Solvothermal reactions are designated as the reactions which use high temperatures and/or high pressure solvents. It is possible to control the acid–base reaction rate, morphology and agglomeration of the products, i.e., well dispersed nanoparticles with high crystallinity can be obtained by solvothermal reactions. Therefore, solvothermal reactions are expected to be used to generate environmentally friendly functional ceramic materials. Actually, various functional ceramics, such as tetragonal zirconia, with excellent thermal stability and mechanical properties, visible light responsive photocatalyst for environmental clean-up, high performance UV-shielding materials, etc. have been fabricated by solvothermal reactions. Unique plate-like ceria microparticles and the new Sn(II) titanate based compound which are impossible to be formed via a normal solid state reaction have also been formed.

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Silica (SiO₂), magnesia (MgO), and alumina (Al₂O₃) are principal oxides composed of third period elements. These oxides are prerequisite materials in the field of ceramic science and technology but are not regarded as functional materials in their pure forms. In our recent publications, however, we have demonstrated that these refractive oxides can exhibit efficient ultraviolet/visible emissions by carefully controlling their microscopic structure and stoichiometry without adding any activator metals. Some intriguing properties, such as white light emission, random lasing, photoinduced reversible interconversion of color centers, have been achieved. The present approach will open up new routes and new strategic issues to produce highly functionalized materials consisting solely of third period elements.

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Intercalative inorganic–organic hybrids with useful properties have attracted much attention owing to their potential applications in various kinds of devices. The development of thin film process is crucial to realize a novel device using the hybrid materials. Thin films of the intercalated organic/MoO₃ hybrids have been prepared by an ex-situ intercalation process. The host MoO₃ films were first deposited on substrates by using a CVD method followed by the intercalation of organic components into the MoO₃ films. The preparation of highly b-axis oriented MoO₃ films is essential to prepare the organic/MoO₃ films. The organic/MoO₃ films show semiconducting-like transport. The organic/MoO₃ films show a distinct response to VOCs by changing their electrical resistivity and exhibit higher sensitivities to aldehyde gases, whereas almost no response to toluene and xylene. The VOC sensing performance is closely related to the microstructure of the organic/MoO₃ thin films, which is able to be controlled by the growth conditions of the host MoO₃ thin films.

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Porous glasses with the surface area of ≈300 m²/g were prepared utilizing the spinodal-type phase separation of Al₂O₃-doped Na₂O–B₂O₃–SiO₂ glasses. The proton conductivity under humidified conditions and their relations to the amount of doped Al₂O₃ were investigated. The proton conductivity of the glass doped with 2 mol % of Al₂O₃ was about 6 times higher than that of the undoped glass. Fourier transform infrared (FT–IR) measurements revealed that the absorption by the strongly hydrogen-bonded OH groups increased with increasing the amount of Al₂O₃. Bond overlap populations (BOPs), which are directly related to the strength of the covalent bond, between the surface OH groups and an absorbed water molecule were calculated based on a first-principles theory (DVXα). The BOP values between O and H of the surface OH groups decreased by the Al₂O₃ doping. Substitution of Si atoms of the Si–O–Si silica networks with Al atoms, and formation of the Al–OH–Si bonds effectively improved the proton conductivity under humidified conditions.

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BaTi₄O₉ ceramics with Sm₂O₃ addition were prepared in a form of xSm₂O₃+BaTi₄O₉ (x = 1, 3, 5, 7 mol %) and the microstructures and microwave dielectric properties of the ceramic samples were characterized. SEM shows when x greater than 3 mol %, BaSm₂Ti₄O₁₂ crystallized in a fiber shape along the crystalline boundary. With the increase of Sm₂O₃ addition, the dielectric constant increases from 36.65 to 39.8, while the quality factor decreases from 28000 to 19000, τ_f from +20.2 to +10.1 ppm/°C. Results of curve fitting of FIRS show extrinsic dielectric loss could account for the increase of dielectric loss, which should be attributed to the substantial increase of Ti³⁺ and Ti²⁺.

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Fine-structured ZnO patterns with sub-micrometer based on a replication method was fabricated. A replication method was used mixtures of polyvinyl alcohol (PVA) and ZnO nanosized particles in water. The mixtures were then filled in a quartz mold with different pattern sizes and dried at room temperature. After the drying, the PVA and ZnO dried film was detached from the mold. Through burn-out at various sintering temperatures, ZnO patterns with line and space patterns as smalls as sub-micrometer in size were successfully fabricated. The results demonstrated possibilities to produce inorganic materials with various compositions and structures with a facile approach and a simple method.

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La_0.6Sr_0.4Al_xFe_1−xO_3−δ (LSAF) mixed ionic electronic conducting membranes have been sintered, and the substitution of Al for Fe reduced the density of the sintered body including large defect of pore channels. The sintering behavior of the La_0.6Sr_0.4Al_0.1Fe_0.9O_3−δ samples have been studied under different oxygen partial pressure, P_{O_2}, and a post process of hot isostatic pressing (HIP) has been carried out. The thermal expansion coefficients and the differential expansion ratios measured in air and under reducing atmosphere for these samples were 15.6 × 10⁻⁶/K⁻¹ and 0.37%, respectively, and were not affected by the sintering process. The density of the sample sintered in air was 96.5% and the HIP increase the density of the sample up to 99.6%, eliminating the pores. The three point flexural strength of the HIP sample at 25 and 1000°C were 265 and 208 MPa, respectively, and the oxygen permeation rate of the HIP treated membranes with the thickness of 0.5 mm was 8 cc/min/cm².

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Carbide based ceramics are frequently used for the tribological applications, such as mechanical seals, owing to their good mechanical and chemical properties. Recently, studies of the tribological properties of these applications have become increasingly important due to the increasing need for severe operating conditions. In this study, the surface modification of carbide ceramics was attempted to improve the triblogical properties. Carbon layers were prepared on SiC–TiC ceramics using a moderate and high temperature chlorination process. The microstructure and worn surfaces were analyzed by scanning electron microscopy and an α-step profilometer, respectively. Tribological tests were carried out on chlorinated SiC–TiC surfaces using a ball on disc wear tester. Since carbon atoms in TiC were derived at lower temperatures than SiC, the distribution of carbon atoms within the modified layers were synthesized by the difference in reaction temperature and reaction time. The tribological properties were varied by the volume fraction of carbon and SiC in the modified layer. The friction coefficient and wear rate were decreased by controlling the structure and composition of the carbon based layer from 0.22 to 0.18 and 7.91 to 1.92 (×10⁻⁶ mm³/N·m), respectively.

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The lithium intercalation properties of alkai tetratitanate (Li₂Ti₄O₉·1.1H₂O, Na_1.5H_0.5Ti₄O₉·0.53H₂O) and octatitanate with various amounts of hydrated water (H₂Ti₈O₁₇·nH₂O; n = 0.41, 0.96, 1.5) were examined. Alkali tetratitanates were obtained by ion exchange of the starting tetratitanate hydrate (H₂Ti₄O₉·1.9H₂O) and subsequent heat treatment. Octatitanates were prepared by heat treatment of the starting tetratitanate hydrate. The prepared titanates exhibited a reversible capacity corresponding to a reduction of half of the Ti atoms from a tetravalent state to a trivalent state. This indicates that the reaction activity of the host oxide layer of titanates is not affected by the condensation reaction during transformation from tetratitanate to octatitanate. H₂Ti₈O₁₇·0.41H₂O showed the largest capacity and best rate capability among the prepared titanates; this is because of its relatively small chemical formula weight per Ti atom. The difference in the rate capability of the titanates is caused by the steric effects of hydrated water molecules in the lithium diffusion path along the b-axis.

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We have developed the high ionic conducting glass-ceramics with the crystalline phase of Li_1+x+yAl_x(Ti_2−yGe_y)P_3−zSi_zO₁₂ with the NASICON type structure. This type of glass-ceramics exhibits high lithium-ion conductivity of 10⁻⁴ S cm⁻¹ or more at room temperature. Although this glass-ceramics reacts with Li metal gradually with the passage of time, we have improved the thermal and electrochemical properties by controlling constitution of Ti and Ge in the Li-ion conducting glass-ceramics with the NASICON type structure. Those glass-ceramics worked well as electrolyte of a lithium-ion secondary battery by the charge–discharge test using a half cell with LiFePO₄ cathode at room temperature.

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SiO₂ surface layer of SiC filler particles decreased thermal stability and creep resistance of particulate-reinforced Si–C–N-based ceramic composites made by precursor-impregnation and pyrolysis (PIP) method due to the decomposition of SiO₂ at and above 1350°C. The oxide layer could be removed by a pre-treatment of SiC particle compact at 1750°C in Ar before precursor impregnation. The composites fabricated with pre-treated SiC compact show clear improvements in thermal stability and creep resistance.

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Scandium aluminum nitride alloy (Sc_xAl_1−xN) thin films were prepared using rf magnetron sputtering with a scandium aluminum alloy (Sc_0.42Al_0.58) target on n-type (100) silicon substrates. We have investigated the effects of 4 sputtering control factors, which are substrate temperature, sputtering pressure, nitrogen (N₂) concentration and cathode power, on the piezoelectric constant d₃₃ of Sc_xAl_1−xN films using design of experiments. Consequently, it is statistically proved that N₂ concentration in sputtering gas is the most important control factor. The piezoelectric constant d₃₃ indicates the maximum value of 19.0 pC/N at N₂ concentration of 25%. The composition of Sc_xAl_1−xN films prepared under optimized sputtering conditions is Sc_0.38Al_0.62N, and there is the composition difference between the ScAl alloy target and the thin film. However, the piezoelectric constant of the Sc_0.38Al_0.62N film is coincident with that of Sc_0.38Al_0.62N films prepared by dual co-sputtering. Thus, it is possible to prepare high piezoelectric Sc_xAl_1−xN films by using the ScAl alloy sputtering target. ScAl alloy targets are effective for keeping scandium concentration constant in Sc_xAl_1−xN thin films.

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Anatase-type titania nanoparticles co-doped with niobium and gallium (Ga_XTi_1−2XNb_XO₂ solid solutions in the range of X = 0–0.20) were formed from precursor solutions of TiOSO₄, NbCl₅, and Ga(NO₃)₃ under hydrothermal conditions at 180°C for 5 h using the hydrolysis of urea. The effect of dopant materials on the structure, crystallite growth, photocatalytic activity, and phase stability of anatase-type TiO₂ was investigated. The lattice parameters a₀ and c₀ of anatase slightly and gradually increased with increase in niobium and gallium content doped into TiO₂. The anatase solid solutions doped with niobium and gallium (X = 0.10–0.15) showed good photocatalytic activity. Co-doping niobium and gallium into TiO₂ shifted the anatase-to-rutile phase transformation to lower temperature. The temperature range of the anatase-to-rutile phase transformation for the Ga_XTi_1−2XNb_XO₂ solid solutions became narrower than that for pure TiO₂. The rutile-type Ga_XTi_1−2XNb_XO₂ solid solutions were formed via the phase transformation.

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In this paper, the 0.98(Na_0.5K_0.5)NbO₃–0.02Ba(Sn_0.02Ti_0.98)O₃ ceramics with the addition of 0–4.0 wt % Mn₂O₃ have been prepared following the conventional mixed oxide process. The disc samples were sintered in alumina crucible at 1100°C for 3 h in air. For 0.98(Na_0.5K_0.5)NbO₃–0.02Ba(Sn_0.02Ti_0.98)O₃ ceramics, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.31 and 0.39, respectively. In the low Mn₂O₃ content region (≤1 wt %), the decrease of dielectric constant, dielectric loss tangent and planar coupling factor together with the enhancement of mechanical quality factor correspond well to the feature of a hard doping effect on the electrical properties. For 0.98(Na_0.5K_0.5)NbO₃–0.02Ba(Sn_0.02Ti_0.98)O₃ ceramics by doping 1.0 wt % Mn₂O₃, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.29 and 0.47, respectively, at the sintering of 1100°C for 3 h. The significant rise of dielectric loss tangent and degradation of mechanical quality factor in the high Mn₂O₃ content region (≥2 wt %) may be attributed to the appearance of distinct pores in the microstructure. With suitable Mn₂O₃ doping, a dense microstructure and good electrical properties were obtained.

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Hybrids of β-tricalcium phosphate (β-TCP) and poly(L-lactic acid) (PLLA) have been fabricated, which can be expected to be a novel filler for biodegradable bone grafting. Firstly, porous β-TCP ceramics have been made of calcium-phosphate fiber synthesized by homogeneous precipitation method. Then, the hybrids have been fabricated by introducing PLLA having high-molecular-weight into the open pores of the porous β-TCP ceramics. The mechanical property was enhanced, for example, by annealing the hybrids at 140°C for 24 h; the bending strength was 17.1 MPa, which was about 1.5 times that of the porous β-TCP ceramics. The biocompatibility has been examined using osteoblastic cell, MC3T3-E1, and found to be comparable to that of pure β-TCP ceramics.

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Silicon nitride films were deposited in SiH₄–NH₃–N₂ plasma at room temperature by using a plasma-enhanced chemical vapor deposition system. SiN film characteristics examined as a function of radio frequency bias power include a deposition rate, a refractive index, and a surface roughness. Ion energy diagnostics was also conducted to analyze in detail the bias power effect. An increase in ion energy and a decrease in ion energy flux were observed with increasing the bias power. Several relationships between ion energy variables and film properties were identified. For all the variations in the bias power, the deposition rate, the refractive index, and the surface roughness varied in the range of 185–532 Å/min, 1.89–2.48, and 0.24–0.96 nm, respectively. Very high refractive index could be achieved by controlling the bias power.

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X-ray computed tomography (X-ray CT) was performed to evaluate defects in a joined silicon nitride sample. The resolution of the X-ray CT was about 10 µm. ZrO₂ particles (ZrO₂ was added as a sintering additive), segregation of Zr, and cracks were successfully observed. These defects were most likely introduced during the fabrication procedure, i.e., by insufficient milling of the ZrO₂, separation of ZrO₂ in the slurry, and cracking during drying after slip-casting. X-ray CT is demonstrated to be a useful evaluation method, since these defects are introduced not only by joining but also by usual ceramics processing.

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Hydrothermal synthesis proves to be a feasible route to fabricate hydroxyapatite nanoparticles. The study reports the combinational effects of temperature and various counterions, such as SO₄²⁻, Cl⁻, and K⁺, on the morphology of hydroxyapatite nanoparticles. The resultant nanoparticles are investigated using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The results show that the effects of temperature and different counterions are significant, and hydroxyapatite nanoparticles with the morphology of nano-platelet and nano-rod are produced without the addition of any organic surfactants. The process described will be beneficial to industry by lowering production costs, and contributing to ever increasing need to eliminate contamination to environment.

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A simple thermal decomposition technique to convert asbestos-containing wastes (ACWs) into non-asbestos products has been developed by heating ACWs in a water vapor atmosphere. It was confirmed that cement slates containing 18 mass % chrysotile were converted into non-asbestos products by the thermal treatment in a water vapor atmosphere at 800°C for 2 h. In contrast, the thermal treatments in air required temperatures as high as 900°C to convert the cement slates into non-asbestos products. It should be noted that any chrysotile particles were not detected by the phase-contrast microscopic observation in the products after the thermal treatments in a water vapor atmosphere at temperatures beyond 800°C but three or less chrysotile particles remained after the thermal treatments in air at high temperatures beyond 900°C. In a water vapor atmosphere, ACWs were successfully converted into non-asbestos products at low temperatures below 800°C for 2 h by accelerated solid-state reactions between decomposed products of chrysotile and cement components to form calcium magnesium silicates. This technique may contribute to large-scale decomposition of ACWs with low energy consumption in comparison with the traditional melting method.

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La_0.8Sr_0.2MnO₃ (LSM) cathode films for a solid oxide fuel cell (SOFC) were formed on a solid electrolyte sheet using the electrophoretic deposition (EPD) technique. The EPD process was undertaken in methanol suspensions containing LSM particles with different mean particle sizes. The zeta potentials of the LSM dispersions in methanol tended to decrease with increased sintering temperature during powder preparation. The morphology of the cathodic films was significantly dependent on the mean particle size and the grain sizes in the films after sintering at 1100°C were in the order of LSM600 > LSM1000 > LSM800, with corresponding cathodic performance in the order of LSM800 > LSM1000 > LSM600. The morphology of the LSM 800 films varied with the DC voltage applied during the EPD process (7.5 and 15 V), and a more densely deposited phase with finer pores was achieved with lower applied voltage. Increase in applied voltage tended to induce particle growth; therefore, the film applied at low voltage exhibited the highest cathodic performance. The cathodic performance was not dependent on the film thickness in the range between 5 and 15 µm, which implies that the LSM800 film was sufficiently porous to provide a suitable rate of oxygen gas diffusion.

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MgFe₂O₄ microspheres having a 20–32 µm diameter range were prepared by a spray dryer using bead-milled nano-sized particles. A commercial powder having a several µm particle size was bead-milled to an approximate 6.2 nm crystallite size. The microspheres were obtained using the spray dryer when the air pressure was low (0.03 MPa). The yield of the MgFe₂O₄ 20–32 µm microspheres was improved by combination of a low air pressure and high ferrite concentration in the slurry. The heat generation ability in an AC magnetic field (370 kHz, 1.77 kA/m) was improved by the bead milling.

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Porous ceramics based on refractory double oxides are promising for light-weight structural components and high-temperature filter materials. In this study, porous MgTi₂O₅ ceramics with pseudobrookite-type structure have been prepared by in situ processing (viz. reactive sintering). High-temperature XRD revealed the in situ reaction behavior of the mixed powder, and indicated suitable sintering temperatures to obtain single phase MgTi₂O₅ (≥1000°C). Uniformly porous MgTi₂O₅ ceramics with very narrow pore-size distribution at the diameter of ∼1 µm were obtained by the pyrolytic reactive sintering at 1000–1200°C, where decomposed CO₂ gas from a carbonate source acted as an intrinsic pore forming agent. Thermal expansion behavior of bulk porous MgTi₂O₅ (porosity: 42%) is also discussed.

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CuLa_1−xEu_xO₂ polycrystalline specimens were successfully prepared by the solid-state reaction method. X-ray diffraction measurement revealed that CuLa_1−xEu_xO₂ (0.01 ≤ x ≤ 0.2) was a single phase with the delafossite structure with successful substitution of Eu³⁺ into the La³⁺ site at the center of the LaO₆ octahedron. Orange luminescence due to ⁵D₀–⁷F_0,1 transitions was observed in photoluminescence spectra of CuLa_1−xEu_xO₂, although Eu³⁺-containing materials usual show red luminescence due to the ⁵D₀–⁷F₂ transition. This luminescent color difference suggests that rare earth ion doping into a delafossite-type oxide is promising for constructing new color-luminescent materials.

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