Showing papers in "Journal of the Ceramic Society of Japan in 2014"

Evaluation of young’s modulus of Li2S–P2S5–P2O5 oxysulfide glass solid electrolytes

Abstract: Mechanical properties such as elastic modulus of solid electrolytes are important for all-solid-state batteries. To investigate the effects of a partial substitution of oxide for sulfide on Young’s modulus, 70Li2S·(30 1 x)P2S5·xP2O5 (mol%) (x = 0, 3 and 10) oxysulfide glasses were prepared and characterized. Young’s moduli were measured by ultrasonic pulse echo method for the dense pellets prepared by hot pressing at around glass transition temperature. The Young’s moduli of 70Li2S·(30 1 x)P2S5·xP2O5 glasses were 22­27GPa and increased with an increase in the P2O5 content. The highest Young’s modulus in this report was 27GPa for the glass with 10mol% P2O5. ©2014 The Ceramic Society of Japan. All rights reserved.

Electronic structures of hexagonal boron-nitride monolayer: strain-induced effects

Abstract: First-principles electronic-structure calculations have been performed to examine electronic properties of hexagonal boron nitride (h-BN) monolayers. The dispersion of the energy bands and the width of the band gaps are calculated under biaxial strains. It is found that the band gap decreases as the tensile strain increases, whereas the band gap increases and then it decreases as the compressive strain increases. The relationship between the energy-band structures and the applied strains is reported to clarify the unique behaviors of the band gaps induced by biaxial strains.

Low-cost clay-based membranes for oily wastewater treatment

Abstract: Low-cost clay-based membranes with an excellent flexural strength were successfully prepared by a simple pressing route using low cost starting materials, such as kaolin, bentonite, talc, sodium borate, and carbon black, and subsequent sintering at 1000°C. Carbon black was added as a template. The effect of carbon black content on porosity, flexural strength, pore size distribution, pure water permeability, oil rejection rate, and flux of low-cost clay-based membranes was investigated. It was found that the porosity and pore size of membranes increased with increasing carbon black content, whereas the flexural strength decreased with an increase in carbon black content. The pure water permeability increased with an increase in porosity. The oil rejection rate decreased with increasing applied pressure and carbon black content. Typical porosity, flexural strength, oil rejection rate, and flux of clay-based membranes sintered at 1000°C were 34%, 58MPa, 96.7%, and 6.3 © 1015m3/m2 s at an applied pressure of 101 kPa, respectively.

Tough and dense boron carbide obtained by high-pressure (300 MPa) and low-temperature (1600°C) spark plasma sintering

Abstract: Dense boron carbide (above 95%) was achieved through high pressure (300 MPa) and low temperature (1600°C) Spark Plasma Sintering (SPS). This approach resulted in improvement of fracture toughness and of dynamic toughness when compared to corresponding toughness values of the sample sintered by conventional SPS (2100°C, 50 MPa). Dynamic toughness was extracted from Split Hopkinson Pressure Bar measurements. Results are understood based on microstructure and on very different behaviour of the samples in respect to residual B2O3 and carbon available in the raw B4C powder.

Phase formation of BaTiO3–Bi(Zn1/2Ti1/2)O3 perovskite ceramics

Abstract: Materials based on BiMO3-modified BaTiO3 have been shown to exhibit a number of attractive electrical and electromechanical properties. In addition, many of the materials in this broad family exhibit reduced sintering temperatures for densification as compared to pure BaTiO3. We report here a study of the phase evolution and sintering behavior of Bi(Zn1/2Ti1/2)O3-modified BaTiO3 materials from low-cost mixed oxide/carbonate precursor powders. By accelerating the reaction of the BaCO3 species and increasing the diffusion kinetics associated with densification, Bi(Zn1/2Ti1/2)O3 additions reduce the calcination and sintering temperatures by ³200°C compared to unmodified BaTiO3. This system provides an example of the important and often overlooked role of additives in the calcination, phase evolution, and densification processes, and provides insight into mechanisms that may be further exploited in this and other important materials systems. We are quite honored to have the opportunity to publish in a special issue dedicated to the life and work of our dear late colleague Prof. Marija Kosec. The topic of this paper is fitting as well, since the work was in large part directly inspired by her work on the importance of reactions and intermediate phases in the alkali niobate systems 1)­4) and heavily informed by her work on the Pb-based perovskites. 5),6) Marija appreciated better than most the importance of careful processing in the formation of fine ceramics, and the global ceramics community is grateful to her for all of the lessons that she taught us®and through her papers and her students, continues to teach us.

High-pressure synthesis, electronic states, and structure–property relationships of perovskite oxides, ACu3Fe4O12 (A: divalent alkaline earth or trivalent rare-earth ion)

Abstract: Recent investigations on the quadruple perovskite series, ACu3Fe4O12 (A = divalent alkaline-earth metal or trivalent rare-earth metal ion), have demonstrated anomalous electronic phase transformations such as charge disproportionation and charge transfer. These behaviors originate from the unusual high valence Fe4+ (or Fe3.75+) ions that are dominated by ligand holes. In this review, various structural transformations and electronic properties in ACu3Fe4O12 perovskites are shown. Furthermore, intriguing structure­property relationships of the ACu3Fe4O12 perovskites are presented. The local structural distortions on metal-oxygen bonds, which are represented as bond discrepancies and global instability indices, are closely related to the electronic phase transformations at low temperature generating a wide range of remarkable phenomena such as negative thermal expansion, ferromagnetism, and metal­nonmetal transitions.

Oxide ion conductivity in defect perovskite, Pr2NiO4 and its application for solid oxide fuel cells

Abstract: Oxide ion conductivity in defect perovskite, mainly Pr2NiO4 with K2NiF4 structure, was studied in details. Defect perovskite oxide consists of perovskite block connected series to oxygen deficient block and although it is known that oxygen deficient block traps mobile oxide ion in lattice, interstitial oxygen introduced at rock salt block in Pr2NiO4 shows high mobility resulting in the high oxide ion conductivity. Oxide ion conductivity is much increased by doping Cu and Ga for Ni site and Pr deficient. The observed oxide ion conductivity was high like log (·/Scm11) = 10.25 at 1173K. Conducting property of Pr1.91Ni0.75Cu0.21Ga0.05O4(PNCG)/ Ce0.8Sm0.2O2(SDC) nano laminated film was further studied and the conductivity was much increased by formation of residual strain and the ion blocking method shows the transport number of the laminated film is almost unity and so high conductivity of PNCG/SDC laminated film could be assigned to pure oxide ion. Application of PNCG for anode of SOFC was further studied and it was found that surface activity of Pr2NiO4 doped with Cu and Ni shows high and so superior cathodic property was achieved at low temperature by mixing Pr2NiO4 with SDC. The maximum power density of the cell using LaGaO3 thin film electrolyte was achieved at 0.12W/cm2 at 673K.

Synthesis and modification of two-dimensional crystalline silicon nanosheets

Abstract: Soft chemical synthesis of silicon nanosheets (SiNSs) and functionalized modified SiNSs are reviewed. Free standing SiNSs with sub-nanometer thicknesses have been prepared by exfoliating layered silicon compounds, and they are found to be composed of crystalline single-atom-thick silicon layers. SiNSs are new silicon nanomaterials, as are silicon nanoparticles and nanowires. Organic modified SiNS can be prepared by modifying a layered polysilane, which has an analogous structure to that of graphite, and this allows the properties of the SiNS to be controlled in order to make it suitable for particular applications. The potential applications of these SiNSs and organic modified SiNSs are also reviewed.

Rudimental research progress of rare-earth silicate oxyapatites: their identification as a new compound until discovery of their oxygen ion conductivity

Abstract: Rudimental research progress of oxyapatite-type rare-earth silicates is reviewed based on the published papers mainly from 1959 to 1993 that have not yet been discussed in detail. The knowledge of oxyapatite-type rare-earth silicates significantly increased during this period. Chemical compounds of rare-earth oxides and silica were discovered around 1960. Because of the complex chemical composition of the oxyapatite phase, the composition was initially considered as 2RE2O3·3SiO2, which was called orthosilicate. “RE” is the rare-earth elements. Different compositions of 2RE2O3·3SiO2 have been proposed by crystal structure analysis based on the crystal chemistry and the leaping model. With respect to crystal structure analysis, knowledge has gradually improved step-by-step, including the implicit distinction between oxygen-stoichiometric apatite and oxygen-deficient apatite. Based on the published work, the rare-earth silicate oxyapatites are considered to have an apatite-like structure. Initially, application research focused on the optical properties of oxyapatite because rare-earth metals were constituent elements of the crystals, and on the use of oxyapatite as a stabilizer of unwanted radioactive waste produced in nuclear power reactors because oxyapatites can dissolve the actinide elements.

Amorphous-nanocrystalline lead titanate thin films for dielectric energy storage

Abstract: Many high permittivity crystalline dielectric thin films have a low breakdown strength, which is unfavorable for dielectric energy storage devices. In contrast, many amorphous linear dielectrics have much lower permittivities but larger breakdown strengths. Here, composite thin films with nanocrystalline particles in an amorphous matrix were explored to increase the stored energy density of dielectrics. For this purpose, thin films of lead-rich lead titanate, Pb1.1TiO3.1, were fabricated via chemical solution deposition and heat-treated at temperatures <= 400 degrees C. Transmission electron microscopy indicated the presence of dense lead oxide nanocrystals in an amorphous lead titanate network. The films exhibit a relative permittivity of 32.6 and a low dielectric loss of 0.0008. The leakage current is approximately 10(-8)A/cm(2), with a DC breakdown strength between 2 and 3MV/cm. The 1 kHz breakdown strength exceeds 5MV/cm. At an electric field of 5MV/cm and a measurement frequency of 1 kHz, the maximum in energy storage density was similar to 28 J/cm(3). These properties suggest that nanocomposite Pb1.1TiO3.1 films may be a suitable candidate for integration into energy storage devices. (C)

Formation of Si-based nanosheets by extraction of Ca from CaSi2 layers on Si substrates

Abstract: It was demonstrated that flake-like structures containing Si-based nanosheets were successfully synthesized on Si(111) substrates. By exposure of CaSi2/Si substrates to CrCl2 vapor, Ca atoms were extracted from CaSi2, then, the Si-based nanosheets were formed. The structural properties of the Si-based nanosheets formed at the edge of the flakes were examined. It is noted that the flake-like structures were rooted to the substrates, and that the Si-based nanosheets were easily exfoliated from the flake-like structures, to expose the surfaces corresponding to the Si{111} planes of the nanosheet, originated from the corrugated Si(111) layers linked by Ca in CaSi2. ©2014 The Ceramic Society of Japan. All rights reserved.

Chemical processes employing inorganic layered compounds for inorganic and inorganic–organic hybrid materials

Abstract: Recent developments in the preparation of inorganic and inorganic­organic hybrid materials from inorganic layered compounds are reviewed. The focus is placed on three topics: preparation of new ion-exchangeable layered perovskites and a tungstic acid from Aurivillius phases via selective leaching of bismuth oxide sheets; grafting reactions for the preparation of two-dimensional inorganic­organic hybrids; and conversion of two-dimensional inorganic­organic hybrids into inorganic compounds.

Development of nano-sized superparamagnetic ferrites having heat generation ability in an AC magnetic field for thermal coagulation therapy

Abstract: Thermal coagulation therapy using powdered magnetic materials in an alternating (AC) magnetic field has been expected as a treatment of cancerous tissues. For nano-sized superparamagnetic particles, the magnetic energy is mainly converted to a heat generation ability by the rotation of the magnetic moment (Néel relaxation) along with the rotation of the particles (Brownian relaxation). Fe3O4 (magnetite) nanoparticles have been mainly investigated as the candidate material for this type of therapy. In this review, an outline of the ferrite materials having heat generation ability in the AC magnetic field is described for the application of the thermal coagulation therapy. In particular, I focused on the preparation of a nano-sized magnetic material using physical bead milling to develop a magnetic material of Y3Fe5O12 and its high heat generation ability. The preparation of Y3Fe5O12 microspheres with a 20­32 ̄m diameter range using the bead-milled powder was also described for the embolization method of cancer treatment.

Synergistic effect between TiO2 and ubiquitous metal oxides on photocatalytic activity of composite nanostructures

Abstract: We studied photocatalytic activity of highly porous nanotubular TiO2 films modified with nanoclusters of ubiquitous metal (Ti, Al, Zn, Sn, Cu, W) oxides prepared by chemical bath deposition and atomic layer deposition as well as nanoclusters of metal rich suboxides and mixed titania suboxides prepared by atomic layer deposition by following decomposition of methylene blue under simulated solar light. The mixed titania suboxide clusters constructed on the surface of TiO2 nanotubes by atomic layer deposition demonstrated significantly enhanced photocatalytic activity in comparison to the naked TiO2 nanotubes attributed to the better absorption of visible light due to the upward shift of the valence band near the TiO2 surface induced by the suboxide clusters that feature low valence states and metal-metal bonds.

Fabrication of textured Ti3SiC2 ceramic by slip casting in a strong magnetic field and pressureless sintering

Abstract: Sinterable Ti3SiC2 powder was synthesized from a powder mixture with a molar ratio of 1.0Ti:0.3Al:1.2Si:2.0TiC by heating at 1200°C in Ar flow. Almost single-phase peaks of Ti3SiC2 were observed in X-ray diffraction patterns. The powder was dispersed in ethanol using polyethylenimine (PEI) as the polymer dispersant. Textured dense Ti3SiC2 ceramics were successfully fabricated by slip casting in a strong magnetic field followed by pressureless sintering at 1400°C for 2 h. The relative density of these Ti3SiC2 ceramics was 99.4%, and the bending strength, fracture toughness and electrical resistivity were 623 « 9MPa, 5.9 « 0.1MPa·m1/2 and 0.31 ̄3·m, respectively. Compared with those of nontextured pressureless sintered samples of almost full density, the bending strength and fracture toughness of the textured Ti3SiC2 ceramics were increased by factors of 1.6 and 1.4, respectively. ©2014 The Ceramic Society of Japan. All rights reserved.

Influence of composition on near infrared reflectance properties of M-doped Cr2O3 (M=Ti,V) green pigments

Abstract: Ti-Al-V-doped Cr2O3 green pigments could present a higher near-infrared (NIR) reflectance compared to pure Cr2O3. The amount of Ti and V introduced in the Cr2O3 matrix has been systematically varied respectively, in order to evaluate the effects of Ti and V contents on the NIR properties of the doped Cr2O3. For comparison, experimental reflectance measurements and meanNIR reflectance (780­2000 nm) of samples are given. The results reveal significant variations in the NIR region as a function of nominal composition for both Ti-doped Cr2O3 and V-doped Cr2O3. Moreover, the NIR reflectance of a Ti-Al-V-doped Cr2O3 pigment sample was measured. It has been found that it exhibits lower NIR reflectance compared to that reported in previous study. The correlations between electronic structural and spectroscopic features are discussed. For the Ti-doped Cr2O3 samples, the decrease of free carriers and the electronic transitions between defect energy levels within the band gap and the conduction band, could be responsible for the variable NIR reflectance. However, for V-doped Cr2O3, apart from light absorptions of free carriers, there are new light absorption peaks range from 1190 to 2000 nm, resulting in the variations of the NIR reflectance.