Gel-derived Precursor Research Articles

Printing Formation of Flexible (001)-Oriented PZT Films on Plastic Substrates.

High-quality, uniaxially oriented, and flexible PbZr0.52Ti0.48O3 (PZT) films were fabricated on flexible RbLaNb2O7/BaTiO3 (RLNO/BTO)-coated polyimide (PI) substrates. All layers were fabricated by a photo-assisted chemical solution deposition (PCSD) process using KrF laser irradiation for photocrystallization of the printed precursors. The Dion-Jacobson perovskite RLNO thin films on flexible PI sheets were employed as seed layers for the uniaxially oriented growth of PZT films. To obtain the uniaxially oriented RLNO seed layer, a BTO nanoparticle-dispersion interlayer was fabricated to avoid PI substrate surface damage under excess photothermal heating, and the RLNO has been orientedly grown only at around 40 mJ·cm-2 at 300 °C. The prepared RLNO seed layer on the BTO/PI substrate showed very high (010)-oriented growth with a very high Lotgering factor (F(010) = 1.0). By using the flexible (010)-oriented RLNO film on BTO/PI, PZT film crystal growth was possible via KrF laser irradiation of a sol-gel-derived precursor film at 50 mJ·cm-2 at 300 °C. The obtained PZT film showed highly (001)-oriented growth on the flexible plastic substrates with F(001) = 0.92 without any micro-cracks. The RLNO was only uniaxial-oriented grown at the top part of the RLNO amorphous precursor layer. The oriented grown and amorphous phases of RLNO would have two important roles for this multilayered film formation: (1) triggering orientation growth of the PZT film at the top and (2) the stress relaxation of the underneath BTO layer to suppress the micro-crack formation. This is the first time that PZT films have been crystallized directly on flexible substrates. The combined processes of photocrystallization and chemical solution deposition are a cost-effective and highly on-demand process for the fabrication of flexible devices.

Microstructure and dielectric properties of silver–barium titanate nanocomplex materials by wet chemical approach

To develop ceramic capacitors with a high effective dielectric constant, we attempted to fabricate BaTiO3 (BT) complexes with embedded Ag nanoparticles by wet chemical processes. Ag nanoparticle-adsorbed dendritic BT particles, Ag–BT hybrid particles, were synthesized from the sol–gel-derived precursor gel powders containing Ag, Ba, and Ti by hydrothermal treatment. These particles were pressed with BT fillers and TiO2 precursor nanoparticles into green compacts, and then, the green compacts were chemically converted into the Ag/BT nanocomplex compacts in Ba(OH)2 aqueous solution under the hydrothermal condition at 160 °C. The effective dielectric constant of the resultant Ag/BT nanocomplexes increases with an increase in Ag content. The maximal effective dielectric constant of approximately 900 was recorded for the nanocomplex with the Ag content of 10.7 vol %.

Detailed FT-IR spectroscopy characterization and thermal analysis of synthesis of barium titanate nanoscale particles through a newly developed process

BaTiO3 nanopowders were prepared at lower temperature and in shorter time span through a newly developed process. To reach an in-detail understanding of mechanism of the process, thermal analysis were performed using DTA/TGA and FT-IR techniques aided by in-depth discussions. The results indicated that thermal evolution of sol–gel-powder transformation consists of following steps: the vaporization of volatile organic solvents, the deformation of gel structure and pyrolysis of the Ba–Ti organic precursors, the decomposition of BaCO3 into BaO and CO2, reaction of resulted BaO with TiO2 to form BaTiO3. The results also elucidated the reaction pattern and formation mechanism of BaTiO3 nanopowders from gel-derived precursor.

Effect of sintering temperature on microstructure and transport properties of Li 3 xLa 2/3− xTiO 3 with different lithium contents

Li 3 x La 2/3− x TiO 3 (LLTO) powder with different lithium contents (nominal 3 x = 0.03–0.75) was synthesized via a simple sol–gel route and then calcination of gel-derived precursor at 900 °C which was much below the calcination temperature required for synthesizing the LLTO powder via solid state reaction route. The LLTO powder of sub-micron sized particles, derived from such sol–gel method, showed almost no aggregation. Starting from the sol–gel-derived powder, the LLTO ceramics with different lithium contents were prepared at different sintering temperatures of 1250 and 1350 °C. It demonstrated that our sol–gel route is quite simple and convenient compared to the previous sol–gel method and requires lower temperature for the LLTO. Our results also illustrated that lithium content significantly affects the structure and ionic conductivity of the LLTO ceramics. The dependence of the ionic conductivity on the lithium content, lattice structure, microstructure and sintering temperature was investigated systematically.

Mesoporous silica thin films prepared by argon plasma treatment of sol–gel-derived precursor

Argon plasma is used to generate the mesoporous silica thin films from sol–gel-derived precursor. Poly(ethylene glycol) (PEG, MW = 400) is employed as the template, i.e., the pore-directing agent as well as the binder. The influence of the plasma parameters (plasma power and processing time) on the mesoscopic properties of silica films are investigated by scanning electron microscopy (SEM), FT-IR, low-angle X-ray scattering (SAXS), and nitrogen adsorption isotherm. It is concluded that the plasma treatment is a promising way to remove organic templates and generate mesoporous thin films. Compared to the conventional thermal calcination methods, the plasma treatment provides a promising low-temperature, low-cost and time-saving preparation process.

Phase evolution of barium titanate from alkoxide gel-derived precursor

An acetate derived barium titanate gel was prepared and the phase developments were investigated by an in situ XRD technique at elevated temperatures in air and in O2, XPS and Raman spectrum measurements. The thermal conversion behavior of the precursor powder was followed by thermal analysis (DSC and TGA). BaCO3 could be formed through the organic substances combustion with the appearance of intermediates. It was found that the intermediate phases contained BaTi2O5, graphite and non-crystal carbon, which could react with BaCO3 to form BaTiO3 evolving large heat at 740.3°C (BaCO3 + BaTi2O5 + C + O2 = 2BaTiO3 + 2CO2). The oxygen atmosphere facilitates the formation reaction of barium titanium.

Green Cathodoluminescence Properties of Zinc Oxide Films Prepared by Excimer Laser Irradiation of a Sol–Gel-Derived Precursor

Green cathodoluminescent (CL) zinc oxide (ZnO) films were successfully prepared at a low substrate temperature (473 K) in air by KrF-excimer laser irradiation of a sol–gel-derived precursor (ELISG method). Structures and CL properties of the films irradiated by the laser at different energy fluences (Ef) were studied and compared with those of a film prepared by conventional heat treatment in a reducing atmosphere. The prepared ZnO films showed a green CL band peaking at around 510 nm, in addition to an ultraviolet CL band. The maximum intensity of the green CL was obtained from a film produced by laser irradiation at an Ef of 130 mJ/cm2. Near-IR spectroscopy suggested that the green CL intensity depends on free-carrier concentration of the films and is maximized at an appropriate concentration. The formation process of the green CL films by the ELISG method was discussed in terms of thermal and photoinduced effects induced by the laser irradiation.

Effect of LiF addition on the phase transition of sinterable β-spodumene precursor powders prepared by a sol-gel process

β-Spodumene (Li2O · Al2O · 4SiO2, LAS4) precursor powders were obtained through a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as starting materials and LiF as a sintering aid. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy with a wavelength dispersive spectrometer, and electron diffraction analysis were utilized to study the phase transition of the β-spodumene glass–ceramics prepared from the gel-derived precursor powders with LiF additive. For the LAS4 precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4.0 wt% LiF and sintered at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution and β-eucryptite (Li2O · Al2O3 · 2SiO2, LAS2) solid solution. When the LiF content was 5.0 wt% and the sintering process was carried out at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution, β-eucryptite solid solution (triclinic), and eucryptite [rhombohedral (hex.)]. When the LiF addition attains 3.0 wt%, the fully densified grains are formed, accompanied with an increase in grain size for LiF addition. At the triple junction of grain boundaries a second phase segregates which is identified to be β-spodumene solid solution. In the sintering period of LAS4 precursor powders with LiF additive, the grains converted to β-eucryptite solid solution and β-spodumene solid solution remains at the grain boundaries.

Characterization of nickel titanate synthesized by sol–gel processing

Previous studies indicated that oxides of titanium and nickel might be effective solid lubricants. In the current work, we synthesized a range of titanium and nickel oxides including nickel titanate (NiTiO 3) via wet-chemical processing. Coatings and powders made from the sol–gel-derived precursor solutions were characterized by X-ray diffraction, ellipsometry, and pin-on-disk tests. Nickel titanate monoliths were also made by traditional powder processing and characterized by X-ray diffraction, ellipsometry, dilatometry and micro-hardness measurements. These data assisted the characterization of the sol–gel-derived materials. Nickel titanate proved to be a stable oxide at elevated temperatures and exhibited lubricity under certain conditions.

A sintering study on the β-spodumene-based glass ceramics prepared from gel-derived precursor powders with LiF additive

Beta-spodumene (Li2O·Al2O3·4SiO2, LAS) powders were prepared by a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as precursors and LiF as a sintering aid agent. Dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED) were utilized to study the sintering, phase transformation, microstructure, and properties of the β-spodumene glass-ceramics prepared from the gel-derived precursor powders with and without LiF additives. For the LAS precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4 wt pct LiF and sintered at 1050 °C for 5 hours the crystalline phases were β-spodumene and β-eucryptite (Li2O·Al2O3·2SiO2). When the LiF content was 5 wt pct and the sintering process was carried out at 1050 °C for 5 hours, the crystalline phases were β-spodumene, β-eucryptite (triclinic), and eucryptite (rhombohedral (hex.)) phases. With the LiF additive increased from 0.5 to 4 wt pct and sintering at 1050 °C for 5 hours, the open porosity of the sintered bodies decrease from 30 to 2.1 pct. The grains size is about to 4 to 5 µm when pellect LAS compact contains LiF 3 wt pct as sintered at 1050 °C for 5 hours. The grains size grew to 8 to 25 µm with a remarkable discontinuous grain growth for pellet LAS compact contain LiF 5 wt pct sintered at 1050 °C for 5 hours. Relative densities greater than 90 pct could be obtained for the LAS precursor powders with LiF > 2 wt pct when sintered at 1050 °C for 5 hours. The coefficient of thermal expansion of the sintered bodies decreased from 8.3 × 10−7 to 5.2 × 10−7/°C (25 °C to 900 °C) as the LiF addition increased from 0 to 5 wt pct.