We prepared HfO₂–Al₂O₃ nanocomposite films using chemical vapor deposition. Fibrous and lamellar microstructures formed in the monoclinic and tetragonal HfO₂ (m/t-HfO₂)–α-Al₂O₃ films at deposition temperature of 1573 K and Al mole fraction in the precursor vapor of 36–74 mol %Al₂O₃. Characterization by electron microscopy revealed that the m/t-HfO₂ fibrous and lamellar structures are present throughout the α-Al₂O₃ columnar matrix above 50 mol %Al₂O₃ (55 vol %Al₂O₃), while α-Al₂O₃ lamellar structure was formed in m-HfO₂ matrix below 50 mol %Al₂O₃.

To investigate the texture formation mechanism in aerosol deposition (AD), coatings were deposited under various conditions using pure α-Al₂O₃ powder particles. The deposition rate increased with increasing gas flow rate when the gas flow rate was in the range from 6 to 30 L/min. Furthermore, the deposition rate increased with increasing substrate heating temperature. No large difference in the microstructure of the α-Al₂O₃ coating was observed. The formed α-Al₂O₃ coatings was fully dense and crystalline. X-ray diffraction analysis of the coating surfaces revealed specific textures. A texture with (0001) planes tilted approximately 15° from the coating plane was detected in the as-deposited specimen at a nozzle angle of 90°. Whether the nozzle angle was 90 and 60°, almost the same texture was formed indicating that the shear force does not contribute to texture formation. Texture formation was due to plastic deformation of the α-Al₂O₃ powder during collisions with the substrate. This is thought to be due to activation of basal and pyramidal slip systems. When the substrate was heated during AD, the texture changed to a (0001) fiber texture where the (0001) planes were parallel to the coating surface. The change in texture during substrate heating can be explained by a change in the critical resolved shear stress for the slip systems. The authors have previously reported that (0001) fiber texture has formed when the specimen was heat treated after the coating was deposited at room temperature. However, the mechanism of (0001) fiber texture formation by heat treatment is different form this research. During heat treatment, the texture is formed by the preferential growth of grains having (0001) plane at the surface of the coating.

SrHfO₃ films were prepared using metal–organic chemical vapor deposition (MOCVD) with hafnium tetrakis(acetylacetonate) and two different Sr precursors, and the effects of Sr content in the vapor and deposition temperature on crystal phase and microstructure were investigated. With the strontium bis(dipivaloylmethanate) [Sr(dpm)₂] precursor, low Sr content of the deposited films regardless of Sr supply ratio resulted in no detectable SrHfO₃ formation. With the strontium bis(hexafluoroacetylacetonate) [Sr(hfa)₂] precursor, along with linear increase of Sr content in the deposited films, the primary crystal phase of the film changed from monoclinic HfO₂ to orthorhombic SrHfO₃ to SrCO₃. A single-phase orthorhombic SrHfO₃ film was prepared with the Sr(hfa)₂ precursor at 1373 K and 42 mol %Sr (corresponding to 50 mol %Sr in the film).

The oxygen shielding properties and structural stability of polycrystalline Y₂Ti₂O₇ (YT) solid solution wafers, which were cut from a sintered body and served as models for environmental barrier coatings, were evaluated by the oxygen permeation technique at high temperatures. Here, we examined the effect of compositions by using two samples with slightly different Y/Ti molar ratios. The oxygen permeability constants for YT increased dramatically with a slight increment in the Y/Ti molar ratio, and the activation energy for oxygen permeation markedly decreased. Oxygen permeation in the YT was controlled by the diffusion of oxide ions in the crystal. Almost no decomposition of the YT phase occurred due to migration of the constituent cations at high temperatures, indicating high structural stability under an oxygen potential gradient. The crystal structure was identified as the YT-based pyrochlore structure from Rietveld refinements of synchrotron radiation X-ray powder diffraction data, based on information on the composition dependence of the defect concentrations in the crystals estimated by first principles calculations. The diffusion path for oxide ions in the crystal at high temperature was also investigated based on a spatial distribution map described by the bond valence sum method. Finally, the mechanisms for the uptake of oxygen molecules on the YT surface exposed to a high oxygen partial pressure and the subsequent diffusion of oxide ions in the YT crystals were clarified.

In a pilot study zirconia/zircon, and zirconia/yttrium-monosilicate composite coatings for oxide ceramic matrix composites (Ox-CMC) with highly porous matrices were fabricated by deposition of powder dispersions (‘slurries’) and subsequent firing. During firing, thermal degradation of Ox-CMC as well as constrained sintering of powder compacts deposited on the rigid CMC substrate are key challenges. The oxidation-related volume expansion of zirconium-disilicide starting powders and reactivity of oxidation products zirconia and silica were used to compensate shrinkage and provide consolidation of powder compacts at process temperatures of 1300 °C. Similar processes are commonly referred to as ‘reaction-bonding’. Well-adherent, crack-free reaction-bonded coatings could be fabricated on Whipox-type Ox-CMC. Resulting microstructures are strongly depending on the composition, morphology, and reactivity of constituents, in particular of transient oxide phases. Zirconia/zircon reaction-bonding systems yield composite coatings with relative low porosity whereas as much lower densification capability of the zirconia/yttrium-monosilicate system was observed.

A new interface fracture test was developed for ceramic environmental barrier coatings (EBCs) on ceramic matrix composites (CMCs). The proposed test modifies an existing test in order to simplify specimen preparation. An asymmetric double cantilever beam (ADCB) test specimen with a stiffener adhering to the coating was used, and a wedge was inserted into the notch to open it. A formula to calculate interface toughness using the notch opening load and displacement was derived; it was expanded so that the toughness could be obtained from the wedge insertion load and displacement. The interface toughness of a model EBC/substrate system consisting of a mullite layer and Si bond coat on a monolithic SiC plate was measured to examine the validity of the test. The obtained interface toughness was in good agreement with that obtained by the original test in the previous study. The interface to be fractured was controllable by adjusting the position of the notch.

The fluorination of Yttria (Y₂O₃) coatings in the inner chamber wall of a plasma-etching equipment causes a process drift. In this paper, we investigate the relationship between the microstructure and fluoride layer of Y₂O₃ coatings prepared by aerosol deposition (AD) method compared with Y₂O₃ coatings prepared by atmospheric plasma spraying (APS) and ion plating (IP). The plasma corrosion of AD-coating, which has a highly dense microstructure without any pores, proceeded homogeneously and the specific surface area maintained its initial smooth surface. Moreover, F atoms slightly penetrated the AD-coating and formed a very thin, 45-nm fluoride layer after plasma exposure. The total area of the surface fluoride layer did not increase with plasma exposure time because the surface remained smooth. Therefore, Y₂O₃ coating prepared by AD can suppress surface fluorination and process drift compared with Y₂O₃ coatings prepared by APS and IP.

We developed a simple, rapid, and accurate method to determine the quantity of sulfur in soda-lime silicate glass using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and sulfur separation using an alumina column. This method requires a smaller number of samples and takes less time for the analysis than conventional methods. The samples of glass were decomposed using hydrofluoric acid, perchloric acid, and an oxidizing agent. For the amber glass samples, the oxidizing agent used was potassium permanganate. The decomposed solution was diluted with perchloric acid. The solution was passed through an alumina column to enable sulfur adsorption on the column. To desorb sulfur from the column, diluted ammonia was passed through it after rinsing it with diluted perchloric acid. ICP-AES was used to determine the quantity of sulfur in the ammonia eluent. The method was validated using three certified glass samples. The sulfur quantities determined by this method were within the certified values. The relative standard deviation of the determined values was less than 2 %.

The spherical porous granules of octacalcium phosphate (OCP) and hydroxyapatite (HA) have the potential for applications in scaffolds for bone regeneration. The spherical porous alpha-tricalcium phosphate granules were immersed in a pH 5.0 buffer solution that contained 0.1 mM of ascorbic acid phosphate (AscP), an osteogenesis-promoting drug, at 60 °C. This resulted in the fabrication of the AscP-loaded spherical porous HA/OCP granules. The OCP and HA phases were concentrated at the surface and interior of the granules, respectively. Furthermore, the HA/OCP core/shell-like structure of the granules was observed for the first time. The loaded AscP in the HA/OCP granules was slowly released in a pH 7.4 buffer solution. The differentiation of the osteoblast-like cells was promoted by the AscP-loaded HA/OCP granules. These granules possessed the potential for applications in artificial bones to promote bone regeneration.

In Y₂O₃ ceramics densified at 1000 °C by spark plasma sintering (SPS), non-uniform sintering behavior of grains and pores occurred for a heating rate of 20 °C/min. The sintered Y₂O₃ was translucent at the periphery but white and opaque at the center. According to microstructural analysis, the non-uniform sintering was caused by rapid grain growth and pore coarsening at the center. Under complicated electric and magnetic fields during SPS, an assumption of the movement of defects toward the center enables to explain the microstructural non-uniformity. For the non-uniform sintering behavior, spectroscopic analysis was used to investigate the introduced impurities (C, H, O) and by-products (carbonates). In the spectroscopic analysis, the peaks located at 2555, 2950, and 3560 cm⁻¹ (O–H stretching band of H₂O) were weakly detected for low heating rates but clearly detected for high heating rates. This is because H₂O adsorbed to the initial Y₂O₃ powder was not sufficiently removed and was trapped during rapid densification at high heating rates. Due to the carbon-rich environment during SPS, carbonate was formed by the reaction of carbon with –OH. Most carbons were detected as a C–O peak, indicating that a reaction of carbon with –OH occurred.

Recently, perovskite-type BaTiO₃ showing sharp X-ray diffraction peak comparable to that synthesized by a conventional solid-state reaction was obtained by mixing Ba(OH)₂ and TiO₂ hydrous gel and by leaving the mixture at 323 K or less. However, the obtained BaTiO₃ was cubic crystal system, which was different from that synthesized by a conventional solid-state reaction. In this study, the structural analysis of cubic-BaTiO₃ obtained by this technique was conducted, and the factors to form cubic structure were investigated. Since no second harmonic generation signal was observed, the structure of BaTiO₃ was essentially different from that of traditional tetragonal-BaTiO₃. Rietveld analysis with the initial structure model of ideal cubic perovskite structure exhibited that Ti⁴⁺ had exceptionally large isotropic atomic displacement parameter. A reasonable isotropic atomic displacement parameter was obtained by considering the static site disorder in the initial structural model, that is, Ti⁴⁺ locates at off-center position in TiO₆ octahedron by displacing in a disordered direction, resulting in pseudo-cubic symmetry.

A direct oxygen diffusion study using isotopes in dense La₂O₃ ceramics fabricated with the addition of Sr and Ge oxides was performed by secondary-ion mass spectrometry. The experiments using the ¹⁸O isotope were carried out in the temperature range 400–700 °C for 1 h. The surface concentration of ¹⁸O was found to depend on the annealing temperature. The temperature dependence of oxygen diffusion was determined to be expressed as D^*(cm²/s) = (8.9 × 10⁻³)exp(−128.8[kJ/mol]/RT), where D^* is the diffusion coefficient, R is the gas constant, and T is temperature. On the basis of a comparison with the results of oxygen diffusion studies of CeO₂ and LaGaO₃, we concluded that oxygen diffusion in La₂O₃ occurs via a vacancy mechanism.

Cu-doped titania powders were prepared from the sol–gel reaction systems containing titanium tetraisopropoxide (TTIP) and copper(II) nitrate with different compositions. The copper(II) nitrate was added to the sol containing TTIP after a specific reaction period of the TTIP polymerization in order to control the Cu distribution in the titania. The Cu localization on the titania nanoparticle surface was indirectly estimated by the Cu chelation of 8-hydroxylquinoline on the surface. The photocatalytic activities of the samples concerning the decomposition of organic substances were quantified by the amount of the hydroxyl radical formed during ultraviolet (UV) and visible irradiations. The titania with dispersed Cu on the surface demonstrated a higher activity than that with dispersed Cu inside the bulk titania. The electrons in the titania conduction band caused by the UV photoexcitation were effectively transferred to the impurity states of Cu²⁺ on the titania surface. Some electrons in the titania valence band were directly transferred to the impurity states of Cu²⁺ upon the visible photoexcitation. Consequently, these processes suppressed the electron–hole charge recombination in the titania. It was confirmed again that a slight amount of the Cu highly dispersed only on the titania surface rather than inside the titania bulk was favorable for its high photocatalytic performance.