Structure and magnetic properties of La0.67Sr0.33MnO3 thin films prepared by sol–gel method

La_1?xSr_xMnO₃ (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO₃ (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively.     

The study of thermal,microstructural and magnetic properties of manganese–zinc ferrite prepared by co-precipitation method using different precipitants

Mn–Zn ferrite was prepared from the solution after acid leaching of spent batteries by co-precipitation method using ammonia oxalate, sodium carbonate and sodium hydroxide as precipitating agents. The co-precipitation process was performed at temperature of over 50 °C by continuous magnetic stirring. The precipitates were pre-sintered at 850 °C in air. Dilatometric study has revealed that lowest shrinkage (only 5.6%) showed a material obtained from an oxalate precipitant. After pressing and high-temperature sintering at 1325 °C, it showed both insufficient density and the presence of pores, which contribute to the deterioration in the magnetic properties of the ferrites: the low magnetic permeability value and high magnetic losses. Ferrite prepared from hydroxide and carbonate precipitant showed a much higher shrinkage, sintered density and much higher magnetic permeability compared with the ferrite prepared from oxalate precursor.     

Silica–silver nanostructured spheres prepared by spray pyrolysis of sol containing silver precursor

Silver–silica nanostructured composites were prepared by spray pyrolysis of aqueous sols of silica nanoparticles containing silver nitrate. The physical and chemical characteristics of the composites prepared at different Ag/Si atomic ratio in the sols and temperatures of pyrolysis were examined by TEM, SEM, XRD, FT-IR and UV-visible spectra. For the low silver ratios up to 0.2, well-dispersed silver particles were produced in the pore of the silica agglomerates with their size and surface plasmon resonance depending on the pore size and silver mobility, in addition to the loading and temperature. The formation of silver silicate and new-phase silica as well as crystallinity of the silver prepared was discussed. There was also explained how the temperature of preparation affected the morphologies of the composites produced with higher Ag/Si ratios greater than 1. Mechanism on the formation of silver–silica composites was proposed for the wide range of the ratios from 0.01 to 3.     

Effects of Cu addition on the structure and magnetic properties of L10-FePt nanoparticles prepared by sol–gel method

(FePt)₁₀₀Cu₀, (FePt)₉₅Cu₅ and (FePt)₉₀Cu₁₀ nanoparticles (NPs) were successfully synthesized by the sol–gel method. The relationship between Cu doping and structure and magnetic properties of L1₀-FePt NPs was studied. The results indicated that all three samples originated a L1₀-FePt structure and Cu doping did not destroy the ordered structure of L1₀-FePt. By increasing the Cu content, c/a ratio of the FePtCu NPs linearly decreased. Pawley refinement showed symmetry of (FePt)₉₅Cu₅ NPs was still tetragonal. When the Cu concentration increased from 0 to 10 %, coercivity increased from 7,050 to 11,250 Oe. This result confirms that the prepared alloys can be promising candidates for magnetic storage applications.     

Investigation of structural,morphological, optical,and magnetic properties of Sm-doped LaFeO3 nanopowders prepared by sol–gel method

Journal of Sol-Gel Science and Technology - Pure orthorhombic phase of La1?xSmxFeO3 (x?=?0, 0.1, 0.2, and 0.3) nanoparticles can be obtained by sol–gel method after...     

The investigation of some physical properties and microstructure of Zn-doped hydroxyapatite bioceramics prepared by sol–gel method

In this study, the effect of Zn-dopant on the physical properties and microstructure of hydroxyapatite (HAP) bioceramics was investigated. The average crystallite size, phase composition and degree of crystallization of the pure hydroxyapatite and Zn-doped hydroxyapatite bioceramic samples prepared by sol–gel method were determined by X-ray diffraction method. It was seen that all the bioceramic samples were composed of the nanoparticles (29–46 nm). Fourier transform infrared spectroscopy was used to determine the functional groups in the samples. The dielectric properties of the bioceramics were investigated by dielectric impedance spectroscopy method, and the surface morphologies of them were analyzed using scanning electron microscopy technique. When the densities of the samples were measured by Archimedes method, it was seen that the densities of the samples increased with the increase of the molar ratio of Zn. The crystallization degree for all the samples dramatically decreased with the increasing content of the Zn dopant. With the increase of Zn to HAP, a change was observed in the degree of the crystallization, phase compositions, dielectric properties and microstructures of the samples.     

Thermal and luminescent properties of Eu2+-doped aluminates prepared by the sol–gel method

Alkaline earth aluminates with the overall nominal compositions Ca_0.5Sr_0.5Al₂O₄, Ca_0.5Mg_0.5Al₂O₄ and Mg_0.5Sr_0.5Al₂O₄ doped with 1 mol% of Eu²⁺ ions were prepared by the modified aqueous sol–gel method. The thermal behaviour of the xerogels was studied by the TG/DSC-MS technique under an argon and a reductive atmosphere (Ar/H₂–5 %). Appropriate luminescent efficiency of the materials was achieved after annealing at temperatures lower than those in conventional solid state reactions. All three aluminates are mixtures of at least two phases; the monoclinic phase of CaAl₂O₄, the hexagonal phase of SrAl₂O₄ and the cubic phase of MgAl₂O₄ were identified. Solid solubility was recognised in the Ca_0.5Sr_0.5Al₂O₄:Eu²⁺ composition due to the similar ionic radii of Ca²⁺ and Sr²⁺. UV excited luminescence was observed in the blue region (λ_max = 441 nm) in the aluminates containing the monoclinic phase of CaAl₂O₄ and in the green region (λ_max = 520 nm) in the Mg_0.5Sr_0.5Al₂O₄:Eu²⁺ composition.     

Dielectric and energy storage properties of barium strontium titanate based glass–ceramics prepared by sol–gel method

Ba_0.6Sr_0.4TiO₃ based glass–ceramics were prepared by sol–gel process. Influences of B–Si–O glass content on the microstructure, dielectric, and energy storage properties of the BST based glass–ceramics have been investigated. Perovskite barium strontium titanate phase was found at annealing temperature 800 °C. A secondary phase Ba₂TiSi₂O₈ was detected and lowered by declining the mole ratio of element Si (from 50 to 25 mol%) in glass additive. Microstructural observation indicated that the microstructure homogeneity can be improved by glass addition till 2 mol%, while worsened by excessive glass concentrations. Due to relatively homogeneous microstructure, the maximum discharged energy density and breakdown strength were also obtained in samples with 2 mol% glass additive, which were found to be 0.553 J/cm³ and 43.2 kv/mm, respectively. Microscopic observation of the breakdown area was performed and the mechanical failure, including the formation and accumulation of micro-cracks during the dielectric breakdown process, was considered to be the main cause of dielectric breakdown. Results of the charging and discharging energy densities show that the BST based glass–ceramics prepared by sol–gel method has a potential for pulse power applications.     

Effect of increasing pH value on the structural,optical and magnetic properties of yttrium iron garnet films prepared by a sol–gel method

Yttrium iron garnets (Y₃Fe₅O₁₂, YIG) nanoparticles thin films with different pH values (pH 1, 2, 3, 4 and 5) were prepared by a sol–gel method. The films were deposited on quartz substrates using a spin coating technique. Annealing of the films was performed at 900 °C in air for 2 h. The structural analysis using an X-ray diffractometer (XRD) exhibited that all films were single phases regardless the differences in pH value. The lattice parameters calculated from the XRD patterns revealed that the distortion of lattice occurred at a high pH value. The crystallites sizes of films also increased from 27.6 to 33.3 nm when the pH value increases from 1 to 5. The films were high agglomeration due to increasing of pH value which caused difficulty to measure the grain size. The films with different pH values showed transmission >80 % in visible range. Additionally, the absorption coefficient (α) of films was found to be of the order of 10⁷ cm^?1. A strong absorption of the films caused by charge transfer transition centered in UV and optical transitions between crystal field levels within the 3d levels of Fe³⁺ ions. The YIG films exhibit highest saturation magnetization value of 76 emu/cm³ at pH 1. The increment of pH value up to 5 caused a decreasing of coercive field due to multidomain formation and the easy movement of the domain walls.     

Structure and electrorheological properties of nanoporous BaTiO<Subscript>3</Subscript> crystalline powders prepared by sol–gel method

In this paper, a novel nanoporous barium titanate (BaTiO₃) crystalline powder was synthesized by using triblock poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) based systems (P-123) as the soft template via a sol–gel method and their structure-dependent electro rheological property was studied. The pore diameter and specific surface area of BaTiO₃ were precisely controlled by varing the calcined temperature. The chemical composition, structure and surface morphology of BaTiO₃ were characterized by X-ray diffraction (XRD), thermo gravimetric analysis (TGA), and nitrogen adsorption–desorption method, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The result revealed that the pore volume and specific surface area of BaTiO₃ decreased with the increment of calcined temperature. The electro rheological fluids (ERFs) were obtained by dispersing BaTiO₃ crystallites in silicon oil and three kinds ERFs were fabricated by using three kinds of BaTiO₃ which were prepared under different calcined temperature (550, 600 and 900 °C) as the precursors. The behaviors of the ERFs were evaluated via a rotational rheometer fixed with electric field generator. The results showed that electro rheological effect was related to the pore volume and specific surface area of BaTiO₃. Due to the distinct advantage of sol–gel method for preparing nanoporous BaTiO₃ without contamination of the materials, the markedly low current destiny of the ERFs was obtained. The yield stress of ERFs with large specific surface area of BaTiO₃ reached the maximum of 3 kPa, which is higher than that of ERFs using traditional pure BaTiO₃ crystallites (lower than 1 kPa).     

Structural,dielectric and electrical properties of zinc doped nickel nanoferrites prepared by simplified sol–gel method

Zinc doped nickel ferrite nanoparticles having the general formula Ni_1−xZn_xFe₂O₄ (x = 0.1, 0.2, 0.3, 0.4, 0.5) were prepared with simplified sol–gel method. The structural and dielectric properties of these samples sintered at 750 ± 5 °C were studied. X-ray diffraction patterns confirm the single phase spinel structure for prepared samples. The scanning electron microscope images indicated that the particle size of the samples lies in the nanometer regime. The dielectric constant (ε_r) and dielectric loss tangent (tan δ) of nanocrystalline nickel ferrites were investigated as a function of frequency and Zn concentration. The dependence of ε_r and tan δ on the frequency of the alternating applied electric field is in accordance with the Maxwell–Wagner model. The prepared samples have a lowest dielectric constant compared to the already reported samples of the same composition to the best of our knowledge. The effect of Zn doping on the dielectric properties of nickel ferrites is explained on the basis of cations distribution in the crystal structure.     

Compound-induced changes in thermal,structural and optical properties of indium–gallium–zinc oxides prepared by sol–gel method

In this study, IZO/IGZO powders and films of different composition ratios were fabricated by sol–gel method. The influences of the composition ratio on the decomposition temperature, crystallization behavior, structural and optical properties of multi-component oxides were thoroughly examined. Thermogravimetric/differential scanning calorimetric results revealed that in contrast to zinc and indium oxides, the high crystallization temperature and low crystallinity of gallium oxide were attributed to the high dehydroxylation temperature of gallium hydroxide, which led to the high decomposition and crystallization temperatures of IGZO compound. The XRD analysis of the IGZO films confirmed that the addition of Ga amount made the films turn into amorphous easily. However, TEM analysis suggested that the IZO film (In:Zn = 1:2) and the IGZO (In:Ga:Zn = 1:1:1) film consisted of short-range-order nanostructure although the selected area diffraction of both samples indicated that they are amorphous. The transmittance measurements agreed well with the XRD results; that is, the band gaps of the IZO/IGZO films obviously depend on the composition ratio and are closely related to the change of the structural properties.     

Physical and optical properties of organo-modified silica nanoparticles prepared by sol–gel

A comparative study on the physical and optical properties of silica nanoparticles prepared by sol–gel has been carried out. Post-modification of as-synthesized silica nanoparticles produced organo-functionalized silica nanoparticles slightly increased in size (~20%) and relatively high aggregation. However, in situ method produced sixfold bigger functionalized particles with good dispersion and less aggregation. Higher organic content was observed for in situ modified nanosilica, leading to a higher surface hydrophobicity that improved compatibility and dispersion in preparation of silica-polymer nanocomposite. Furthermore, in situ and post-modified nanosilica demonstrated a distinct optical activity, photoluminescence and UV compared to the unmodified nanoparticles.     

Photocathodic protection properties of three-dimensional titanate nanowire network films prepared by a combined sol–gel and hydrothermal method

A combined sol–gel and hydrothermal method was developed for preparing a three-dimensional titanate nanowire network film on titanium substrates to achieve an especial photocathodic protection effect for 403 stainless steel. Photopotential measurements were performed to study the protection effect of the film. The results indicated that the titanate film exhibited a special all-dimensional uniform porous structure composed of branched titanate nanowires. When we coupled the steel in a 0.5 M NaCl solution to the titanate film photoanode in a 1.0 M NaOH solution under illumination, its potential decreased by 560 mV. Especially after the light source was cut off, the photopotential of the steel increased by only 50–145 mV, and kept at the lower values than the corrosion potential under dark conditions for over 10 h, indicating that the titanate nanowire network film could produce a striking photocathodic protection effect for 403 stainless steel under illumination and dark conditions.     

The morphologies and optoelectronic properties of delafossite CuFeO2 thin films prepared by PEG assisted sol–gel method

Single phase delafossite CuFeO₂ thin films were synthesized by a simple sol–gel method. The influence of polyethylene glycol (PEG) on the morphology and optoelectronic properties of the films was studied by addition of 1.0 g PEG in 10 ml precursor solution. The crystal sizes of the derived CuFeO₂ films with and without addition of PEG were 49 nm, but the sample with addition of PEG (labeled as CFO-PEG) showed weaker c-axis orientation growth. The sample without addition of PEG (labeled as CFO) showed a compact surface without detectable pores and had a thickness around 50 nm. However, the sample CFO-PEG exhibited a porous surface with worm-like grains in nanometric scale and had a thickness around 310 nm. Enhanced absorbance in UV–vis region was observed for the sample CFO-PEG which might ascribe to both the thickness and porous surface. The optical direct bandgaps at near-UV were estimated to be ~3.0 and 3.38 eV for the sample CFO-PEG and CFO, respectively. Though the porous surface of CFO-PEG has improved the absorbance in UV–vis region, the resistivity has also been increased due to the homogeneous distribution of interspaces between the worm-like grains, which makes the incident photon to current efficiency of CFO-PEG lower than that of CFO.