Effect of annealing temperature on the electromagnetic properties of La0.8Sr0.2MnO3 prepared by sol–gel process

Journal of Materials Science: Materials in Electronics - La0.8Sr0.2MnO3 (LSMO) powder was prepared using the sol–gel method and treated at different annealing temperatures (AT), and the...     

Preparation and luminescent properties of Eu-doped BaTiO3 thin films by sol–gel process

Eu-doped BaTiO₃ thin films with a pseudo-cubic perovskite structure were successfully fabricated on magnesia substrates at low temperature by using a high-concentration sol–gel process, in which the newly developed gel-aging process on substrate was employed. Film microstructure, crystallinity, sintering properties and photoluminescence (PL) were investigated. The xerogel thin films exhibited strong PL associated with Eu³⁺ ions under ultraviolet excitation at room temperature; the PL was visible to naked eyes. The intensity maximum of PL was reached with doping concentration of about 8 mol%. Sintering above 600 °C caused reduction of europium, resulting in a rapid quenching of Eu³⁺ emission and enhancement of Eu²⁺ emission.     

Characteristics of CeOx–VO2 composite thin films synthesized by sol–gel process

Pure vanadium dioxide (VO₂) and CeOx–VO₂ (1.5 < x < 2) composite thin films were grown on muscovite substrate by inorganic sol–gel process using vanadium pentaoxide and cerium(III) nitrate hexahydrate powder as precursor. The crystalline structure, morphology and phase transition properties of the thin films were systematically investigated by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, FE-SEM and optical transmission measurements. High quality of the VO₂ and CeOx–VO₂ composite films were obtained, in which the relative fractions of +4 valence state vanadium were above 70 % though the concentrations of cerium reached 9.77 at %. However, much of cerium compounds were formed at the edge of grains and the addition of cerium resulted in more clearly defined grain boundaries as shown in SEM images. Meanwhile, the composite films exhibited excellent phase transition properties and the infrared transmittance decreased from about 70 to 10 % at λ = 4 μm bellow and above the metal–insulator phase transition temperature. The metal–insulator phase transition temperatures were quite similar with about 66 °C of the pure VO₂ and CeOx–VO₂ composite thin films. But hysteresis widths increased with more addition of cerium, due to the limiting effect of grain boundaries on the propagation of the phase transition. Particularly, the CeOx–VO₂ composite film with an addition of 7.82 at % Ce showed a largest hysteresis width with about 20.6 °C. In addition, the thermochromic performance of visible transmittance did not change obviously with more addition of cerium.     

Biocompatible Nb2O5 thin films prepared by means of the sol–gel process

Thin biocompatible oxide films with an optimised composition and structure on the surface of titanium and its alloys can improve the implant integration. The preparation of these thin oxide layers with the intended improvement of the surface properties can be realised by means of the sol-gel process. Nb2O5 is a promising coating material for this application because of its extremely high corrosion resistance and thermodynamic stability. In this study, thin Nb2O5 layers ( < 200 nm) were prepared by spin coating of polished discs of cp-titanium with a sol consisting of a mixture of niobium ethoxide, butanol and acetylacetone. The thickness, phase composition, corrosion resistance and the wettability of the oxide layers were determined after an optimisation of the processing parameters for deposition of oxide without any organic impurities. The purity of the oxide layer is an important aspect in order to avoid a negative response to the cell adhesion. The biocompatibility of the oxide layers which was investigated by in vitro tests (morphology, proliferation rate, WST-1, cell spreading) is improved as compared to uncoated and TiO2 sol-gel coated cp-titanium concerning the spreading of cells, collagen I synthesis and wettability.     

Fabrication and characteristics of La,Cd and Sn doped BST thin films by sol–gel method

Ba_1−x Sr _x TiO₃ (BST) thin films doped with La, Cd and Sn were prepared by sol–gel method on the Pt/Ti/SiO₂/Si substrate. X-ray diffraction analysis and atomic force microscopy showed that dopant La and Cd causes decreased grain size of BST thin films obviously, and Sn-doped BST thin films was similar to BST films in grain size. La and Cd doped decreased the tunability of BST thin films and Sn doped increased it, which may be explained by stress, electronegativity and oxygen vacancies factors. All the doped BST thin films improved the leakage current characteristic.     

Optical properties and electrical resistivity of boron-doped ZnO thin films grown by sol–gel dip-coating method

Sol–gel dip-coating was used to grow ZnO thin films doped with various concentrations of B ranging from 0 to 2.5 at.% on quartz substrates. The effects of B doping on the absorption coefficient (α), optical band gap (E_g), Urbach energy (E_U), refractive index (n), refractive index at infinite wavelength (n_∞), extinction coefficient (k), single-oscillator energy (E_o), dispersion energy (E_d), average oscillator strength (S_o), average oscillator wavelength (λ_o), moments M₋₁ and M₋₃, dielectric constant (ε), optical conductivity (σ), and electrical resistivity (ρ) of the BZO thin films were investigated. The transmittance spectra of the ZnO and BZO thin films show that the transmittance of the BZO thin films was significantly higher than that of the ZnO thin films in the visible region of the spectrum and that the absorption edge of the BZO thin films was blue-shifted. The BZO thin films exhibited higher E_g, E_U, and E_o and lower E_d, λ_o, M₋₁ and M₋₃ moments, S_o, n_∞, and ρ than the ZnO thin films.     

Diffuse phase transition and leakage current characteristics of (Pb0.25Sr0.75)TiO3 thin films prepared by a sol–gel process

Nanocrystalline (Pb_0.25Sr_0.75)TiO₃ (PSrT25) thin films were grown on Pt/Ti/SiO₂/Si substrates by using a sol–gel process. The dielectric constant and loss tanδ of Au/PSrT/Pt thin-films capacitor were 345 and 0.016 at 100 kHz, respectively. The dielectric constant of PSrT film changes significantly with applied dc bias field and has a tunability of 22.7 % under an applied field of 150 kV/cm. Phase transition of the PSrT25 film has shown the diffuse-type phase transition behavior. The leakage current varied depending on the voltage polarity. At low electrical field and with Au electrode biased negatively, the Au/PSrT interface exhibits a Schottky emission characteristic, while at higher fields, Poole–Frenkel dominated the electronic conduction.     

The effect of stress on the magnetic properties of sol–gel-derived Pr0.9Ca0.1MnO3 thin films

The Pr_0.9Ca_0.1MnO₃ (PCMO) thin films prepared by sol–gel method suffered tensile and compressive stress grown on SrTiO₃ and LaAlO₃ substrates. The hysteresis loops at different temperatures show that the coercivity field with tensile stress is larger and the pinning potential of ferromagnetism motion is much stronger. The temperature dependence of the ZFC and FC magnetizations indicates that the stress significantly affects the ferromagnetic (FM) and antiferromagnetic transition temperature of PCMO, and the Curie temperature (T_C) decreases with tensile stress. The films show strong anisotropy properties that the magnetization increases much faster with the magnetic field when H⊥c, but the coercive field and saturation magnetization do not change significantly. In addition, the persistent photoinduced magnetization is investigated, and significant improvement of the FM ordering was observed in low temperature. And the saturation magnetization of each Mn ion is significantly affected by orientation and illumination.

     

La0.67Sr0.33MnO3中Ag-Ti的掺杂效应

将La0.67Sr0.33MnO3（LSMO）、Ag2O及TiO2粉混合经高温烧结后制备了钙钛矿相/xAg两相复合体系（x是Ag与钙钛矿材料的物质的量比）,系统地研究了Ag-Ti的共掺杂对LSMO电性和磁电阻效应的影响.0.07摩尔比Ti4＋离子的B位掺杂使LSMO的居里温度降至室温.Ag的掺入对Tc影响不大,Tp逐渐升高.由于钙钛矿颗粒属性的改善和金属导电通道的出现,材料的电阻率明显下降.Ag掺杂使室温磁电阻得到显著增强,室温下从x=0.30样品中得到最大的磁电阻,约为32%,是La0.67Sr0.33MnO3样品的8倍,La0.67Sr0.33Mn0.93Ti0.07O3样品的1.6倍.     

La0.67Sr0.33MnO3中Bi的掺杂效应

将Bi2O3掺杂到用溶胶—凝胶法制备的La0.6Sr0．33MnO3(LSMO)微粉中,XRD测量结果证实有过量的Bi析出。随着Bi掺杂量的增加,LSMO／(Bi2O3)x/2材料电阻率发生明显变化,在x=(0—0．10)摩尔比的掺杂范围内,电阻率先上升后突然下降。当X=0．1时,电阻率比未掺杂样品下降了一个数量级。Bi掺杂对低温和室温磁电阻有着完全不同的影响。低温下,随掺杂量增加,磁电阻下降;室温下Bi的微量掺杂可以使磁电阻增大,掺入x=0.03Bi使室温磁电阻由-4.4％提高到-5．6％。     

Post annealing effect on structural and optical properties of ZnO thin films derived by sol–gel route

Zinc oxide thin films have been spun coated on p-Si (100) substrates by sol–gel route. These films were annealed at different annealing temperatures from 300 to 1,000 °C in the oxygen ambient. In this way a suitable annealing temperature window for the sol–gel derived ZnO films exhibiting minimum defects (points and dislocations) and better quality (crystal and optical) was investigated. The structural and optical features of ZnO thin films have been examined by X-ray diffraction, atomic force microscopy, UV–Vis spectroscopy, and photoluminescence spectra. The results revealed that the crystallization in the films initiated at 300 °C, improved further with annealing. All the deposited films exhibited wurtzite phase with c-axis orientations. The variations in the position of characteristic (002) peak, stress, strain and lattice parameters are investigated as a function of annealing temperature. The optical band gap is not significantly affected with annealing as observed by UV–Vis transmission spectroscopy. The Photoluminescence spectra exhibited three luminescence centers. The near band edge esmission was observed in UV region which enhanced with the heat treatment, is an indication of improvement in the optical quality of films. The other two visible emissions are related to native defects in ZnO lattice were appeared only for higher annealing (≥700 °C).     

Preparation of nanocrystalline nickel oxide thin films by sol–gel process for hydrogen sensor applications

Preparation of nanocrystalline NiO thin films by sol–gel method and their hydrogen (H₂) sensing properties were investigated. The thin films of NiO were successfully deposited on the glass and SiO₂/Si substrate by a sol–gel coating method. The films were characterized for crystallinity, electrical properties, surface topography and optical properties as a function of calcination temperature and substrate material. It was found that the films produced by this method were polycrystalline and phase pure NiO. The H₂ gas sensitivity of these films was studied as a function of H₂ concentration and calcination temperature. The results indicated that the sol–gel derived NiO films could be used for the fabrication of H₂ gas sensors to monitor low concentration of H₂ in air quantitatively at low temperature range (< 200 °C).     

Characterization of integrated heterostructures of SbSI–La0.67Ca0.33MnO3

Heterostructures of ferroelectric antimony sulpho iodide (SbSI) and colossal magnetoresistive La_0.67Ca_0.33MnO₃ (LCMO) have been grown on NdGaO₃ substrates by pulsed laser deposition (PLD) technique. The integrated structure, with SbSI acting as a gate insulator and LCMO as a semiconductor channel, exhibited field effect along with a channel modulation of about 10%. This ferroelectric field effect has been observed at a voltage of only 2 V. The field effect was non-volatile, and very little change was observed in the channel resistance after more than 2 h. Polarization switching tests showed a small polarization loss of about 5% after more than 10⁷ bipolar switching cycles.     

Structure,morphology, photocatalytic and antibacterial activities of ZnO thin films prepared by sol–gel dip-coating method

ZnO thin films were deposited on soda lime glass substrates by the sol–gel dip-coating method with variations of the initial Zn²⁺ concentrations. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were used to investigate the effects of the initial Zn²⁺ concentrations on the structure, and surface morphology and topography of the prepared films. All prepared ZnO thin films showed a high transparency of over 88% in the visible region. The particle size increased with an increased initial Zn²⁺ concentration. This also reduced the surface denseness and the energy band gap of the ZnO thin films. All the prepared films showed photocatalytic properties through photodegradation of the methylene blue (MB) dye. The ZnO thin film prepared from the 0.1 M Zn²⁺ concentration showed the greatest efficiency as it had the highest surface area because of its greatest surface roughness. Furthermore, the prepared ZnO thin film showed antibacterial activities against the Escherichia coli bacterium.     

Effect of the Brij 30 porogen on the properties of sol–gel derived thin polymethylsilsesquioxane films

Thin polymethylsilsesquioxane films with Brij 30 porogen concentrations in the range ω_surf = 15.5–52.5 wt % have been produced by a sol–gel process. Their dielectric permittivity, refractive index, relative porosity, and shrinkage have been measured as functions of heat treatment temperature and porogen concentration.     

Orientation-dependent microwave dielectric properties of Ba0.6Sr0.4TiO3 thin films prepared by sol–gel method

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thin films have been prepared on the (100) LaAlO₃ single-crystal substrates by sol–gel technique. The X-ray diffraction study indicated that the thin films exhibited (100) preferred orientation and random orientation depending upon the concentration of precursor solution. The nonlinear dielectric properties of the BST films were measured using an interdigital capacitor. The temperature dependence of dielectric constant of the BST thin films was measured at 1 MHz in the temperature range from ?100 to 80 °C. The Curie temperature T _c of the films derived from 0.1, 0.2 and 0.3 M was found to be ?18.5, ?32.5 and ?39.9 °C, respectively. The tunability of BST films with the (100) preferred orientation was 30.74 %, which was much higher than that of thin films with random orientation at the frequency of 10 kHz with an applied electric field of 80 kV/cm. The microwave dielectric properties of the BST thin films were measured by a vector network analyser from 1 to 10 GHz.     

Effects of Mg doping on sol–gel derived nanocrystalline hydroxyapatite thin films

Abstract

Both pure and Mg doped thin films were fabricated by sol–gel dip coating. The films were sintered either at 800 or 1000°C. The average grain size of the films was significantly affected by Mg substitution in the hydroxyapatite (HA) structure and change in the sintering temperature. The grains were considerably larger in the films sintered at higher temperatures. In addition, Mg doped films contained significantly larger grains compared to undoped HA films. Mg doping also caused rodlike grains at 800°C, and led to whitlockite (β-TCP) formation at 1000°C. The ratio of the existing phases was estimated as β-TCP/HA=27 : 73. All the films had rough surfaces with high porosity. It was also observed that undoped films had higher surface roughness than Mg doped ones.     

Influence of precursor source on sol–gel deposited ZnO thin films properties

Zinc oxide thin films were deposited by sol gel technique on glass substrates using different precursors (zinc acetate, zinc nitrate and zinc chloride). In the present work we investigate the precursor nature influence on structural, morphological, optical, electrical properties and photocatalytic activity of ZnO thin films. For this purpose we have used X-rays diffraction (XRD), atomic force microscopy (AFM), UV–visible spectroscopy and Hall effect measurements for films characterization. The obtained results indicated that ZnO films properties are strongly influenced by the nature of the used precursor as reactant. Films photocatalytic activity was evaluated by the photo-degradation of methylene blue (MB) dissolved in aqueous solution under UV-A light. The obtained results indicated that ZnO thin films prepared from zinc acetate are more efficient than those prepared from zinc nitrate and zinc chloride.     

Influence of pH on ZnO nanocrystalline thin films prepared by sol–gel dip coating method

ZnO nanocrystalline thin films have been prepared on glass substrates by sol?Cgel dip coating method. ZnO thin films have been coated at room temperature and at four different pH values of 4, 6, 8 and 10. The X-ray diffraction pattern showed that ZnO nanocrystalline thin films are of hexagonal structure and the grain size was found to be in the range of 25?C45?nm. Scanning electron microscopic images show that the surface morphology improves with increase of pH values. TEM analysis reveals formation of ZnO nanocrystalline with an average grain size of 44?nm. The compositional analysis results show that Zn and O are present in the sample. Optical band studies show that the films are highly transparent and exhibit a direct bandgap. The bandgap has been found to lie in the range of 3 $\boldsymbol\cdot$ 14?C3 $\boldsymbol\cdot$ 32?eV depending on pH suggesting the formation of ZnO nanocrystalline thin films.