Ag⁺ ions were intercalated into the transition-metal dichalcogenide TaS₂ using the recently developed method of proton-driven ion introduction. Single-crystalline Ag_0.58TaS₂ with a stage 1 structure and Ag_0.21TaS₂ with a stage 2 structure were prepared using this method. The stage 2 structure of Ag_0.21TaS₂ was formed by exploiting the differences in ion diffusion properties among the polytypes of TaS₂. Furthermore, our intercalation method can forcibly insert Ag⁺ ions into interlayers by applying a high voltage at low temperature (100°C), resulting in the formation of thermodynamically metastable phase. Such a synthesis approach offers a potential route for diversifying intercalation compounds with different stage structures. The first observations of superconductivity in Ag_xTaS₂ were demonstrated in this study. The onset of superconductivity of Ag_xTaS₂ was estimated to be 0.4 and 1.7 K in the samples with x = 0.58 and x = 0.21, respectively. Some anomalies, which were speculatively attributed to charge density wave order, were confirmed in the resistivity measurements of Ag_xTaS₂. The results suggested that the anomalies were closely correlated with the superconducting transition temperature.

This study reviews the development of fabrication processes for silicon nitride ceramics with excellent mechanical properties, such as high fracture strength and fracture toughness. Silicon nitride ceramics with high wear resistance and thermal conductivity have been produced by tuning their composition and utilizing highly efficient processing techniques. The nitridation behavior of silicon powder in the presence of Zr compounds has been studied in order to assess the nitridation enhancement effect of zirconium during formation of reaction bonded silicon nitride. Thermogravimetric analysis has revealed that the addition of ZrO₂ to Si powder reduces the temperature of the main nitridation reaction. It is possible to produce reaction-bonded silicon nitride using a rapid nitridation technique with a heating rate of over 5 °C/min, which is 80 times higher than that for the conventional reaction bonding process. A nitridation enhancement effect has also been observed with the addition of some rare-earth oxides. The reaction bonding process has been used to fabricate high-thermal-conductivity silicon nitride ceramics with a relatively short processing time. Si₃N₄/carbon fiber composites have been developed using randomly dispersed high-tensile-modulus carbon fibers. The aligned silicon nitride grains and short carbon fibers in the composites result in both high fracture strength and toughness and a low friction coefficient under dry and water sliding conditions. The mechanical properties of the composites are anisotropic with respect to the grain alignment, with both strength and toughness being highest parallel to the extrusion direction. In this direction, the seeded specimen, with both silicon nitride grains and carbon fibers aligned, has higher fracture toughness and higher fracture strength than those of the non-seeded specimen, with only fibers aligned.

In this paper, the morphology of CA₆ was adjusted by changing the particle sizes of alumina powders (D₅₀ = 7.26, 5.33 and 2.37 µm), and the effect of this on the thermo-mechanical properties of corundum based high temperature composites was investigated. The results indicated that when the alumina particle size was decreased from 7.26 to 2.37 µm, the morphology of calcium hexaluminate (CA₆) transformed from equiaxial to platy shape. The microstructure changes of CA₆ may be due to differences in CA₆ nuclei numbers and the contact area between alumina and calcium dialuminate. This transformation process can proceed without liquid. Because of the transformation of the CA₆ morphology, the hot modulus of rupture and residual cold modulus of rupture of corundum composites fired at 1600°C increased by 143 and 192%, respectively. The loop areas of in-situ elastic modulus also increased by 20%. The fracture ways of composites were transformed from intergranular to transgranular. Therefore, corundum-based composites with excellent properties including room temperature and high temperature properties can be obtained by adjusting the microstructure of CA₆.

Monolithic refractory ceramic materials have outstanding heat resistant properties at elevated temperature and possess high stiffness but are generally brittle. To toughen a typical matrix of natural traditional monolithic quartz ceramic, functionalized multiwalled carbon nanotubes (FMWNTs) were added to the matrix as filler for the first time and processed by a wet method using conventional powder processing; involving consolidation by pressureless sintering technique, to obtain the novel nanocomposite. The effect of the varied amount of carbon nanotubes (0.01, 0.1, 0.5, 1 & 4 wt.%) on densification and mechanical properties of the composites were studied. 1 wt.% FMWNTs/quartz (QF-1) possesses moderate tensile and compressive strengths, modest Young’s modulus and toughness, and high fracture strain in tension. Good combination of strengths and toughness in QF-1 nanocomposite, suggest the possibility of using 1 wt.% FMWNTs as an additive in the preparation of silica/silica-based refractory mixture for optimum mechanical properties.

The coordination structure around Bi atoms has been studied in Li₂O–Bi₂O₃–B₂O₃ glasses by X-ray diffraction method. It was found that Bi atoms were coordinated by five or six oxygen atoms. The number of Bi atoms around a Bi atom through Bi–O–Bi bonds increased with an increase in Bi/O ratio. It was inferred that BiO_x polyhedra were clumped in the glasses, although BiO_x polyhedra were more clumped in Li₂O–Bi₂O₃–B₂O₃ glasses than in Bi₂O₃–B₂O₃ glasses.

The Soret effect or thermodiffusion is temperature-gradient-driven diffusion in a multicomponent system. A physical model to accurately predict the Soret coefficient of oxide melts has not yet been proposed. Here, for the first time, we report a quantitative comparison between experiment and theory concerning the Soret coefficient in binary glass-forming oxide melts. We measured the Soret coefficient of 11Na₂O–89B₂O₃ (mol %) after 90- and 180-h heat treatment under a temperature gradient near 1200 K and estimated the Soret coefficient for the steady state. We used a vertical furnace to reduce the effect of natural convection on the Soret effect by heating the sample from the top side. The Soret coefficient estimated for the steady state near 1200 K was 5.12 × 10⁻³ K⁻¹, whereas that obtained by the adjusted Kempers model, in which we adjusted the original Kempers thermodynamic model for binary oxide melts, was 6.09 × 10⁻³ K⁻¹. The sign and order of magnitude were consistent, which suggests that the adjusted Kempers model is a promising model to explain the Soret effect and that the equilibrium thermodynamic parameters of partial molar volume, partial molar enthalpy, and chemical potential are important factors in the phenomenon.

Hydrothermal reactions of a hydrated sodium bismuth oxide, NaBiO₃·1.4H₂O were performed with transition-metal salts MCl₂, M(NO₃)₂ and MSO₄ (M: Co, Ni, Cu). The common identified products from nitrate and chloride solutions were (Bi,M)₂O₂(OH)NO₃ and (Bi,M)OCl, respectively and every product contained a small amount of unknown impurity phases. Various unknown phases also appeared in the products from the sulfate solutions, and no common crystalline phases were observed. During the course of these hydrothermal reactions, a new bismuth sulfate, BiOHSO₄ was found by using a H₂SO₄ solution, and its crystal structure was clarified by using single-crystal X-ray diffraction data. No photocatalytic activity for the phenol degradation of BiOHSO₄ was observed under ultraviolet and visible light irradiation.

In this study, the particle size control of (Ba,Sr)₂SiO₄:Eu²⁺, a green-emitting phosphor, was evaluated via reduction firing using various flux agents. Phosphor particles grown to ∼10–50 µm in diameter and having high internal quantum efficiency of 77.3% were obtained via reduction firing at 1473 K using 10 wt % BaCl₂ as a flux. To reduce the particle size, the reduction firing temperature was lowered to 1223 and 1273 K respectively and the amount of BaCl₂ was increased to 20 wt %. The diameter of phosphor particles significantly reduced; however, fibrous fine particles were formed and the internal quantum efficiency decreased to 60.7%. Using BaCl₂–KCl and BaCl₂–CsCl mixed fluxes to increase the amount of molten flux while suppressing the dissolution of (Ba,Sr)₂SiO₄ into the molten flux, a phosphor with fewer fibrous fine particles was obtained. In particular, the phosphor obtained via reduction firing at 1273 K using a 10 wt % BaCl₂–10 wt % CsCl mixed flux had an improved internal quantum efficiency of 73.4%. The ionic radius of Cs⁺ (0.167 nm for CN = 6) is considerably larger than that of Ba²⁺ (0.135 nm for CN = 6) and Sr²⁺ (0.118 nm for CN = 6); therefore, high-quality host crystals with few defects could be possibly obtained without the substitution of Cs⁺ for Ba²⁺ and Sr²⁺ during reduction firing. To control the particle size of phosphor while maintaining a high internal quantum efficiency, the solubility of the host crystal into the molten flux as well as the substitution of the cation between the flux and host must be considered.

Materials with high thermal conductivity have attracted considerable attention for thermal management of electronic devices. Therefore, focusing on formability and anisotropic heat transfer, we fabricated glass-ceramics containing the spin-chain compound SrCuO₂ and demonstrated its high thermal conductivity in the previous work, where SrCuO₂ is known to exhibit high thermal conductivity owing to the presence of quasiparticles, i.e., spinons. In this study, we attempt to confirm the presence of spinons by analyzing temperature dependence of specific heat and investigate relationship between spinons and thermal properties.