Electrochromic properties of Al doped B-subsituted NiO films prepared by sol–gel

In this paper, Al doped B-substituted NiO films were prepared by sol–gel method. The effect of the Al content on the structure of the Al_xB_0.15NiO films were studied with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical and EC properties were examined by cyclic voltammetric (CV) measurements and UV–Vis spectrophotometry, respectively. Al doping could prevent the crystallization of the films, which exhibited much better electrochemical and electrochromic properties than undoped samples. The bleached state absorbance could be significantly lowered when the Al added. EC efficiencies measured at λ = 500 nm of the films with different Al doping content reach ～30 cm² C^?1, with a change in transmittance up to 70%.     

Optical properties of Nb-doped TiO2 thin films prepared by sol–gel method

In this work, we studied optical properties of pure and Nb-doped TiO₂ synthesized using a sol–gel method and deposited as thin films by spin-coating followed by annealing in air at 500 °C for 1 h. The surface elemental composition was derived from X-ray photoelectron spectra, while structure and surface morphology were investigated using X-ray diffraction and atomic force/scanning electron microscopy. Finally, the optical properties were investigated by means of UV–vis spectrophotometry and spectroscopic ellipsometry.The Nb content was determined from XPS measurements to vary between 1.8 and 4.3 at%. The XRD patterns of the deposited thin films, with a maximum thickness of about 56 nm, showed no diffraction peaks. As proven both by microscopy and spectroscopic ellipsometry studies doping TiO₂ with Nb modified the surface morphology of the samples; the grain size is increasing while the surface roughness decreases with the increase in Nb content. This is accompanied by a decrease in the refractive index and an increase of the extinction coefficient.     

Morphological,structural and ellipsometric investigations of Cr doped TiO2 thin films prepared by sol–gel and spin coating

Pure and chromium doped titanium dioxide (TiO₂) thin films at different atomic percentages (0.5%, 1.3% and 2.9%) have been elaborated on ITO/Glass substrates by sol–gel and spin–coating methods using titanium (IV) isopropoxide as a precursor. The surface morphology of films was investigated by scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM), the structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission microscopy (HRTEM). SEM and HRTEM show homogenous and polycrystalline films. XRD patterns indicate a phase transition from anatase to anatase-rutile leading to expand the absorption band of TiO₂ molecules around 520 cm⁻¹ in FTIR spectra. The optical constants such as the refractive index (n), the extinction coefficient (K) and the band gap (E_g) as well as the film thickness are determined using spectroscopic ellipsometry technique and Fourouhi–Blommer dispersion model. Results show three major changes; (i) the thickness of pure TiO₂ layer is 54 nm, which linearly decreases when the layer is doped with chromium and reaches 33 nm for a doping concentration of 2.9%, (ii) the band gap energy (E_g) is also linearly reduced from 3.24 eV to 2.80 eV when the Cr-doping agent increases, and, (iii) a phase transition from anatase to anatase-rutile is observed causing an increase in values of n(λ) for wavelength greater than 350 nm.     

The sintering behaviour,mechanical properties and creep resistance of aligned polycrystalline yttrium aluminium garnet (YAG) fibres,produced from an aqueous sol–Gel precursor

Continuous ceramic fibres are finding applications as reinforcements in ceramic matrix composites, and yttrium aluminium garnet (YAG) is a particularly attractive candidate material on account of its creep resistance at high temperatures. A continuous, aligned, 5·5 μm diameter polycrystalline YAG fibre was manufactured from an aqueous sol–gel precursor which contained chlorine, and compared to a similar nitrate containing YAG precursor fibre we have reported previously. The precursor sol was found to be stable at a higher concentration than the nitrate containing sol, and this resulted in denser gel fibres which demonstrated better sintering at equivalent temperatures, giving a 98·5% sintered YAG fibre at 1550°C with a grain size of only 1 μm. However, on firing in air, the fibres formed fully crystalline YAG between 800 and 900°C, a temperature 100°C higher than the fibres containing nitrate, and they were weakened by the presence of many hemispherical faults. It was shown that both of these features were due to the retention of chlorine until the onset of formation of the crystalline YAG phase, and a series of steaming experiments were devised to remove the halide before this process could occur. It was found that steaming the precursor fibre from 200 to 500°C over 3 h, followed by firing to the required temperature in air, removed the chlorine and the problems it caused in the formation of the YAG phase without any change in the sintering characteristics or grain size. The steamed fibres were of a strength and quality comparable to fibres drawn from organometallic precursors. Empirical friability measurements showed the strength was maintained after firing to 1550°C, although there was a deterioration in apparent strain to break of the aligned blanket product above 1200°C. Conversely, the creep resistance, measured using the BSR test, improved with increase in temperature. The fibres fired to 1550°C were fully relaxed at temperatures 100–150°C below that of coarser, larger YAG fibres previously reported with a 3 μm grain size and 120 μm diameter. However, when allowance was made for grain size, the difference in creep rates was within the range obtained by extrapolating previous data using lattice diffusion and grain boundary effect models. Fibres fired to 1400°C were much finer grained but only slightly inferior to the 1550°C fibre in terms of creep. The alumina sol used in this work contained a significant level of sodium, and this suggests that the creep rates are effected by grain boundary impurities, especially sodium. A sodium free sol has been procured and further work is recommended to clarify the effect of impurities and improve fibre properties.     

The study of BiCrxFe1−xO3 thin films synthesized by sol–gel technique

Cr-doped bismuth ferrite (BiCr_xFe_1?xO₃, BCFO) thin films were prepared by a sol–gel method with the value of x varying from 0 mol% to 10 mol%. The structures of the BCFO thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis was employed to represent the surface and cross-sectional morphologies of the thin films. Dielectric, electrical, ferroelectric and magnetic properties were measured by HP4294A, Keithley 4200, RT6000 and 6700 Magnet Controller at room temperature, respectively. The dielectric behaviour and insulation are improved in 3% Cr-doped BFO thin film which may be due to the reduced concentration of oxygen vacancies by 3% Cr doping.     

Crystallization behavior and sintering of cordierite synthesized by an aqueous sol–gel route

The purpose of the research was to investigate crystallization behavior and sintering of cordierite synthesized by a low-price aqueous sol–gel route starting from silicic acid and magnesium and aluminum salts. Viscous sintering of the gel occurred in the temperature range of 800–850 °C, followed by μ-cordierite crystallization at about 900 °C, which proves the homogeneity of the gel. Decreasing of μ-cordierite crystallinity in a wide temperature range prior to commencing of α-cordierite crystallization at about 1200 °C indicates reconstructive type of μ- → α-cordierite transformation. The transformation was fully completed at 1350 °C. The value of the Avrami parameter indicates that μ-cordierite crystallization was controlled by surface or interface nucleation, which implies that viscous sintering occurred in the primary gel particles, which leads to shrinkage, and thereafter nucleation occurred on the surface or interface of the particles. The overall activation energy of μ-cordierite crystallization was 382.0 kJ/mol. The sinterability of the powder obtained by calcination at 1300 °C, where well-crystallized α-cordierite was formed, was better than that of the powder obtained by calcination at 850 °C, where the most intensive shrinkage occurred before the onset of crystallization of μ-cordierite.     

Characterization of doped tin dioxide anodes prepared by a sol–gel technique and their application in an SPE-reactor

Anodes for the electrocatalytic oxidation of organic pollutants in water have been prepared by depositing novel Sb-doped SnO₂ material on Ti supports by the sol–gel technique. Surface analysis of the anodes by nuclear microprobe and XPS-measurements confirmed the formation of a doped film on the substrate. Large scale porous titanium electrodes, up to 50 cm², have been coated with doped SnO₂ for a galvanostatic solid polymer electrolyte (SPE) application, resulting in very low voltage across the stack, even without adding supporting electrolytes to the water. Assessment of the cell performance was carried out using N,N-dimethyl-p-nitrosoaniline (RNO) as a spin trap for ·OH-radicals and phenol as a standard organic contaminant. Kinetic studies were done for the formation of the ·OH-radicals.     

Phase evolution and electrical properties of lead zirconate titanate thin films grown by using a triol sol–gel route

Lead zirconate titanate (PZT) precursor sols were prepared using a triol based sol–gel route. Inorganics salts metal alkoxides lead acetate trihydrate [Pb(OOCCH₃)₂·3H₂O], titanium (IV) isopropoxide [Ti(OCH(CH₃)₂)₄], and zirconium n-propoxide [ZrOC₃H7)₄] were used as starting materials. Thin films were deposited by spin coating onto Pt/Ti/SiO₂/Si substrates. The samples were pre-heated (pyrolysis) on a calibrated hotplate over the temperature range of 200–400 °C for 10 min then firing at a temperature of 600 °C for 30 min. Randomly-oriented PZT thin films pre-heated at 400 °C for 10 min and annealed at 600 °C for 30 min showed well-defined ferroelectric hysteresis loops with a remanent polarization of 27 μC/cm² and a coercive field of 115 kV/cm. The dielectric constant and dielectric loss of the PZT films were 621 and 0.040, respectively. The microstructures of the thin films are dense, crack-free and homogeneous with fine grains about 15–20 nm in size.     

Structural,morphological, and magnetic characterization of bulk and thin films Y3Al5–xFexO12 (YAIG): From the perspective of aqueous sol–gel processing

An aqueous sol–gel method was used for the preparation of bulk Y₃Al_5–xFe_xO₁₂ (yttrium aluminum–iron garnet, YAIG) with the composition of x?=?0.0, 1.0, 2.0, 2.5, 3.0, 4.0, 5.0 and thin films with the composition of x?=?0, 3.0, 4.0, 5.0. The dip-coating technique was used for the preparation of Y₃Al_5–xFe_xO₁₂ films on a silicon (Si) substrate. The phase composition and surface morphology of both bulk and coatings were determined and compared. The synthesized powder samples were investigated by X-ray diffraction analysis, infrared spectroscopy, scanning electron microscopy, and Mössbauer spectroscopy. The data provide evidence that some sol–gel-derived powder specimens consist of magnetically ordered component, while others show paramagnetic behavior depending on the composition of the product. It was also shown that sol–gel processing route could be successfully used for the preparation of mixed-metal YAIG thin films.     

Coating of nano-sized ionically conductive Sr and Ca doped LaMnO3 films by sol–gel route

In this study, Sr and Ca doped LaMnO₃ thin ceramic films were coated on Al₂O₃ substrates by using a sol–gel route as the cathode material for SOFC. Nitrate precursors were used for the preparation of the thin film coating solution, and methanol and acetyl acetone were also used as the solvent and chelating agent, respectively. After the solution was prepared, an Al₂O₃ single crystal substrate was dipped into the solution. Then it was fired at 500 °C and annealed at 1025 °C for the crystallization. Coated films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), focused ion beam (FIB) and atomic force microscopy (AFM). Conductivity of the coated films was measured by the four probe Van der Pauw method. XRD, SEM, AFM and FIB characterizations of the coated film showed that the LaMnO₃ phase was formed, surface of the films was uniform and had homogenously distributed pores sized about 10 nm, mean grain size was about 60–80 nm and the film thickness was about 180 nm. The specific resistivity of the film was calculated to be 0.524 Ω m.     

Effects of annealing temperature on the microstructure,optical, ferroelectric and photovoltaic properties of BiFeO3 thin films prepared by sol–gel method

Bismuth ferrite thin films were prepared via sol–gel spin-coating method and the effects of annealing temperature on microstructure, optical, ferroelectric and photovoltaic properties have been investigated. The results show that the bismuth ferrite thin films annealed at 550 °C is single phase and the grain size increases with the rise of annealing temperature. The band gap of bismuth ferrite thin films annealed at 550–650 °C is between 2.306 eV and 2.453 eV. With the rise of the annealing temperature, the remnant polarization gradually decreases and the coercive electric field increases. The short circuit photocurrent density decreases with the rise of annealing temperature, and the open circuit photovoltage and the power conversion efficiency of bismuth ferrite thin films annealed at 550 °C are higher than the thin films annealed at higher temperature.     

Structural and electrical properties of sol–gel-derived Al-doped bismuth ferrite thin films

Al-doped BiFeO₃ (BiFe_(1?x)Al_xO₃) thin films with small doping content (x=0, 0.05, and 0.1) were grown on Pt(111)/TiO₂/SiO₂/Si substrates at the annealing temperature of 550 °C for 5 min in air by the sol–gel method. The crystalline structure, as well as surface and cross section morphology were studied by X-ray diffraction and scanning electron microscope, respectively. The dielectric constant of BiFeO₃ film was approximately 71 at 100 kHz, and it increased to 91 and 96 in the 5% and 10% Al-doped BiFeO₃ films, respectively. The substitution of Al atoms in BiFeO₃ thin films reduced the leakage current obviously. At an applied electric field of 260 kV/cm, the leakage current density of the undoped BiFeO₃ films was 3.97×10^?4 A/cm², while in the 10% Al-substitution BiFeO₃ thin films it was reduced to 8.4×10^?7 A/cm². The obtained values of 2P_r were 63 μC/cm² and 54 μC/cm² in the 5% and 10% Al-doped BiFeO₃ films at 2 kHz, respectively.     

Synthesis and microwave dielectric properties of pseudobrookite-type structure Mg5Nb4O15 ceramics by aqueous sol–gel technique

Pseudobrookite-type Mg₅Nb₄O₁₅ ceramics were prepared by aqueous sol–gel process and microwave dielectric properties were investigated. Highly reactive nanosized Mg₅Nb₄O₁₅ powders were successfully synthesized at 600 °C in oxygen atmosphere with particle sizes of 20–40 nm firstly and then phase evolution was detected by DTA-TG and XRD. Sintering characteristics and microwave dielectric properties of Mg₅Nb₄O₁₅ ceramics were studied at different temperatures ranging from 1200 °C to 1400 °C. With the increase of sintering temperature, density, ?_r and Q·f values increased, and then saturated at 1300 °C. Excellent microwave properties of ?_r ～11.3, Q·f ～43,300 GHz and τ_f ～?58 ppm/°C, were obtained finally. The sintering temperature of Mg₅Nb₄O₁₅ ceramics was significantly reduced by aqueous sol–gel process compared to conventional solid-state methods.     

Formation and characterization of p-type semiconductor CuCrO2 thin films prepared by a sol–gel method

This study adopted the sol–gel method to synthesize p-type semiconductor CuCrO₂ films and analyzed the effects of an annealing treatment, under a controlled argon atmosphere by changing the temperature and time, on the phase transformation, micro- and nano-structure, composition, and semiconductor properties of thin films. In the Cu–Cr–O phase transformation system, CuO, Cr₂O₃, and CuCr₂O₄ were the intermediate phases of the reaction for forming CuCrO₂: in the metastable state reaction process, the composite phases changed into a single phase, CuCrO₂; in the stable-state reaction process of CuCrO₂, carbon elements of precursors were released and eliminated; and finally the optoelectronic properties of the CuCrO₂ thin film were adjusted and changed. The CuCrO₂ thin film possessed cell- and polygon-like shaped microstructures. The carbon content in the CuCrO₂ film decreased, so the copper, chromium, and oxygen contents increased accordingly. The optical band gap of CuCrO₂ thin film increased from 2.81 eV to 3.05 eV, while the resistivity decreased. The nanoscale crystal was identified which also of the delafossite CuCrO₂ structure. Using the sol–gel method to prepare the CuCrO₂ thin films, an appropriate annealing temperature and time were helpful in forming the single-phase CuCrO₂; the decrease of precursor elements in the thin film could enhance the band gap and the conductivity of the material.     

Structural and optical studies on sol–gel derived ZnO thin films by excimer laser annealing

High-quality polycrystalline ZnO thin films were deposited onto alkali-free glasses at a temperature of 300°C in air ambience by combining sol–gel spin coating and KrF excimer laser annealing. The effects of laser irradiation energy density on the crystallization, microstructure, surface morphology, and optical transmittance of as-prepared ZnO thin films were investigated and compared to the results of thermally annealed ZnO thin films. The crystallinity level and average crystallite size of laser annealed ZnO thin films increased as laser energy density increased. The crystallinity levels and average crystallite size of excimer laser annealed (ELA) thin films were greater than those of the thermally annealed (TA) thin films. However, laser annealed thin films had abnormal grain growth when irradiation energy density was 175 mJ/cm². Experimental results indicated that the optimum irradiation energy density for excimer laser annealing of ZnO sol–gel films was 150 mJ/cm². The ELA 150 thin films had a dense microstructure, an RMS roughness value of 5.30 nm, and an optical band gap of 3.38 eV, close to the band gap of a ZnO crystal (3.4 eV).     

Corrosion protection behaviour of sol–gel derived N,N-dimethylthiourea doped 3-glycidoxypropyltrimethoxysilane on aluminium

The present work describes the anticorrosion features of inhibitor doped sol–gel coating on Al metal. Sol–gel coatings were prepared by using 3-glycidoxypropyltrimethoxysilane (GPTMS) as parent precursor. In order to improve the corrosion resistance property of coating, N,N-dimethylthiourea was added into the sol–gel matrix. The corrosion inhibitor doped sol–gel coating on metal was characterized by Fourier transform infrared analysis (FTIR) and scanning electron microscope (SEM). Inhibition effect of N,N-dimethylthiourea doped GPTMS coating on Al substrates in 1% NaCl solution was investigated using electrochemical impedance (EIS) and polarization studies. EIS results showed that the corrosion resistance of sol–gel coating significantly improved upon addition of N,N-dimethylthiourea. The study had outlined the nuances of doping an organic inhibitor to enhance the protection ability of sol–gel coating on Al metal.     

Effect of yttria on crystallization and microstructure of an alumina–YAG fiber prepared by aqueous sol–gel process

Continuous fiber development is needed for high performance and high temperature composites. Various methods have been used to make ceramic fibers. In this research, composite fibers (yttrium aluminum garnet (YAG)/Al₂O₃) were prepared by a sol–gel method using aqueous solution. They were synthesized from aluminum salt, aluminum metal, yttrium oxide and water used as solvent. Transparent gel fibers were obtained by immersing a thin wire into the viscous sol, then pulling it out by hand. The obtained fibers contained very fine grains with diameter ranging from 10 to 80 μm after heat treatment. When yttria content was increased, the crystallization of YAG shifted to a lower temperature, whereas the transformation temperature to α-Al₂O₃ shifted to a higher temperature. Nevertheless, the fibers with different amounts of yttria contained alumina and YAG after heat treatment at 1400 °C. The composite fibers had vermicular structure and were denser than alumina fibers. The yttria percent concerning the limits of this study (≤10 wt%) effected on fiber diameter. As the yttria content was increased, the fiber diameter increased, whereas grain size and densification of the composite fibers decreased.     

Conductivity of Co and Ni doped lanthanum-gallate synthesized by citrate sol–gel method

Solid solutions of Sr and Mg doped lanthanum-gallate (LSGM) with addition of 3 and 5 at% of cobalt and nickel at the B-site in ABO₃ perovskite structure were obtained using citrate sol–gel method. The synthesized powders were calcined at 900 °C and then finally sintered at 1450 °C for only 2 h, which resulted in approximately 95% density. Impedance spectroscopy was utilized for electrical characterization in the temperature range 200–600 °C. The activation energies calculated from impedance spectra for bulk and grain boundary conductivities were decreased by the addition of transition metals (Co and Ni) and subsequently the conductivity was increased. Two different regions were clearly distinguished in the plots ln(σT) vs. 10,000/T for grain boundary conductivities, indicating changes in the mechanism of charge transport with the temperature. It is concluded that addition of cobalt above 5 at% in the LSGM prepared by citrate sol–gel method does not enhance the electrolytic properties of LSGM. XRD results suggested possible coexistence of two perovskite crystalline phases in nickel doped samples. However, it is still more favorable for use in IT-SOFC applications than cobalt since it has less influence on the electrolytic domain of LSGM.     

Influence of annealing temperature on the structural and anti-corrosion characteristics of sol–gel derived,spin-coated thin films

Recently, an aqueous particulate sol–gel process using metallic chloride precursors was introduced to synthesize zirconium titanate. In this paper, the effect of annealing temperature on the structural and corrosion protection characteristics of spin-coated thin films obtained from this sol–gel system was investigated. Based on scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic reflectometry studies, it was found that the flatness and thickness of the thin films were decreased by increasing the annealing temperature. Also, the corrosion protection of stainless steel AISI 316L provided by the prepared coatings, as analyzed by electrochemical potentiodynamic polarization experiments in a simulated body fluid, was improved in this order: 500 °C-annealed sample<900 °C-annealed sample<700 °C-annealed sample, attributed to a compromise between the defect density and the adhesion of the films to the substrate.     

Leakage current and dielectric breakdown in lanthanum doped amorphous aluminum oxide films prepared by sol–gel

Dielectric Al_2−2xLa_2xO₃ (x=0.00, 0.005, 0.02, 0.05, and 0.10) thin films were fabricated on Pt/Ti/SiO₂/Si substrates by sol–gel spin coating. The surface morphology of Al_2−2xLa_2xO₃ thin film was observed by field emission scanning electron microscopy. The chemical state of the lanthanum in aluminum oxide films was analyzed using X-ray photoelectron spectroscopy (XPS), indicating that lanthanum reacts with absorbed water to form lanthanum hydroxide. J–E measurements were used to investigate the current conduction mechanism and breakdown behavior. The results show that La doping changes the conduction mechanism and makes influences on leakage current. The dominating conduction process of 10% La doped Al₂O₃ films turns into the space charge limited current (SCLC) mechanism in the field region ranging from 25 to 150 MV/m. The leakage current of the films with 10% La doping decreases by three orders of magnitude from 10⁻⁶ to 10⁻⁹ at the electric field of 25 MV/m. The breakdown strength increases with the increasing content of lanthanum.