Seana Seraji

Template‐Based Growth of Various Oxide Nanorods by Sol–Gel Electrophoresis

The ability to form oxide nanorods is of great interest in a number of areas. In this paper, we report the template-based growth of nanorods of several oxide ceramics, formed by means of a combination of sol–gel processing and electrophoretic deposition. Both single metal oxides (TiO2, SiO2) and complex oxides (BaTiO3, Sr2Nb2O7, and Pb(Zr0.52Ti0.48)O3) have been grown by this method. Uniformly sized nanorods of about 125–200 nm in diameter and 10 μm in length were grown over large areas with near unidirectional alignment. Desired stoichiometric chemical composition and crystal structure of the oxide nanorods was readily achieved by an appropriate procedure of sol preparation, with a heat treatment (700 °C for 15 min) for crystallization and densification.

Organic–inorganic hybrid coatings for corrosion protection

Abstract The corrosion resistance of sol–gel derived, organic–inorganic, silica-based hybrid coatings with various amounts of organic content was studied. Hybrid sols were prepared by copolymerizing tetraethylorthosilicate (TEOS) and 3-methacryloxypropyltrimethoxysilane (MPS) with a two-step acid-catalyst process. Hybrid coatings were dip-coated on 304 stainless steel substrates and annealed at 300 °C for 30 min. Such prepared hybrid coatings were found to be relatively dense, uniform and defect free. The adhesion and flexibility of the coatings were characterized. The influences of the amount of organic component incorporated into the coatings and the aging of sols on corrosion protection were studied. Electrochemical analyses showed that the relatively dense hybrid coatings provided excellent corrosion protection by forming a physical barrier, which effectively separated the anode from the cathode. Some preliminary biocompatibility tests were also conducted on the hybrid coatings.

Electrophoretic Growth of Lead Zirconate Titanate Nanorods

rise to mesoporous nanoparticles with radial channels. The uniform fragment length within the interior of the nanoparticles can be explained by the radial nature of the deformation field around each defect, or site-specific breakage of the 300 nm long native TMV rods. Indeed, chemical degradation of TMV does produce a stable fragment about 50 nm in length, which is similar in size to those encapsulated in the silica shell of the nanoparticles. However, we observed only a random distribution of particle lengths in control samples containing broken TMV tubes. Further work is in progress to confirm the model. In conclusion, nematic liquid crystals of TMV can be used to prepare silica mesostructures and nanoparticles with parallel or radial arrays of linear channels, respectively. The mesostructures are produced as micrometer-size inverse replicas of the nematic phase, and have a periodicity of approximately 20 nm, which is larger than that generally attainable by current methods. In contrast, the nanoparticles are less than 150 nm in size and consist of a dense silica core surrounded by an unusual radial array of mineralized TMV fragments, 50 nm in length. The channeled nanoparticles are produced at lower reactant concentrations and appear to originate from topological defects associated with the deformation and fracturing of silica±TMV clusters as the liquid crystalline state is re-established in the reaction mixture. The general stability of TMV liquid crystals suggests that it should be possible to use a similar approach to prepare a wide range of inorganic oxides, semiconductors and metal-based mesophases and nanoparticles with mesostructured interiors.

Doping effect in layer structured SrBi2Nb2O9 ferroelectrics

This article reports a systematic study of doping effects on the crystal structure, microstructure, dielectric, and electrical properties of layer-structured strontium bismuth niobate, SrBi2Nb2O9 (SBN), ferroelectrics. Substitution in both the A site (Sr2+ by Ca2+ and Ba2+) and B site (Nb5+ by V5+) up to 30 at % were studied. It was found that crystal lattice constant, dielectric, and electrical properties of SBN ferroelectrics varied appreciably with the type and amount of dopants. The relationships among the ionic radii, structural constraint imposed by [Bi2O2]2+ interlayers, and properties were discussed.

Oxygen-vacancy-related dielectric relaxation in SrBi2Ta1.8V0.2O9 ferroelectrics

The strontium bismuth tantalate vanadate, SrBi2Ta1.8V0.2O9, (SBTV) layered perovskite ferroelectrics were made by solid state powder sintering. It was found that the SBTV ferroelectrics had the same crystal structure as that of strontium bismuth tantalate, SrBi2Ta2O9 (SBT), but an increased paraferroelectric transition temperature at ∼360 °C as compared to 305 °C for SBT. In addition, SBTV ferroelectrics showed a frequency dispersion at low frequencies and broadened dielectric peaks at the paraferroelectric transition temperature that shifted to a higher temperature with a reduced frequency. However, after a postsintering annealing at 850 °C in air for 60 h, SBTV ferroelectrics showed reduced dielectric constants and tangent loss, particularly at high temperatures. In addition, no frequency dependence of paraferroelectric transition was found in the annealed SBTV ferroelectrics. Furthermore, there was a significant reduction in dc conductivity with annealing. The prior results implied that the dielectric ...

Patterned Microstructure of Sol–Gel Derived Complex Oxides Using Soft Lithography

While the semiconductor industry continues to push the limits of small-scale devices, the cost of the equipment needed to achieve such small geometries has also kept similar pace. The average research lab does not have the funds to acquire, nor maintain the photolithographic and etching equipment needed to create such patterned structures. This unavailability of resources effectively prevents many groups from being able to perform research in cutting edge fields, such as microelectromechanical system (MEMS) technology, which require the ability to pattern a wide range of materials on a very small scale. Recently however, much attention has been given to a collection of non-photolithographic patterning techniques collectively known as soft lithography, which have the potential of becoming versatile and low cost methods for creating micrometer and sub-micrometer sized structures. To date, several devices have been fabricated using soft lithographic techniques, such as polymeric field effect transistors (FETs), electro-optic devices, Schottky diodes, and silicon metal oxide FETs (MOSFETs), to name a few. In addition to cost benefits, soft lithography has many advantages over traditional photolithography. Photolithography is very sensitive to surface topography. If the substrate to be patterned is not extremely flat, then acceptable results can not be obtained. In contrast, since an elastomeric mold is used in soft lithography, good conformity over curved surfaces is possible, and thus non-planar substrates can be patterned with ease. Material selection is another limitation of photolithography. Only photosensitive materials (such as photo-resists) can be directly patterned, and any other material that needs to be patterned must be susceptible to some type of etching technique. These restrictions seriously limit the arsenal of materials that can be used. On the other hand, with soft lithography, any material that can be derived from liquid precursor can be patterned, provided that the solvent used does not swell the elastomeric mold. Another benefit of this method is that it is an inherently mild process. As a result, many chemically and physically sensitive materials such as dyes and biomolecules can be patterned using this technique, showing again the versatility of this process. As a result of the vast potential of these techniques, many reports describing the use of soft lithography to create patterned structures can be found in the open literature. However, most of these experiments were focused on relatively simple, single component oxide systems or polymeric materials. No work on the direct patterning of complex oxide materials has been reported in the literature. However, these materials possess many important physical properties such as ferroelectricity, piezoelectricty, pyroelectricity, and high Tc superconductivity, which make complex oxides very useful for industrial and modern technological applications. For example, piezoelectric materials play a critical role in MEMS. As such, it would be very beneficial to develop a convenient and low cost method of patterning these materials. This report describes our preliminary work on patterning complex oxide ceramics using soft lithography in conjunction with sol±gel processing. Pb(ZrTi)O3 (PZT) and strontium niobate (Sr2Nb2O7), both of which are piezoelectric ceramics, were chosen as model systems to form patterned structures on silicon substrates using soft lithography. Specifically, the microstructures were patterned by micro-molding in capillaries, or MIMIC molding. In the preparation of the Sr2Nb2O7 sol, the inorganic precursors used were strontium nitrate Sr(NO3)2 (99 %) and niobium pentachloride (NbCl5) (99.8 %). The procedure implemented is outlined in the flowchart, Figure 1, which differs from other reported methods. Using ethylene glycol as a cross-linking agent and ethanol as a solvent, a transparent, stable sol was obtained. Although only 0.018 mol of water was added, hydrated citric acid was used, which provided the extra water needed to achieve the desired molar ratio of Sr/

Impedance study of SrBi2Ta2O9 and SrBi2(Ta0.9V0.1)2O9 ferroelectrics

This paper reports the electrical impedance properties of strontium bismuth tantalates (SBT) and strontium bismuth tantalate vanadate (SBTV) ferroelectric ceramics. AC impedance analysis was used to study the influences of vanadium doping and post sintering annealing on the microstructure and electrical properties. It was found that the vanadium doping resulted in the formation of fine-grained microstructure and an appreciable increase in dielectric constants, and Curie temperature. Post sintering annealing led to an increase in dielectric constants, but a reduction in dc conductivity. Possible mechanisms of the influences of vanadium doping and post sintering annealing on the electrical properties are discussed.

Influence of oxygen annealing on the dielectric properties of SrBi2(V0.1Nb0.9)2O9 ceramics

The influences of O2 and N2 annealing on the dielectric properties of SrBi2(V0.1Nb0.9)2O9 (SBVN) ferroelectrics were studied. Ceramic samples were prepared by reaction sintering a powder mixture of constituent oxides at 950 °C for 2 h in air. Some samples were also subsequently annealed at 800 °C for 3 h in O2 or N2. With O2 annealing, the Curie point of the SBVN ferroelectrics changed from ~433 to ~438 °C and the peak dielectric constant increased from ~760 to ~1010 (at 100 kHz). However, no change in the Curie point was found with N2 annealing. Furthermore, O2 annealing was found to reduce significantly both the dielectric constant and loss tangent of the SBVN ferroelectrics at frequencies below 1000 Hz. XRD results revealed a small reduction in the lattice constants with O2 annealing, but no appreciable change with N2 annealing. In addition, no detectable change in the microstructure of the SBVN samples was found with annealing. These results imply that some V4+ ions, which are compensated by the formation of oxygen vacancies, existed in the SBVN ferroelectrics prior to O2 annealing. V4+ ions were oxidized to V5+ with O2 annealing, which resulted in improved dielectric properties.

Processing and properties of vanadium doped strontium niobate

Strontium niobate was doped with vanadium and the resulting effects on the dielectric properties of the material were studied. It was shown that the single-phase slab perovskite structure was maintained with up to 10 at.% vanadium doping. Microstructure and dielectric properties of the samples were studied. The average grain size of the samples appeared to increase with increasing vanadium content and dielectric properties were significantly enhanced by the addition of vanadium. It is hypothesized that this is due to the smaller atomic radius of vanadium in comparison to niobium, which results in more ‘rattling space’ within the oxygen octahedron in the structure of the Sr2Nb2O7.