Polycrystalline samples of perovskite-type Ba(ZnxNb1−x)O3−δ with 0 ≤ δ ≤ 0.5 [δ = (3x − 1)/2; 1/3 ≤ x ≤ 2/3] were characterized by means of thermogravimetry (TG) combined with gas chromatography (GC). The TG-GC experiments on the Ba(ZnxNb1−x)O3−δ samples revealed that these oxides are subject to water incorporation under humid atmospheres, and exhibit multiple steps of water desorption upon heating up to 873 K. The largely different desorption temperatures among these steps indicate a variety of water species being incorporated in different forms, such as physically/chemically adsorbed water molecules and hydroxide ions. For each sample, the number of hydroxide ions and thereby a nominal composition in an oxy-hydroxide form were quantitatively estimated. The total amount of the incorporated water species tends to increase as the oxygen deficiencies (δ) increase. The highly oxygen-deficient samples with δ = 0.4 and 0.5 were found to show significantly enhanced electrical conductivity at temperatures between 623 and 773 K in a humid atmosphere. The enhancement may be attributed to the additional contribution of proton conduction associated with the incorporated hydroxide ions.
As ionization potential (Ip) and electron affinity tunable amorphous oxide semiconductors, n-type amorphous Cd–In–Ga–O thin films are fabricated on SiO2 glass substrates by radio-frequency magnetron sputtering method. The Ip and electron affinity of the thin films are determined using ultraviolet photoelectron spectroscopy and ultraviolet–visible-near-infrared spectroscopy. The Ip is tuned from 6.5 to 7.1 eV by varying Ga concentration from ∼20 to ∼50%. In addition, the electron affinity shifts from 3.8 to 4.3 eV by varying Cd concentration. Carrier concentration and mobility strongly depend on Cd concentration for Cd concentrations greater than 50%. Carrier concentration (mobility) decreases (increases) with increasing Cd concentration. In contrast, the influence of Ga concentration seems to be greater for Cd concentrations less than 50%. Carrier concentration varies in the range of 1017 to 1020 cm−3. The maximum value of the mobility is 16 cm2 V−1 s−1.
Ionic conductivity of dodecyl sulfate (DS) anion [CH3(CH2)11OSO3−]-intercalated Mg–Al layered double hydroxide (LDH) was examined. Mg–Al DS LDH showed higher ionic conductivity under low humidity than Mg–Al CO32− LDH, the most typical LDH. The conductivity of Mg–Al DS LDH was 7.6 × 10−4 S cm−1 at 80°C 30%RH, whereas that of Mg–Al CO32− LDH was 1.1 × 10−4 S cm−1. This higher ionic conductivity is attributed to the increased amount of the adsorbed water with intercalation of DS anion. The increase of surface water probably provides a path for hydroxide ion conduction, which results in the higher ionic conductivity under low humidity. Additionally, Mg–Al DS LDH retained high ionic conductivity for a longer storage under low humidity.
A first-principles energy band calculation is performed with respect to the V5+- and (Ca2+, V5+)-doped Y2Ti2O7 supercells to elucidate the effect of Ca2+ doping on the electronic structure and optical properties of a V5+-doped Y2Ti2O7 pigment in the present study. The structural optimization calculation reveals that the theoretical lattice constant of the Y2Ti2O7 unit cell slightly increases when compared with that in the experimental data. The forbidden gap at the Γ point is estimated to be 2.78 eV. On the basis of the density-of-states analysis, the valence band (VB) of Y2Ti2O7 mainly comprises the O 2p states and hybridizes with the Ti 3d and Y 4d states. The conduction band (CB) can be divided into two energy regions. The lower CB comprises the Ti 3d states and hybridizes with the O 2p states, whereas the upper CB comprises the Y 4d, Ti 3d, and O 2p states. When Y2Ti2O7 is doped with a V atom, the VB width and bandgap are observed to expand by 0.7 and 0.2 eV, respectively, with respect to the pristine Y2Ti2O7. Two strongly localized peaks, corresponding to the V 3d states, appear in the bandgap. Further, three strongly localized peaks appear in the bandgap when V5+-doped Y2Ti2O7 is doped with a Ca atom. In the dielectric function calculation of the V5+-doped Y2Ti2O7, there is broad absorption from the O 2p VB states to the V 3d gap states as well as a VB–CB optical transition in the host crystal. When the V5+-doped Y2Ti2O7 is doped with a Ca atom, the distortion of the VO6 octahedron becomes large, leading to an increment of O 2p state densities near the valence-band maximum of the host. Thus, it is considered the momentum matrix elements between occupied states (O 2p states) and unoccupied states (V 3d states) becomes large in comparison with the case before a Ca doping.
In this study, wet impregnation method and sol–gel technique were used to prepare CoMo-based catalysts supported on two types of porous silicas containing calcium phosphate. The prepared catalysts were characterized using various techniques, such as N2 adsorption–desorption measurement, scanning electron microscope, X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), differential thermal analysis, and X-ray photoelectron spectroscopy. The catalysts were tested for ammonia decomposition to produce COx-free hydrogen. The results of the XRD and FT-IR measurements elucidated that the crystal structure of calcium phosphate on the silica supports was attributed to calcium hydroxyapatite (HAp). The addition of calcium phosphate changed the porous structures of the catalysts, and decreased their BET surface areas and total pore volumes. Furthermore, the catalytic activity of the CoMo-based catalysts was influenced by the amount of calcium phosphate added. It was observed that the ammonia conversion at 873 K was increased by a maximum of 12.6% when 0.5 wt% of calcium phosphate was added to the catalyst, while a further addition of calcium phosphate beyond 1.0 wt% inhibited the ammonia conversion. From this study, it was concluded that HAp could work as a promoter for ammonia decomposition.
We propose a facile and continuous direct nitridation method for synthesizing fine aluminum nitride (AlN) particles using a drop tube furnace. Aerosolized Al powder as the raw material was continuously supplied through the top of the furnace together with N2 as a carrier gas. Once in the furnace, the Al powder reacted with the N2 to form AlN. A particular advantage of this process is that it allows the continuous synthesis of fine AlN particles. In this study, either a mullite (Al2O3–SiO2) or an alumina tube was used to fabricate the furnace, and the products were collected in a crucible placed at the bottom. Upon heating the mullite tube from 1200 to 1400°C, AlN was formed once the temperature exceeded 1250°C, and its product content increased with temperature. When the flow rate of the N2 carrier gas was decreased from 4 to 2 L min−1, the amount of AlN formed increased due to the increased residence time in the reactor. The morphology of the particles obtained was radially aligned nanofibers with droplets on the tips of the fibers. Transmission electron microscopy revealed that the Si in the mullite tube reacted with Al to form eutectic Al–Si droplets on the Al surface, in which these droplets acted as a catalyst of vapor–liquid–solid AlN fiber growth. When the alumina tube was used (1800°C), nitridation of Al was enhanced and radially aligned AlN nanofibers with no droplets on the tips were collected, mainly in a filter at the exhaust port. These AlN nanofibers are thought to form via vapor–solid growth and are easily carried along with the N2 gas flow, resulting in their deposition on the filter. The products collected in the crucible contained coarse Al particles, which are formed via Al particle agglomeration and coarsening through melting.
Low content (0.1–3.4 wt %) Ag added ZrO2 catalysts were synthesized by a hydrothermal method for soot combustion catalysis. The thermal stability and microstructure were characterized by X-ray diffractogram, field emission scanning microscopy, surface area and X-ray Absorption Fine Structure (XAFS) measurement. Soot oxidation temperature of Ag/ZrO2 catalysts was able to be controlled by changing heat-treatment temperature for starting powders. The mixture of metallic Ag and ionic Ag2O was observed by the XAFS spectra, and catalysts maintaining thermal stability were modified by active Ag/Ag2O mixed state on ZrO2. The catalysts with only 0.9 and 3.4 wt % doping of Ag in ZrO2 were effective and a better candidate for diesel soot oxidation catalysis.
In this study, we investigated the preparation conditions of titanium nitride (TiN) through nitridation of nano-sized titanium dioxide (TiO2) without particle agglomeration. Synthesis of nanocrystalline TiN powder was attempted via ammonia (NH3) nitridation of nanocrystalline TiO2 powder. The nitridation behavior was investigated using thermogravimetry (TG) in an NH3 atmosphere. Non-isothermal TG experiments showed that nitridation of the nanocrystalline TiO2 powder began at ∼750°C. Two types of experiments were performed using isothermal TG. In the first experiment, an argon atmosphere was used while heating at 5 °C/min. On reaching the holding temperature (900 or 1,000°C), the atmosphere was changed to NH3/Ar (50/50 kPa). This atmosphere was used throughout the second experiment. The first experiment produced a nitride powder with severely agglomerated particles. In the second experiment, nano-sized powder particles with inhibited agglomeration were obtained, and long holding time of 6 h at 900 or 1,000°C was effective in obtaining the small nitrided particles.
Intercalation treatments of azo compounds were performed in the interlayer space of α- and γ-zirconium phosphates (ZrP). X-ray diffraction patterns confirmed that the intercalation of the azo compounds into α-ZrP occurred via an octylamine intercalated intermediate. CHN elemental analysis indicated that the azo compounds were substituted for pre-intercalated octylamine. In contrast, all azo compounds tested except for p-hydroxyazobenzene were directly intercalated into the interlayer space of γ-ZrP without octylamine. Photoisomerization of p-aminoazobenzene and p-hydroxyazobenzene included in γ-ZrP was observed along with their reversibility, as determined by alternate ultraviolet and visible photoirradiation for 30 min. The adsorption competency of the prepared materials for rare earth cation significantly increased depending on the azo molecule density.
Influence of both surface roughness and surface morphology on frictional behavior of ceramics during run-in period under dry sliding was investigated simultaneously. Similar average surface roughness (Ra = 0.01–0.02 µm) was produced for the three ceramics: monolithic boron carbide ceramics, boron carbide-silicon carbide composite ceramics and monolithic silicon carbide ceramics. Surface roughness parameters show some influence on friction processes, however, surface morphology is considered as a more important competitive factor. Lower friction coefficient during run-in period and shorter sliding distance up to the steady state condition were observed for the B4C–SiC composite ceramics, which has a different surface morphology from those of monolithic B4C ceramics and monolithic SiC ceramics.
NiCo2O4-based materials are promising for high-performance energy storage materials. Here, we report the synthesis of urchin-like NiCo2O4 particles via the hydrothermal urea precipitation process, and studied the effect of urea concentrations on phase purity, microstructure, and electrochemical capacitor performance. NiCl2·6H2O, CoCl2·6H2O and urea, were weighed as Ni:Co:urea = 1:2:[5, 10 or 15] in molar fraction, and they were dissolved in distilled water and hydrothermally heated at 140°C for 6 h. The three precursors were calcined at 350°C for 3 h in air atmosphere. The three products were mainly composed of 3–10 µm sized urchin-like particles. All the final samples had 5–20 nm sized mesopores and ∼50–70 m2/g of specific surface area, but the distributions of Ni and Co in the urchin-like particles were affected by the starting urea concentration. The sample of single-phase NiCo2O4 from Ni:Co:urea = 1:2:15 showed the best electrochemical capacitor performance among the three urea concentrations.
A simple technique to control the specimen electric current during flash sintering was developed using AC electric fields in 3 mol% Y2O3-doped ZrO2. Flash sintering is characterized by the occurrence of a flash event, i.e., a spike in the specimen electric current, which makes it difficult to control the specimen electric current at/after the flash event for AC electric fields. However, AC electric fields are very attractive from the viewpoint of a suppression of the severe reduction arising from the unidirectional ionic flow during the flash event, which is a fatal phenomenon with DC electric fields. In this study, we develop a simple technique to control the AC electric fields at/after the flash event by limiting the AC electric fields under certain values. As a result, the flash state after the flash event is successfully maintained. Further, it is found that 3 mol% Y2O3-doped ZrO2 compacts prepared by DC- and AC-flash sintering emit blue fluorescence (FL) under 254 nm ultraviolet light. The blue FL is not obtained in the compacts prepared by conventionally-sintering. The application of electric fields is confirmed to result in the blue florescent properties of 3 mol% Y2O3-doped ZrO2 compacts.