Sol-gel Precursor Solution Research Articles

Processing and characterization of Pb(Zr,Ti)O 3 thick films on platinum-coated silicon substrate derived from sol–gel deposition

Crack-free Pb(Zr,Ti)O 3 films up to 20 μm thick have been prepared on the Pt/Ti/SiO 2/Si substrate using a novel sol–gel route. In this route, surface-modified fine PZT crystalline particles are well dispersed in a sol–gel precursor solution to form uniform slurry. The slurry is then spin-coated onto a substrate, pre-heated and annealed at relatively low temperatures as the conventional sol–gel process. The surface modification of the added particles, microstructure and the crystallization process of the films have been investigated using field emission scanning electron microscopy (FESEM) and the X-ray diffraction (XRD). Finally, the ferroelectric and dielectric properties of the thick films have been reported. The novel route is promising to integrate ferroelectric thick films on the silicon substrate for potential applications in microelectromechanical systems (MEMSs).

The effect of the viscosity in the precursor solution on the structure of sol-gel derived silica films containing cobalt

Silica coatings containing cobalt have been prepared from sol-gel precursor solutions having a viscosity in the range of 3 to 40 cP. The different values of viscosity were achieved by aging the solutions with various amount of solvent (ethanol). The structure of these samples was analyzed using x-ray diffraction, Raman scattering, infrared absorption and Auger depth profiles. These measurements show that, upon heat treatments in air at 500°C, the cobalt oxidizes to form small oxide particles. However, when the coatings are prepared from precursor solutions with viscosity lower than about 9 cP, the cobalt migrates to the outer surface of the coating were it is oxidized to form the particles. On the other hand, if the coatings are prepared from solutions with a higher viscosity, the oxide particles are formed in the bulk of the coating. The infrared and Raman spectra indicate that the structure of this later set samples is more ordered with fewer amount of voids.

Studies of Lead Zirconate Titanate Sol Aging Part II: Particle Growth Mechanisms and Kinetics

The kinetics of particle growth in lead zirconate titanate sol gel precursor solutions has been investigated. It was found that chemical reaction limited aggregation was responsible for most of the sol aging, followed by diffusion limited aggregation in the later stage. At the beginning, particles grow by reaction between initial polymers and particles. As the particle number-density increases, a particle-particle aggregation characterised by an exponential growth law becomes the predominant mechanism. When particles grow larger, towards gel formation, the aggregation changes to diffusion limited. Mathematical models derived according to the above mechanisms agreed well with experimentally measured particle growth profiles.

Fabrication of Photocatalytic TiO<SUB>2</SUB> Films on Pure Aluminum Plates

TiO2 films were formed on aluminum plates by a dip-coating in an advanced sol-gel precursor solution, and the effect of sintering conditions on the photocatalytic properties of the oxide were investigated by UV adsorption. The samples prepared in this way exhibit photocatalytic activity in a range of suitable sintering conditions compatible with the region of crystallization of anatase characterized by X-ray diffraction. The surface morphology and adhesion between the TiO2 nano-film and aluminum plate were confirmed by energy filtering transmission electron microscopy, and the surface morphology was found to affect the photocatalitic activity. The TiO 2 film was 30 nm thick and was confirmed to be finely crystallines with a mean diameter of 12 nm.

Seeding effect on micro- and domain structure of sol–gel-derived PZT thin films

Current trend to miniaturization requires precise control of micro- and domain structure of ferroelectric materials at the nanoscale level. This is essential for future applications of ferroelectric thin films in non-volatile memories, microactuators and pyroelectric arrays. In this work, the seeding effect on the nanoscale properties of ferroelectric Pb(Zr,Ti)O 3 (PZT) thin films is investigated using scanning force microscopy (SFM) capable of simultaneously resolving topographic and domain features on the surface of the films. It is shown that the addition of 5 mol% seeds (fine PZT powder) into the sol–gel precursor solution completely modifies the film's microstructure leading to the improved morphology of the grains, reduced roughness and smaller microporosity. At the same time, significant imprint and instability of the written domain pattern is reduced due to the smaller influence of the bottom electrode interface.

Synthesis and luminescence properties of colloidal lanthanide doped YVO4

ABSTRACTAqueous colloidal solutions of well dispersed YVO4:Ln (Ln = Eu, Nd) nanoparticles are synthesized through precipitation reactions at room temperature. In the case of YVO4:Eu, a luminescence quantum yield of 15% is found, which is not as high as in the bulk due to the existence of residual crystalline defects and nonradiative relaxations from the hydroxylated surface. Appropriate hydrothermal annealing and deuteration of the surface allow to rise the yield up to 38%. Incorporation of the nanocrystals into a transparent silica matrix is achieved through preliminary coating of the particles with a functionnalized silicon alkoxide and further dispersion into a sol-gel precursor solution. Such sol-gel materials doped with YVO4:Nd nanocrystals are transparent and exhibit the typical emission at 1.06 μm of the Nd3+ ion.

Thick piezoelectric coatings via modified sol-gel technique

A hybrid sol-gel approach is reported for the deposition of high-quality composite PZT films of the thickness ⩾ 1 μm. In this approach, the metallo-organic sol-gel precursor solution is mixed with fine piezoelectric powders and dip-coated onto Pt/Ti/SiO2/Si substrates. Different organic viscous additives and deposition strategies were tried in order to deposit dense films with the properties approaching to those of bulk PZT. Using commercial PZT powder (TRS600FG) and ultrasonic mixing during deposition process, composite films having dielectric permittivity of ∼2500 and saturation polarization ∼35 μC/cm2 were obtained. These values are intermediate between bulk ceramics and conventional sol-gel PZT films and therefore are indicative of good piezoelectric properties.

Patterned Deposition of Sol-Gel Thin Films Using an Airbrush

ABSTRACT In this article, we present a method to pattern glass substrates with sol-gel derived thin films. This method is based on the aerosol deposition of sol-gel precursor solutions using an inexpensive, commercially available airbrush. The technique was demonstrated using Cy5-doped sol-gel thin films for the creation of wavelength conversion devices. The films deposited were mechanically and chemically rigid, and patterns could be achieved with a resolution limit of approximately 250 μm. Constructing channel waveguides was also attempted using both zirconium- and titanium-based sol-gel thin films. Deposited thin films of these materials showed graininess that limited the ability to couple light into the films and increased the observed scatter. However, light was successfully coupled into the titanium-based sol-gel film using small lens-like structures created on the glass surface.

Low temperature preparation of BaCeO 3 and Ce 0.75Zr 0.25O 2 thin films using sol-gel processing techniques

Barium cerate, BaCeO 3, powders and films were produced from sol-gel precursors. The formation of BaCeO 3 was achieved by calcining the sol-gel precursors either at 800°C overnight or at 1000°C for an hour, in contrast to 1400°C overnight in conventional solid-state preparation. Films with (200) preferred orientations were obtained on SrTiO 3(100) single-crystal substrates. Sol-gel precursor solution was also used to produce cerium zirconium oxide, Ce 0.75Zr 0.25O 2, at temperatures as low as 400°C. The Ce 0.75Zr 0.25O 2 so generated showed no structural change on heating up to 1100°C. The Ce 0.75Zr 0.25O 2 films produced were polycrystalline.

Low temperature formation of sol-gel derived ferroelectric lead zirconate titanate (Pb(ZrxTi1-x)O3, x = 0.3) thin films

Crack-free transparent thin films of ferroelectric Pb(Zr 0.3 ,Ti 0.7 )O 3 (PZT) with the perovskite structure were prepared by spin-coating a solution of complex alkoxides, followed by drying and then firing at the temperatures less than 500°C. The preparation of stock solution, erring, and firing of films are described. The coatings with selective orientations have been prepared by using selective processing parameters. The influence of low-temperature processing steps on texture development will be reported. The formation and growth of polymeric particles in the hydrolysis and condensation of PZT sol-gel precursor solutions have been investigated by using photon correlation spectroscopy (PCS). small angle x-ray scattering (SAXS) and by measuring their rheological properties. It has been possible to follow the growth of the particles in the sol by the different techniques used from initial values of <4nm up to ca 100nm. It has been shown that the particles are rods rather than spheres. The effects of particle shape and solution chemistry on the crystal phase formation and texture development will be discussed.

Size selected silicon particles in sol-gel glass by centrifugal processing

Centrifugal processing was used to induce size selectivity in Si particles suspended in a silica sol-gel precursor solution. A model was developed to describe Stokes settling of the silicon particles in the sol-gel medium whose viscosity increases exponentially with time eventually leading to hardening to a solid glassy material. An empirical modification to the theoretical model accounts for settling of particle agglomerates. Experimental results for polydisperse silicon particulates centrifuged in a sol-gel of tetraethyl orthosilicate catalyzed by phosphoric acid are reported; the particle size and spatial distribution in the gelled matrix are explained by the model. The utility of centrifugal processing to produce functionally graded materials and semiconductor nanostructures is discussed.

Determination of Particle Size and Shape during the Hydrolysis of Pb(Zr0.3Ti0.7)O3 Precursor Solutions

The formation and growth of polymeric particles during the hydrolysis and condensation of PbZr0.3Ti0.7 O3 (PZT 30/70) sol-gel precursor solutions have been investigated by using photon correlation spectroscopy (PCS), small angle X-ray scattering (SAXS) and by measuring their rheological properties. The measurements showed that the growth of the particles in the transition of PZT sol to gel followed a simple polymerisation process. Solution A (containing ‘by-products’) and Solution B (‘by-products’ removed) displayed a similar plot of logarithmic viscosity against logarithmic time, indicating that the particles in both solutions have similar structures after hydrolysis. The changes in viscosity and particle size with time were described by single logarithmic growth models. However, the increasing rate of logarithmic particle size in Solution B is higher than that in Solution A. A model for the form of the aggregates is discussed which is applicable to PZT organometal-particle aggregation process in systems with acetic acid as a modifier.

Preparation of SrBi2Ta2O9 thin films with a single alkoxide sol–gel precursor

Y. Kim, H. K. Chae, K. S. Lee and W. I. Lee, J. Mater. Chem., 1998, 8, 2317 DOI: 10.1039/A806275G

Combined flow and evaporation during spin coating of complex solutions

The flow and evaporation behavior from complex solutions during spin coating have been measured. Methanol/butanol mixtures where chosen as a controlled case-study for intensive evaluation. In addition, a sample sol—gel was evaluated using the same techniques. It was found that binary solutions had two identifiable thinning regions. At first, the thinning behavior is governed by the viscosity and evaporation rate of the starting mixture. However, near the end of the spinning process, the evaporation of the more volatile component has caused the fluid composition to change (toward the less volatile solution member). Therefore, the thinning behavior at the end displays a transition which approaches that of the pure end-member. The thinning behavior for the sol—gel precursor solution was linear until quite close to the gelation point, suggesting that further analysis of sol—gel solutions would be fruitful using this technique.

Preparation and fluorescence properties of nanocomposites of amorphous silica glasses doped with lanthanide(III) benzoates

Lanthanide(III) benzoate complexes are decomposed by a few drops of HCl and, thus, cannot be doped in amorphous silica glasses prepared by the acidic (HCl) hydrolysis of tetraethoxysilane (TEOS). This work presents a novel technique of homogeneous doping these complexes in silica gel glasses. Eu(III) (or Tb(III)) and benzoic acid are co-introduced in sol-gel precursor solutions with suitable pH. The nano-scale Eu(III) (or Tb(III)) benzoate complexes are confirmed to form in amorphous silica glass through controlled gelation and drying. The fluorescence spectra of Eu(III) (or Tb(III)) in nanocomposites and the energy transfer efficiencies between Eu(III) (or Tb(III)) and benzoate are studied.

Highly ordered polymer–inorganic nanocomposites via monomer self assembly: In situ condensation approach

A highly ordered organic inorganic nanocomposite can be synthesized by photopolymerizing an inverse hexagonal lyotropic liquid crystal phase consisting of an amphiphilic monomer and organic crosslinker as the organic matrix and a sol‐gel silica precursor solution as the hydrophilic component (see Figure). In situ silica condensation gives the ordered nanocomposite. A simple example is discussed.magnified image

Crystallization and Electrical Properties of Bi4TiO12 Films Derived from Bismuth Acetate and Bismuth Nitrate Precursor Solutions

ABSTRACTFerroelectric Bi4Ti3O12 thin films were prepared by the sol-gel method to examine the effect of precursors on the variation of ferroelectric properties. Two kinds of Bi4Ti3O12 sol-gel precursor solutions were synthesized by dissolving bismuth acetate and bismuth nitrate in glacial acetic acid and then adding titanium acetate. The films were deposited on Pt coated Si substrates by the spin-coating method and crystallized by double heat-treatment. The Ps, the Pr, and the Ec values of the film derived from the Bi-acetate were 34.8 μC/cm2, 16.2 μC/cm2, and 128 kV/cm, respectively. The Ps, the Pr, and the Ec of the films from the Bi-nitrate were 14.2 μC/cm2, 5.7 μC/cm2, and 105 kV/cm, respectively. The Bi4T3O12 films prepared from the Bi-acetate revealed better ferroelectricity and resistivity compared to those obtained from the Bi-nitrate.

Hybrid materials based on the reaction of polyorganophosphazenes and SiO2 precursors

New molecular composite materials can be prepared based on an inorganic oxide network and an organic polymer. The polymeric component generally requires low process temperatures, due to the presence of the organic backbone or side groups. A sol-gel process therefore is suitable for synthesizing the inorganic component by dissolving soluble polymers into sol-gel precursor solutions in order to obtain ceramic and polymeric solid phases. In this work polyorganophosphazenes were used because they have many technologically interesting properties (chemical, optical, electrical, mechanical). The methods to obtain covalent bonds between polymer and inorganic network and to obtain homogeneous, transparent hybrid materials without phase separation were studied. It was possible to avoid phase separation by preparing phosphazenes containing free hydroxyl functions and by adequately choosing the experimental conditions.

Microstructure of KTaxNb1−xO3 Thin Films on MgO (100) Single Crystals

Thin KTaxNb1−xO3 (KTN) films were prepared by deposition of sol–gel precursor solutions on MgO (100) single crystals. Crystal structure and microstructure of the films as a function of processing parameters, such as rate, duration, and temperature of postdeposition heat treatment, were studied. Several techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to analyze the films. It was observed that slow heating of KTN films promotes pyrochlore formation while fast‐firing of the films results in predominant formation of the perovskioe phase. In slow‐heated samples, TEM showed randomly oriented pyrochlore crystallites with a vermicular nanostructure of 10–30 nm with an interpenetrating porosity of the same range. In fast‐fired samples, large perovskite pockets with pyrochlore crystallites scattered among them were seen. The large perovskite grains were on the order of 0.1–0.5 μm, irregular in shape and porous. Transmission electron diffraction indicated these were single crystals, and ferroelectric domains were observed in them. Films of up to 1 μm thick were obtained by multiple deposition of the sol–gel KTN. Dense films were achieved when each layer was densified at 750°C for 2 h before the next layer was deposited.

An Investigation of Group (IV) Alkoxides as Property Controlling Reagents in the Synthesis of Ceramic Materials

Abstract Chemical synthetic methodologies are frequently employed to fabricate ceramic materials. To assist in determining methods for control over the final properties of ceramic materials, we have begun an investigation of the basic chemistry of solgel precursor solutions for lead zirconate titanate (PZT) thin films. The reactions between “M(OCHMe2)4” (M = Ti, Zr) and acetic acid were monitored by 1H, 13C, 17O NMR, and X-ray crystallography. The results of this investigation, the complexes generated, (Ti6(OCHMe2)12(OAc)4O4 1 Ti6(OCHMe2)8(OAc)8O4 2), and the types of films produced are reported. The synthesis of novel Group (IV) metal alkoxide complexes has been undertaken to generate precursors for ceramic materials with the desired characteristics internalized. In an attempt to reduce hydrolysis, the formation of a variety of metallo-organic compounds containing the sterically bulky adamantan-1-ol ligand (AdamO-H) was studied. It was demonstrated that the OCHMe2 ligands of “M(OCHMe2)4” (M = Ti, Zr) wer...