Dielectric,piezo and ferroelectric properties of microwave sintered PbTiO3 synthesized by sol–gel method

Journal of Sol-Gel Science and Technology - Of all the piezoelectric ceramics, lead titanate (PbTiO3) has an important place as an electromechanical transducer. In the present article PbTiO3...     

Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol–gel process

Combination of the surfactant-free nonaqueous sol–gel approach with the microwave technique makes it possible to synthesize Fe₃O₄, CoFe₂O₄, MnFe₂O₄, and NiFe₂O₄ nanoparticles of about 5–6 nm and with high crystallinity and good morphological uniformity. The synthesis involves the reaction of metal acetates or acetylacetonates as precursors with benzyl alcohol at 170 °C under microwave irradiation of 12 min. Immersion of glass substrates in the reaction solution results in the deposition of homogeneous metal ferrite films whose thickness can be adjusted through the precursor concentration. If preformed nickel nanoparticles are used as a type of curved substrate, the ferrite nanoparticles coat the seeds and form core–shell structures. These results extend the microwave-assisted nonaqueous sol–gel approach beyond the simple synthesis of nanoparticles to the preparation of thin films on flat or curved substrates.     

Effect of Tb content on microstructure and ferroelectric properties of Bi4−x Tb x Ti3O12 thin films grown by sol–gel method

The effects of Tb substitution on the structural and electrical properties of ferroelectric Bi₄Ti₃O₁₂ (BTO) thin films grown on Pt/TiO₂/SiO₂/Si substrates by a sol–gel process have been reported. X-ray diffraction indicated A-site Tb substitutions did not change the polycrystalline bi-layered Aurivillius structure of the BTO, but a lattice distortion was observed. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10^?2 to 10^?4 A/cm² with the increase of x under 150 kV/cm. The remnant polarization (2P _r ) and dielectric constant (ε _r) increase firstly and then decreases with the increase of the Tb content. We observed a substantial increase in the remnant polarization (2P _r ) with Tb substitution and obtained a maximum value of~60 μC/cm² at an applied electric field of 500 kV/cm for x = 0.4. Moreover, this BTT-0.4 capacitor did not show fatigue behaviors after 1.0 × 10¹⁰ switching cycles, suggesting an anti-fatigue character.     

Preparation and properties of VO2 thin films by a novel sol–gel process

Vanadium dioxide (VO₂) thin films were fabricated using a simple and novel sol–gel process in which V₂O₅ was used as the vanadium source; oxalic acid was used as the reducing agent; and polyvinyl alcohol was used as the film former to control the viscosity of the VO₂ precursor solution and bond vanadium ions. The microstructure and surface morphology of VO₂ films were studied by X-ray diffraction and scanning electron microscopy, respectively. The results showed that using polyvinyl alcohol forms porous nanostructure of VO₂ films with a uniform grain size of ~25 nm. The measured optical reflectance shows well-defined phase transition as observed by an increase of reflectance upon heating above the transition temperature from ~11 to ~30 % at 1,100 nm. Upon cooling, the expected hysteresis is observed.     

Deposition of silica thin films formed by sol–gel method

Deposition of silica thin films on silicon wafer was investigated by in situ mass measurements with a microbalance configured for dip coating. Mass change was recorded with respect to deposition time when the substrate was fully immersed in the silica sol. Mass gain during deposition was higher than predicted from monolayer coverage of silica nano particles. This implied that deposition was facilitated by gelling of the nanoparticles on the substrate. The rate of deposition was enhanced by increasing the particle concentration in the sol and by decreasing the particle size from 12 to 5 nm. Increasing the salt concentration of the silica sol at constant pH enhanced the deposition of the silica particles. Reducing the pH of the sol from 10 to 6 decreased the deposition rate due to aggregation of the primary silica particles.     

Effect of BiFeO3 doping on ferroelectric properties of Na0.5Bi0.5TiO3–BaTiO3 based thin film derived by sol–gel method

0.94Na_0.5Bi_0.5TiO₃–0.06BaTiO₃ (NBT–6BT) and (0.94 ? x)Na_0.5Bi_0.5TiO₃–0.06BaTiO₃–xBiFeO₃ (NBT–6BT–xBFO, x = 0.03, 0.05 and 0.08) thin films were deposited on Pt/Ti/SiO₂/Si substrates by a sol–gel process. Relative permittivity and remnant polarization were maximized at 5 % BFO substitution. Compared with 0.94NBT–0.06BT, the leakage current density of 0.89NBT–0.06BT–0.05BFO at 600 kV/cm is reduced by one order of magnitude. Enhanced ferroelectricity was also achieved in 0.89NBT–0.06BT–0.05BFO, the remnant polarization (2P _r) values of 0.89NBT–0.06BT–0.05BFO and 0.94NBT–0.06BT are 46 and 24 µC/cm².     

Structure and magnetic properties of La0.67Sr0.33MnO3 thin films prepared by sol–gel method

La_1?xSr_xMnO₃ (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO₃ (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively.     

Synthesis and characterization of tellurium-doped CdO nanoparticles thin films by sol–gel method

In this work, tellurium (Te) doped CdO nanoparticles thin films with different Te concentrations (1, 3, 5, 7 and 10 %) were prepared by sol–gel method. The effects of Te doping on the structural, morphological and optical properties of the CdO thin films were systematically studied. From X-ray diffraction spectra, it has seen that all of thin films were formed polycrystalline and cubic structure having (111), (200) and (311) orientations. The structure of CdO thin films with Te-dopant was formed the unstable CdTeO₃ monoclinic structure crystal plane ( $ {\bar{\text{1}}\text{22}} $ 1 ¯ 22 ), however, the intensity of this unstable peak of the crystalline phase decreased with the increase of Te-doping ratio. The strain in the structure is also studied by using Williamson-Hall method. From FE-SEM images, it has seen that particles have homogeneously distributed and well hold onto the substrate surface. Additionally, grain size increases from 27 to 121 nm with the increase of Te-doping ratio. Optical results indicate that 1 % Te-doped CdO thin film has the maximum transmittance of about 87 %, and the values of optical energy band gap increases from 2.50 to 2.64 eV with the increase of Te-doping ratio. These results make Te-doped CdO thin films an attractive candidate for thin film material applications.     

Cathodoluminescence properties of Pr3+-doped perovskite-type transparent red luminescent thin films processed by a sol–gel method

Transparent, luminescent films of Pr³⁺-doped (Ca_0.6Sr_0.4)TiO₃ (CSTO) have been prepared for cathodo-excitation of pure red luminescence by a sol–gel method from a stabilized sol with Ca²⁺, Sr²⁺, Pr³⁺ ions and titanium-isopropoxide in acetic acid. The structure and surface morphology of the obtained films are characterized by X-ray diffraction and Atomic Force Microscopy, respectively. The photoluminescence and cathodoluminescence (CL) properties of the films are evaluated. The films exhibit a strong single line of ¹D₂ → ³H₄ red photoluminescence of Pr³⁺ ions doped, which increases almost linearly with the number of the dip-coated layers. It is also found that strong single red photoemission is observed and the CL intensity increases with increasing acceleration voltage. The results demonstrate that it is potential for application in field-emission display devices.     

Structure and voltage tunable dielectric properties of sol–gel derived Bi1.5MgNb1.5O7 thin films

Bi_1.5MgNb_1.5O₇ (BMN) thin films were fabricated on Au/Ti/SiO₂/Si(100) substrates using a sol?Cgel spin coating process. Thermo decomposition of the BMN precursor gel was discussed. The structures, morphologies, dielectric properties and voltage tunable dielectric properties were investigated. The deposited films showed a cubic pyrochlore structure after annealing at 550?°C or higher temperatures. With the annealing temperature increased from 500 to 800?°C, the root-mean-square surface roughness of the films increased from 0.6 to 6.8?nm. Additional phase, MgNb₂O₆, emerged after annealing at 800?°C due to the volatilization of Bi element. The dielectric properties and tunability of the films were annealing temperature dependent. BMN thin films annealed at 750?°C had a high dielectric constant of 135 and low dielectric loss of 0.002 at 1?MHz. The high tunability of 31.3?% and figure of merit of 156.5 were obtained under an applied electric field of 1?MV/cm at room temperature.     

Photocatalytic and antibacterial activities of Ag-doped ZnO thin films prepared by a sol–gel dip-coating method

Silver-doped ZnO thin films with various loadings of Ag in the range of 0–10 mol% were prepared by the sol–gel dip-coating method. All prepared films show X-ray powder diffraction patterns that matched with ZnO in its würtzite structure. The grain size decreased as the Ag loading increased. The prepared films, under UV blacklight illumination, produced a photocatalytic degradation of methylene blue, rhodamine B and reactive orange solutions. Furthermore, they inhibited the growth of Escherichia coli bacteria under UV blacklight irradiation and to a lesser extent in dark conditions. The photocatalytic and antibacterial activities of the prepared films increased with Ag loading, presumably because Ag enhanced the efficiency of generation of superoxide anion radicals (^•O₂ ⁻) and hydroxyl radicals (^•OH).