Perovskite ferroelectrics such as BaTiO₃ and PbTiO₃ provide various functions arising from spontaneous polarization. Here, the history, present status, and future prospects of the defect chemistry for BaTiO₃ are described. Even for non-doped samples, unintentional impurities including Fe govern the defect chemistry and its related properties. By solving multiple nonlinear equations employing the thermodynamic data set reported, majority/minority defect-concentration diagrams are available not only in a high-temperature equilibrium state but also in a low-temperature quenched one. As an example, the defect diagrams of Ba(Ti,Ca)O₃ and Ba(Ti,Mn)O₃ are shown, and the roles of fixed valence (Ca) and variable-valence (Mn) acceptors are explained. I also introduce an example of the defect control in BaTiO₃ single crystals; an activation of visible-light photovoltaic effect, where two redox potentials derived from Fe²⁺ and Fe³⁺ act as scaffolds for generating electron–hole pairs.

In this review, we introduce our work in the field of materials informatics for the prediction of ionic conduction properties in inorganic crystalline solids. Rational material development based on information-derived prediction of the ionic conductivity for the materials listed in the crystal structure database is attractive to reduce processing time and labor costs. For this purpose, the development of general descriptors and a sufficient volume of ionic conductivity datasets are required. As an example, herein we describe machine learning regression and Bayes optimization schemes and their results by using histogram descriptors and a bond valence-based force field approach.

In this study we investigated methods of forming matrices of SiC/SiC composite, which have recently attracted considerable attention as high temperature structural materials that can be used in airplane engines etc. We examined ways of balancing the formation of the dense, strong microstructures with the infiltration into fibrous preforms. A process in which a green body was prepared by polymer infiltration and pyrolysis (PIP) processing, using slurry containing a liquid precursor polymer and fine powders, was densified using melt infiltration (MI) processing. Promising combinations of raw materials and their ratios were selected based on past research results. The microstructures and elemental distributions obtained from those materials after the last PIP processing and after the MI processing, as well as the thermal and mechanical properties of the composites, were comparatively evaluated. Thus, favorable conditions of raw material combinations to fabricate a high-performance matrix were determined.

A crystalline SiC coating was prepared by laser sublimation deposition from a powder mixture of Si and C as source materials under an Ar atmosphere at slightly reduced pressure (1 × 10⁴ Pa). A continuous-wave fiber laser (λ = 1070 nm) was used to irradiate the Si + C source pellets through a 4H-SiC wafer substrate in order to heat and react the powder mixture of Si and C, and to then sublimate the formed SiC. A (111) oriented dense columnar 3C-SiC coating layer, free from unreacted Si and C, was formed at a deposition rate of 30 µm/min.

Silicon particle preforms with different starch contents (10, 20 and 30 %) and particle sizes (20, 50 and 90 µm) were fabricated by compression mold forming and heat treatment. The pore characteristics of preforms were inspected with a high-resolution (∼1 µm) three-dimensional (3D) X-ray micro-computed tomography (µ-CT). The infiltration of AlSi12 alloys into the preforms were carried out under the condition of 800 °C and 400 kPa with different pressure-applied times (3, 8 and 15 s) in a vacuum-assisted pressure infiltration apparatus. A high-resolution (∼500 nm) vertical scanning white light interfering profilometer was used to detect the front surfaces of composites. The infiltration was simulated at micro-scale by considering the actual pore geometry from the µ-CT inspection based on the Navier-Stokes equation. The results demonstrated that as the starch content and particle size increased, the front surface area of composite increased. Compared with the starch content, the particle size has more influence on the front surface area. In the simulation, as the infiltration progressed, the pressure of liquid AlSi12 decreased. The residual pores of composites increased with infiltration. According to the experiment and simulation results, a larger pressure drop along the infiltration direction leads to more residual pores of composites.

Solid electrolytes are important materials for enhancing the performance of all-solid-state sodium rechargeable batteries. Na_10+xSn_1+xP_2−xS₁₂ (0 ≤ x ≤ 1.2) samples were prepared using a mechanochemical process, followed by heat treatment and their structures and ionic conductivities were investigated. Glassy samples were obtained via the mechanochemical process; the samples with the Na₁₁Sn₂PS₁₂ type crystal structure were obtained for all the prepared compositions through the heat treatment of the glasses. The Na₁₁Sn₂PS₁₂ (x = 1) sample obtained by heat treatment at 300 °C exhibited an ionic conductivity of 2.6 × 10⁻⁴ S cm⁻¹ at 25 °C, which was the highest conductivity observed among all the samples with Na_10+xSn_1+xP_2−xS₁₂ (0 ≤ x ≤ 1.2) compositions.

The plasticity of inorganic semiconductors is affected by light irradiation, which is called the photo-plastic effect (PPE). In this study, we examined the PPE of gallium nitride (GaN) by nanoindentation with controlled light conditions. The nanoindentation experiments revealed that the hardness of GaN {0001} surface is increased up to ∼5 % under ultraviolet (UV) light irradiation in comparison with one measured in darkness. Transmission electron microscopy observations showed the activation of basal slip and pyramidal slip for both samples indented with UV irradiation and in darkness. It can be suggested that the hardening of GaN is originated from the deterioration of dislocation mobility due to UV irradiation.

NiMn₂O₄ has an inverse spinel structure similarly to Co₃O₄ and NiCo₂O₄, but NiMn₂O₄ is much cheaper than these cobalt containing materials. Here, we report synthesis, microstructure and electrochemical characterization of NiMn₂O₄ nanoparticles via a simple citric acid method. Ni(CH₃COO)₂·4H₂O (1.5 mmol) and Mn(CH₃COO)₂·4H₂O (3.0 mmol) were dissolved in distilled water (25 mL), and citric acid (3.75 mmol) was added and stirred for 2 h to obtain transparent blue-green solution. The solution was open-heated at 90 °C for 24 h, and heated at 170 °C for 2 h to obtain a xerogel. The xerogel precursor was pestled and calcined at 400 °C for 4 h in air to obtain a NiMn₂O₄ powder. X-ray diffraction, N₂ adsorption/desorption and transmission electron microscopy with energy dispersive X-ray spectroscopy revealed that single-phase NiMn₂O₄ mesoporous nanoparticles were successfully synthesized from eco-friendly acetates ingredients by the low-cost citric acid method. The specific surface area and pore size of the NiMn₂O₄ mesoporous nanoparticles were 211.3 m²/g and ∼4 nm, respectively. The NiMn₂O₄ electrode successfully worked as a supercapacitor.