Key Engineering Materials Vols. 421-422

Abstract: Proton conducting ZrO2－yP2O5 (y = 1.0, 1.2, 1.4. 1.6, 1.8) electrolytes based on a shell-core structure were synthesized with diammonium hydrogen phosphate by a solid state reaction, and their conductivities were investigated by ac-impedance spectroscopy. Among the ZrO2-yP2O5 compositions, ZrO2－1.6P2O5 showed the highest proton conductivity of 0.13 Scm-1 at 250°C. The conductivity increased with increasing P2O5 molar ratio and were significantly influenced by heat-treatments in the preparation process. Polytetraflouroethylene (PTFE) was also mixed into these electrolytes in order to improve the mechanical strength and long term durability.

Abstract: Spherical C/LiFePO4 cathode materials were successfully prepared by spray pyrolysis. The saccharides such as monosaccharide and disaccharide or organic acid were used as carbon source. SEM observation showed that they had spherical morphology with particle size of about 1m. XRD analysis revealed that the olivine phase was obtained by heating at 700 °C under the atmosphere of argon/hydrogen (5 %). Electrochemical measurement revealed that the rechargeable capacity of LiFePO4 was significantly improved by the addition of carbon. The use of sucrose was most effective for the high rechargeable capacity and cycle stability.

Abstract: The Mn-doped pyrochlores Pb2Ru1.5Mn0.5O7- (PRMns) samples were synthesized by a precipitation method, followed by heat-treatments at temperatures of 300-800oC. Effects of the heat-treatments on their electrocatalytic activities for oxygen reduction reaction (ORR) were examined by semi-steady state voltammetry with a rotating ring-disk electrode in 0.1 M KOH solution at 70oC. The PRMns showed the best ORR activity for the 500oC-heat-treated PRMn. The onset potential of the ORR current was over 1.0 V vs RHE, and the efficiency of 4-electron reduction was almost 100%. The maximum in the ORR activity for the 500°C-heat-treated PRMn resulted from a trade-off effect between their crystallinity and specific surface areas.

Abstract: Effect of screen printing parameter such as squeegee speed was studied in this paper for the surface roughness of gold paste on the Ferro A6M LTCC tape. Roughness measurement was evaluated by 3D profilometer of the Ferro A6M LTCC tape co-fired with Au conductor paste.

Abstract: Spherical Ce0.8Sm0.2O1.9 precursor powders were synthesized by Aerosol Plasma pyrolysis using aqueous solution of metal nitrate. As-prepared powders obtained by this method have a spherical morphology with a nano size and submicron size. They had bimodal size distribution. The average size of primary particles was less than 100 nm. The concentrations of starting solution influenced to average particle size. The relative density of SDC pellet was highest when it was sintered at 1623 K. The relative density was 86 %. XRD, SEM, DTA-TG and BET analysis were used for determination of the composition, morphology, particle size and surface area.

Abstract: We synthesized nano-sized Eu-doped Y2O3 (Y2O3:Eu) phosphor powder by an ion-exchange po-lymer/water/oil (W/O) emulsion method using carboxymethyl cellulose (CMC) as the ion-exchange polymer, in which the CMC-(Y, Eu) gel formed was calcined at 800°C in air to convert into Y2O3:Eu particles. The obtained phosphor powder consists of unagglomerated particles with sizes in the range of 30-80 nm and exhibits strong red emission at 612 nm. This CMC/W/O method for producing nano-sized oxide powder has significant advantages over conventional solid-phase and chemical solution-based methods because this method can provide unagglomerated nanoparticles of oxide phosphor without employing any mechanical pulverizing process for reducing the particles’ size into the nanometer range; mechanical grinding, such as ball milling, of phosphor powders has been well known to cause a significant degradation of their luminescent properties.

Abstract: Fine TiO2 particles were synthesized from titanate precursor, Na16Ti10O28, dissolved in aqueous HNO3 solution. Crystalline rutile TiO2 powders were prepared by reflux of dissolved powders in the aqueous HNO3 solution under 100 °C. Prepared TiO2 powders were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy and BET specific surface area analysis.

Abstract: In order to perform the growth position control, PbTiO3 (x=0) (PTO) nanocrystals were deposited on atomically flat and non-atomically flat -Al2O3 substrates by RF magnetron sputtering. The atomically flat substrates with atomic steps and terrace are expected to induce the lateral growth along a terrace between the surface steps. In the case of the atomically flat, the nanocrystals got lined up along the atomic steps, and uniform nanocrystals were obtained on surface in same pitch.

Abstract: Barium titanate (BaTiO3) nanoparticles were prepared by two-step thermal decomposition method of barium titanyl oxalate nanoparticles with a size of 30 nm. The BaTiO3 particle sizes were changed from 12.3 to 142 nm by control of temperature at 2nd step. The X-ray diffraction (XRD) measurement revealed that a clear splitting of 002 and 200 planes was observed over 40 nm, and the c/a ratio of 1.0089 was obtained for the BaTiO3 nanoparticles with a size of 62.3 nm. This high c/a ratio in the BaTiO3 nanoparticles suggested that its mesoscopic particle structure was composed of very thin surface cubic layer below 5 nm. Thus, synchrotron XRD data were analyzed using a “two layers” model and a “three layers” model. The Rietveld analysis using the three layers model resulted in the particle structure with a cubic layer thickness of 2.5 nm and structure gradient layer thickness of 7.5 nm. Finally, the dielectric constant of these BaTiO3 nanoparticles with thin surface cubic layer was measured at room temperature, and the maximum dielectric constant over 30,000 was obtained at the nanoparticles with a size of 83.6 nm.

Abstract: Using the electrophoretic deposition (EPD) method, we prepared barium titanate nanoparticle (BT-NP) thin films by depositing BT-NP monodispersed in ethylene glycol monomethyl ether (EGMME) onto an electrically conductive substrate coated with polyacrylic acid (PAA). Deposition efficiency was increased compared to conventional EPD, and the uniformity of the film thickness was also improved as a result of the BT-NPs cohesion effect of the PAA coating on the substrate in addition to the electrophoretic deposition effect of the electric field. When low-molecular-weight PAA was used, the film was reinforced since PAA, which coats the substrate, diffused close to the surface of the BT-NP film during film formation. A crack-free BT-NP film was produced with a film thickness of several micrometers.