Hybrid Sol-gel Process Research Articles

Preparation of functional poly (vinyl acetate)-Silica nanocomposites by hybrid sol-gel process

Nanocomposites of polyvinyl acetate and silica are prepared by sol-gel method. Samples are characterized using Infrared Spectroscopy, Thermal Analysis (TGA-DTGA) and X-ray photoelectron spectroscopy. In the hybrids with higher content of silica, it is evidenced the presence of hydrogen bonding between the residual silanols on the silicate network and the carbonyl of PVAc, this is determined by FTIR and XPS. It was also found that the hybrid containing 75% of silica suspension and 25% of polyvinyl acetate was the most thermally stable by TGA-DTGA.

Preparation and Characterization of Mullite Fiber-Reinforced Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Aerogel Composites

Mullite fiber-reinforced Al2O3-SiO2 aerogel composite was prepared through hybrid sol-gel process, vacuum pressure impregnation technology and ethanol supercritical drying technology using aluminum chloride hexahydrate (AlCl3·6H2O), tetraethoxysilane (TEOS) and mullite fiber as raw materials. The samples were characterized by XRD, SEM, BET, Hot Disk and Universal Testing Machine. The results showed that mullite fiber-reinforced Al2O3-SiO2 aerogel composite possessed excellent heat-insulation performance, high-temperature stability and mechanical property. The thermal conductivities of composite increased from 0.0186W/mK at 150°C to 0.1198W/mK at 1200°C. The surface area of Al2O3-SiO2 aerogel increased from 589m2/g at ambient temperature to 667m2/g at 600°C, and correspondingly the pore diameter increased from 21.47nm to 27.82nm. The phase of Al2O3-SiO2 aerogel was from boemite at ambient temperature to γ-Al2O3 at 600°C, and to mullite at 1200°C. The compressive strength was 1.8MPa, when the shape variables reached 10%, the tensile strength was 0.69MPa, the bending strength was 6.4MPa.

Phase and electrical properties of PZT thin films embedded with CuO nano-particles by a hybrid sol-gel route

Pb(Zr0.52Ti0.48)O3 or PZT thin films embedded with CuO nano-particles were successfully prepared by a hybrid sol-gel process. In this process, CuO (0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1 wt. %) nanopowder was suspended in an organometallic solution of PZT, and then coated on platinised silicon substrate using a spin-coating technique. The influence of CuO nano-particles’ dispersion on the phase of PZT thin films was investigated. XRD results showed a perovskite phase in all films. At the CuO concentration of 0.4–1 wt. %, a second phase was observed. The addition of CuO nano-particles affected the orientation of PZT thin films. The addition was also found to reduce the ferroelectric properties of PZT thin films. However, at 0.2 wt. % CuO concentration, the film exhibited good ferroelectric properties similar to those of PZT films. In addition, the fatigue retention properties of the PZT/CuO system was observed, and it showed 14% fatigue at 108 switching bipolar pulse cycles while the fatigue in PZT thin films was found to be 17% at the same switching bipolar pulse cycles.

Fabrication and Characterization of PZT/CuO Thin Film

Pb(Zr0.52Ti0.48)O3 or PZT thin films embedded with CuO nano-particles were successfully prepared by a hybrid sol-gel process. In this process, CuO (0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1wt%) nanopowder was suspended in an organometallic solution of PZT, and then coated on platinised silicon substrates using a spin-coating technique. X-ray diffraction patterns showed a perovskite phase in all the films. The CuO particles were not detected in the film, but the small amount of second phase was present when CuO concentration was above 0.4 wt%. The addition of CuO nano-particles also affected the orientation of PZT films. The CuO nano-particles were generally found to reduce both dielectric and ferroelectric properties of PZT films. However, at 0.2 wt% CuO concentration, the film exhibited good ferroelectric properties which were comparable to those of pure PZT thin films.

Preparation and Characterization of Amorphous SiO<sub>2</sub> Coating SiC<sub>p</sub>/Cu Composites

Hybrid sol–gel process was used to fabricate the precursor particles of amorphous SiO2 coating at the composites of SiCp⁄Cu, and then formed by Vacuum hot-pressed method. Various methods were used to measure the sintered compacts of different SiC volume fraction. The results showed that the densities, bending strength and conductivity were decreased slightly with the increases in the amounts of SiC, and the vickers hardness were increased first and then decreased. The techniques of DTA–TG, SEM–EDS and XRD were used to characterize the phases and the morphologies of the composite particles and composites. It was inferred that the formation of SiO2–Cu2O eutectic mixture in this system and the viscous interaction of amorphous SiO2 improved the interfacial modification of the composites of SiCp⁄Cu.

Ferromagnetic composite coatings on carbon fibers

Alumina- and titania-based composite coatings containing ferromagnetic nanoparticles have been produced on UKN-5000P carbon fibers by an in situ organo-inorganic hybrid sol-gel process using appropriate aqueous metal chloride solutions containing Fe(III) and Co(II). The morphology, phase composition, and elemental composition of the coatings have been studied by high-resolution electron microscopy, X-ray diffraction, and energy-dispersive X-ray microanalysis. The results demonstrate that the oxide coatings containing ferromagnetic nanoparticles are uniform in thickness along and across the fibers and adhere well to the fiber surface. The coatings range in thickness from 100 to 500 nm. In all of the systems studied, the coatings produced on carbon fibers differ in phase composition from powders prepared from identical hydrosols.

Microstructures, ferromagnetic, and ferroelectric properties in polyvinylpyrrolidone-assisted CoFe2O4/Pb(Zr0.53Ti0.47)O3 multiferroic composite thick films

CoFe2O4/Pb(Zr0.53Ti0.47)O3 (CFO/PZT) multiferroic composite thick films with different CFO mass fractions have been prepared onto Pt/Ti/SiO2/Si substrate by a hybrid sol–gel process and spin coating technique. Polyvinylpyrrolidone (PVP) was employed to be an assistance to the sol–gel solution for enhancing the film thickness and promising a crack-free film surface. After annealing at 650 °C in air for 1 h, phase structure, microstructure, magnetic and ferroelectric properties as well as leakage current of multiferroic thick films were investigated. X-ray diffraction indicated a deeply buried distribution of CFO particles in the PZT matrix. Scanning electronic microscopes showed crack-free surfaces and a decreasing film thickness from 7.2 μm to 6.2 μm with increasing CFO content. Furthermore, the saturated magnetization and remanent magnetization were also hence increased. In addition, mass fraction of CFO in PZT matrix was also estimated from 0.36% to 4.58% according to the relationship between Ms and magnetic content. Ferroelectric hysteresis loops revealed saturated polarization (Ps) and remanent polarization (Pr) were diluted by CFO till its mass fraction rising to 1.8%. After that, polarization was increased with further increasing CFO content. Enhanced leakage was demonstrated to be partially contributed to them. A critical content of 1.8% was hence confirmed, where ferroelectric and magnetic properties can be balanced, indicating a possible stress-transferred magnetoelectric coupling effect in this composite.

Ferromagnetic, ferroelectric and dielectric properties of Pb(Zr0.53Ti0.47)O3/CoFe2O4 multiferroic composite thick films

Pb(Zr0.53Ti0.47)O3/CoFe2O4 (abbreviated as PZT/CFO) multiferroic composite thick films have been prepared on the Pt/Ti/SiO2/Si substrate by using a hybrid sol–gel process. The thick films were finally annealed at 650 °C in air and the ferromagnetic, ferroelectric and dielectric properties of these films were investigated. Both the PZT pervoskite phase and the CFO spinel phase were detected from x-ray diffraction. The thickness of the film was measured to be about 3.55 µm using a surface profiler and was confirmed with scanning electron microscopy. Effective saturated magnetization (Mes) estimated from the measured saturated magnetization (Ms) was defined and the result shows that the Mes of the film fabricated in this work is larger than that of the thickest PZT/CFO film reported so far, so are the coercive magnetic fields (Hc). The properties of the films can be attributed to less constraints from the substrate to the composite thick films. The remanent polarization (Pr) of 12.5 µC cm−2 is comparable to that of the thickest PZT/CFO film reported so far due to the lack of polyvinylpyrrolidone (PVP), while the coercive electric field (Ec) of 252.8 kV cm−1 is much larger than it. In addition, the PZT/CFO thick films exhibit a smaller dielectric permittivity of about 200 within the whole measured frequency range due to the introduction of the low dielectric permittivity CFO phase. Furthermore, dielectric loss decreases to ∼0.01 with increasing frequency to 1 MHz, even lower than that of the PZT thick films. Although the ferroelectric properties and the dielectric constant of the PZT/CFO thick film were degraded compared with a pure PZT thick film, the coexistence of a promising ferromagnetic and ferroelectric response with a lower loss indicated that the PZT/CFO film is a good candidate for future applications in a reasonably high frequency range.

Electrical and physicochemical properties of Poly(3,4-ethylenedioxythiophene)-based organic–inorganic hybrid conductive thin films

Conductive polymer coating precursors were prepared using poly (3, 4-ehtylenedioxythiophene) (PEDOT) and three kinds of silane precursors (Q type, T type, and bridged T type) through an in-situ organic/inorganic hybrid sol–gel process. The spin-coated precursor films on Poly(ethyleneterephthalate) substrate exhibited fairly good surface resistance (~ 10 4 Ω/□), transparency (~ 80%) and pencil hardness (2 – 4 H). The solvent resistance of the film using 2, 5-bis (triethoxysilyl)-3, 4-ethylenedioxythiophene (BTES-EDOT) was excellent as compared with the films that used silane precursors due to a high degree of BTES-EDOT crosslinking in the hybrid film. Moreover, EDOT moiety in the BTES-EDOT molecule may contribute to homogeneous dispersion of the PEDOT in the organic–inorganic hybrid film.

Improving fatigue resistance of Pb(Zr,Ti)O3 thin films by using PbZrO3 buffer layers

Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films with PbZrO3 (PZ) buffer layers were prepared on Pt(111)∕Ti∕SiO2∕Si(100) substrates using a hybrid rf magnetron sputtering and sol-gel process. Texture of PZT films was found to depend on Pb content of PZ buffer layers. Buffered PZT films displayed comparable ferroelectric properties (2Pr=38–53μC∕cm2,2Ec=136–170kV∕cm) with unbuffered PZT. Asymmetric leakage current and fatigue behavior with superior fatigue resistance was observed in PZ buffered PZT compared to unbuffered films. PZ buffer layers were found to affect crystallization and texture of PZT, and act as a capacitive interface layer possibly blocking charge injection from electrodes.

Photoluminescence of Nanocrystalline Bismuth Titanate Thin Films Synthesized by the Sol-Gel Method

The present study is devoted to synthesis and investigation of photoluminescence in the nanosized Bi4Ti3O12 (BTO) thin films. The randomly oriented BTO thin films have been obtained by a modified hybrid sol-gel process. Bismuth nitrate and titanium (IV) butoxide were used as the starting materials. The thin films were deposited on silicon, glass and stainless steel by spin coating and crystallized by the conventional thermal annealing at temperature T=650°C. Formation of the layer perovskite-type structure of the orthorhombic symmetry was confirmed by X-ray diffraction method. Conservation of the chemical composition was investigated by energy dispersive spectroscopy. The UV luminescence has been observed in BTO thin films at room temperature. Results on luminescence excitation and emission in bismuth titanate thin films are given in the present paper.

Microstructure and properties of PZT53/47 thick films derived from sols with submicron-sized PZT particle

A hybrid sol–gel process technology has been developed for the fabrication of thick films of lead zirconate titanate (PZT) thick films. In this paper, submicron-sized PZT powder was dispersed into a 2-methoxyethanol (MOE) diluted PZT sol solution uniformly to obtain a suspension/slurry for spin-coating purpose. Thick films on platinized silicon substrate with thickness of 10 μm were obtained after annealing at 650 °C for 30 min. A higher sol solution concentration had larger single layer thickness, but a smaller one resulted in a more uniform surface. The resultant films have a composite microstructure. Dielectric and ferroelectric properties were investigated for all samples made from such process. Ferroelectric P– E hysteresis loop were obtained for most of them and the dielectric constant, remanent polarization, and coercive field for sample 3023 were 884, 20 μC/cm 2, and 95 kV/cm, which was comparable with bulk PZT ceramic.

Randomly oriented Bi 4Ti 3O 12 thin films derived from a hybrid sol–gel process

Randomly oriented ferroelectric Bi 4Ti 3O 12 thin films have been prepared by a hybrid sol–gel process. Crack-free and crystalline films of ∼1 μm thickness have been deposited on Pt/Ti/SiO 2/Si substrates. X-Ray diffraction (XRD) results show that predominant phase of Bi 4Ti 3O 12 can be obtained at 550°C, and the films are randomly orientated up to 700°C. The film annealed at 700°C, was measured to have a dielectric constant of 105, dielectric loss of 0.04, remnant polarization of 13.5 μC/cm 2, and coercive field of 60 kV/cm. The random orientation mechanism and the effect of annealing temperature on the dielectric and ferroelectric properties of the films were qualitatively discussed.