Vibrational spectroscopic studies on crystallisation of sol–gel derived thin films of calcia–alumina binary compound

An optimized sol–gel process has been developed to produce homogeneous thin films of calcium aluminate binary (12CaO·7Al₂O₃) compound, on magnesium oxide substrates via spin coating. Fourier transform infrared and Raman spectroscopies have been employed to investigate the effect of annealing temperature and duration on the phase transformations in the films. Heat treatment at 1,300 °C under air atmosphere for 2 h produced single-phase 12CaO·7Al₂O₃ films. However, annealing at a lower temperature of 1,100 °C in air for a period of 4 h in total resulted in the crystallization of 5CaO·3Al₂O₃ rather than 12CaO·7Al₂O₃. The X-ray photoelectron spectrum of the thin film annealed at 1,300 °C corresponds to the binding energies of C12A7 compound. The annealing temperature of 1,300 °C for 2 h is found to be sufficient for formulating single phase calcia–alumina binary films in correct stoichiometric ratio of 12:7.     

Textural and structural studies of sol–gel derived SiO2–CaO–P2O5–MgO glasses by substitution of MgO for CaO

The partial substitution of MgO for CaO in the ternary SiO₂–CaO–P₂O₅ glass system was conducted by the sol–gel method and a comparison of the textural and structural properties was reported. The textural properties (specific surface area and pore size distribution) were obtained by N₂-adsorption measurement and the glasses structure was elucidated by Fourier transform infrared spectroscopy. It is observed that, in general, all synthesized glasses show high specific surface area and present porous nature in mesopore region. The presence of MgO in glass composition has little influence on its textural properties, however, with increasing MgO concentration the frequency of Si–O(s,asym) group shifts towards lower energy and the absorbance intensity ratio of Si–O–NBO(Q³)/Si–O–Si(s,sym)(Q⁴) declines, indicating the structure modification of MgO in glass composition.     

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.     

Fabrication and optical features of the sol–gel derived silica glasses doped with copper oxide nanoparticles and europium

Novel sol–gel derived silica glasses doped with copper oxide nanoparticles and europium ions have been fabricated in order to design a multicomponent luminescent material. The photoluminescence studies indicated the significant effect of copper oxide upon the light emission due to europium ions while the emission from copper oxide is similar with that due to Cu⁺. The emission of europium ions in the Cu₂O:Eu³⁺-codoped glasses can be done through excitation of copper oxide.     

Albumin-containing sol–gel glasses: Chemical and biological study

Glasses incorporating increasing amounts of bovine serum albumin were prepared by sol-gel techniques from a tetra methoxy silane precursor. The surface of the glass samples was studied by X-ray photoelectron spectroscopy, revealing that the protein is present also in the superficial layer of the silica network. Moreover, the protein is distributed in a dose-dependent way, since the N/Si atomic ratio increases linearly with the albumin concentration in the reaction mixture. Angle-dependent measurements show that the protein distribution occurs homogeneously and is the same at different sampling depths. Protein incorporation in the bulk SiO2 network, with a uniform protein distribution between bulk and surface, is confirmed by infrared spectroscopy measurements, performed both in reflectance and transmittance mode. The reaction with a specific antibody and the adhesivity assay of osteoblastic cells show that embedded albumin present on the glass surface is able to interact with other proteins.     

Fire retardancy of sol–gel derived titania wood-inorganic composites

Sol–gel technology was applied in tailoring novel wood-made-inorganic composites with improved thermal and fire properties. In practice, composites materials were prepared by impregnating pine sapwood wood with nano-scaled precursor solutions derived from titanium(IV) isopropoxide followed by a thermal curing process. Thermal and fire properties were evaluated by thermal analysis and cone calorimetry, whereas flammability was specified by oxygen index (LOI) and UL 94 test. Peak heat release rates were moderately reduced indicating fire retardance potential in terms of flame spread attributed to the appropriate protection layer action of the titania-based depositions. LOI (oxygen index) values of these composites were increased up to 38 vol.% in comparison to 23 vol.% for untreated wood. The flame retardancy performance depends on the fire scenario and is strongly influenced by wood loading and crack-free deposition of the titania layers inside the composite.     

Surface morphology and optoelectronic studies of sol–gel derived nanostructured CdO thin films: heat treatment effect

Morphological dependence of the optoelectronic properties of sol–gel derived CdO thin films annealed at different temperatures in air has been studied. After preparing, the films were investigated by studying their structural, morphological, d.c. electrical and optical properties. X-ray diffraction results suggest that the samples are polycrystalline and the crystallinity of them enhanced with annealing temperature. The average grain size is in the range of 12–34?nm. The root mean square roughness of the films was increased from 3.09 to 6.43?nm with annealing temperature. It was observed that the electro-optical characteristics of the films were strongly affected by surface roughness. As morphology and structure changed due to heat treatment, the carrier concentration was varied from 1.13?×?10¹⁹ to 3.10?×?10^19?cm^?3 with annealing temperature and the mobility increased from less than 7 to 44.8?cm² V^?1 s^?1. It was found that the transmittance and the band gap decreased as annealing temperature increased. The optical constants of the film were studied and the dispersion of the refractive index was discussed in terms of the Wemple–DiDomenico single oscillator model. The real and imaginary parts of the dielectric constant of the films were also determined. The volume energy loss increases more than the surface energy loss at their particular peaks.     

Structural and pyroelectric properties of sol–gel derived multiferroic BFO thin films

Multiferroic BFO/PZT multilayer films were fabricated by spin-coating method on the (1 1 1)Pt/Ti/SiO₂/Si substrate alternately using PZT(30/70), PZT(70/30) and BFO alkoxide solutions. The structural and ferroelectric properties were investigated for uncooled infrared detector applications. The coating and heating procedure was repeated six times to form BFO/PZT multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without presence of the second phase such as Bi₂Fe₄O₃. The thickness of BFO/PZT multilayer film was about 200–220 nm. The ferroelectric properties such as dielectric constant, remnant polarization and pyroelectric coefficient were superior to those of single composition BFO film, and those values for BFO/PZT(70/30) multilayer film were 288, 15.7 μC/cm² and 9.1 × 10^?9 C/cm² K at room temperature, respectively. Leakage current density of the BFO/PZT(30/70) multilayer film was 3.3 × 10^?9 A/cm² at 150 kV/cm. The figures of merit, F_V for the voltage responsivity and F_D for the specific detectivity, of the BFO/PZT(70/30) multilayer film were 6.17 × 10^?11 Ccm/J and 6.45 × 10^?9 Ccm/J, respectively.     

Characterization and catalytic activity studies of sol–gel Co–SiO2 nanocomposites

Silica embedded with transition metals exhibits adequate properties for applications in catalysis, sensors and optics. Cobalt–silica (Co–SiO₂) nanocomposites were prepared by the sol–gel method and thermally treated at 700, 900, 1100 and 1250 °C. Characterization of the samples was performed by XRD and BET nitrogen adsorption. The performance of the nanocomposites was investigated by catalysis reactions of oxidation. These catalysts were found to be recyclable showing a catalytic activity even after a third recovering. The results indicate that thermal treatment of sol–gel nanocomposites at temperatures higher than 900 °C is essential for the preparation of active heterogeneous catalysts.     

FTIR and Raman spectroscopic investigation of some strontium–borate glasses doped with iron ions

Structural investigation of xFe₂O₃·(100 − x)[3B₂O₃·SrO] glass system, with 0 ≤ x ≤ 40 mol%, was performed by means of X-Ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies. The purpose of this work was to investigate the structural changes that appear in the 3B₂O₃·SrO glass matrix with the addition and increasing of iron ions content. The XRD pattern for the prepared samples shows that vitreous phase is present only for x ≤ 40 mol%. For sample containing 50 mol% Fe₂O₃ was evidenced the presence of a unique crystalline phase, Fe₂O₃, embedded in an amorphous matrix. FTIR data show that BO₃ and BO₄ are the main structural units of the glass system and the iron ions are located in the network. The Raman spectrum of glass matrix indicates a structure with several borate groups (di-, meta-, pyro-borate, etc.). In higher concentrations the iron ions break the regulate glass network and determines the appearance of BO₄ isolated units.     

Synthesis and thermomechanical characterization of polyimides reinforced with the sol–gel derived nanoparticles

Polyimide-based nanocomposites prepared by the in situ generation of inorganic nanoparticles (silica) through the sol–gel process were characterized by kinetics of water uptake, ther mogravimetry and dynamic mechanical analysis.

Silica particles turned out to possess a rather loose inner structure characterized by enhanced water diffusivities andby dynamic elasticity moduli comparable to that of the pristine, glassy PI. Thermal stability and thermomechanical properties of nano composites in the glassy state remained nearly the same as those of the pristine PI, while a significant reinforcement effect was observed for the rubbery PI matrix.     

Synthesis and thermomechanical characterization of polyimides reinforced with the sol–gel derived nanoparticles

Polyimide-based nanocomposites prepared by the in situ generation of inorganic nanoparticles (silica) through the sol–gel process were characterized by kinetics of water uptake, thermogravimetry and dynamic mechanical analysis.Silica particles turned out to possess a rather loose inner structure characterized by enhanced water diffusivities and by dynamic elasticity moduli comparable to that of the pristine, glassy PI. Thermal stability and thermomechanical properties of nanocomposites in the glassy state remained nearly the same as those of the pristine PI, while a significant reinforcement effect was observed for the rubbery PI matrix.     

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.     

Electrical and dielectric properties of sol–gel derived mullite doped with transition metals

Highly crystallized mullite composite has been synthesized at 1000 °C and 1300 °C via sol–gel technique in the presence of transition metal ions such as cobalt, nickel and copper. The dielectric properties (dielectric constant, loss tangent and a.c. conductivity) of the composites have been measured at room temperature and their variation with increasing frequency and concentration of the doped metals has been investigated. The composite doped with nickel exhibits minimum dielectric constant of 3.15 at 0.002(M) concentration at a frequency of 1.5 MHz. Experimental data shows a linear increase in a.c. conductivity with increasing concentration of metal doping ions .The dielectric constant and loss tangent of the composites are within the range of requirements for commercial use in electronics.     

IR and Raman studies and effect of γ radiation on crystallization of some lead borate glasses containing Al2O3

IR and Raman spectra of glass ceramics based on PbO-Cr₂O₃-B₂O₃glass composition system have been studied. The bands characteristic of BO₃. and BO₄ functional groups are present in all the samples. An incorporation of Al₂O₃(up to 5 mol%) in the initial glass composition considerably changes the glass network structure and relative concentrations of BO₃ and BO₄ groups. The composition 50 PbO-20 Cr₂O₃-25 B₂O₃-5 Al₂O₃(in mol%) reveals a maximum fraction of boron in the BO₄ group. A sample of this composition heat treated at 850° C for 25 h shows a maximum crystallization fraction with Pb₂O · CrO₄ as a prominent crystalline phase. The glasses irradiated with rays inhibit the crystallization into the Pb₂O · CrO₄ phase. They also show relatively smaller thermal conductivity.     

Adsorptive properties of sol–gel derived hybrid organic/inorganic coatings

Hybrid organic-inorganic sol–gel derived coatings have been prepared by dip coating on glass substrates from alcoholic solutions of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), 3-aminopropyltriethoxysilane (APTES), 3-glycidoxypropyltrimethoxysilane (GPTMS) and phenyltriethoxysilane (PhTES). The hybrid materials have been fully characterized by means of solid state NMR spectroscopy and X-ray diffraction. The degree of cross-linking and the extent of interaction between silica and silsesquioxane phases appear dependent on the ratio between TEOS and organotrialkoxysilane and on the chemical features of the organic function linked to silicon, and influence the sorption ability towards aromatic compounds of hybrid films. The hybrid coatings have been put into an optical-grade quartz chamber placed into a UV–VIS–NIR spectrophotometer and the organic compounds have been allowed flowing through the chamber recording of molecule absorption spectra vs. time. Absorbance curves vs. time have also been collected at a fixed wavelength for different molecule-coating couples and simple kinetic models have been used for comparing the adsorption capability of the different films, which has been related to the chemical interactions between molecules and coatings.     

Structural and electrical studies on sol–gel synthesized fine particles of Mg–Ni ferrichromite

This is a novel way of synthesis with a unique combination of the chemical sol–gel and combustion process. The process is simple, inexpensive and less time consuming as compared to other wet chemical methods which resulting a nano-sized, homogeneous, highly reactive powder. The results revealed that the nitrate–citrate gel exhibits self-propagating combustion behaviour. The structural and electrical properties of the compounds were studied. X-ray diffraction measurements confirm the formation of single phase cubic spinel structure. We note a nonlinear relationship between the structure and composition due to Ni, which demonstrates that structural properties are strongly tied to the Ni substitution.     

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.