A vector material is defined as the one to manipulate surrounding inorganic and organic compounds, microorganisms, and tissues using a force irradiated locally and continuously from the material itself. The effect given by a vector material is ca materials are of unparalleled importance under the circumstance of the limited use of external forces such as in vivo. We have recently experimentally demonstrated the effectiveness of electrically polarized hydroxyapatite (HA) electrets as vector ceramics, which can independently irradiate an electrostatic force to the surrounding constituents; crystal growth from a simulated body fluid was accelerated or decelerated and proliferation of a microorganism was controlled on the surfaces of polarized HA, depending upon the electric signs of surface charges. Prior to our study, certain types of vector effects have already been employed in biomedical applications; the so-called 45S5-type bioactive glass (Bioglass^®), developed by Hench et al., has long been recognized to be bioactive because of its solubility in a aqueous medium. Radioactive ceramics irradiate β-ray to and work on surrounding cancer cells. These are also vector materials. In addition to these examples, various kinds of vector effects and ceramics are now under development. This advanced report presents the concept of vector effects and reviews the examples of vector ceramics.

View full abstract

This article reviews novel electrical and optical properties found for epitaxial thin films of wide-gap semiconductors, LnCuOCh (Ln=lanthanide, Ch=chalcogen). This material series has a two-dimensional crystal structure composed of alternately stacked (Ln₂O₂)²⁺ and (Cu₂Ch₂)^2- layers. Distinctive properties such as high hole mobility, degenerate p-type conduction, room temperature exciton, and large optical nonlinearity were found and these are attributed to two-dimensional electronic structure arising from the layered structure, i.e., a narrow-gaped and hole-conductive (Cu₂Ch₂)^2- layer is sandwiched by wide-gaped insulating (Ln₂O₂)²⁺ layers. In particular, the wide-gap p-type metallic conduction was the first demonstration among any class of wide-gap materials including GaN: Mg. Realization of epitaxial thin films for these materials by reactive solid-phase epitaxy led to these discoveries which make LnCuOCh promising materials for optoelectronic devices utilizing the high p-type conductivity and/or the room temperature exciton.

View full abstract

Amorphous silica and related silica-based materials have been widely developed in optoelectronics and optical telecommunications technology. Despite comprehensive research for over the decades, the subject of amorphous silica continues to excite the interest of researchers in the field of chemistry, physics, and geology. This paper reviews some of the recent experimental and theoretical developments in the field, including medium-range order, structural changes under pressures, vibrational and thermodynamic anomalies, and photoluminescence properties.

View full abstract

The controlled development of texture is one of the ways for effectively improving physical and mechanical properties. In this review paper, we introduce a new processing of textured ceramics with a feeble magnetic susceptibility by slip casting in a high magnetic field and subsequent heating. As an example of feeble magnetic ceramics, we demonstrate the fabrication of textured alumina in details. The susceptibility of diamagnetic α-alumina is very small, but the orientation energy of the alumina particle by a high magnetic field becomes greater than the thermal energy. α-Alumina with a rhombohedral structure shows anisotropic susceptibility, but this anisotropy has up to now been more or less ignored due to its very low value. However, in a high magnetic field, the energy of crystal anisotropy becomes comparable to or greater than the energy of thermal motion. The degree of orientation depends on the processing factors, such as heating temperature, particle size, applied magnetic field, concentration of the suspension, etc. This process technique confers several advantages and it is possible for this type of processing to be applied to other non-cubic ceramics, such as TiO₂, ZnO, SnO, hydrooxy apatite (HAP), AlN, SiC, Si₃N₄, etc.

View full abstract

This article reviews the fabrication and properties of sulfide glasses and thin films consisting of non-toxic elements: alkaline-earth, rare-earth, germanium and gallium sulfides for optical applications. Refractive indexes, transmission and the fluorescence property of rare-earth ions in sulfide glasses are presented. Factors affecting rare-earth solubility in sulfide glasses are summarized. Thermally-stable BaS-Ga₂S₃-GeS₂ glasses for optical fibers and Nd³⁺-doped transparent Ga-La-S-O glass-ceramics are described as new optical materials. Sm-doped SrS-Ga₂S₃ non-crystalline and nano-crystalline metallic SmS films were irradiated by focused femtosecond laser pulses and new photoinduced phenomena are introduced.

View full abstract

O1s binding energy measured by X-ray photoelectron spectroscopy (XPS) is candidate as a new tool to determine a new scale of Lewis basicity of oxide ions in glass. Some mathematical expressions for the basicity or XPS chemical shift, such as charge parameter and optical basicity, were compared with the experimental O1s binding energy in binary alkali oxide glasses. The expressions so far in use needed some modification in parameters. A new empirical expression introduced in this paper gives a new concept and universal scale of basicity.

View full abstract

α- and β-SiC powders and their powder mixtures with 0.3 mass% of AlB₂ additive were sintered at 2200°C. Porous materials having approximately 55-57% theoretical density were obtained from the powders. Grains in the porous material prepared from α-SiC powder grew into round-shaped grains with a 4 μm size, and those prepared from β-SiC powder grew into plate-shaped grains with the same size. Grain growth was considerably enhanced in the powder mixtures forming a locking structure with plate-shaped grains. The mean grain sizes of the porous materials from the powder mixtures were 5.6-8.2 μm. β(3C)-SiC in the powder mixtures was transformed completely to α, that is, 6H and small amounts of 4H and 15R. An energy difference accompanied by β-to-α transformation enhanced grain growth. The strength of the porous materials prepared from the mixtures was 70-83 MPa.

View full abstract

Cubic perovskite-type Sr(Mn_1-xNb_x)O₃ (0.03≤x≤0.2) was synthesized by a standard ceramic technique. The cell constant increased linearly with increasing x. Sr(Mn_0.97Nb_0.03)O₃ (x=0.03) exhibited a metal-insulator transition at ca. 390 K, whereas Sr(Mn_1-xNb_x)O₃ (0.05≤x≤0.2) was an n-type semiconductor in a temperature range of 80-773 K. From the magnetic measurement, it is obvious that the metal-insulator transition was caused by the change in the spin state of the Mn³⁺ ion. The Seebeck coefficient of Sr(Mn_1-xNb_x)O₃ (0.03≤x≤0.2) was negative and showed no significant difference in the composition.

View full abstract

Ba₅Nb₄O₁₅ was successfully crystallized from Ba5-Nb4 ethoxide by heating. Microstructual characterization of specimens annealed at various temperatures was performed by using a transmission electron microscope (TEM). Below 673 K, the ethoxide was decomposed to an amorphous matrix. At 773 K, small crystals with a size of 2-3 nm formed in the amorphous phase. The crystal was grown by heating, and then Ba₅Nb₄O₁₅ crystals 70-150 nm in size formed at 1173 K. The crystallization process was successfully observed in situ by TEM using a thermal specimen stage. The grain growth process from polycrystal to five single crystals could be recorded. We propose a formation mechanism of Ba₅Nb₄O₁₅ from Ba₅-Nb₄ ethoxide.

View full abstract

ZnO powder, which was composed of sub-micrometer particles, was synthesized by sol-gel method. SEM image shows that the mean size of the particles was about 70 nm. X-ray diffraction patterns revealed that the particles had hexagonal structure with the c-axis and a-axis lattice constants of 0.520 nm and 0.324 nm, respectively. The lattice constants are in well accordance with those of ZnO single crystal. Photoluminescence spectra at room temperature showed the green emission with the peak at 500 nm. In addition, the intensity of the green emission increased upon increasing the heating temperature.

View full abstract

Nanopowders of La₂Ti₂O₇ have been successfully prepared by metallorganic decomposition method (MOD). In comparison with the higher reaction temperature of conventional preparation methods, such as solid-state reaction (about 1100°C), the nanocrystal La₂Ti₂O₇ phase can be formed at an evidently lower temperature of 700°C by MOD. The resulting powders exhibit small and uniform grains. The imagines of FT-IR show that acetylacetone can associate with La³⁺ to form La-acetylacetone chelate complexes, and the absorption peak of La³⁺ in precursor solution disappears, while the peaks of chelate complexes located at 1580 and 1420 cm^-1 are found correspondingly. The probable reason is that small precursor particles can be formed at a homogeneous and low La³⁺ concentration by control release from the complexes; these small, uniform and more active precursor particles probably make it possible to form La₂Ti₂O₇ nanocrystal at significantly lower preparation temperature.

View full abstract

We have reported that the Pd-perovskite catalyst regenerates itself through the solid solution and segregation of Pd in and out of the perovskite crystal during the inherent fluctuation of engine exhaust gases. We named this innovative ceramic the “intelligent catalyst.” In this study, the structural stability and the catalytic activity of Pd-perovskite catalysts such as LaFePdO₃, LaCoPdO₃ and LaMnPdO₃ prepared by the alkoxide method are compared. Although it was reported that the catalytic activity of perovskite catalysts without Pd is, in the order, LaCoO₃>LaMnO₃»LaFeO₃, the catalytic activity of perovskite catalysts containing Pd after heat treatment under redox conditions was superior and in the order LaFePdO₃»LaMnPdO₃>LaCoPdO₃. It was confirmed that the LaFePdO₃ catalyst's superior catalytic activity was due to a highly efficient suppression of particle growth. We found out that the structural stability of perovskite crystal was the key to suppressing the particle growth of Pd, and thereby maintaining the catalytic activity of Pd-perovskite.

View full abstract

Sol-gel-derived hafnia films containing formic acid as an organic ligand were hardened by ultraviolet (UV) irradiation. Transparent hafnia sols were prepared by treating hafnium hydroxide with a formic acid aqueous solution. The gel films were hardened to scratch hardness of over 9H by UV irradiation using a high-pressure mercury lamp for 2.5-10 min. A formato ligand was found to be bridged to Hf ions in a bond involving two metal ions by analyzing the FTIR spectra of the hafnia powders before and after UV irradiation. The hardening process of the hafnia gel films was investigated using the thermal programmed desorption (TPD) technique. The amount of CO and CO₂ generated from the formato ligands decreased after UV irradiation, as did the amount of H₂O generated from Hf-OH in the gel, indicating that the formato ligands and OH in the gel were eliminated by UV irradiation, resulting in pencil hardness of over 9H.

View full abstract

In order to prepare geopolymeric materials, sodium disilicate solution (1.48 mol/L) added with caustic soda solution (15 N) in 3 : 1 proportion and fly ash were used as geopolymer liquor (W) and filler (S), respectively, and were mechanically mixed with ratio W/S 0.45. The mixtures were cast into molds and steam-cured at 80°C up to 16 h under variable humidity, 40%RH, 60%RH, 80%RH and 100%RH, to make monolithic materials. As a result, relatively higher strength was obtained under 40%RH and 100%RH curings, while relatively lower strength under 60%RH and 80%RH curings. On the contrary, relatively larger shrinkage was noted, when cured under 40%RH, while relatively larger expansion, when cured under 100%RH. Monoliths cured under 60%RH and 80%RH showed little expansion and shrinkage in the entire range of curing time. On the other hand, monoliths cured under 40%RH showed relatively lower bulk density despite the shrinkage, while monoliths cured under 100%RH showed relatively higher bulk density despite the expansion. Monoliths cured under 60%RH and 80%RH showed intermediate bulk densities. These two extreme phenomena were discussed in terms of hydration-polycondensation process of silica complexes of the geopolymer liquor containing foreign metallic ions leached out of the fly ash filler. SEM-EDX analysis showed that binder portions were zeolitic gels in amorphous state consisting of Na₂O, Al₂O₃ and SiO₂ as main components associated with K₂O, MgO, CaO and Fe₂O₃ as well as free C. In hollow type of fly ash particulates so called cenospheres, needle-like or blade-like crystallites were encountered, which were composed of chemical components similar to the binder portions and zeolite Y (faujasite) formation was suggested. Furthermore, the CaO component was concentrated both in zeolitic gels and in zeolitic crystallites.

View full abstract

We have developed a new eco-friendly fabrication process for porous ceramics using hydraulic alumina (HA) and water. In the present study, we fabricated porous alumina ceramics using this new process. A boehmite gel 3-D network was formed by the hydration of HA in HA slurry. The HA slurry was hardened by the formation of this 3-D network. Even without the addition of an organic binder, green bodies containing the 3-D network demonstrated high compressive strength. Furthermore, the water acted as a fugitive material in the green bodies. Consequently, the open porosity of sintered alumina ceramics could be controlled over a wide range of 56.6-69.1% by addition of water (ratio of water to HA powder: 1.0 to 2.0 by weight) without the use of organic fugitive materials. The results of evolved gas analysis-mass spectrometry measurements showed that the emissions from the hardened green body mostly consisted of water. Consequently, the new fabrication process for porous alumina ceramics was confirmed to be eco-friendly.

View full abstract

Thermal properties of bimodal porous silica and silica-zirconia with humidity control ability are investigated in order to clarify their potential as a multi-functional building material. Thermal conductivity of the silica decreases with increasing the porosity of the silica, and 0.06 W m^-1K^-1 is achieved when the porosity exceeds 90%. The silica shows thermal resistance of ca. 800°C, which is much higher than conventional thermal insulators. The thermal resistance can be improved by the addition of zirconia: a silica-zirconia sample maintains its high porosity up to 1050°C. Thus, the bimodal porous silica and silica-zirconia are expected to be a thermal insulator with humidity control and thermal resistance abilities.

View full abstract

Synthesis of europium ion doped yttrium oxide (Y₂O₃:Eu³⁺) phosphor nanoparticles using a relatively high molecular weight polyethylene glycol is reported. Y₂O₃: Eu³⁺ materials could be prepared by simply heating in air provided that, water-soluble polymer be added into solutions containing metal nitrates. The polymer was expected to form carbonaceous materials around the produced primary particles to reduce the tendency of those particles to agglomerate. The carbonaceous materials could be removed by heating at higher temperatures, resulting in softly-agglomerated particles in the size range of 20-100 nm. The effect of synthesis parameters on particle morphology, crystallinity, and photoluminescence properties was investigated.

View full abstract

Three different methods of synthesis of ceria-gadolinia (CGO) nanopowders are presented. We established a technique of the synthesis of uniformly aggregated, agglomerate-free CGO in which ceria-gadolinia composite nano-aggregates (15-40 nm) are prepared by nucleation and crystallization of ceria on the surface of preliminary synthesized, hydrolyzed and ultrasonically de-agglomerated gadolinia (3-17 nm). Nano-size aggregates (12-65 nm) of CGO were produced during subsequent non-isothermal calcination. The incorporation of the small concentrations of gadolinia in the ceria lattice was studied using the electron spin resonance technique. It was confirmed that Gd³⁺ occupies the sites of both cubic and axial symmetry. With increasing concentration, Gd³⁺ forms a defect complex with the oxygen vacancy.

View full abstract

Long columnar nano-defects were formed in a Bi₂Sr₂CaCu₂O_x (Bi2212) single crystal irradiated by 230 MeV Au and 180 MeV Fe ions. As expected, the width of the columnar defects induced by the heavy Au ion irradiation gradually decreased with the loss of ion energy in the target along the ion trace. However, in the case of irradiation by the lighter Fe ions, the width of the columnar defects remained almost constant along the ion trace. The conditions required for producing the same type of damage morphology in the same target are very different for the two types of ions, strongly depending on the ion momentum, and hence mass. The relationships between the ion energy and the columnar defect size produced by the two types of irradiation are discussed quantitatively. The relationships are found to be useful for predicting the diameters and distribution of the columnar defects formed by ion irradiation.

View full abstract

Organic template-directed crystallization of hydroxyapatite (HAp) was studied in-situ via Fourier transform IR external reflection spectroscopy. Langmuir monolayer of arachidic acid was formed on a surface of simulated body fluid, which possesses inorganic ion concentrations and a pH value almost equal to those of human blood plasma. Owing to the chemical interactions between inorganic ions and carboxyl groups, heterogeneous nucleation of HAp occurred below the monolayer. The absorbances of the antisymmetric and symmetric methylene stretching bands in the IR spectra varied during the nucleation process, which means that conformational change of hydrocarbon chain occurred. Interfacial interactions between organic templates and induced crystals are often discussed only through static experimental models. However, the organic matrices should also be treated as elastic template and their structural changes due to the formation of HAp crystals should be recognized, when the biomineralization mechanism is discussed.

View full abstract

In this study, carbon-coated ZnO powders were prepared via polymer pyrolysis method, polymer being used as poly (vinyl alcohol) and poly (vinyl chloride). Initial conditions, Type of polymer as carbon sources and particle-particle distance during the coating operation, were located as important parameters which directly affect the high quality of carbon-coated ZnO powders. After coating, morphologies and crystal structure of the carbon-coated samples were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and specific surface area measurement (BET). From BET data, the increase in specific surface area was observed after coating, irrespective of carbon source. The reason why the specific surface area increased after coating was based on nanoporous formation in the carbon film coated on the surface of powder. By TEM observation, it was found that nano-structure of carbon prepared from poly (vinyl alcohol) was different from that obtained from poly (vinyl chloride).

View full abstract

Emission spectra of Er³⁺ ions at 1.5 μm band were measured in bismuthate, tellurite and silicate glasses. The bandwidth of the emission spectrum was well correlated to the optical basicity of the host glasses irrespective of the glass systems. This result indicates that the lower basicity of the host glass reduces the covalency between Er³⁺ and oxide ions, and thus electron density of relevant vacant orbital of Er³⁺ ions in glasses, resulting in the broader emission spectrum. It was found that the optical basicity calculated from glass composition may work as a guiding principle to obtain broadband fiber amplifier for wavelength division multiplexing systems.

View full abstract

Highly toughened nickel dispersed alumina-based nanocomposites were fabricated using our developed soaking method, based on our previously proposed toughening mechanism of nanocomposites. Commercially available γ-alumina agglomerate with high porosity was used as a starting material. Nickel nitrate solution was penetrated into the nano-pores of the γ-alumina agglomerate using this new technique. The alumina-nickel composite powder with α-alumina seeds was then sintered using a pulse electric current sintering technique. To disperse dislocations generated around the nano-particles into alumina grains, the sintered materials were annealed. The results showed that the maximum fracture toughness was 7.6 MPam^1/2, which was about two times higher than that of dense alumina.

View full abstract