Assembly of sol-gel-grown $Li _{(x)} CoO_{2}$ nanocrystals through electromagnetic irradiation

We report the fabrication of assembled nanostructures from the pre-synthesized nanocrystals building blocks through optical means of exciton formation and dissociation. We demonstrate that Li (x) CoO2 nanocrystals assemble to an acicular architecture, upon prolonged exposure to ultraviolet-visible radiation emitted from a 125 W mercury vapor lamp, through intermediate excitation of excitons. The results obtained in the present study clearly show how nanocrystals of various materials with band gaps appropriate for excitations of excitons at given optical wavelengths can be assembled to unusual nanoarchitectures through illumination with incoherent light sources. The disappearance of exciton bands due to Li (x) CoO2 phase in the optical spectrum of the irradiated film comprising acicular structure is consistent with the proposed mechanism of exciton dissociation in the observed light-induced assembly process. The assembly process occurs through attractive Coulomb interactions between charged dots created upon exciton dissociation. Our work presents a new type of nanocrystal assembly process that is driven by light and exciton directed.

Structural and optical investigations of TiO2 films deposited on transparent substrates by sol-gel technique

An inexpensive and effective simple method for the preparation of nano-crystalline titanium oxide (anatase) thin films at room temperature on different transparent substrates is presented. This method is based on the use of peroxo-titanium complex, i.e. titanium isopropoxide as a single initiating organic precursor. Post-annealing treatment is necessary to convert the deposited amorphous film into titanium oxide (TiO2) crystalline (anatase) phase. These films have been characterized for X-ray diffraction (XRD) studies, atomic force microscopic (AFM) studies and optical measurements. The optical constants such as refractive index and extinction coefficient have been estimated by using envelope technique. Also, the energy gap values have been estimated using Tauc's formula for on glass and quartz substrates are found to be 3.35 eV and 3.39 eV, respectively.

Structural and optical investigations of TiO2 films deposited on transparent substrates by sol-gel technique

An inexpensive and effective simple method for the preparation of nano-crystalline titanium oxide (anatase) thin films at room temperature on different transparent substrates is presented. This method is based on the use of peroxo-titanium complex, i.e. titanium isopropoxide as a single initiating organic precursor. Post-annealing treatment is necessary to convert the deposited amorphous film into titanium oxide (TiO2) crystalline (anatase) phase. These films have been characterized for X-ray diffraction (XRD) studies, atomic force microscopic (AFM) studies and optical measurements. The optical constants such as refractive index and extinction coefficient have been estimated by using envelope technique. Also, the energy gap values have been estimated using Tauc's formula for on glass and quartz substrates are found to be 3.35 eV and 3.39 eV, respectively. (C) 2008 Elsevier B.V. All rights reserved.

Sol → gel transition with rings in a finite polycondensing system in solution

We report a theoretical formulation for the mean cluster size distribution in a finite polycondensing system. Expressions for the mean number of n-mers with j bonds ( nj) are developed. Numerical calculations show that while the non-cyclic molecules make the dominant contribution to the small clusters, the large clusters are dominated by cyclic structures. The number of particles in ringless chains, n n,n-1, decays monotonically with n at all extents of reaction, but n n becomes bimodal near the gel point. We also find that the solvent plays an important role in the cluster size distribution.

Hybrid Sol-Gel Combustion Synthesis of Nanoporous Anatase

Nanoporous anatase with a thin interconnected filmlike morphology has been synthesized in a single step by coupling a nonhydrolytic condensation reaction of a Ti precursor with a hybrid sol-gel combustion reaction. The method combines the advantages of a conventional sol-gel method for the formation of porous structures with the high crystallinity of the products obtained by combustion methods to yield highly crystalline, phase-pure nanoporous anatase. The generation of pores is initiated by the formation of reverse micelles in a polymeric polycondensation product, which expand during heating, leading to larger pores. A reaction scheme involving a complex formation and nonhydrolytic polycondensation reaction with ester elimination leads to the formation of ail extended Ti-O-Ti network. The effect of process parameters, such as temperature and relative ratio of cosurfactants, on phase formation has been studied. The possibility of band gap engineering by controlled doping during synthesis and the possibility of attachment of molecular/nanoparticle sensitizers provide opportunities for easy preparation of photoanodes for solar cell applications.

Sol-Gel Template Synthesis, Structural Characterization and Growth Mechanism of Barium Zirconate Nanotubes

In this paper, we report the synthesis of barium zirconate, BaZrO3, (BZ) nanotubes fabricated by the modified sol-gel method within the nanochannels of anodic aluminum oxide (AAO) templates. The morphology, structure, and composition of as prepared nanotubes were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), selected-area electron diffraction ( SAED), high resolution TEM (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). The results of XRD and SAED indicated that postannealed (at 650 degrees C for 1 h) BZ nanotubes (BZNTs) exhibited a polycrystalline cubic perovskite crystal structure. SEM and TEM analysis revealed that BZNTs possessed a uniform length and diameter (similar to 200 nm) and the thickness of the wall of the BZNTs was about 20 nm. Y-junctions, multiple branching and typical T-junctions were also observed in some BZNTs. EDX analysis demonstrated that stoichiometric BaZrO3 was formed. HRTEM image confirmed that the obtained BZNTs were composed of nanoparticles in the range of 5-10 nm. The possible formation mechanism of BZNTs was discussed.

Fabrication and Phase Transformation in Crystalline Nanoparticles of PbZrO3 Derived By Sol-Gel

In this research fabrication of crystalline PbZrO3 (PZ) nanoparticles and their phase transformation behavior is investigated. A novel sol-gel method was used for the synthesis of air-stable and precipitate-free diol-based sol of PZ, which was dried at 150 degrees C and then calcined at 300-700 degrees C for 1 h. The morphology, crystallinity and phase formation of as synthesized nanoparticles were studied by the selected-area electron diffraction (SAED), X-ray diffraction (XRD), thermal gravimetric analysis/differential scanning calorimetry (TGA-DSC), and high resolution transmission electron microscope (HRTEM). The XRD, SAED, and TGA-DSC analyses confirmed the tetragonal lead rich zirconia phase (t-Z phase) and monoclinic zirconia phase (m-Z phase) as the intermediate phases during the calcinations process followed by crystallization of single orthorhombic PZ phase at about 700 degrees C. The average PZ particle size was observed about 20 nm as confirmed by TEM study. Energy-dispersive X-ray spectroscopy (EDX) analysis demonstrated that stoichiometric PbZrO3 was formed.

Dielectric anomaly in Li-doped zinc oxide thin films grown by sol-gel route

Sol-gel route was employed to grow polycrystalline thin films of Li-doped ZnO thin films (Zn1-xLixO, x=0.15). Polycrystalline films were obtained at a growth temperature of 400-500 degrees C. Ferroelectricity in Zn0.85Li0.15O was verified by examining the temperature variation of the real and imaginary parts of dielectric constant, and from the C-V measurements. The phase transition temperature was found to be 330 K. The room-temperature dielectric constant and dissipation factor were 15.5 and 0.09 respectively, at a frequency of 100 kHz. The films exhibited well-defined hysteresis loop, and the values of spontaneous polarization (P-s) and coercive field were 0.15 mu C/cm(2) and 20 kV/cm, respectively, confirming the presence of ferroelectricity.

Slim P‐E hysteresis loop and anomalous dielectric response in sol-gel derived antiferroelectric PbZrO3 thin films

Sol-gel derived PbZrO3 (PZ) thin films have been deposited on Pt(111)/Ti/SiO2/Si substrate and according to the pseudotetragonal symmetry of PZ, the relatively preferred (110)t oriented phase formation has been noticed. The room temperature P‐E hysteresis loops have been observed to be slim by nature. The slim hysteresis loops are attributed to the [110]t directional antiparallel lattice motion of Pb ions and by the directionality of the applied electric field. Pure PZ formation has been characterized by the dielectric phase transition at 235 °C and antiferroelectric P‐E hysteresis loops at room temperature. Dielectric response has been characterized within a frequency domain of 100 Hz–1 MHz at various temperatures ranging from 40 to 350 °C. Though frequency dispersion of dielectric behaves like a Maxwell–Wagner type of relaxation, ω2 dependency of ac conductivity indicates that there must be G‐C equivalent circuit dominance at high frequency. The presence of trap charges in PZ has been determined by Arrhenius plots of ac conductivity. The temperature dependent n (calculated from the universal power law of ac conductivity) values indicate an anomalous behavior of the trapped charges. This anomaly has been explained by strongly and weakly correlated potential wells of trapped charges and their behavior on thermal activation. The dominance of circuit∕circuits resembling Maxwell–Wagner type has been investigated by logarithmic Nyquist plots at various temperatures and it has been justified that the dielectric dispersion is not from the actual Maxwell–Wagner-type response.

Template-Assisted Sol-Gel Synthesis of Nanocrystalline BaTiO3

Nanocrystalline perovskite barium titanate with an average particle size less than similar to 10 nm is produced using sol-gel route involving ligand-assisted templating. BaTiO3 is obtained by the controlled hydrolysis and condensation reaction of barium acetate (Ba(CH3COO)(2)) with titanium tetra chloride (TiCl4) in the reverse micelles of dodecylamine (DDA) which is used as the template. Our attempts to produce mesoporous BaTiO3 have resulted in the formation of nanocrystalline BaTiO3. The synthesis of nanostructured BaTiO3 is carried out using the ligand-assisted templating approach which proceeds through the sol-gel route. Dodecylamine is used as the template. The sol-gel process in general presents inherent advantages because the nanostructure of the desired materials can be controlled together with their porous structure. Ligand-assisted templating approach involves the formation of covalent bond between the inorganic analogue and the template. Ba(CH3COO)(2) and TiCl4 are used as barium-source and titanium-source respectively. The reaction between Ba(CH3COO)(2) and TiCl4 is found to take place deliberately on the pre-assembled species which acts as the template or occurring with in them which in turn will lead to the generation of the desired nanoscale structure (nanopores or nanoparticles).

Sol-Gel Synthesis, characterization and optical properties of Tio2 thin films deposited on ITO/Glass substrates

TiO2 thin films have been deposited on glass and indium tin oxide (ITO) coated glass substrates by sol-gel technique. the influence of annealing temperature on the structural , morphological and optical properties has been examined. X-ray diffraction (XRD) results reveal the amorphous nature of the as-deposited film whereas the annealed films are found to be in the crystalline anatase phase. The surface morphology of the films at different annealing temperatures has been examined by atomic force microscopy (AFM). The in situ surface morphology of the as-deposited and annealed TiO2 films has also been examined by optical polaromicrograph (OPM). TiO2 films infatuated different structural and surface features with variation of annealing temperature. The optical studies on these films suggest their possible usage in sun-shielding applications.

Effect of La modification on antiferroelectricity and dielectric phase transition in sol-gel grown PbZrO3 thin films

Antiferroelectricity of sol-gel grown pure and La modified PbZrO3 thin films, with a maximum extent of 6 mol%, has been characterized by temperature dependent P-E hysteresis loops within the applied electric field of 60 MV/m. It has been seen that on extent of La modification electric field induced phase transformation can be altered and at 40 degrees C its maximum value has been observed at +/- 38 MV/m on 6 mol% modifications whereas the minimum value is +/- 22 MV/m on 1 mol%. On La modification the variation of electric field induced phase transformations at 40 degrees C has been correlated with the temperature of ntiferroelectric phase condensation on cooling. The critical electric fields for saturated P-E hysteresis loops have been defined from field dependent maximum polarizations and their variations on La modification show a similar trend as found in their dielectric phase transition temperatures. (C) 2010 Elsevier Ltd. All rights reserved.

Synthesis and Studies of Pb0.76Ca0.24TiO3 Nanoparticles Derived by Sol-Gel

Pb0.76Ca0.24TiO3 (PCT24) nanoparticles were synthesized by modified sal gel method and characterized by a number of experimental techniques such as X-ray diffraction, TGA-DTA, FTIR and transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDX). X-ray diffraction (XRD) and selected-area electron diffraction (SAED) investigations demonstrated that the postannealed (650 degrees C for 1 h) PCT24 nanoparticles have tetragonal perovskite crystal structure. TEM have been employed to characterize the morphology, structure and composition of the as prepared nanoparticles. Dielectric results indicates the evidence for relaxor type behavior while observed leaky ferroelectric loops may be because of the defects such as grain boundaries and the pores in the sample as the sample was not heated at higher temperature, to retain the nanosize dimension of the particles.

Wide Ranged La Modification in CCTO Ceramics Through Sol-Gel: Effect on Microstructure and Dielectric Properties

Sol-Gel method was employed to synthesize pure and wide ranged La-modified CaCu3Ti4O12 ceramics using mixed acetate-nitrate-alcoxide individual metal-ion precursors. SEM pictures revealed that grain size monotonously decreases with the extent of La incorporation. All the prepared ceramics manifested dielectric constant in the range similar to 10(3)-10(4). Dielectric loss was found to decrease with La incorporation and got optimized for 20% La3+ while retaining its high dielectric constant which may be industrially important. Room temperature Impedance spectroscopy suggested that decrease in grain resistance is responsible for reduction in dielectric loss according to Internal Barrier Layer Capacitor (IBLC) model.

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si Si(111)/SiO2/TiO2/Pt(111)]substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 degrees C) for 15 min. The films are polycrystalline at 650 degrees C and at other annealing conditions below 650 degrees C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 degrees C. These polycrystalline films exhibit spontaneous polarization of 1.5 mu C/cm(2) at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal. (C) 2010 Elsevier B.V. All rights reserved.