Monoborides of iron, cobalt and nickel, and their solid solutions having FeB crystal structures, were prepared by solid state reaction at 950°C in a vacuum and were then HIPed using hydrothermal water as a fluid at 900°C for 2 h at 100 MPa. Electrical conductivity and Seebeck coefficients of the specimens were measured in order to evaluate thermoelectric properties. Electrical conductivities were greater than 10⁵ Sm^-1 and Seebeck coefficients range from +20 to -30 μVK^-1 as metal atoms changed. The electrical densities of states of these borides were calculated by a first principle method (DV-Xα). The Fermi level of these borides was near the 3d orbital of the metal atom and this seemed to be a reason for the relatively high Seebeck coefficients.

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Crystal structure and electrical properties of the K₂NiF₄-type oxides in the La-Sr-In-Ga-O system were investigated. Ga substituted LaSrInO₄ solid solutions were synthesized at 1573-1673 K for 36 h in air. The crystal structures of LaSrIn_1-yGa_yO₄ changed from orthorhombic for y=0-0.3 to tetragonal for y=0.4, 0.5 and 0.9, indicating that distortion of (In,Ga)O₆ octahedra network decreased with increasing Ga content. These compounds exhibited semiconducting behavior in the temperature range of 550-1050 K in air. From oxygen partial pressure dependence of the conductivity, it is clarified that they exhibited oxide ion conduction at low oxygen partial pressure region and hole conduction in air. The conductivity also decreased with decreasing unit cell volume due to Ga substitution in In site.

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Glass-ceramics of the germanium- or tellurium-containing Na₅RSi₄O₁₂-type (R=rare earth; Sm) Na⁺-superionic conductors (N5SXS) were prepared by crystallization of glasses with the composition Na_3+3xSm_1-xX_ySi_3-yO₉ (X=Ge; NSGS, X=Te; NSTS), and the effects of X elements on the separation of the phase and the microstructural effects on the conduction properties of glass-ceramics were discussed. Their conductivities and activation energies are of the order of 10^-2 S/cm at 300°C and of 19 to 23 kJ/mol, respectively. The conductivity of the phosphorus-containing N5SPS and N5SXS decreases with the increase of the (P, X)-O bond length, giving the order N5SPS>N5SGS>N5STS.

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We investigated the change in magnetoresistive properties with the change in microstructure of manganite ceramics with nominal chemical composition of La_0.6Sr_0.4MnO₃ by sintering them with various additives. SiO₂, CuO, V₂O₅, or Bi₂O₃ were selected as the additives. The average size of grains of the ceramic samples with additives increased in comparison with that of the sample without additives. The result indicates liquid phase sintering for the samples with additives. The samples with additives have a perovskite-phase and various second phases, and their lattice constants were slightly different from those of the sample without additives. It is supposed for the samples with additives except the sample containing CuO that the ratio of La/Sr changes with the addition of the above oxides. It is also supposed that Cu was introduced to the B-sites of the perovskite-type structure, which is confirmed by the fact that the ferromagnetic transition temperature of the sample is 13 K lower than that of the sample without additives. The differences in the chemical compositions between the sample without additives and those with additives were roughly estimated to be within 10%. The temperature dependences of the electric resistivity and magnetoresistance of the samples were different from each other. The results were thought to originate from the difference in the microstructure from the slight difference in the chemical composition of the perovskite-phase in the samples.

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Amorphous solid electrolytes in the system Li₂S-Al₂S₃ were prepared by a mechanical milling technique for the first time. The 60Li₂S•40AlS_1.5 (mol%) amorphous solid electrolyte showed the maximum conductivity of 3.4×10^-5 S cm^-1 at room temperature in tablet shape. The Li₂S-Al₂S₃ system proved to show lower conductivity than the Li₂S-SiS₂ and Li₂S-P₂S₅ systems in an amorphous state because the latter two systems exhibited the conductivities of 10^-4 S cm^-1 at room temperature. Glass-ceramics in the system Li₂S-Al₂S₃ were directly obtained by mechanical milling at a higher rotation speed, suggesting that glass-ceramic electrolytes as well as glassy ones were prepared by controlling the milling conditions. The crystal Li₅AlS₄ precipitated from the system Li₂S-Al₂S₃ lowered the conductivity. On the contrary, the conductivity enhancement by crystallization was observed for the 67Li₂S•33PS_2.5 (mol%) glass and the obtained glass-ceramic exhibited high ambient temperature conductivity of about 10^-3 S cm^-1. The crystallization of a superionic crystal analogous to the thio-LISICON Li_3.25Ge_0.25P_0.75S₄ was responsible for the marked conductivity enhancement.

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Relationship between electrical conductivities and local structure was studied for SrCeO₃-based perovskite-type oxides doped with various rare earth metals, M (M=Sc³⁺, Yb³⁺, Y³⁺, Gd³⁺, Sm³⁺ and La³⁺). The conducting behavior was considered to be protonic bellow 973 K. The local distortion around dopant ions in perovskite-type oxide was evaluated by examining relative area of the Raman band at around 345 cm^-1 which is connected with stretching vibrational modes of CeO₆ octahedra. The maximal band area was obtained for Yb-doped SrCeO₃. The electrical conductivity increased with increasing the relative area of this Raman band, and the maximal conductivity was observed for Yb³⁺ doped SrCeO₃.

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The proton conductive CsHSO₄-SiO₂ composite electrolytes prepared by vacuum infiltration using CsHSO₄ aqueous solution and porous SiO₂ sheets with pore sizes of 1000-4 nm were investigated. XRD and DTA analyses revealed that the crystallization and phase transition of the CsHSO₄ phases filled inside the pores could be controlled by the pore sizes of the porous SiO₂ sheets. The low-temperature conductivities of the composites obtained after both drying and annealing processes were improved significantly with the decrease in pore sizes of the porous SiO₂ matrix. Particularly, the composite obtained by using the porous SiO₂ sheet with average pore size of 4 nm exhibited the superprotonic conducting characteristic down to lower temperatures below 100°C. It was evidenced that the CsHSO₄ phase filled inside the nano-pores existed in the form of mostly amorphous phase.

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Lithium ion conducting Li₂S-P₂S₅-based solid electrolytes with P₂O₅ and Li₂O as an oxygen source were synthesized by the mechanical milling method. P₂O₅ effectively reacted with Li₂S-P₂S₅ compared to Li₂O. ³¹P MAS-NMR spectroscopy revealed that the 80Li₂S•18P₂S₅•2P₂O₅ (mol%) glass included PO_nS_4-n (n=1, 2, 3) tetrahedral units where phosphorus was coordinated with both sulfurs and oxygens. The 80Li₂S•19P₂S₅•1P₂O₅ (mol%) glass attained a minimum value of the glass transition and crystallization temperatures. In addition, the glass exhibited high ambient temperature conductivity of 1.7×10^-4 S•cm^-1 and low activation energy of 36 kJ•mol^-1 for conduction which were comparable to the glass without P₂O₅. Further increase in P₂O₅ to the Li₂S-P₂S₅-P₂O₅ glasses led to a decrease in conductivities at room temperature and an increase in activation energies. The higher conductivity and lower activation energy for conduction of the 80Li₂S•(20-x)P₂S₅•xP₂O₅ (mol%) glass-ceramics compared to those of the corresponding glasses were caused by the fact that the highly conductive thio-LISICON analog phase was precipitated by heating of the glass over the crystallization temperature.

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Glasses in the systems SnO-B₂O₃ and SnO-P₂O₅ were prepared by melt-quenching and mechanical milling procedures. Glasses with higher SnO content, which could not be obtained by melt-quenching, were prepared by mechanical milling. Glass transition temperatures (T_g) in the SnO-P₂O₅ glasses were lower than those in the SnO-B₂O₃ glasses. The mechanically milled glasses showed lower T_g than the melt-quenched glasses. ³¹P MAS-NMR suggested that local structure around phosphorus atoms of the 67SnO•33P₂O₅ (mol%) glass obtained by mechanical milling was almost the same as the corresponding melt-quenched glass. The electrochemical properties of the SnO-based glasses were examined using a simple three electrodes cell with a conventional liquid electrolyte. The milled glasses as well as the quenched glasses worked as anode materials for lithium secondary batteries and exhibited high charge-discharge capacities.

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Clay-based layered nanocomposites in which conductive transition metal oxides, TMO₂ (TM=Mn and Co), with CdI₂-type structure are confined in the interlayer space of smectite clay have been successfully synthesized through a combination of intercalation and soft chemical reactions. The synthesis procedure consists of three processes: (1) ion exchange; (2) intercalation of metal hydroxide sheets into the interlayer space; (3) oxidation of the hydroxide sheets inside the space. The resulting composites have an expanded layer structure with about 2.0 nm periods along c-axis. The TMO₂ sheets are separated by a clay silicate sheet and hydrated sodium ion layers, thus two different types of sheets are stacking alternately. The composites are found to have multi functionalities associated with the structure, e.g. ion exchange, electric conduction as well as unique magnetic property.

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The preparation and oxygen permeability of (Ba_0.33Sr_0.17La_0.5)₂(In_1-xFe_x)₂O_5+δ mixed conductors, where 0.4=x=0.9, have been investigated. Single-phase samples were prepared by a citrate-based liquid-mix technique. An XRD analysis revealed that the samples had a cubic perovskite-type structure regardless of the Fe content. The lattice parameter linearly decreased from 0.407 nm for x=0.4 to 0.394 nm for x=0.9 with increasing the Fe content. (Ba_0.33Sr_0.17La_0.5)₂(In_0.4Fe_0.6)₂O_5+δ with a membrane thickness of 0.2 mm showed a maximum oxygen flux density of 10.8 μmol•cm^-2•s^-1 at 1000°C under a methane conversion test. The P(O₂) dependence of electrical conductivity indicated that p-type electronic conduction was dominant for these mixed conductors.

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The diffusion mechanism of mobile Cu ions in the superionic conductor CuI is studied by means of ab initio molecular-dynamics simulations. The superionic behavior is successfully reproduced by our simulations. Our analyses including the gross populations, the overlap populations and the spatial distribution of electron density reveal that the time evolution of local bonding plays an important role in the high ionic conductivity.

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The presence of vanadium and iron in phosphate glasses has been found to exhibit properties similar to the mixed alkali effect observed in oxide glasses. While conduction in the latter is caused by a classical barrier crossing mechanism of alkali ions, a quantum-mechanical process, comprising hopping of small polarons, is generally accepted to be the mechanism of charge transport in phosphate glasses containing transition metals. The substitution of one transition ion by another significantly increases dc resistivity activation energy for dc conduction and glass transition temperature, reaching maxima at an intermediate transition ion ratio.

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The relationship between the crystal phase and the electrical conductivity was investigated for the pyrochlore-type composition systems, A₂B₂O₇ (A³⁺=Rare earth element, B⁴⁺=Zr, Ce) and their solid solution systems. The crystal phase of these systems varied among rare-earth C-type, fluorite- and pyrochlore-type phases depending on both the lattice constant and the cationic radius ratio (r_A/r_B), where r_A and r_B denote ionic radii of A- and B-sites in the pyrochlore-type composition, respectively. The lattice constant decreased with increasing the Zr content in the A₂(Zr_1-xCe_x)₂O₇ (A=La, Sm and Yb) systems. Even if the oxygen vacancy concentration was kept constant in all sample systems, the electrical conductivity changed in the wide range. The oxide-ion conductivity increased in proportion to the unit cell free volume in the fluorite-type phases with or without rare-earth C-type superstructure, and decreased sharply in the pyrochlore-type phase range because of the ordering of oxygen vacancy.

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To account for the doping effects on the protonic conductivity of perovskite-type oxides, the optimized geometries, formation energies of hydrogen defect and activation energies for hydrogen diffusion in SrZrO₃ doped with Al, Sc, Ga, Y, Rh, In, Yb were calculated using the density functional theory (DFT) under the generalized gradient approximation (GGA). It was shown that large local distortion was induced around hydrogen and dopant ion, and affected the activation energy greatly. There is good agreement between the measured and calculated activation energies. The hydrogen diffusion seems to become more difficult as the distance between hydrogen and dopant ion decreases. Also, the calculated formation energy of hydrogen defect in doped SrZrO₃ increased in the order, Al, Ga, Sc, Yb, Y, Rh, In. This indicates that there is a difference in the hydrogen concentration among these SrZrO₃ under the same equilibrium conditions.

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The effect of CO₂ addition to CH₄ on the carbon deposition has been studied at the nickel and yttria-stabilized zirconia cermet anode with the platinum-mesh current collector for a solid oxide fuel cell operated at 800°C and at a constant discharge current density. Increasing the volume ratio of CO₂ to CH₄ in a fuel-gas mixture suppressed the carbon deposition from CH₄ without a significant loss of the cell performance. The size of the platinum-mesh current collector and its structure affect the amount of carbon deposited during the cell operation and the cell performance. It was found that a small amount of CO₂ addition up to approximately 5 vol.% to CH₄ inversely acts as a promoter for the decomposition of CH₄ to form carbon over the surface of nickel particles. Carbon deposition occurring at the anode is most likely caused by the competition between the decomposition of CH₄ and the reverse disproportionation reaction of CO occurring at the electrolyte-electrode-gas triple-phase boundary.

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A new transparent conducting SnO₂-based oxide: Ga-In-codoped SnO₂ (GIT) was investigated. Sintering was carried out at 1500°C for 2 h in air. The sintered body of the GIT including 3.3 mol% Ga₂O₃ and 2.8 mol% In₂O₃ had a high bulk density of 5.9 g•cm^-3, in comparison with 3.8 g•cm^-3 for pure SnO₂. Thus, the sintering characteristics of SnO₂ dramatically improve by adding both Ga₂O₃ and In₂O₃. The resistivity of the sintered body was 6×10^-2 Ω•cm. This value is low enough to be used as DC sputtering targets. The resistivity of the films deposited by DC sputtering using the target at room temperature was 5.6×10^-3 Ω•cm. Moreover, it decreases to less than 2×10^-3 Ω•cm on heat-treating at 250°C in air. The luminous transmittance of the films is more than 80%. These films show high durability for acid, even for hydrofluoric acid.

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This paper gives a review of the recent progress in high-density magneto-optical data storage. Three new types of magneto-optical data recording, there are the short wavelength recording, near-field recording and magneto-optic hybrid recording, have been discussed. The great attention has been paid on blue laser (410 nm) recording, therefore several groups of magneto-optical materials, such as magnetic multilayers of Pd/Fe, Co/Pt(Pd), TbFe/Si, different rare earth elements doped dysprosium iron garnets and MnBiAl, CoPt magnetic alloys, have been reviewed. The possible applications in digital high resolution image and video recording are also shown.

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A new fabrication method for photonic crystals in the millimeter and sub-millimeter wave region is described. The method is based on the co-firing technique of low-temperature-co-fired-ceramics (LTCCs), and is easily applicable to mass production. Two low and high dielectric constant materials were used simultaneously to achieve both miniaturization and high mechanical strength of photonic crystals. A honeycomb structure was examined because of its low volume fraction of dielectric cylinders. A photonic crystal was fabricated using optimized preparation conditions. A photonic crystal with the dimension of 10.6×4.3×18.0 mm was successfully prepared and exhibited a 30 dB attenuation between 21.5 and 26.5 GHz. The experimental result was in good agreement with the calculated data.

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3D photonic crystals with a diamond structure, which are composed of the SiO₂ coated TiO₂ ceramic particles dispersed in an epoxy lattice, were fabricated by stereolithography. The diamond structure showed a photonic band gap in the 14.0-17.0 GHz range along Γ-X <100> direction. Lattice defects named `air cavity' were introduced into the diamond structure by removing a unit cell of diamond structure. Two types of air cavity, which were differed in the volume fraction, were also fabricated by stereolithography. The transmission of millimeter waves affected by multiple reflections at the air cavity was measured in the photonic band gap. When the volume fraction of the air cavity became larger, the resonant mode was shifted to the lower frequency range.

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Electromagnetic wave is being used in various fields by the advancement of information and communication technology, as a result electromagnetic environment turned worse. In particular, electromagnetic wave obstacles became a serious problem. We developed sintered porous ferrite for electromagnetic wave absorbers and found that the absorption band became high and wide. These effects were larger with the increase of pore ratio. As a result, we developed an absorber for the wide band, which covered all UHF bands of TV frequencies. Furthermore, we developed new electromagnetic wave absorbers, which could support an absorption band more than 1 GHz that sintering ferrite was not able to be equivalent till now. These are useful for Bluetooth and ETC frequencies.

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BaTiO₃-CaTiO₃ (BCT) system ceramics composites with various chemical compositions were prepared by the conventional solid state reaction, and their crystal structures and electric properties were investigated on a function of a chemical composition. Below Ca contents of 23 at%, BCT ceramics was a single solid solution with tetragonal phase while above Ca contents of 23 at%, two phases of BCT ceramics coexisted, i.e., tetragonal BCT ceramics with Ca content of 23 at% and orthorhombic BCT ceramics with Ca content of over 95 at%. In the coexistence region of the two phase, some structural and electrical anomaly were observed. In this region, lattice parameter of Ba-rich BCT ceramics must be constant, but with increasing Ca content, a-axis increased while c-axis decreased. As a result, c/a ratio decreased with increasing Ca contents, and approached to 1.0 over the Ca content of 50%. The measurement of the chemical composition in this region revealed that the chemical composition of Ba-rich BCT ceramics was always constant. Thus, the structural anomaly was independent of the chemical composition. Moreover, the measurement of the dielectric properties showed some anomaly in this region. Especially, polarization (P) vs. electric field (E-field) curves exhibited that remanent polarization (Pr) decreased with increasing Ca content, and at the Ca content of 50%, a clear double hysteresis loop was observed. To explain the above some anomaly, a model that the anisotropic residual stress can produce a new antiferroelectric phase was proposed.

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The ferroelectric silver niobate (AgNbO₃) single crystals were grown using two kinds of crystal growth methods, and their dielectric properties were investigated. At first, the pure AgNbO₃ single crystals were grown using a conventional flux method with a AgCl solvent. Using this method, the AgNbO₃ single crystals with a size of 5 mm cube were obtained. The dielectric measurement of the AgNbO₃ crystals indicated the two additional dielectric maximums of 460°C and 520°C as well as some dielectric peaks reported in the AgNbO₃ ceramics. Thus, these two additional peaks were investigated using an in-situ domain observation. As a result, this observation revealed that these two peaks at 460°C and 520°C originated from the melting behavior of the residual AgCl (m.p.=455°C) in the crystals. To study an intrinsic dielectric property of the AgNbO₃ crystals, the impurity-free single crystals must be required. Fortunately, it was found that the AgNbO₃ crystals completely melted above 1200°C, and from these liquid phase, the AgNbO₃ crystals with their stoichiometric composition were formed with decreasing temperature. Thus, we developed this new crystal growth technique from the stoichiometric melts for the AgNbO₃ crystals, and named as a slow cooling method. Finally, we obtained the impurity-free AgNbO₃ crystals with sizes of around 3 mm cube. Using these crystals, their dielectric properties were investigated.

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Very low inductance capacitors using Barium Strontium Titanate (BST) based thin films have been developed for use in decoupling applications for GHz LSI operations. Increasing clock frequency and integration density of high performance logic LSI such as the CPU requires very low power line impedance over wide frequency ranges up to GHz order. BST thin film capacitors are promising for GHz LSI applications due to excellent electrical properties of low leakage current and high capacitance. Fundamental electrical and reliability properties of Pt/BST/Pt thin film capacitor structures were also investigated. BST thin films deposited by RF magnetron sputtering achieved a C/A>1000 nF/cm² and a leakage current density<10^-9 A/cm². The fabricated thin film chip capacitors of 0.15 mm bump pitch show a low equivalent series inductance (ESL) of 17 pH and a low ESR of 0.05 ohm. The impedance of the chip capacitor at 1 GHz is 100 times lower than conventional multilayered ceramic capacitors.

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Calcite monolith has been prepared by exposing calcium hydroxide compact to carbon dioxide in the presence of saturated water vapor. The mechanical strength of calcium hydroxide compacted disk increased with prolonged exposure time to carbon dioxide along with its gradual transformation to calcite. The transformation reaction was completed within approximately 72 hours at 25°C. The mechanical strength of the calcite monolith was also dependent on the pressure applied for the preparation of calcium hydroxide compact. For example, diametral tensile strength of calcite monolith was 1.84±0.25 MPa, 3.34±0.39 MPa and 4.64±0.69 MPa when they were prepared from the calcium hydroxide disk compacted with a pressure of 1 MPa, 3 MPa and 5 MPa, respectively. We concluded that this method is useful for the preparation of calcite monolith since pure calcium monolith with enough mechanical strength for bone filler can be obtained without having any complicated procedure.

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Biocomposite scaffold composed of bone-like apatite and a serum protein was formed on a ceramic hydroxyapatite (HAp) and surface-modified titanium. Formation of the biocomposite scaffold on titanium plate was made possible by alkali-heat treatment. The formed biocomposite scaffold had low crystalinity and had a Ca/P ratio lower than that of synthesized HAp. MC3T3-E1 cells closely adhered to the biocomposite scaffold. The morphology of the biocomposite scaffold depended on the substrate surface. It was suggested that the close adhesion was caused not only by surface roughness but also the composition of the biocomposite scaffold. The adsorbed serum protein on the HAp surface inhibited the deposition of the bone-like apatite. On the other hand, the adsorption of serum protein to the bone-like apatite enhanced cell adhesion. It was suggested that the serum protein operated through a different process to form the cell active biocomposite scaffold. The biocomposite scaffold can be formed on various materials, and it could play a great role in cell adhesion.

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The reaction of tricalcium phosphate (TCP) with 25-40 mass% NaOH solutions was investigated at 90°C. At 25-33 mass% TCP was converted consecutively into portlandite (Ca(OH)₂) and hydroxyapatite (HAp). The first step of the consecutive reaction TCP→Ca(OH)₂→HAp was fast and completed. The second step proceeded gradually and completely at 25 mass%, whereas at 30-33 mass% seemed to reach an equilibrium mixture of ca. 85% HAp and 15% Ca(OH)₂. At 34-40 mass% a simple reaction of TCP→Ca(OH)₂ occurred fast and completely. The solubility singular point in the system HAp-Ca(OH)₂-NaOH-H₂O was 32 mass% (10.7 mol/dm³) NaOH. These chemical properties of TCP in NaOH concentrated solutions are of very interest as TCP has been thought to be stable in high pH solutions.

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Novel fast proton conductors could be chemicovectrially prepared by introducing a large amount of water into calcium metaphosphate glass. When fine-sized calcium metaphosphate glass powders were contacted with water, hydrogelation started immediately, resulting in formation of calcium polyphosphates with high viscosity. Calcium metaphosphate glass has a long-chain structure and nonbridging oxygens (NBOs), and calcium ions serve as ionic cross-links between the NBOs of two different chains. The hydration breaks the long-chain phosphate structure and protons break the cross-links, resulting in connection to the NBOs. Subsequently, water molecules are hydrogen-bonded around the protons connected to the NBOs. The hydrogel is the cluster consisting of such hydrated phosphate chains. The hydrogel showed high conductivity of 5 mS/cm even at 30°C. By heat-treatment in saturated vapor at 90°C, monocalcium phosphate monohydrate (MCPM) crystal was precipitated in the hydrogel and its conductivity was much improved to 20 mS/cm at 30°C. The high conductivity was regarded as the fast proton transfer promoted by coexistence of large amounts of acidic POH groups and water molecules.

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This paper presents the preparation of the novel composites consisting of calcium carbonates and poly(L-lactic acid) (PLLA) and their apatite-forming ability in simulated body fluid (SBF). It is well known that calcium carbonate has three polymorphs, i.e., calcite, aragonite and vaterite. On the PLLA composites containing aragonite or vaterite, bone-like apatite particles formed on the surface after soaking in SBF for 7 days or 3 hours, respectively, while no apatite formed on the composite consisting of calcite and PLLA even after 30 days of soaking in SBF. The composites containing vaterite have much higher apatite-forming ability than the other composites containing calcite or aragonite without vaterite. The rapid apatite formation on the composites containing vaterite was suggested to originate from the integration of PLLA having carboxy groups bonded with calcium ions for the apatite nucleation and vaterite having an ability to effectively increase the supersaturation of the apatite.

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Porous glass-ceramics with bone-bonding ability, i.e. bioactivity, have been attractive as scaffold materials for bone regeneration, since their bioactivity and bioresorbability can be easily controlled by varying their composition. The prerequisite for artificial materials to show bioactivity is formation of a bone-like apatite layer on their surfaces in the body environment. This type of apatite formation can be observed in a simulated body fluid (Kokubo solution) which mimics the composition of human extracellular fluid. Previous studies revealed that the CaO-SiO₂ system is quite effective for the deposition of apatite in the body environment. Magnesium is one of the major inorganic elements existing in body fluid, and has already been used in bioactive glass-ceramics. Dissolution of glasses in the system CaO-SiO₂ could be controlled by addition of MgO. In this study, we synthesized porous glass-ceramics by heat treatment of glass powder with composition of 10MgO•40CaO•50SiO₂ mol% at various temperatures. Porous bodies with continuous pores about 500 μm in diameter were obtained after sintering and crystallization. Precipitation of para-wollastonite and diopside appeared after heat treatment at 900°C and more. The amount of precipitated diopside increased with increasing temperature of the heat treatment. The synthesized specimens formed apatite on their surfaces after soaking in Kokubo solution. Consequently, glasses in the system MgO-CaO-SiO₂ give easy production of porous glass-ceramics with bioactivity and bioresorption by a conventional sintering process.

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In this work, mechanical properties of α-tricalcium phosphate (α-TCP)-tetracalcium phosphate (TTCP)-dicalcium phosphate dehydrate (DCPD) system bone cement, was studied. This research examined the effect, which it follows in particle size distribution change of starting materials. The composition of α-TCP/TTCP/DCPD system bone cement was fixed Ca/P=1.50. 20 groups of cement were prepared with the particle size distribution. The highest compressive strength of the specimen(P/L ratio=2.5) after curing 7 days in simulated body fluid(SBF) was 60±2 MPa. That particle size distribution of the highest compressive strength was 10.33 μm(α-TCP=9.7 μm, TTCP=6.73 μm and DCPD=16.02 μm).

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Tricalcium phosphate (TCP) ceramics are bioresorbable materials that are used in several applications, such as filling for bone defects. A porous TCP body also shows promise as a drug delivery system. Recently, we developed an α-TCP porous ceramic with a continuous pore structure ranging between 10 and 50 μm. The higher surface area of the α-TCP porous body confers higher drug carrier performance. In the present study, the formation of mesopores on the surface of a scaffold consisting of an α-TCP porous ceramic has been attempted by treatment with a buffer solution. Porous bodies of α-TCP ceramic having continuous pores ranging between 100 and 200 μm and between 10 and 50 μm in size were fabricated by sintering a slurry composed of β-TCP and potato starch that was impregnated into a urethane sponge. The porous α-TCP ceramic body was exposed to a buffer solution at pH=4 at 36.5°C. The formation of octacalcium phosphate (OCP) and OCP incorporated with dicarboxylate (d-OCP) was observed on the surface and on the inside the porous body after soaking for 3 d. The OCP and d-OCP formed spherical particles of about 100 μm in diameter, which consisted of agglomerated finer, plate-like crystals. A peak in the pore-size distribution, occurring between 10 and 100 nm, appeared after soaking in the buffer solution. The formation of OCP and d-OCP brought about a remarkable increase in surface area of about 300X the value before soaking (43 and 0.13 m²/g, respectively). On the other hand, the porosity of samples soaked in the buffer solutions was lower than the porosity before soaking (60% and 73%, respectively). This decrease was due to the degradation of the α-TCP framework, and the formation of coarse OCP spherical particles. The formation of OCP and d-OCP was initiated by a slight dissolution of α-TCP on soaking, followed by precipitation of OCP and d-OCP on the porous body by the consumption of the calcium and phosphate ions from the surrounding solution. Consequently, treatment of an α-TCP porous body with a buffer solution can easily fabricate a calcium phosphate body that has a higher surface area through the formation of OCP with finer pores ranging from 10 to 100 nm, including mesopores.

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Electrical polarization processes were investigated on 45S5 type bioactive glass (BG) with the composition of 24.5 Na₂O, 24.5 CaO, 45.0 SiO₂ and 6.0 P₂O₅ (wt%). From the results of the thermally stimulated depolarization current measurements, two polarization processes were confirmed, which are considered due to the two migration processes of sodium ions during polarization. The processes depended on a magnitude of a dc field applied during polarization. Besides, the polarized surface reactions with blood interaction were studied. The surface charges on the BG were found to cause a change in the adhesion of some plasma proteins to the surface.

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Composites of hydroxyapatite (HA) granules implanted into the surface of a titanium alloy (Ti-4.5Al-3V-2Fe-2Mo) were successfully formed at a granule density of about 0.08 mg HA/mm² on titanium alloy disks 10 mm in diameter and 0.7 mm thick under the conditions of 1073 K, 10 min, 17 MPa. The entire material surface, with no damaged HA granules, became covered with proliferating human gingival epithelial (HGE-15) cells. This composite and the proposed method are expected to be useful for orthopaedic and dental implants such as stems, dental roots, and so on.

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Four types of commercial calcium phosphate ceramics, i.e. tricalcium phosphate, biphasic calcium phosphate, hydroxyapatite and near stoichiometric hydroxyapatite, were prepared by sintering at 1200°C for 2 h in air with moisture protection. Their dissolution characteristics were investigated by microstructural observations after immersion in distilled water at 37°C for 3 or 7 days. For all samples, no significant damage was observed after 3 days of exposure. However, after immersion for 7 days, grain boundary dissolution, even in pure hydroxyapatite, followed by grain separation occurred on the surfaces. The dissolution extended to interior region of the ceramics following along the grain boundaries. In the severely dissolved area, pitting similar to that normally attributed to osteoclast resorption lacunae was observed. In case of the material having a high percentage of porosity, dissolution was concentrated on those grains adjacent to pores rather than those in the dense region.

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Four kinds of hydroxyapatite powders (HAp) containing 1 mass% metal oxide (Al₂O₃, ZrO₂, TiO₂, SiO₂), together with dopant-free HAp, were prepared from analytical grades calcium hydroxide and phosphoric acid by a wet chemical synthesis. Metal butoxides were used as the metal sources. Obtained powders were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area analysis, and zeta potential measurement. XRD patterns showed that each of the metal-doped HAps was a single phase of HAp. The specific surface area of the Zr- and Al-doped HAps was greater than that of dopant-free HAp, while that of the Ti- and Si-doped HAps was smaller. Bovine serum albumin (BSA) adsorption on those HAps was also measured and the difference in the BSA adsorption was discussed in correlation to the zeta potential of HAps that was modified by doping the metal oxides.

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An effect of doping amount of MnO₂ in ZnO-MnO₂ solid solution on antibacterial activity was studied. ZnO-MnO₂ solid solution powders were prepared by heating at 1400°C for 3 h in air. A single phase with hexagonal structure was obtained in the samples mixed with the molar ratio (MnO₂/ZnO) below 0.11. The ratio above 0.15, however, resulted in γ-Mn₂O₃ phase in addition to solid solution. After milling the solid solution powders by planetary ball mill, the specific surface area of these powder samples became about 10 m² g^-1, which was used in the antibacterial activity tests by a colony count method. In antibacterial tests, it was found that the antibacterial activity increased with increasing the doping amount of MnO₂ in the range below the molar ratio of 0.11. The activity when the doping amount was above 0.15 in the ratio decreased and was similar to that of ZnO itself; that is, the antibacterial activity was less than that of ZnO doped with MnO₂ below the molar ratio of 0.11. The amount of hydrogen peroxide that contributes to the occurrence of antibacterial activity increased with increasing the doping amount of MnO₂ below the molar ratio of 0.11. Above the ratio of 0.15, however, hydrogen peroxide was found to decrease with increasing the doping amount of MnO₂ in powder sample.

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A wear characterization of commercial hip joint prostheses was conducted by means of a hip wear simulator. Bovine serum solution was used as a lubricant, and tests were conducted up to 5×10⁶ cycles. At first, the effect of testing conditions on wear of the hip joint prostheses was examined in order to determine the optimum conditions for hip simulator testing. As a result, it could be clarified that the serum concentration in the lubricating fluid and the intervals of time between lubricant replacements highly affect the wear of ultra-high molecular weight polyethylene (UHMWPE). Formation of a protein film on the acetabular cup and increasing wear at initial stage after lubricant replacement are likely the reasons for this phenomenon. By using standardized conditions, long-term simulator tests are conducted against six types of commercial hip joint prostheses. The results clearly reveal the difference in wear resistance of each combination. The present data can be considered to be reference data for developing new types of hip joint prosthesis.

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In the present study, the effect of a high magnetic field, “magneto vector field effects”, on the development of their microstructure of ceramics was mainly investigated. The compactions of hydroxyapatite with an addition of disodium phosphate were in-situ sintered at 1000°C and 1100°C in air atmosphere under a high magnetic field of 10 tesla. Their microstructures of hydroxyapatite sintered bodies were evaluated by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM) observation. It was found that hydroxyapatite with an additive prepared by in-situ sintering with a high magnetic field in an air atmosphere possessed significantly higher relative density than ones sintered under 0 tesla. These results might show the enhancement of densification on in-situ sintering with the effect of magnetic field.

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So-called bioactive ceramics have attractive features on bone repair because they spontaneously bond to living bone when implanted in bony defect. However, they are much more brittle than natural bone, leading to limitation of their clinical application to low loaded conditions. Metallic materials with high fracture toughness are clinically utilized for bone repair under load-bearing conditions. Their problem is that they do not possess ability of bone-bonding, i.e. bioactivity. The prerequisite for artificial materials to show bioactivity is formation of a bone-like apatite layer on their surfaces in the body environment. This type of apatite formation can be reproduced in a simulated body fluid (SBF) which has inorganic ion concentrations similar to those of human extracellular fluid. It is known that heterogeneous nucleation of the apatite is triggered by specific functional groups such as Si-OH, Ti-OH, Zr-OH, Ta-OH, Nb-OH, COOH, phosphate groups. We previously found that the apatite was deposited on titanium and tantalum metals in SBF, when they were subjected to chemical modification using alkali solution and subsequent firing to form such functional groups. This means that bioactivity can be induced on these metals by the modification. In the present study, we precisely observed interface between the apatite layer and the bioactive metals. Sodium titanate and sodium tantalate layers formed on the titanium and tantalum metals, respectively, after the NaOH and heat treatments. Both the sodium titanate and sodium tantalate layers showed smooth graded structure where the surface regions are rich in sodium and oxygen and the metal components increase with increasing the depth from the surface. This type of graded structure was maintained even after the apatite deposition in SBF, where the concentrations of apatite gradually changed from the surface to the interior metal. Tight bonding of the apatite layer to the metal substrates was observed. The tight bonding is attributed to this type of specific structure. Modification of the surface of titanium and tantalum with chemical and subsequent heat-treatment produces gradient structure showing not only bioactivity but also tight bonding of the metals to living bone.

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Role of albumin on the biomimetic formation of calcium phosphate on collagen fibrils has been studied. Studies were done on the co-precipitation of BSA and calcium phosphate on collagen fibrils and precipitation of calcium phosphate on the collagen fibrils pre adsorbed with BSA. Appreciable changes in the morphology and crystallinity of the precipitates were observed with increase in concentration of BSA in the case of co-precipitation. The formation of spherical precipitates along the fibrils tended to change partially to a plane deposit along the fibrils. Thin film XRD and EDX study has confirmed that the precipitates formed were apatite. While the morphology of the precipitates were affected even for 1 mg/ml of BSA when pre adsorbed but crystallinity was affected gradually with increase in concentration of BSA. FT-IR study has confirmed the formation of B-type carbonated bone-like apatite and the presence of BSA in the precipitates formed from both methods.

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#80 and #200 titanium meshes were coated with apatite using a hydrothermal-electrochemical method. The deposits on the titanium mesh were compared with those on a titanium plate. Apatites were homogeneously formed and vertically oriented to the surface of the titanium woven fiber and grid. Both the morphology and dimensions of the deposited apatites could be easily regulated by the electrolytic conditions. The results indicate that the apatite coating by the hydrothermal-electrochemical method is suited to a substrate such as mesh having a complex shape and a large specific area.

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We are trying to fabricate porous grafts with an optimum macropore network for bone regeneration by integrating hydroxyapatite (HA) tiny units. In this study, φ1 mm spherical HA ceramics with a φ300 μm through-hole (HA beads) were prepared as a model of the unit. By integrating the HA beads, the through-holes could be connected through gaps between the HA beads, thus constructing an interconnected macropore network. Micro X-ray CT analysis of the integrated HA beads proved that the through-holes and the gaps produced an interconnected network. The macro-porosity of the integrated beads was 47.7±1.9%. Bone regeneration in the macropore network was evaluated by an animal test. After 7 days, favorable developments for bone repair were confirmed in the macropore network. This result showed that the HA beads can be the minimum unit to construct an effective macroporous graft for bone regeneration.

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Biodegradable porous composites were fabricated from hydroxyapatite (HAp) and Poly(lactic acid) (PLA) microspheres for bone grafts. A novel surfactant-free emulsification method was employed for preparation of HAp/PLA microspheres containing hydrophobic material which was used as a substitute for therapeutic agents. The microspheres were molded into porous composite discs by use of PLA as a glue. Composites having hierarchically ordered structure were obtained from only biodegradable microspheres under the condition at ordinary temperature.

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The recent development of fabrication process for thermal barrier coatings (TBCs) has been reviewed. Yttria stabilized zirconia (YSZ) is commonly applied to TBCs for Ni-based super alloys. Although YSZ coatings have been commercially produced by atmospheric plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD), the increase in operation temperatures of gas turbines demands another fabrication process to develop high quality TBCs. Chemical vapor deposition (CVD) can be an alternative route to provide high performance TBCs due to its excellent conformal coverage and controllability of microstructure. This review paper has focused on the fabrication of YSZ films by CVD. A new laser CVD technique enabling high deposition rates competitive to APS and EB-PVD has been also briefly introduced.

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Magnetic properties of La_1-xSr_xMnO₃ nanoparticles (φ≈2∼3 nm) of x=0 and 0.15 embedded in amorphous SiO₂ were examined. Both the antiferromagnetic (x=0) and ferromagnetic (x=0.15) samples exhibited superparamagnetism with the blocking temperature of ≈40 K. In the temperature dependence of dc susceptibility, the x=0 sample showed a hump at ≈40 K overlapping with a paramagnetic divergence. Aside from the blocking at ≈40 K, the x=0.15 sample demonstrated ferromagnetic characteristics below ≈250 K. The field dependence of magnetization of the x=0 sample is consistent with the prediction of a system consisting of randomly oriented and noninteracting antiferromagnetic fine particles (φ≈2.5 nm). Ferromagnetic moments of the x=0.15 sample was largely suppressed from that expected for the system of independent ferromagnetic fine particles (φ≈2.5 nm).

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Nanostructures and nonlinear optical properties of cobalt oxide (Co₃O₄, CoO) thin films were studied. Both the Co₃O₄ and CoO thin films consisted of grains with a 7.5 nm average grain size. Complex refractive index (ñ=n-ik) of the Co₃O₄ thin film changed from 1.91-0.85i to 2.70-0.65i by laser beam irradiation at a wavelength of 405 nm, and it also changed from 3.31-1.15i to 3.05-0.60i for λ=650 nm irradiation. On the other hand, ñ of the CoO thin films irradiated at λ=405 and 650 nm were 1.75-0.32i and 2.41-0.18i, respectively, and they were constant as a function of laser intensity. Co₃O₄ had band gap energies of 2.0 and 1.3 eV, while that of CoO was about 3.7 eV. Therefore, Co₃O₄ absorbed the irradiated laser beams and interacted with them, but CoO did not because it was transparent to them. The reversible change of ñ of the Co₃O₄ thin films by thermal treatment was also observed, and a band structural change of the Co₃O₄ thin film induced by thermal treatment was identified. The band gap energy near 2.0 eV did not show any significant changes when treated. However, the other band gap energy near 1.3 eV had a large shift, and absorption coefficient, α₀, decreased greatly when thermally treated. Therefore Co²⁺O₄ ^2- tetrahedrons in Co₃O₄ normal spinel did not change remarkably, but a drastic deformation of Co³⁺O₆ ^2- octahedrons occurred on thermal treatment, which caused the large change of refractive index of the Co₃O₄ thin film.

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TiO₂-3YSZ (ZrO₂-3 mol%Y₂O₃) and TiO₂-8YSZ (ZrO₂-8 mol%Y₂O₃) solid solutions were prepared by solid state reaction. With increasing TiO₂ contents in 3YSZ, the crystal structure changed from a monoclinic, tetragonal and cubic mixture to a tetragonal single phase. The thermal conductivity of TiO₂-3YSZ decreased from 5.7 to 3.0 W/mK with increasing TiO₂ content from 0 to 20 mol%. In the TiO₂-8YSZ, the crystal structure changed from a monoclinic single phase to a tetragonal and cubic mixture with increasing TiO₂ contents. The thermal conductivity of TiO₂-8YSZ was almost independent of TiO₂ contents indicating slight minimum of the thermal conductivity of 1.7 W/mK at about 10 mol%TiO₂.

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ZnO nanowires with tetrapod shape were formed on the surface of the sample by the directive oxidation process of Al-Zn alloy at 1000°C in air. The average diameter of the nanowires was 50 nm and the length was several tens of micrometers. X-ray diffraction data of the nanowires proved that the nanowires were ZnO with wurtzite structure of hexagonal phase. Energy dispersive X-ray spectrum revealed that the nanowires were composed of Zn and O. Their estimated c- and a-axis lattice parameters of 0.520 nm and 0.325 nm were in well accordance with those of bulk ZnO single crystal, indicating high quality crystallinity. The green light emission at wavelength of 510 nm was observed at room temperature, which was attributed to higher density of oxygen vacancies in nanowires in comparison with bulk crystal.

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The following is a report on the photosensitivity of Ag-doped glasses. Success was achieved in the precipitation of silver particles into glasses by the irradiation of femtosecond laser pulses. A condensation area of silver particles was observed at a bottom of the irradiated area. The condensation area was approximately 5 microns in diameter, measured by Electron Probe Micro Analyzer (EPMA). A diffraction grating was also fabricated inside the Ag-doped glass by the irradiation of femtosecond laser pulses. This grating shows high diffraction efficiency. We also demonstrated the possibility of an electrical wiring in the glass precipitated with silver particles. These results will be applicable to three-dimensional (3D) wiring and functional optical devices such as optical memory, optical switches, and 3D photonic crystal devices.

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