Papers by Keyword: Perovskite-Type Oxide

Abstract: Ceramics powder of BaCe_0.54Zr_0.36Y_0.1O_2.95 (BCZY) was synthesized using three different methods namely sol-gel (SG), supercritical fluid (SC) and sol-gel assisted supercritical fluids (SGSF).The respective prepared samples were denoted as S1, S2 and S3. The calcined powder (T= 1100 °C) was analyzed using particle size analyzer (PSA), Pcynometer and scanning electron microscope (SEM). PSA showed a single particle size distribution (PSD) for all samples except for S3 which exhibits bimodial particle distribution. PSD of the samples were in the range of 295-396 nm for the primary powder and 712-820 nm for secondary powder. High relative powder density for S1, S2, S3 were recorded at 95 %, 93 % and 99 %, respectively. Morphology of the calcined powders by SEM micrograph revealed that S1 is in spherical shape, S2 is in cubic structure and S3 showed a mixture of spherical and rod-like structure. It was found that SG and SC produce a single shape of powder with lower density compared with SGSF.

Abstract: Electrochemical sensors based on tubular yttria-stabilized zerconia (YSZ) with the perovskite-type oxide as a sensing-electrode (SE), which is prepared by sol-gel method, were fabricated and examined for NO₂ detection in the temperature range 400~700°C. The results show that La_0.75Sr_0.25Cr_0.5Mn_0.5O₃(LSCM), shows extreme sensitivity to NO₂. The EMF varies linearly as a function of the concentration of NO₂ (0 ~ 463 ppm) at 500 °C.

Abstract: Perovskite-type oxide (LaCoO₃) fine powders were prepared by a polymer precursors (PP) methods at 300~500°C. The LaCoO₃ fine powder could be prepared at 380°C when the use of EDA and PEG for organic-and polymer-additives, respectively. The surface area of LCO was ca. 39m²/g. LCO thick-film could be prepared from the steady state suspension with the addition of AcAc or PVAby the EPD method at +10V, 3min.The current density of the LaCoO₃ film sensor was changed with changing HPO₄^2- concentration at +1.00 V vs. SCE. The device showed relatively good amperometoric response to H₂PO₄^- from 1.0x10^-5M to 1.0x10^-3M with the 90% response time of ca 2min. The LaCoO₃-based sensor also showed a good selectivity among the examined anions of NO₃^-, Cl^- and SCN^-.

Abstract: Polystyrene spheres were prepared by soap free emulsion polymerization method. The effects of styrene concentration, polymerization time and self-assemble methods on the diameter of the polystyrene spheres were investigated. Different size of polystyrene microspheres could be obtained by changing styrene concentration and polymerization time. Polystyrene templates with good uniform and highly ordered can be assembled by means of vertical deposition method. Based on this template, three-dimensional ordered macroporous (3DOM) perovskite-type oxides LaFeO₃ were successfully prepared which were confirmed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was also found that 1mol/L metal precursor solution which used ethanol solution of metal nitrates with citric acid addition gave the best 3DOM perovskite-type LaFeO₃ oxides. The pores are uniform, flexible and arranged in a highly ordered form.

Abstract: In this paper, a density functional theory based on the first-principles was employed to evaluate the adsorption of CH₄ onto the surfaces of BaZrO₃ catalysts. The absorption mechanism was derived by population and electronic states analysis on the basis of the electronic and surface structure calculations for BaZrO₃. The (001) surface was calculated to be the adsorption surface for CH₄ owing to its high stability. Comparing to that for CH₄ absorbed on (001) surfaces, the frontier energy state was found to the key factor in controlling the adsorption behavior, which is mainly contributed by oxygen and Zr ions of the B-site. The most favorite adsorption site for CH₄ was located at B-sites of BaZrO₃, where the A-site ions would adjust the charge of B-site ions and moreover affect the CH₄ adsorption. The results reported in this work may provide the fundamental understanding about the absorption of CH₄ inflammation catalysts with high-activity and high-stability.

Abstract: Novel sol-gel processing techniques of ceramic materials were developed for designing new functional environmental ion sensors. Wet-chemical preparation methods for metal-oxide thin-films, perovskite-type oxide thin-films, and solid-electrolyte discs could be developed by using solution techniques based on polymer precursors, etc. New electrochemical sensing techniques to hydrogen-phosphate ion with high sensitivity and selectivity were developed by the use of ceramic-based sensors. A sol-gel processing technique was developed for the preparation of La-based perovskite-type oxide thin-films using an acetylacetone (AcAc)-modified poly(vinyl alcohol) (PVA)-based polymeric precursor method. The AcAc modified PVA-based sol made it possible to deposit a thin-film as well as to lower the sintering temperatures. The La0.8Sr0.2CoO3 perovskite-type oxide thin-film electrode prepared at 500°C showed good properties of amperometric sensing to hydrogen-phosphate ion. A new solid-electrolyte ion sensor device using a Na+-ion conductor (Na5DySi4O12: NaDyCON) as an impedancemetric transducer and a perovskite-type oxide thin-film as a receptor has been further developed. The AC impedance of the device with a LaCoO3 receptor was found to vary logarithmically with increasing K2HPO4 concentration between 1.0 x 10-5 and 1.0 x 10-2 M at 10 kHz. The 90% response time was ca. 2 min at room temperature. The sensor showed a little sensitivity to NO3- at higher concentration, while no response was observed to the examined anions of Cl- and ClO4-.

Abstract: The electron density distributions in a series of metal oxides are calculated using the DV-Xα molecular orbital method. It is found that the logarithm of the electron density, logρ(r), decreases with the distance, r, from the oxygen nucleus, while keeping a constant slope relevant to oxygen atom. The magnitude of the slope is about 15.75 for O-1s electrons, and about 6.61 for O-2s, 2p electrons, being nearly close to the respective values of 16 and 8, expected from the radial distribution functions of hydrogen-like atom containing only one electron. The extent of the region for the O-2s, 2p electrons changes with metal species in the oxides, but the slope remains unchanged. Furthermore, it is shown that the nature of the chemical bonding is well represented in log (ρ _minZ-3) vs. 2(Z/n) r_{minb plots, where ρmin is the minimum electron density, rmin is the distance r at ρmin, Z is the atomic number, and n is the principal quantum number.}