Crystallization process of lanthanum-substituted bismuth titanate synthesized by a facile sol–gel method

We present a facile sol–gel route to synthesize lanthanum-substituted bismuth titanate (BLT). The chemical reactions and crystallization process of this method using the initial materials of bismuth subnitrate [4BiNO₃(OH)₂·BiO(OH)], lanthanum nitrate [La(NO₃)₃·6H₂O] and tetrabutyl titanate [Ti(C₄H₉O)₄] were investigated by thermogravimetric and differential thermal analysis, IR spectroscopy, gas chromatography/mass spectrometry, Raman spectroscopy and XRD. The evaporation of the dissolved CO₂ in the amorphous BLT matrix is associated with the crystallization of BLT. The BLT gel is pure BLT perovskite when calcination temperature is higher than 500 °C. The grain size of the obtained nanoparticles ranges from 15 to 82 nm. The Arrhenius curve is obtained from the representation of the reduced sizes with respect to the calcination temperature. The activation energy of grain growth in BLT nanoparticles is 0.36 eV, which shows a rapidly growth process in the temperature range of 500–850 °C.     

Structural,electrical and optical properties of tin doped cadmium oxide thin films obtained by sol–gel

Transparent and conducting tin doped cadmium oxide thin films were obtained by mixing cadmium oxide and tin oxide precursor solutions by the sol–gel method. Different tin contents in solution were studied: 0, 0.5, 1, 2, 3, 5 and 10 at.%. The films were sintered at 550 °C and, after that, annealed in N₂/H₂ gas mixture, in order to decrease their resistivity. X-ray diffraction patterns showed that doping of tin diminishes the [111] light preferred orientation of films and provokes a decrease of the average crystallite size from 30 to 12 nm. Atomic force microscopy images revealed morphological changes with the addition of tin content. All the films showed a high transmission around 75 % in the 600 < λ < 1,700 nm range and a shift of the absorption edge towards the blue region as the tin concentration was increased. The cadmium oxide films doped with 1 at.% of tin showed the lowest resistivity of 5.7 × 10^?4 Ω cm and a band gap energy value of 2.7 eV. For their characteristics, these CdO:Sn films are good candidates as transparent conductive electrodes in CdS/CdTe and CdS/CIGS type solar cells.     

Structural and optical characterization of Ag-doped TiO2 nanoparticles prepared by a sol–gel method

Undoped and silver-doped TiO₂ nanoparticles (Ti_1?x Ag _x O₂, where x?=?0.00?C0.10) were synthesized by a sol?Cgel method. The synthesized products were characterized by X-ray diffraction (XRD), particle size analyzer (PSA), scanning electron microscope (SEM), and UV?CVisible spectrophotometer. XRD pattern confirmed the tetragonal structure of synthesized samples. Average crystallite size of synthesized nanoparticles was determined from X-ray line broadening using the Debye?CScherrer formula. The crystallite size was varied from 8 to 33?nm as the calcination temperature was increased from 300 to 800?°C. The incorporation of 3 to 5% Ag⁺ in place of Ti⁴⁺ provoked a decrease in the size of nanocrystals as compared to undoped TiO₂. The SEM micrographs revealed the agglomerated spherical-like morphology of particles. SEM, PSA, and XRD measurements show that the particles size of the powder is in nanoscale. Optical absorption measurements indicated a red shift in the absorption band edge upon silver doping. Direct allowed band gap of undoped and Ag-doped TiO₂ nanoparticles measured by UV?CVis spectrometer were 3.00 and 2.80?eV, respectively, at 500?°C.     

Synthesis and characterization of M-MCM-48 (M = Cr,Ce) from silatrane via sol–gel process

Chromium and cerium incorporated into MCM-48 framework are hydrothermally synthesized via sol–gel process without any additives and characterized by X-ray diffraction, N₂ adsorption/desorption, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Diffuse reflectance UV–vis spectroscopy, and Thermogravimetric analysis. Results indicate that the materials possess a long-range ordered structure, high specific surface area, and narrow pore size distribution. SEM images illustrate the edge-truncated octahedron morphology of Cr-MCM-48 while Ce-MCM-48 preserves the truncated octahedron of the MCM-48 parent material. TEM images show the pore network of Ia3d symmetry after loading metals. Spectroscopic data confirm the existence of metals in the framework and extra-framework. At low Cr content, Cr-MCM-48 contains only Cr(VI) species while rich Cr content loading results in both the Cr(VI) and Cr(III) species. The hydrothermal stability of MCM-48 is enhanced by carefully incorporating metals into the parent material.     

Structural and optical properties of Na doped ZnO nanocrystalline thin films synthesized using sol–gel spin coating technique

Sodium (Na) doped Zinc oxide (ZnO) thin films have been deposited on a glass substrate by the sol–gel spin coating method. Effect of doping with various percentages of Na at a particular annealing temperature of 500 °C is studied. The samples were characterized by X-ray diffraction (XRD), micro-photoluminescence, Raman and Polarized Raman spectroscopy. The X-ray diffraction and micro-Raman spectroscopy confirmed the presence of Na substitution in zinc oxide and the wurtzite structure of the lattice is retained. An enhancement of resonant Raman scattering processes as well as longitudinal optical phonon overtones up to the fifth order were observed in the micro Raman spectra. The similar values of depolarization ratios obtained from Polarized Raman studies recommend no change in the symmetry. Photoluminescence showed a strong emission peak in the near UV at 3.2 eV and negligible visible emission.     

Characterization, conductivity and photocatalytic studies of AHfM(PO4)3 (A = Na and Ag; M = Ti and Zr) powders synthesized by sol–gel method

Materials belonging to NASICON family of compositions NaHfM(PO₄)₃ and AgHfM(PO₄)₃ (M = Ti and Zr) are prepared by sol–gel and ion exchange methods, respectively. Ethylene glycol is used as a gelating agent. All the compositions are characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, ³¹P MAS NMR, UV–Vis DRS, XPS and energy dispersive spectral methods. All these phosphates are crystallized in rhombohedral lattice with space group $R\overline{3} c$ R 3 ¯ c . These compounds exhibit characteristic PO₄ vibrational modes in their FT-IR spectra. The ³¹P MAS NMR gave broad signals indicating distribution of chemical environments around P ion. The dc and ac conductivity of AgHfM(PO₄)₃ (M = Ti and Zr) are higher compared to their sodium containing compounds. The Cole–Cole plots of impedance show semicircles between 373 and 623 K. The variation of dc conductivity with temperature follows the Arrhenius equation. The photocatalytic activity of all the samples was studied against methylene blue decomposition using sun light. AgHfM(PO₄)₃ (M = Ti and Zr) have shown higher photoactivity than the sodium containing Nasicons.     

Synthesis of tin oxide nanoparticles by sol–gel process: effect of solvents on the optical properties

Tin oxide (SnO₂) nanoparticles were synthesized by the reaction of SnCl₄·5H₂O in methanol, ethanol and water via sol–gel method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared, Scanning electron microscopy and Transmission electron microscopy. The optical properties of the as-prepared samples were investigated. The XRD analysis showed well crystallized tetragonal SnO₂ can be obtained and the crystal sizes were 3.9, 4.5 and 5 nm for the sample calcined at 400 °C for 2 h. It was found that solvents played important roles in the particle size effect of nanocrystalline SnO₂.     

Thermal,chemical and antimicrobial characterization of bioactive titania synthesized by sol–gel method

Journal of Thermal Analysis and Calorimetry - Chemical stability, anticorrosive properties and photocatalytic activity of titanium dioxide (TiO2) are among the most important characteristics for...     

Structural and electrosurface characteristics of titanium dioxide xerogel prepared by the sol–gel method

Stable highly concentrated TiO₂ sol has been synthesized using binary titanyl ammonium sulfate monohydrate, (NH₄)₂TiO(SO₄)₂ · H₂O. Treatment of the sol with an ammonia solution has yielded a stable hydrogel, which, after being dried, is transformed into a TiO₂ xerogel. Study of the structure-related sorption and crystalline-chemical properties of the synthesized xerogel has shown that it represents a semicrystalline micro/mesoporous material with a rather developed specific surface area (S_sp = 120 m²/g). According to potentiometric titration data, the point of zero charge (PZC) of this material is located at pH 3.9. Measurements of the electrophoretic mobility (by microelectrophoresis) of TiO₂ xerogel particles in solutions of HCl, NaOH, and salts of mono-, bi-, and trivalent cations have shown that (1) the isoelectric point (IEP) of the particles lies in the vicinity of pH 6.2, i.e., at a much higher pH than that for PZC; (2) the presence of increasing amounts of 1: 1 and 2: 1 electrolytes causes a gradual and a dramatic reduction in the ζ potential of the particles, respectively; and (3), in the presence of an electrolyte with a trivalent counterion, the surface charge is reversed. The behavior of TiO₂ xerogel in an electric field is similar to that of lyophobic particles, with the difference that there is no maximum in the ζ potential versus 1: 1 electrolyte concentration dependence and the measured IEP of the xerogel is much higher than its PZC. Possible reasons for this discrepancy have been discussed.     

Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...     

Microstructural and optical characterizations of sol–gel based antimony doped indium oxide coatings on glass

Thin films of antimony doped indium oxide on glass has been developed by sol–gel dipping process. Four different Sb: In atomic ratios, 1:99, 4:96, 7:93, 10:90 were selected for the precursors. Pressure flow curve of the precursors were Newtonian which apparently developed homogeneous films baking at 500 °C in air. The EDS study restricted to the study of the films of only two Sb: In atomic ratios, namely 7:93, 10:90 as antimony sublimes during baking. Polycrystalline nature of the nanostructured films were revealed by X-ray diffractogram and SAED analysis. Transmission electron microscopy study shows the presence of nanoclusters of maximum average size, ~11 nm. The band gap evaluation from the absorption spectra suggested the presence of bulk indium oxide, nanoclustered indium oxide and antimony doped indium oxide. Presence of Sb(V) in the system was evidenced from the characteristic absorption spectra in the UV region. Visible transmissivity and electrical resistivity suggested the films to be prospective transparent conducting oxide material. The photoluminescence study exhibited the characteristic emissions for defect centres.     

Fabrication and characterization of Zn3V2O8 phosphor by sol–gel process

By choosing zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O) and ammonium metavanadate (NH₄VO₃) as starting materials, we succeeded in fabricating Zn₃V₂O₈ phase suitable for broad light emission by sol–gel process. X-ray diffraction (XRD), scanning electron microscope, photoluminescence (PL) and PL quantum yield (PL-QY) measurements have been performed for analyzing the relation between crystallographic and light emission characteristics. The PL-QY is determined by both the crystalline phase purity of the Zn₃V₂O₈ phase defined by XRD patterns and the crystalline size. With optimizing the sintering condition at a slightly Zn-rich side, a pure Zn₃V₂O₈ phase with enough large crystalline size was obtained with the PL-QY value of 52 %, which was higher than our previously obtained value by solid state reaction.     

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.     

Low temperature synthesis of Li5La3Nb2O12 with cubic garnet-type structure by sol–gel process

A cubic Li₅La₃Nb₂O₁₂ phase with a garnet framework was synthesized by the sol–gel process, in which lithium hydroxide, niobium oxide and acetic lanthanum were used as starting materials, while water was used as solvent. Pure garnet-like Li₅La₃Nb₂O₁₂ powders were obtained after heating the gel precursor at 700 °C for 6 h with 10 % excess lithium salt. The calcination temperature is nearly 250 °C lower than that by the solid state reaction. The phase transforms from cubic to tetragonal symmetry with loss of lithium at 717 °C, but the garnet framework remains stable to above 900 °C. A pellet annealed at 900 °C for 6 h had a room-temperature Li⁺-ion conductivity σ_Li (22 °C) = 1.0 × 10^?5 S cm^?1, a little higher than that attained by solid-state synthesis. The Li₅La₃Nb₂O₁₂ compound was chemically stable against two commonly used cathode materials, LiMn₂O₄ and LiCoO₂, up to 900 °C and against metallic lithium.     

Structural study of the MO–Nd2O3 system obtained by a sol–gel procedure

The aim of the present work was to prepare a binary MO–Nd₂O₃ system by the sol–gel method and to characterise a series of mixed oxides belonging to the binary MO–Nd₂O₃ system (M = alkaline earth metal = Mg, Ca, Sr) to obtain suitable materials with catalytic properties. The molar ratio between the two oxides was MO/Nd₂O₃ = 95/5. Different precursors as alkaline earth metal oxide source (MO), various starting solution compositions expressed in various molar ratios between reactants and different synthesis parameters (pH, temperature and time of reaction) have been used. The structural study by X-ray diffraction analysis was accomplished based on the X-ray 5.0 program, which has established the presence of the mixtures of crystalline polyphases. The lattice constants, the average size of the crystallites, the average lattice strains and the mass of unit cell variation have been calculated. The program also allowed the calculus of the anisotropy factor, which can give the image of the structural disorder. The surface defects are a consequence of structural changes inside of the crystalline lattice of the solid solutions and are quite important for catalytic properties. Some catalytic activity measurements have established the potential of the prepared sol–gel mixed oxides to be used in the oxidative dehydrogenation process of light alkanes (C₁C₄). Sample 3SrNd was shown to present the best catalytic activity and selectivity in olefins in propane conversion (${\text{C}}_2^{=}\&{\text{C}}_3^{=}$) compared with 4Ca-Nd and 1Mg-Nd samples, which was interpreted as due to a better solid solution formation of Nd³⁺ in SrO, favoured by the close ionic radius of Sr²⁺ and Nd³⁺, as well as by the high basicity of Sr and the presence of a greater number of point defects.