β-AlN thin films with different thickness were grown on sapphire(0001) substrates with a smooth surface in a nitrogen atmosphere by pulsed laser deposition using a sintered AlN target, and their films were evaluated by X-ray diffraction and transmission electron microscopy. Zincblend-type β-AlN with a lattice constant of 7.89 Å was epitaxially grown on sapphire(0001) near the interface with the substrate. The electron diffraction patterns of its area along the close-packed planes exhibited streaking spots caused by dislocation defects. On the other hand, with increasing film thickness, the upper area of the AlN thin films became polycrystalline, and simultaneously the streaking disappeared there. Dislocation defects near the interface might be due to a large lattice mismatch or a shift in the close-patching sequence, and they disappears in the polycrystalline area.
Effects of silver nanoparticle (AgNP) and gold nanoparticle (AuNP) on photon upconversion based on sensitized triplet-triplet annihilation were examined in the system of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA). The ITO electrodes immobilized with AgNPs and AuNPs were prepared by electrophoretic method. Samples were prepared by sandwiching the solution of PtOEP and DPA between glass and the ITO electrode modified with AgNPs or AuNPs. In the sandwich samples, the enhancements of upconversion fluorescence from DPA were observed in the presence of AgNP, while the quenching of the upconversion fluorescence in the presence of AuNPs. The enhancements are most likely attributable to large electric fields due to localized surface plasmon resonance of AgNP. The quenching is most likely attributable to nonradiative metallic quenching of AuNP.
Long-afterglow phosphors of strontium aluminates doped with Yb3+ and Dy3+ were prepared via a solid-phase reaction. The starting material powders (SrCO3, Al(OH)3, Eu2O3, and Dy2O3) were pulverized and mixed in a ball mill. The most emissive nominal composition was Sr3.84Eu0.08Dy0.08Al14O25 sintered at 1450 °C in a reducing environment of 3 % H2 in N2 for 4 h. When the mixing and sintering cycle was repeated three times, the green emission intensity increased 28 times in comparison with that of the initial cycle. However, the emission intensity further increased to 120 times the initial upon addition of H3BO3 as a flux. The increase in the emission intensity is related to an increase in the presence of Sr4Al14O25 and Sr3Al32O51 phases. These crystalline phases doped with Yb2+ and Dy3+ are the most probable emission centers of the afterglow.
Anodic porous alumina (APA) prepared in sulfuric acid solution was dyed by immersing in N,N-dimethylformamide (DMF) or in an aqueous micellar anionic surfactant solution of sodium dodecyl sulfate (SDS) containing the following molecules: tris(8-quinolinolato)aluminum, tris(dibenzoylmethane)mono(1,10-phenanthroline)europium(III), and pyrene. Absorbance increased with dye concentration in all cases, except for pyrene in DMF. Interestingly, the absorbance of adsorbed dyes on the APA surface immersed in SDS micellar solutions was larger than that for dyes immersed in DMF solution. These results suggested that the increased adsorption amount is attributed to the electrostatic interactions between the positive charge of the APA surface and the negative charge of SDS micelles solubilizing dye molecules inside the micelles.
Hydrophilic copolymers containing N-isopropylacrylamide and acrylate with coumarin or 4-methylcoumarin moieties have been synthesized. We reveal that the copolymers with a very small content of coumarin and 4-methylcoumarin units exhibit macroscopic photoinduced and reversible sol-gel conversions. UV light (λ＞310 nm) irradiation of aqueous solutions for the copolymers causes the increase in viscosity and the formation of hydrogels, based on photodimerization of coumarin moieties. Subsequent irradiation with UV light (λ＝254 nm) of the hydrogels induces the return of fluidity and the change to sol state, due to the decomposition of coumarin dimers. The amount of crosslink structures in the copolymers can be regulated by the reversible photoreaction of coumarin moieties.
The reaction of ethylene molecules with a Ni cluster was investigated by ab initio molecular simulations. We found that hydrogen atoms on the Ni cluster hamper dehydrogenation of ethylene molecules, which implies that carbon atoms are not supplied into the Ni cluster when the number of the hydrogen atoms is saturated. However, the hydrogen atoms were removed from the cluster by producing hydrogen molecules and carbon atoms are continuously supplied. This fact suggests that the production of the hydrogen molecules determines the rate of supplying carbon atoms. We investigated activation energies to form the hydrogen molecules on the Ni cluster, and discussed the mechanism of efficient removal of the hydrogen atoms.
The thermoelectric material β-FeSi2 was produced by a rapid eco-process involving induction-field-activated combustion synthesis / static pseudo-isostatic compaction (IFACS/SPIC). A dense Fe-Si alloy (Fe/Si = 3/7) was synthesized by IFACS/SPIC using a powder compact of high purity Fe and Si. An induction time (5 min) of IFACS/SPIC and the annealing time (at 1123 K for 5 min) for β-transformation were extremely shorter than those of conventional synthesis. When the Fe/Si ratio of the alloy used in the eutectoid reaction α-FeSi2→β-FeSi2+Si was 3/7, the main annealing product was β-FeSi2 with a small amount of free Si, and the formation of metallic ε-FeSi was prevented. The relative density and the β-transformation ratio were 95% and 96%, respectively. The thermoelectric properties of the p-type Mn-doped (Fe2.94Mn0.06Si7) and the n-type Co-doped (Fe2.94Co0.06Si7) products were investigated from room temperature to 1123 K.
(111)-oriented tetragonal barium titante (BaTiO3, BT) ceramics with the degree of (111) orientation of 100 % were fabricated by sintering (001)-oriented hexagonal BT accumulations prepared by a magnetic field assisted electrophoretic deposition (EPD) method. Apparent piezoelectric constant d33* value calculated from the slope of a unipolar strain vs. electric field curve of the (111)-oriented tetragonal BT ceramics was 597 pm/V, which was larger than that of randomly oriented ceramics (d33* = 460 pm/V). This enhancement was associated with an electric field induced phase transition.
Strain fields around dislocation pairs were measured using geometrical phase analysis of high-resolution TEM images. Single crystalline (011) silicon wafers were employed. The wafers were deformed using three-point bending at 1123K in order to introduce dislocations. The observed dislocations were found to be Lomer sessile dislocations. The strain fields around the dislocations experimentally measured were in good agreement with those calculated from the elastic theory. Experimental results showed that the strain field of two dislocations can be regarded as a single dislocation when their distance is less than 6b.
The present work describes the preparation of potassium niobate (KNbO3) nanocrystals by wet chemical reaction at low temperature. Nanocube is particularly paid attention in dielectric materials. The KNbO3 have perovskite structure and indicate ferroelectrics property. In this study, preparation of the KNbO3 nanocubes was investigated using solvothermal and microwave reactions. Microwave method enable to the rapidly increasing temperature. 40 mL ethanol was used as reaction medium while 1 mmol niobium oxide (Nb2O5) and 10 mmol potassium hydroxide (KOH) were used as raw materials. The microwave-assisted solvothermal reaction was carried out at 200℃ for 30 minutes. Then, solvothermal reaction was performed at 230℃ for 18 h. The characterization was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). KNbO3 was not obtained from the XRD measurement after the microwave-assisted solvothermal reaction at 200℃ for 30 minutes. However, the main XRD peaks indicated KNbO3 after solvothermal reaction at 230℃ for 18 h. The shape of obtained powders was nanocube from SEM observation. That is to say, KNbO3 nanocubes were obtained by combining microwave and solvothermal reactions.
We propose the solvothermal solidification method to prepare dense ceramics at lower temperature. The procedure of the solvothermal solidification method are mainly composed of a preparation of green compact containing precursor particles and a conversion from the precursors into the desired compound via the solvothermal reaction inside the compact. This solvothermal reaction is accompanied by a densification of the ceramics; synthesized particles fill the pores inside the compact and are connected with each other by crystal growth. To prepare dense BaTiO3 (BT) ceramics, the green compacts consisting of BT and TiO2 mixed nanoparticles, or TiO2 nanoparticles were prepared and were converted into BaTiO3 by the solvothermal treatment below 200 °C. The relative density of the compacts significantly increases by the solvothermal reaction because the conversion reaction of TiO2 into BT is accompanied by a volume increase. BT ceramics with a high relative density up to approximately 90% could be obtained by optimizing the solvothermal reaction conditions. However, the dielectric constant of these BT dense ceramics prepared by the solvothermal solidification method is much smaller than that of BT ceramics prepared by the solid-phase method because of the defect in the synthesized BT crystals and/or a size effect.
Boron-doped ultrananocrystalline diamond/amorphous carbon composite films were deposited in the hydrogen pressure range up to 26.7 Pa by coaxial arc plasma deposition with a boron-blended graphite target, and the effects of hydrogenation on the electrical properties and chemical bonding structures of the films were discussed by near-edge X-ray absorption fine structure (NEXAFS) studies. The electrical conductivity decreased with increasing hydrogen pressure. Whereas the nonhydrogenated films showed a semimetallic behavior in the temperature dependence of the electrical conductivity, the hydrogenated films exhibited semiconducting behavior. The boron content estimated from X-ray photoelectron spectroscopic measurements hardly changed with the hydrogen pressure. NEXAFS spectra showed that π* resonance related to sp2-bonded carbon is evidently enhanced with decreasing hydrogen pressure, which is accompanied by a selective etching of sp2 carbon. The results indicate that the carrier transports in UNCD/a-C films are strongly influenced by chemical bonding structure at a-C or grain boundaries.
Open circuit voltage is an essential factor to judge the performance of the photovoltaic cells. Basically, the photo-electrochemical (PEC) measurement shows the solid/electrolyte chemical interaction under light illumination. The PEC measurement reflects the electrical and optical properties of the semiconductors. The optical sensitivity of a semiconductor is used to derive an equation. In the present study, we introduced an equation to estimate the open circuit voltage of a pn junction from the PEC measurements of the individual layers.
The preparation method of hydrophobic gold nanoparticles (AuNPs) with the diameters of 17, 30 and 48 nm has been developed. So as to clarify the size effects of AuNPs on the hydrophobization processes, time courses for the formation of the self-assembled monolayers (SAMs) of octadecanethiol (ODT) molecules on the surfaces of the AuNPs have been investigated by means of FT-IR and Raman spectroscopies. In all cases, the alkyl chains were mainly arranged as all-trans conformation (solid-like) at the completion of the reaction. Observation of the time course of ODT-SAM formation revealed that smaller curvature (larger size) resulted in the faster formation of SAM because of smaller conical volume snugly available for the alkyl chain on the surface of the AuNP.
To increase the Curie temperature (TC) of barium titanate (BaTiO3: BT) ceramics, we tried to fabricate BT complex ceramics with an internal electric field. We propose that the electric field originating from poled potassium niobate (KNbO3: KN) layers is applied on a BT layer by injecting the BT layer between the poled KN layers. Since such multi-layered ceramics is difficult to be fabricated without forming solid solution by a conventional sintering process, we fabricated the KN-BT multi-layered ceramics by a solvothermal solidification method at 230 °C. The TC of BT layer in the fabricated KN-BT multi-layered ceramics did not changed even after poling and it is attributed to insufficiently poling of the KN layers. Therefore, we intensively investigated the polarization of KN layers to optimize the microstructures and fabrication condition of the KN-BT multi-layered ceramics. We prepared the KN ceramics with various microstructures by the solvothermal solidification method, and the poling treatment was performed. The polarization of the KN ceramics can be improved by formation of strong necks and/or a densification of the ceramics.
Open-cell nickel aluminide (Ni-Al) intermetallics foams have attracted much attention in industries at which high temperature and severe environment are concerned, due to their good physical and chemical properties. A combination of different pore structures and morphologies in a single monolithic matrix can extend the properties of a material from which a wide range of applications can be applied. In the present study, open-cell Ni-Al intermetallic foams with hierarchical porosities have been developed through a sintering and dissolution process (SDP) and reactive synthesis techniques. The carbamide particles of various contents were used as a space holder material to create macropores in the foams. Micropores were formed as the result of to the formation of initial fine pores between the powders in the compacts, the volatilization of gases evolved during reactive sintering and different diffusion coefficients between Ni and Al. After sintering, only Ni3Al is present in the matrix.
A series of metal/insulator composite capacitors with embedded metal particles in an insulator layer has attracted attention because of their high effective dielectric constant. We tried to improve dielectric breakdown strength of these metal/insulator composite capacitors by covering individual metal particles with insulator ceramics nanolayers. Micrometer-sized Ti metal particles were homogeneously covered by BaTiO3 (BT) nanolayers with different thicknesses by the hydrothermal method, and these Ti (core)-BT (shell) particles were used for the fabrication of Ti/BT composites. The dielectric constant of the resultant Ti/BT composite capacitors with a Ti metal content of approximately 22 vol% is ranged around 800-1000, and the dielectric breakdown strength (Eb) is slightly enhanced by using the Ti-BT core-shell particles as compared to the Ti/BT composite prepared by using uncoated Ti metal particles. However, the Eb of the Ti/BT composites is independent of the BT shell-layer thickness of the core-shell particles. It can be considered that the BT shell layers are helpful for an enhancement in homogeneity of the metal-particle distribution, but cannot suppress the current leakage at high voltage due possibly to their low-crystallinity and/or porous structure.
Graft copolymers with temperature-responsive units were designed and synthesized using a macromonomer method. A hydrophilic monomer was copolymerized with a macromonomer with a hydrophobic oligo segment. The copolymer spontaneously formed polymer colloids by intermolecular interactions in aqueous solutions. The copolymers were analyzed by UV–Vis spectroscopy, dynamic light scattering, and a fluorescence probe technique under different temperatures. The particle size of the copolymer colloids ranged from 20 to 60 nm at 25°C and larger aggregates were observed at higher temperatures. Increasing the hydrophilic N-hydroxyethyl acrylamide monomer units in the copolymer was induced by decreasing of lower critical solution temperature along with polymeric aggregation. The molecular incorporation of the copolymer was estimated using pyrene as a fluorescence probe, and the change in critical association concentration (CAC) was estimated. The CAC values for the copolymers with hydrophobic segments were estimated to be between 3.0 × 10–2 and 4.0 × 10–2 mg/mL. In addition, the copolymers formed stable colloids in aqueous media.
Plate-like LaTaON2 was prepared by the nitridation of plate-like LaTaO4 precursor synthesized by hydrothermal method to improve the photocatalytic activity for H2 evolution from an aqueous methanol solution under visible light irradiation. LaTaON2 samples derived from hydrothermal method consisted of only slightly aggregated particles 5–10 μm in size. In contrast, LaTaON2 samples derived from solid-state reaction method consisted of irregular-shaped and aggregated primary particles 0.5–1.5 μm in size. For photocatalytic H2 evolution using Pt as a co-catalyst, plate-like LaTaON2 exhibited higher photocatalytic activity than irregular-shaped LaTaON2. In addition, ultraviolet-visible diffuse reflectance spectra suggested that plate-like LaTaON2 had a lower density of defects due to the presence of anion vacancies or reduced Ta5+ species than irregular-shaped LaTaON2, as demonstrated by the reduced intensity of absorption at longer wavelengths (λ ＞ 660 nm). Therefore, using a LaTaO4 precursor synthesized by hydrothermal method, we obtained LaTaON2 with reducing the density of defects that act as recombination centers for photogenerated carriers.
Shape recovery effect of the specimens made by knitting of a TiNi shape memory alloy wire has been investigated. Since there are hundreds of knitting method in the knitting world, we selected the main two methods of knitting for fabrication of the specimen, i.e., Stockinet knitting and Garter knitting, and made tensile tests to get the mechanical properties of these specimens experimentally. These specimens are made of SMA wire of 0.3 mm diameter. The experimental results show that the maximum of the output strain is more than 100 % and the maximum of the output stress is 1.8MPa.
Yttrium silicate nanoparticles were synthesized by the reverse micelle method, and their optical properties were investigated. Span 80 was used as a surfactant for the reverse micelle method. The matrix of the particles was Y2Si2O7. The particle size measured by scanning electron microscope was 10–20 nm. Photoluminescence of Y2Si2O7:Tb,Ce nanoparticles showed typical green emission from the Tb3+ ion based on transition from 5D4 to 7FJ (J = 6, 5, 4, and 3). An increase in Ce concentration increased the green emission by ultraviolet excitation because energy was transferred from the Ce3+ ion to the Tb3+ ion. The nanoparticles would be useful for various applications.
We attempted to fabricate the high-capacitance insulator/conductor composite ceramics with embedded conductive oxide particles insulated by insulator-oxide epitaxial layers to enhance their dielectric breakdown strength. We selected BaTiO3 (BT)/LaNiO3 (LN) composite ceramics because perovskite-type BT is possible to grow epitaxially on the perovskite-type LN due to the similarity of their lattice constants. The LN nanoparticles prepared by the sol-gel method were mixed with TiO2 precursor particles and pressed into green compacts. The BT/LN composite ceramics were fabricated from these green compacts by the conversion reaction of TiO2 into BT in the hydrothermal condition at 175 °C. The effective dielectric constant of the BT/LN composite ceramics with the LN content of 17 mol% is slightly enhanced as compared to the BT ceramics prepared by the hydrothermal treatment because the LN particles acted as the internal electrodes. However, the low resistivity of the fabricated BT/LN composite ceramics suggests that the LN particles were not completely insulated by the insulator epitaxial layer. The decomposition of LN in the hydrothermal treatment and the agglomeration of the LN nanoparticles gave rise to current leakage.
Pseudo-cubic 0.3BaTiO3-0.1Bi(Mg0.5Ti0.5)O3-0.6BiFeO3 ceramics with a high electric resistivity were prepared via a low-temperature powder synthesis and the ceramics were used for synchrotron X-ray diffraction measurements conducted under electric fields of 0 – 50 kV/cm to understand their ferroelectric polarization – electric field (P-E) response. The XRD measurements showed no diffraction peak splitting while changes in the intensities of peaks as the electric fields applied, which suggested that the ferroelectric P-E response was not caused by an electric-field-induced phase transition from the pseudo-cubic phase to a ferroelectric phase, but probably caused by domain switching in nanodomains. The lattice spacings of the ceramics increased along the electric field (33-directon) and contracted in the direction normal to the electric field (31-direction). The piezoelectric constant calculated from the peak shift of the 200 peak was 960 and −260 pm/V in the 33- and 31-directions, respectively.
Shape memory alloys (SMAs) have been employed to apply to heat-engines using low temperature thermal energy (such as hot exhaust heat and hot spring water). However, since previous SMA heat-engines use wire- or coil-shape SMA elements, it is necessary to increase the applied strain of SMA elements for increasing engine power. Furthermore, a certain part of the SMA element is locally heated and cooled repeatedly in the mechanism adapted by previous engines, which leads to inhomogeneous temperature variation and deformation of the SMA element which causes the overload at that part of the SMA element. Accordingly, the product life of SMA heat engines decreases as engine power increases. Hence SMA heat-engines have not been put into practical use. Then, we produced the heat engine using spiral spring actuators joined by multistage gear (the gear-driven type) to improve product life. However, the output efficiency of this SMA heat-engine is 50 % lower than that of conventional SMA heat-engines. The decrease of efficiency is due to the mechanical loss of multistage gear. Therefore, we produced a new heat-engine using spiral spring actuator joined by a pulley belt (the belt-driven type), and investigate output characteristics of the engine. In consequence, the output efficiency of the new engine is 20 % higher than that of the gear-driven type heat-engine using a spiral spring actuator.
Porous potassium niobate (KNbO3) ceramics were prepared by a low-temperature fabrication method of solvothermal solidification. The green compacts consisting of KNbO3 and niobium oxide (Nb2O5) were prepared by a uniaxial press and were immersed in KOH-K2CO3 ethanolic solution. Then, the solvothermal treatment was carried out at 230 °C in autoclaves to convert Nb2O5 into KNbO3. The X-ray diffraction patterns of the samples showed formation of KNbO3. SEM observation showed porous microstructures in the ceramics, and the relative density was as low as 73%. The apparent piezoelectric constant d33* (calculated from the slope of an strain - electric field curve) of the porous ceramics was 157 pm/V, which was nearly 1.5 times higher than that of sintered ceramics with the relative density of 94%.