Olivine materials, well-known as a Co-free cathode materials for lithium ion battery, were synthesized by the hydrothermal reaction with the addition of various alcohols in order to control their microstructure. As-synthesized olivine products were characterized by XRD, SEM observation, particle size distribution analysis, and TG-DTA analysis. For olivine products synthesized without alcohol addition, the microstructure was the mixture of plate-like particles and fine particles. On the other hand, in case of hydrothermal synthesis with ethanol as a solvent into H₂O, obtained products had the microstructure of submicron-sized spheres composed of 10~50 nm nanoparticles. In addition, products synthesized with an alcohol consisted of finer and uniformly sized particle. It was found that the particle size, size distribution and microstructure depended on the kinds of alcohol. Furthermore, TG analysis results showed that the adsorption water of the products synthesized with an alcohol addition was less than that with no alcohol.

The recrystallization behavior of pure iron powder cores during the annealing process core is visualized with the Grain Orientation Spread (GOS) map from an SEM/EBSD analysis, and found to be significantly inhomogeneous, leading to an inhomogeneous dislocation density distribution. Nevertheless, a conventional dislocation pinning model well describes the coercive force behavior if the average dislocation density is applied. The pinning model is modified to separate the influence of the grain boundary pinning, and the relationship between the coercive force and the microstructure is discussed comprehensively.

Silicon nitride is well known as a typical structural ceramic material which exhibits excellent mechanical and heat resistance properties. In addition, β-Si₃N₄ single crystal is expected to possess a high intrinsic thermal conductivity over 200 Wm⁻¹K⁻¹. This makes silicon nitride a serious candidate as a substrate material for power devices.

However thermal conductivity of commercially available silicon nitride substrates is as low as 90 Wm⁻¹K⁻¹, and therefore extensive research works have been conducted for improving its thermal conductivity while retaining good mechanical properties. This paper reviews the microstructural factors affecting thermal conductivity of sintered silicon nitrides and investigations so far for improving their thermal conductivity. Recently it has been demonstrated that reaction bonding process followed by post-sintering process is a superior method for increasing thermal conductivity of Si₃N₄. Silicon nitride with high thermal conductivity of about 180 Wm⁻¹K⁻¹ with moderate bending strength of 600 MPa and high fracture toughness of 11 MPa·m^1/2 has been developed by this method. Application of the developed Si₃N₄ to metalized substrates is also introduced.

This study reviews densification behavior, microstructure and mechanical properties of the various composition ZrB₂-ZrC_0.6-Zr cermets prepared by reactive hot-pressing of Zr + B₄C powder mixtures between 1673 K and 2173 K. During reactive sintering, densification consisted of two parts, one resulted from the volume contraction due to the conversion of Zr + B₄C mixture into ZrB₂ and ZrC_0.6, other resulted from the shrinkage due to grain boundary diffusion and grain boundary migration that mostly contributed to the densification. Highly-dense ZrB₂-ZrC_0.6-Zr cermets were obtained for Zr + B₄C mixtures at equal to or greater than 1673 K. The resulting ZrB₂-ZrC_0.6-Zr cermets consisted of platelet-like ZrB₂ grains, equiaxed ZrC_0.6 grains and intergranular Zr. The ZrB₂ and ZrC_0.6 grains were coarsened with increase of the excess Zr amount and/or sintering temperature. On the other hand, the flexural strength and fracture toughness of the cermets strongly depended on the excess Zr amount and/or sintering temperature. In addition, the crack propagation behavior of the cermets was associated with the excess Zr amount. The cracks directly propagated in the samples with less than 16 vol% Zr, however, the multiple cracking behavior was observed for the samples with equal to or greater than 16 vol% Zr.

A simple SPS apparatus was made at low cost. Die current of order of 1,000 A is required for ordinary SPS machines, even for a compact type machine. SPS apparatus made in this study requires a current below 100 A, because the machine uses SiC die. SiC die has too low electric conductivity for the ordinary SPS machines. By preheating the SiC die, sufficient electric current flows by an applied voltage below 100 V. Because the electric conductivity of SiC die at elevated temperature is lower than that of graphite, the same power as the graphite die can be obtained with a current below 100 A. Control of electric current below 100 A is easy. Electric modules having such capacities for the control of electric furnace are commercially available. The apparatus was made combining such modules.

To further enhance thermoelectric (TE) properties of higher manganese silicides (HMSs), the dissipation of layered precipitates of the MnSi phase as well as the optimization of the hole carrier concentration are critical. We have systematically studied electronic structure of partially substituted solid solutions of (Mn_1−xM_x)Si_1.7 with M = transition metals and prepared bulk samples of such solid solutions by spark plasma sintering. A 2 at% substitution of manganese with vanadium is found to dissipate the MnSi-precipitates effectively, results in a substantial increase in electrical conductivity from 3 × 10⁴ S/m to approximately 5 × 10⁴ S/m at 800 K. The resulting TE power factor reaches 1.86 mW/K²m at 710 K, 30% higher than that of V-free samples.

Although numerous papers are published each year, most of the experimental data reported in those papers are only available as two-dimensional plot images. Data-driven materials science using the machine learning technologies will be accelerated by gathering those published experimental data into a database. By taking thermoelectric materials as a test case, we attempted to optimize the processes of collection of papers, extraction of numeric data from plot images, and sample-based data storage into a database. By searching with a keyword “thermoelectric”, we obtained a list of 47,936 papers. Among these papers, we selected 18,471 papers as possible papers with thermoelectric properties, and succeeded to download 14,835 full-text PDF files. We developed a web system named “Starry data”, to assist the sequential data extraction from the images contained in those PDF files. This system also assists materials scientists to annotate experimental samples efficiently, to develop a descriptive database that can be used for machine-learning of the complex, sample-dependent materials properties.

Poly-crystalline Ba₈Au_xSi_46−x clathrate with p-n junction was synthesized for electric power generation from heat under no temperature difference. The n-type Ba₈Au_4.5Si_41.5 and the p-type Ba₈Au_5.5Si_40.5 powder were stacked in the graphite die and sintered by a Spark Plasma Sintering (SPS) method at 1073 K for 5 min with pressure of 50 MPa. The Au composition of Ba₈Au_4.5Si_41.5 and Ba₈Au_5.5Si_40.5 side in the sintered sample were Ba_7.8Au_4.2Si_41.8 and Ba_7.8Au_5.2Si_40.8, respectively. It was found that the Au composition was gradually changed near the interface with thickness of around 500 micrometers. Electric power generation test under no temperature difference was performed by using the sample cut to contain the interface of two layers. The electric power increased by only heating and the maximum voltage can be observed around 2 mV at 773 K. These results suggested that electron excitation occurred near the n/p interface and generated electrons and holes diffuse to n-type and p-type semiconductor side, respectively.