Advanced Materials Research Vols. 11-12

Abstract: Dense Mullite/Al2O3 ceramics with a thermal conductivity of 45 W/m.K were obtained at the sintering temperature of 1500°C using Li2O, CaO and Y2O3 as additives. At temperature below 1500°C, the shrinkage of Mullite/Al2O3 ceramics is promoted by liquid LiAlSi2O6 and Al2Y4O9. Liquid LiAlSi2O6 mainly improves the densification of the sample when the sintering temperature increases to 1500°C. The formation of liquid phase at a relatively low temperature results in homogeneous Al2Y4O9 and Ca(Al2Si2O8) distributed around the Mullite/Al2O3 particles, which benefits the thermal conductivity improved.

Abstract: We investigated the magneto-electric properties and electric properties of Cr2O3 thin films. Cr2O3 thin films were prepared on a thermal-oxidized Si substrate and a c-Al2O3 substrate. The sample prepared on the thermal-oxidized Si substrate had poly-crystalline structure. On the other hand, the sample prepared on the c-Al2O3 substrate has preferentially (006) oriented structure. Both samples had high enough resistivity to get a high induced magnetic moment. The induced magnetic moment by applying external voltage was observed on the oriented sample, although there was no induced magnetic moment on the same voltage for the poly-crystalline sample. This difference may be due to the random distribution of crystal and the leakage current caused by the Pool-Frenkel type defect in the poly-crystalline film.

Abstract: The nano SiC(N) composite powder was synthesized from hexamethyldisilazane ((Me3Si)2NH) (Me:CH3) by a laser−induced gas-phase reaction. The microwave permittivity of the nano SiC(N) composite powder and paraffin wax (or other dielectric materials) composites can be tailored by the content of this nano powder. The dissipation factors (tgδ) of the nano SiC(N) composite powder are high at the microwave frequencies. And ε′, ε″ and tgδ of composites increase with the volume filling factor (v) of nano SiC(N) powder. The nano SiC(N) composite powder would be a good candidate for microwave absorbing material and electromagnetic interface (EMI) shielding material. The classical effective medium functions can not effectively model the microwave permittivities of the SiC(N) nanocomposites. We found that the microwave permittivities of the nanocomposites can be effectively modeled using second-order polynomials. These polynomials are dependent only on the filling factor and are purely mathematical models. The ε′ and ε″ of nanocomposites can be effectively modeled using second-order polynomials (ε′, ε″=Av2+Bv+C).

Abstract: The phenomenon of the incorporation of hydrogen into a single crystal of 0.1 mol% Ba-doped α-alumina was studied using IR absorption analysis. A large wide band of IR absorption was observed. This band was attributed to the stretching vibration of the OH bond. The electrical conductivity of the specimens has been measured by the two-probe ac technique in the temperature range 1073-1673K. The H/D-isotope effect on the conductivity was observed. It was found that the dominant charge carrier of barium doped α -alumina is proton under the reducing atmosphere containing hydrogen.

Abstract: Sol-gel derived high proton conducting P2O5-SiO2-PMA (phosphomolybdic acid, H3PMo12O40 nH2O) glasses as electrolyte were used for the H2/O2 fuel cell performance at 30 °C under humidification with H2- based gas at the anode and O2- based gas at the cathode. The performance of the electrode was evaluated by the measurement of cell potential-current density plots. While the polarization curve yields data related to basic cell performance, more detailed information can be found by electrochemical measurements with an impedance analyzer. The power density shows a similar pattern to current density. The maximum power density value of 16.2 mW/cm2 was achieved with 0.1 mg/cm2 of Pt/C loading electrode and P2O5-SiO2-PMA (4-92-4 mol %) at 30°C with 30 % humidity. The glass membrane here plays a key role as electrolyte medium for proton transport and barrier to avoid the direct contact between fuel and oxygen.

Abstract: When fine-sized 45ZnO·55P2O5 or 50ZnO·50P2O5 glass powders were mixed with distilled water, hydration immediately occurred, resulting in the formation of viscous hydrogels. 31P MAS-NMR spectra showed that the hydrogels contain orthophosphates and long-chain phosphates; no significant differences in their structures between the hydrogels were shown. The 45ZP gel and 50ZP gel showed high conductivities (e.g., 9.9 and 2.8 mS/cm, respectively, at 30°C). The conductivities were related to the proton amount in the hydrogel; the amount in the 45ZP gel was larger than that in the 50ZP gel. Electric double-layer capacitors (EDCs) were prepared using electrolytes consisting of the hydrogels. The specific capacities of the EDC cell for the 45ZP gel and 50ZP gel were 2.40 and 2.06 F/g, respectively. The possibility as an EDC electrolyte may be related to proton conductivities of the hydrogels.

Abstract: Transparent indium-doped ZnO (IZO) films with low In content (<6at%) were fabricated through radio-frequency (rf) helicon magnetron sputtering. Formation of In-Zn-O solid solution was confirmed by X-ray diffraction (XRD) patterns. Incorporation of indium into ZnO films enhances the optical transmission in the visible wavelength. The optical band-gaps slightly increase from 3.25eV (ZnO) to 3.28eV (In0.04Zn0.96O) and to 3.30eV (In0.06Zn0.94O) due to Burstain-Moss effect. The Urbach tail parameter E0, which is believed to be a function of structural disorder, increases from 79meV (ZnO), to 146meV (In0.04Zn0.96O), and to 173meV (In0.06Zn0.94O), which is consistent with increase of Full-Width Half-Maximum (FWHM) in corresponding XRD patterns. Decreasing in crystal quality with increasing indium concentration is also confirmed by photoluminescence spectra.

Abstract: Alpha aluminum oxide (α-Al2O3) ceramics was coupled and reacted with zinc oxide (ZnO) ceramics at 1200°C for 24 h. Energy dispersive X-ray spectroscopy (EDS) analysis revealed the existence of step-shaped distribution of Al and Zn near the interface between α-Al2O3 and ZnO. Intense ultraviolet (3.75 eV) emission was clearly observed from the layer. On the other hand, very weak emissions were observed outside the layer near the interface. The compound in the layer is considered to be an attractive material for ultraviolet optoelectronics.

Abstract: Photochromic material Ag-TiO2 thin films are fabricated on quartz substrate by dual -target helicon magnetron sputtering. The phototchromic behavior is investigated for the sample loaded with 90% Ag. Spheres, ellipsoids and polyhedra shape of Ag particles with wide range size (5∼100 nm) are dispersed in the TiO2 amorphous matrix observed by transmission electron microscopy. The spectral hole burned by the irradiation of laser at the wavelength 532 nm can be explained by a particle-plasmon-assisted electron transfer from Ag nanoparticles to TiO2 and subsequent trapping by adsorbed molecular oxygen. Moreover, the mechanism of the slow recovery after photochromism is suggested as a slow thermal release of electrons from oxygen trapping centers and subsequent capture into the Ag nanoparticles.