In present study, Ho₂O₃ and Dy₂O₃ doped Bi₂O₃ composite materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) were investigated. (Bi₂O₃)_{1-x-y}(Ho₂O₃)_x(Dy₂O₃)_y ternary systems (x=0.11, 0.13, 0.15 and y=0.01, 0.03, 0.05, 0.07) were fabricated using conventional solid-state synthesis techniques. The samples were characterized by means of X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, differential thermal analysis/thermal gravimeter, and the four-point probe technique. X-ray powder diffraction measurements indicated that all samples have the stable fluorite type face centered cubic (fcc) δ-Bi₂O₃ phase. Scanning electron microscopy micrographs of all of the samples showed that grain size distribution was uniform. Four-point probe technique measurements showed that the conductivity of the samples increase with increase of temperature. Additionally, it has been found that the maximum conductivity values of all samples fall in a range 8.44×10^{-2}-4.60×10^{-1} Scm^{-1} and their conductivity values corresponding to the intermediate-temperature region vary in the range 1.65×10^{-3}-2.30×10^{-1} Scm^{-1}. The activation energy values of the samples were calculated from łogσ graphics versus 1000/T using the Arrhenius equation. It was found that there is a good agreement between the activation energy values and conductivity values.
A standard composition for hard porcelain production was prepared by mixing 50 wt% kaolin, 25 wt% potassium feldspar and 25 wt% quartz. Calcined colemanite powders were added to the porcelain formulation by replacing the potassium feldspar up to 5 wt% to explore its effect on the rheological behaviour of porcelain slip casting. A rheological study has been carried out in order to optimize the processing of the slip casting by using a rotational stress-controlled rheometer. The measurements were performed at constant temperature (25°C) using a parallel plate configuration. Sweep measurements were then conducted in the shear rates ranging from about 0.1-1000 s¯¹. The stability of the suspensions with ammonium polyacrylate (Darvan 821A) was determined in order to select the suitable dispersant amount. In order to achieve casting of acceptable characteristics on a plaster of Paris mould, the slurry should have the appropriate thixotropic or shear-thinning behaviours. Therefore, the same favourable thixotropic behaviour of slurries of different amount of calcined colemanite powders, the solid contents of the slurries have been optimised.
In this study, microstructure and electrical properties of Ag-TiO₂ powders, which were prepared by a simple sol-gel method, are investigated. The sol was prepared from titanium iso-propoxide, Ti(OC₃H₇)₄ in iso-propanol (CH₃CHOHCH₃), used as solvent. AgNO₃ was used as the precursor for Ag. For the structural studies, the corresponding gels were allowed to dry naturally for about seven days, dried in an oven at 180°C for 30 min and then calcined at different temperatures (900, 1000 and 1100°C). The Ag-TiO₂ nanoparticles were characterized using differential thermal analysis/thermal gravimetry, scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction. The results X-ray diffraction indicate that pure Ag and TiO₂ powders are in rutile phase. However, calcination temperature had not significantly affected the crystalline structure of TiO₂. Scanning electron microscopy images of powders show an aggregation of small spherical particles of dispersed sizes. Annealing of the Ag-TiO₂ sample at high temperature produced more spherical particles, which aggregated to form bigger particles with porous structures. The electrical properties of the samples were measured using HMS-3000 Hall measurement system. The samples were found to be of n-type. The conductivity of TiO₂ samples have been explicitly increasing with calcination temperature and with Ag doping.
In order to investigate the influence of the number of layers on the properties of ZrO₂ thin films, we prepared one pure ZrO₂ film sample with five layers and Ce, Eu, and Dy-doped ZrO₂ samples with single layer, by spin-coating sol gel-method. The crystal structures of thin films were determined using X-ray diffraction, morphology of the samples was analyzed by scanning electron microscopy, and the optical properties of the samples were determined by ultraviolet/visible absorbance measurements. The results of these measurements have shown that the concentration of the dopants and the thickness of thin film layers play a vital role in the physical, chemical, and optical properties of the pure and doped ZrO₂ thin films.
In this study, using spin-coating sol-gel method we fabricated TiO₂ thin films, doped with different concentrations (1, 2, and 3 mole %) of Ce, Dy, and Eu. Characterization of the prepared samples was performed by means of the X-ray diffraction, scanning electron microscopy, ultraviolet visible absorption, and differential thermal and thermo gravimetric analysis. X-ray diffraction measurements have shown that in Eu and Dy-doped samples crystal structure consists of mixed rutile and the dominant anatase phases, however the Ce doped samples consist of anatase phase only. Scanning electron microscopy images have revealed that while average thin film thickness of the Dy-doped samples decreases with increasing concentration of Dy, the average film thicknesses of samples doped with Ce and Eu increases with increasing concentrations of these dopants. Ultraviolet visible absorption spectroscopy measurements have shown that while absorbances of the samples doped by 1 and 2 mole % of the dopants have nearly similar properties, these properties differ from each other for 3 mole % of the dopants. Finally, differential thermal and thermo gravimetric analyses have shown that the chemical reactions and weight losses of the samples have occurred at the expected temperatures.
TiO₂ with high photoactive wide band gap energy semiconductor has been studied intensively for its attractive applications as photo catalyst and solar cell. TiO₂ has three kinds of different crystal structures; anatase, brookite and rutile. TiO₂-nanoparticles could become valuable light emitting materials when they are doped with highly luminescent rare earth ions. In this study, Dy-Eu-Ag co-doped TiO₂ nano particles were prepared by electrospinning method. The crystal structures of nanofibers were determined X-Ray Diffraction device (XRD), morphology of the samples were analyzed by scanning electron microscope (SEM), and the optical properties of the samples were determined by ultraviolet/visible spectrometer (UV/VIS) measurements. Electrical and electronic properties of the sampled were determined using the data obtained from four point prob technique (FPPT).
GaInP nanofibers were formed on n-Si substrates by electrospinning method, using constant voltage (25 kV), height (6 cm), and flow rate (0.3 ml/h) during various process times (of 10, 20, 25 minutes). Characterization of the prepared samples was performed by X-ray diffraction, differential scanning calorimetry/thermal gravimetric analysis, scanning electron microscopy, and energy dispersive X-ray spectrometry. Furthermore, the current-voltage measurements of the GaInP/n-Si samples have been carried out. The obtained results show that I-V characteristics of all GaInP/n-Si samples fabricated with three thicknesses of GaInP layers are rather in a good agreement with the theory and that they exhibit rectifying properties.
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