treatment temperature and concentration of SnO₂ in the films favour the crystallization of rutile phase. The substrate type influences more substantially the phase composition of the TiO₂–SnO₂ films. It was established that a penetration of elements took place from the substrate into the films. TiO₂ films deposited on quartz substrate include a Si which stabilizes anatase phase up to 600 °C. The films which are deposited on stainless steel substrate and treated at 700 °C show the presence of significant quantity of rutile phase. This phenomenon could be explained by the combined effect of Sn dopant as well as Fe and Cr, which also are penetrated in the films from the steel substrate. The titania films doped up to 10 mol% SnO₂ on stainless steel possess only 12–17 nm anatase crystallites, whereas the TiO₂–(10–50 mol%) SnO₂ films contain very fine grain rutile phase (4 nm).     

Effect of processing parameters on textural and bioactive properties of sol–gel-derived borate glasses

A compositional range of recently developed bioactive sol–gel-derived borate glasses (SGBGs) have demonstrated remarkably rapid rates of conversion to hydroxy-carbonated apatite (HCA) in simulated body fluid (SBF). Although the composition of SGBGs did not greatly impact HCA conversion rates, it is still unknown how the sol–gel processing parameters affect the textural properties and thus bioactivity of the glass. In this study, a borate-substituted Bioglass^® “45S5” formulation [(46.1)B₂O₃-(26.9)CaO-(24.4)Na₂O-(2.6)P₂O₅; mol%] was fabricated using different sol–gel processing parameters including precursor materials, ageing time and temperature, along with calcination rate and temperature. It was found that a higher calcination temperature led to a partially crystallized glass with almost a magnitude decrease in specific surface area relative to the other glasses. All processing routes resulted in highly bioactive glasses according to Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, which confirmed HCA formation in SBF in as little as 2 h. The majority of ion-exchange occurred within 30 min, facilitating this rapid conversion to bone-like HCA. Interestingly, the partially crystallized glasses (i.e., glass–ceramics) also underwent full conversion to HCA in SBF. Furthermore, ageing time and temperature did not affect the bioactive properties of these glasses, which allow for significantly reduced processing times. In summary, this study demonstrates that SGBGs can be tailored for targeted tissue engineering applications by varying the sol–gel processing parameters.     

Structural, vibrational, optical and magnetic properties of sol–gel derived Nd doped ZnO nanoparticles

Nd doped ZnO (Zn_1-xNd_xO, x = 0.0, 0.03, 0.06 and 0.10) nanoparticles were prepared by sol–gel method. Phase identification and effect of Nd ions substitution in ZnO lattice were confirmed by Rietveld analysis of XRD patterns. UV–Visible absorption spectra of pure and Nd doped ZnO nanoparticles showed the variation of the band gap in the range of 3.31–3.26 eV. The FTIR analysis of pure and Nd doped ZnO nanoparticles exhibited similar patterns in Zn/Nd–O bond length as obtained from the Rietveld refinement. Raman analysis confirmed the formation of a wurtzite structure wherein the local structure of ZnO nanoparticles is distorted due to Nd substitution. Magnetization-magnetic field hysteresis curves for pure and Nd doped ZnO nanoparticles revealed diamagnetic and paramagnetic behaviour, respectively. The paramagnetic behaviour of doped ZnO nanoparticles increased with increasing Nd concentration. However, the weak ferromagnetic behaviour of doped ZnO nanoparticles is observed after subtracting paramagnetic components, whereas the ferromagnetic behavior increased up to x = 0.06 samples, which further declined for x = 0.10 sample due to competition between paramagnetic and ferromagnetic ordering. The reduction in the ferromagnetic behavior for x = 0.10 sample indicates that the solubility limit of Nd atoms in ZnO lattice has been reached and paramagnetically coupled Nd atoms increased due to the increasing secondary phases.     

Structural and magnetic properties of Ce3+doped Mg-Co ferrite prepared by sol–gel method

Journal of Materials Science: Materials in Electronics - Ce3+-doped Mg-Co ferrite powder can be prepared by sol–gel spontaneous combustion method. The chemical formula for...     

Structure and optical properties of CuxO- and CuxSe-doped sol–gel silica glasses

Copper oxide and copper selenide nanoparticles were produced within the silica glasses through the sol–gel technique. Chemistry of these copper compounds (variability in stoichiometry and copper oxidation state) provides a variety of optical properties of nanoparticles composed from them. A series of glasses with the nanoparticles different in stoichiometry was fabricated. The linear absorption spectra reveal the changes of the fundamental absorption edge position and appearance of the intense absorption band in the near IR. Photoluminescence is observed both for copper oxide and copper selenide nanoparticles evidencing Cu(I) states.