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

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Zinc oxide (ZnO) is a highly developed oxide semiconductor that has been widely employed in industry as varistor ceramics, transparent conductor films, surface acoustic wave resonators, and so on. However, many questions about its fundamental properties remain unanswered. For instance, density functional theory simulations are currently contradicting the common conception established by many experimental scientists that non-stoichiometry is the primary factor inducing the native conductivity of ZnO. Thus, it may be necessary to reconstruct the conceptual models of the solid-state chemistry and physics of oxide semiconductors. In this context, this paper gathers the knowledge and suggestions presented in previous studies and attempts to find directions for the next steps in further scientific and technological development of ZnO-related materials and structures.

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The performances in methane steam reforming of Ni catalysts supported on (Ce_0.75Zr_0.25)O_2−y (CZ) and (Ce_0.75/1.025Zr_0.25/1.025Pr_0.025/1.025)O_2−y (CZP), which were fired at various temperatures before Ni deposition, were studied. The catalytic activities of the Ni/CZP catalysts were several per cent higher than those of the Ni/CZ catalysts in terms of both CH₄ conversion and H₂ yield. Distinct catalytic activities were observed, even after oxidation, for Ni/CZP with supports pre-fired at 1073 and 1273 K. These observations are discussed in terms of the structural characteristics of the catalysts. The X-ray diffraction profiles and Raman spectra indicated that CZP was a mixture of two phases, i.e., a Pr-rich λ phase and a Ce-rich cubic phase. The higher catalytic performances of the Ni/CZP catalysts than of the Ni/CZ catalysts and the retention of catalytic activity even after oxidation were attributed to a strained but coherent interface between the λ phase and the cubic phase, at which oxygen vacancies were easily formed. The Ni/CZ catalyst with the CZ support pre-fired at 1273 K also showed distinct catalytic activity even after oxidation. The activity of Ni/CZ after oxidation was also attributable to an active interface between a Zr-rich tetragonal phase and a Ce-rich cubic phase, similar to the case of the Ni/CZP catalyst.

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Locally selective formation of gold nanostructures on a silicon wafer without photolithography, electrolysis, or hydrofluoric acid was reported previously. With our previous method, gold nanostructures grow selectively on the locally amorphized surface on a silicon wafer when the silicon wafer is exposed to a customized Au ion-containing solution. The locally amorphized surface is produced by, for example, irradiation of a focused ion beam (FIB) or a femtosecond laser. The Au ion-containing solution is prepared by mixing (3-mercaptopropyl)trimethoxysilane (MPTMS) with an aqueous solution of HAuCl₄. Here, the mechanism of selective growth of gold nanostructures on the amorphized silicon is explained. Au ions in the solution placed on the FIB- or laser-processed silicon are reduced by the amorphized silicon. Silicon-dangling bond defects, which exist in the amorphized silicon, seem to reduce the Au ions. Finally, we find that the use of MPTMS is unnecessary and a simple HAuCl₄ aqueous solution produces desired results.

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Potassium niobate (KNbO₃) nanocubes were synthesized via a solvothermal method using various organic solvents as the reaction medium. The solvothermal synthesis was conducted in different alcohols and ether-type solvents, and in mixtures of alcohol and ether-type solvents. The starting materials for the solvothermal synthesis were niobium oxide and potassium hydroxide. X-ray diffraction confirmed the presence of perovskite-structured KNbO₃. The morphology of KNbO₃ was investigated using scanning electron microscopy, transmission electron microscopy, and scanning transmission electron microscopy (STEM). Energy-dispersive X-ray (EDX) spectrometry was used to determine the elements present in the KNbO₃. The KNbO₃ nanocubes were the same length as the alkyl chain in the solvent that was used. The STEM and EDX analyses indicated that three elements, potassium, niobium, and oxygen, were present in the KNbO₃ nanocubes, and that these elements were distributed homogeneously throughout the nanocubes.

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

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Dielectric properties of (Mg_(1−x)Co_x)₄Ta₂O₉ (x = 0.01 to 0.09) prepared by solid state reaction were investigated. The maximum properties of the (Mg_(1−x)Co_x)₄Ta₂O₉ (x = 0.05) system were namely, an obtained ε_r value of 12.27, a Q×f value of 440,000 GHz, and a τ_f value of −59 ppm/°C sintered at 1325°C. The theoretical polarizability of (Mg_(1−x)Co_x)₄Ta₂O₉ increased with Co substitution, x. (Mg_(1−x)Co_x)₄Ta₂O₉ with Mg²⁺ substituted by and Co²⁺ not only improved the microwave dielectric properties, but also decreased sintering temperature. From the calculation of the covalency of cation–oxygen bonds, it is found that the covalency of the Co–O bond is lower than that of the Mg–O bond and the difference in the covalency between these cation–oxygen bonds influences the temperature dependence of dielectric constant on the compounds. From our experiment, the best microwave dielectric property happens in (Mg_0.95Co_0.05)₄Ta₂O₉ sintered at 1325°C for 4 h, and it’s Q×f is 440,000 GHz with τ_f = 59.5 ppm/°C.

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Upconversion emissive ceramic nanophosphors like Er³⁺-doped LaOCl are useful for advanced security printings and fluorescence bioimaging techniques. For such applications, functional polymers are necessary for surface modification in order to provide adsorptivity, steric stability as well as other processes. Surface modification, however, brings about a potential degradation of the emission intensity of doped rare earth ions contingent upon the vibration energy of the surrounding environment. It is necessary to understand the structure of surface modification in relation to emission intensity. In this study, we demonstrate the surface modification of Er³⁺-doped LaOCl nanophosphor with simple acetate anions using the compounds acetyl chloride and aqueous sodium acetate, respectively. We report that the surface modification using acetyl chloride has little effect upon degrading emission intensity as it does not increase surface hydroxy groups.

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Porous Al₂TiO₅ ceramics with various starches as pore-forming agents have been prepared by the reactive sintering method using fine-grained starting materials. Commercially available corn, potato and rice starches were used as the pore forming agents. TG–DTA and XRD studies revealed that the rice starch most promoted the formation of Al₂TiO₅ among the three starches, presumably due to its strong heat flow during the combustion. Al₂TiO₅ samples sintered with each starch contained a bimodal pore-size distribution, viz., slit-like pores with the size of <~20 µm, and continuous open-pores with the size of several µm. The thermal expansion behavior of the sample with 30 wt.% rice starch was similar to those without starch.

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A simple processing route has been developed for a nano-sized crystalline tungsten mono-carbide (WC) and a novel nano-structural carbon materials. Starting materials for WC synthesis were selected tungstic acid (H₂WO₄) and polyacrylonitrile (PAN) powders. The starting powders were heat-treated at 1200°C for 30 min with a nitorgen gas flow in an alumina tube. The acquired WC powder had a nano-sized crystalline and high-specific surface area (26.0 m² g⁻¹). Crystallite diameter size was estimated to less than 20 nm. Compared with theoretical value, approximately 2.0 mass % of free carbon was measured in the prepared WC. It was observed that layered graphitic carbon was formed around the WC particles. If the graphitic carbon is separated from the WC particles by appropriate techniques or processing conditions, these techniques using PAN as a carbon source may have possibility for processing not only WC but also nano-structural carbon materials such as graphene.

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In this study, a method for observing the internal pore structure of a ceramic powder compact using micro-X-ray computed tomography (micro-CT) was examined. Powder compacts have low densities, which makes it difficult to distinguish the low-density structures and large pores. In this study, the effect of a contrast agent (potassium iodide solution) on micro CT images was examined. First, the powder compact was made by die-pressing using alumina granules. Then, the powder compact was immersed into the contrast agent in a vacuum. As a result, the large pores in the powder compact were emphasized as white areas in the images.

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