Synthesis and characterization of substitutional solid solutions aLn2O3 · (1 − a)Bi2O3 · 4TiO2

The solubility of 10 lanthanide elements and of scandium is solid Bi₂Ti₄O₁₁ has been determined using Raman spectroscopy and X-ray diffraction. The data obtained were used to construct a diagram of solubility as a function of the ionic radii of bismuth and the lanthanide elements. The thermal stability of the solid solutions as a function of temperature and duration of thermal treatment has been qualitatively established.     

Sol–gel preparation and characterization of ceria stabilized zirconia minispheres

A novel processing technique based on sol–gel drop generation method has been developed to prepare fine zirconia minispheres for use as grinding media. Zirconium oxalate gel formation from the prepared sol was obtained in proper synthesis condition using Zirconium oxy-chloride octahydrate(ZrOCl₂·8H₂O) as starting material. The transparent oxalate gel was then added dropwise into the setting solution for the formation minispheres. To obtain the required fluidity and viscosity a suitable binder was mixed to the sol and stabilizing agent of required mol% was added to stabilize the phase formation. The addition of stabilizing agent transformation toughened the minispheres, with a complete retention of the tetragonal phase in the final product sintered at 1500 °C. Thermogravimetric analysis indicated the removal of most of the volatiles by 600 °C. Density and Crystallite size were found to be increasing linearly with sintering temperature. The phase identification, density variation, chemical decomposition, functional group specification and microstructural features for the dried and sintered final product were studied.     

Sol–gel preparation and structural characterization of Ba2TiSi2O8 powder

Fresnoite (Ba₂TiSi₂O₈, BTS) nano-particles were successfully synthesized at a low temperature of 900?°C by a modified Pechini sol?Cgel process with starting materials of Ba(NO₃)₂, Si(OC₂H₅)₄ and Ti(OC₃H₇)₄. The structural characterization of the precursors and derived synthesized oxide powders is done by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal analysis (TG-DTG) and electron microscopy (SEM, EDX and TEM) studies. The effect of heat-treating temperature on the crystallinity of the fresnoite was investigated. Combined the XRD data and the strong FTIR peaks assigned to Ti?CO and Si?CO vibration, indicate the formation of fresnoite phase at a temperature of 900?°C. Also the nano-crystals size distribution was studied and the main diameter of nanoparticles was about 47?nm.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

Sol–gel preparation and electrochemical properties of La-doped Li4Ti5O12 anode material for lithium-ion battery

A sol–gel method using Ti(OC₄H₉)₄, LiCH₃COO·2H₂O, and La(NO₃)₃·6H₂O as starting materials and ethyl acetoacetate as chelating agent to prepare pure and lanthanum (La)-doped Li₄Ti₅O₁₂ is reported. The structure and morphology of the active materials characterized by powder X-ray diffraction and scanning electron microscopy analysis indicate that doping with a certain amount of La³⁺ does not affect the structure of Li₄Ti₅O₁₂, but can restrain the agglomeration of the particles during heat treatment. The electrochemical properties measured by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling tests show that La-doped Li₄Ti₅O₁₂ presents a much improved electrochemical performance due to a decrease in charge transfer resistance. At current densities of 1 and 5 C, the La-doped Li₄Ti₅O₁₂ exhibits excellent reversible capacities of 156.16 and 150.79 mAh?g^?1, respectively. The excellent rate capability and good cycling performance make La-doped Li₄Ti₅O₁₂ a promising anode material for lithium-ion batteries in energy storage systems.     

Fabrication and characterization of compositionally graded PbxSr1−xTiO3 thin films by the Sol–gel method

Journal of Sol-Gel Science and Technology - Different compositionally graded PbxSr1?xTiO3 (x&nbsp;=&nbsp;0.2, 0.3, 0.4, 0.5 and 0.6; PST) thin films were deposited on...     

Fabrication and properties of xBiFeO3-(1 − x)Bi4Ti3O12 system by sol–gel process

The thin films of mixture of xBiFeO₃-(1 − x)Bi₄Ti₃O₁₂ (x = 0.4, 0.5, and 0.6) system were prepared by a sol–gel process. The thicknesses of the thin films were 540, 500, and 570 nm, respectively. The crystal structure of all thin films annealed at 650 °C was analyzed by X-ray diffraction. It was found that the thin films at x = 0.4 and 0.5 mainly consisted of a Bi₄Ti₃O₁₂ phase while Bi₅Ti₃FeO₁₅ was the major phase of the thin film at x = 0.6. The thin film (x = 0.6) showed better ferroelectric properties in remnant polarization and polarization fatigue than those observed in the thin films (x = 0.4 and 0.5). The values of remnant polarization 2P _r and coercive field 2E c of the thin film at x = 0.6 were 36 μC/cm² and 192 kV/cm at an applied electric field of 260 kV/cm, respectively. There was almost no polarization fatigue up to 10¹⁰ switching cycles. Also weak ferromagnetism was observed in the thin film at x = 0.6.     

Sol–gel preparation and characterization of epitaxial Y0.5Ce0.5O1.75 films on biaxially-textured NiW tapes

Journal of Sol-Gel Science and Technology - High-quality Y0.5Ce0.5O1.75 films were prepared on biaxially-textured NiW tapes using sol–gel method. Y0.5Ce0.5O1.75 precursor sol was prepared...     

Sol–gel preparation of TiO2 and MgF2 multilayers

TiO₂ and MgF₂ thin films were prepared by sol–gel processing. Their microstructure was investigated by scanning electron microscopy, X-ray diffraction and ellipsometric porosimetry as a function of the number of coating-firing cycles with different single layer thicknesses. TiO₂/MgF₂ multilayers were processed in different stacking sequences; the nucleation of the subsequent material was correlated to the underlying crystal structure and the respective film morphology. It was found that dense crystalline MgF₂ films on glass can be manufactured by homoepitaxial growth of multiple thin layers. On an underlying TiO₂ layer the effect of densification and crystallization is increased. In the reverse film order no such effect could be observed.     

Sol–gel processing and electrochemical characterization of monoclinic Li3FeF6

To find new cathode materials for future applications in lithium-ion batteries, lithium transition metal fluorides represent an interesting class of materials. In principle the Li intercalation voltage can be increased by replacing oxygen in the cathode host structure with the more electronegative fluorine. A facile pyrolytic sol–gel process with trifluoroacetic acid as fluorine source was established to synthesize monoclinic Li₃FeF₆ using nontoxic chemicals. The acicular Li₃FeF₆ powder was characterized with X-ray diffraction and a detailed structure model was calculated by Rietveld analysis. For the preparation of cathode films to cycle versus lithium monoclinic Li₃FeF₆ was ball milled with carbon and binder down to nanoscale. After 100 cycles galvanostatic cycling (C/20) 47 % fully reversible capacity of the initial capacity (129 mAh/g) could be retained. To the best of our knowledge the results presented in this work include the first rate performance test for monoclinic Li₃FeF₆ up to 1 C maintaining a capacity of 71 mAh/g. The redox reaction involving Fe³⁺/Fe²⁺ during Li insertion/extraction was confirmed by post-mortem XPS and cyclic voltammetry.     

Preparation and characterization of CaCu3Ti4O12 powders by non-hydrolytic sol–gel method

CaCu₃Ti₄O₁₂ (CCTO) powders were prepared via a non-hydrolytic sol–gel (NHSG) method by using acetylacetone as chelating agent and ethylene glycol as solvent. The samples were characterized by TG–DSC, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope. The dielectric properties of ceramics were also measured. The pure perovskite-like CCTO powders were obtained by heat treatment at 800 °C for 2 h. The average particle sizes of CCTO powders calcined at 800 °C were approximately 350–450 nm. The samples sintered at 1,000 °C showed the mean grain size of 2.5–4 μm. Specially, the ceramics exhibited high dielectric constant (1.19 × 10⁵–1.40 × 10⁵) and low dielectric loss (0.051–0.1) in the temperature range of 30–110 °C. Moreover, with the NHSG method the period of synthesis process was greatly shortened.     

Sol–gel preparation of mesoporous Al2O3–SiO2 glasses: structural evolution monitored by solid state NMR

Glasses along the composition line 0.5Al₂O₃–xSiO₂ (1 ≤ x ≤ 6) were prepared via a novel sol–gel route using tetraethylorthosilicate and aluminum lactate as precursors. The structural evolution from solution to gel to glass is monitored by standard ²⁷Al and ²⁹Si nuclear magnetic resonance (NMR) spectroscopies, revealing important insights about molecular level mechanisms occurring at the various stages of glass formation. Under the experimental conditions reported, silica and alumina precursors undergo homoatomic condensation processes when the gel is heat treated at about 100 and 300 °C, respectively, and only little heteroatomic co-condensation occurs in this temperature range. The latter is promoted only upon elimination of the residual lactate and water ligands upon annealing the gels above 300 °C. Following calcination at 650 °C, mesoporous glasses are obtained, having average pore diameter of about 3 nm and a surface areas near 500 m²/g. Si–O–Al connectivities are detected by ²⁹Si magic angle spinning (MAS)-NMR. ²⁷Al MAS-NMR spectra reveal aluminum in four-, five- and six-coordination. The spectra differ significantly from those of other sol–gel derived Al₂O₃–SiO₂ materials prepared from different precursor routes, suggesting that the lactate route results in a higher degree of compositional homogeneity.     

Sol–gel synthesis of nanocrystalline Zn1−xNixFe2O4 ceramics and its structural,magnetic and dielectric properties

Zn_1?xNi_xFe₂O₄ (0.0 ≤ x ≤ 1.0) nanoparticles are prepared by sol–gel method using urea as a neutralizing agent. The evaluation of XRD patterns and TEM images indicated fine particle nature. The average crystallite size increased from 10 to 24 nm, whereas lattice parameters and density decreased with increasing Ni content (x). Infrared spectra showed characteristic features of spinel structure along with a strong influence of compositional variation. Magnetic measurements reveal a maximum saturation magnetization for Zn_0.5Ni_0.5Fe₂O₄ (x = 0.5); however, reduced value of magnetization is attributed to the canted spin structure and weakening of Fe³⁺(A)–Fe³⁺(B) interactions at the surface of the nanoparticles. Impedance analysis for different electro-active regions are carried out at room temperature with Ni substitution. The existence of different relaxations associated with grain, grain boundaries and electrode effects are discussed with composition. It is suggested that x = 0.5 is an optimal composition in Zn_1?xNi_xFe₂O₄ system with moderate magnetization, colossal resistivity and high value of dielectric constant at low frequency for their possible usage in field sensor applications.     

Preparation and characterization of a new series of solid solutions of Bi1−xYxFeO3 (0 < x < 1) from the thermal decomposition of hexacyanoferrates doped with yttrium

Solid solutions of Bi_1?xY_x[Fe(CN)₆]·4H₂O (0?<?x?<?1) complexes were synthesized and characterized. The crystal structures were refined by Rietveld analysis using X-ray powder diffraction data. The complexes of the series crystallized in the orthorhombic system, space group Cmcm. The gradual decrease in cell volume indicates that the substitution of Bi³⁺ by Y³⁺ was appropriately materialized. The thermal behavior was studied by thermogravimetric and differential thermal analysis. A single phase of perovskite-type Bi_1?xY_xFeO₃ powders was obtained by thermal decomposition of the complexes at about 600 °C. The obtained products were identified and characterized by energy-dispersive spectroscopy, Raman and Fourier transform infrared spectroscopy and powder X-ray diffraction. The size and morphology of the complexes and their thermal decomposition products were evaluated by scanning electron microscopy. Thermal analysis showed that the complexes were good intermediaries for the synthesis of high-purity mixed oxides with a uniform particle size of the order of nanometers. To evaluate the effect of doping with yttrium, electrical transport measurements were performed.

     

Sol–gel combustion synthesis and characterization of nanostructure copper chromite spinel

Nanocomposite copper chromite spinel was fabricated by sol–gel process using copper nitrate trihydrate, chromium nitrate nonahydrate, ethylene glycol, diethyl ether, and citric acid. The thermoanalytical measurements (TG–DTG), X-ray powder diffractometry (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray analysis were used to characterize the structural and the chemical features of the nanocomposites. TG–DTG results showed that the major mass loss for copper(II) nitrate, chromium(III) nitrate as precursors occur at 258 and 140 °C, respectively. The major mass loss for dried gel of copper chromite occurs at 310 °C. XRD data revealed the formation of pure copper chromite after thermal decomposition at 1,000 °C for 2 h. The observation of XRD patterns reveals the presence of single-phase tetragonal spinel CuCr₂O₄. FESEM analysis of calcined composite was found to be in the range of 20–30 nm.