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The 73th CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
Special Article
published : vol. 129, no. 6, June 2021
Yuji NOGUCHI
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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.
The 75th CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
Special Article
published : vol. 129, no. 6, June 2021
Masanobu NAKAYAMA
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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.
Full Paper
published : vol. 129, no. 6, June 2021
Masaki KOTANI, Kohei EJIRI, Takuma TANAKA, Takeshi TAKAGI, Takeo ODA, Takayuki KOJIMA and Shinji OGIHARA
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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.
Full Paper
published : vol. 129, no. 6, June 2021
Satoshi SUEHIRO, Teiichi KIMURA, Daisaku YOKOE, Yongzhao YAO and Yukari ISHIKAWA
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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.
Full Paper
published : vol. 129, no. 6, June 2021
Ruizhe LIU and Haidong ZHAO
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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.
Full Paper
published : vol. 129, no. 6, June 2021
Fumika TSUJI, Kah Loong HOH, Kwang Hyun KIM, Atsushi SAKUDA, Masahiro TATSUMISAGO, Steve W. MARTIN and Akitoshi HAYASHI
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Solid electrolytes are important materials for enhancing the performance of all-solid-state sodium rechargeable batteries. Na10+xSn1+xP2−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 Na10+xSn1+xP2−xS12 (0 ≤ x ≤ 1.2) compositions.
Note
published : vol. 129, no. 6, June 2021
Minjian CAO, Eita TOCHIGI, Ryusuke IMAMURA, Naoya SHIBATA and Yuichi IKUHARA
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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.
Note
published : vol. 129, no. 6, June 2021
Hikaru ISHITSUKA, Yuya NAKAMURA, Hiroya ABE and Yoshikazu SUZUKI
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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.
The 75th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 129, no. 5, May 2021
George HASEGAWA
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Preceramic polymer routes, which produce ceramic products called polymer-derived ceramics (PDCs) from molecular precursors, have been developed as a powerful tool to synthesize reduced ceramics in different morphologies (fibers, coatings and monoliths) for over half a century. In recent years, pore control of porous ceramic monoliths has attracted attention for improving their functionalities, which has driven the preceramic polymer routes to be integrated with other synthetic techniques for porous materials such as templating, foaming, emulsion and phase separation. This article briefly overviews porous PDC monoliths with a special emphasis on those derived from porous preceramic polymer gels which are prepared via the sol–gel process accompanied by spinodal decomposition. Ceramization behaviors of Si- and Ti-based preceramic polymers are highlighted in terms of crystal transition and variation of pore properties in different length scales.
The 75th CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
Special Article
published : vol. 129, no. 5, May 2021
Masato MACHIDA
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Heat- and corrosion-resistant catalytic materials are essential in the field of environmental protection and energy production. In this article, recent progress in material research in this field is reviewed based on publications from the author’s research group. In an automotive three-way catalyst (TWC), thermal deactivation by sintering of platinum group metal (PGM) nanoparticles can be suppressed by controlling the interfacial bonding to the surface of the support, which provides an anchoring effect. A similar concept is useful in solar thermochemical cycles to produce clean fuels, which are conducted in a high-temperature and corrosive environment containing sulfuric acid vapor. A further challenge in both applications is the replacement of PGM catalysts by economically viable catalysts. Thermally stable multicomponent transition metal oxides were proposed as a possible candidate for PGM-free TWC. A positive synergy between the different functionalities of metal elements results in high catalytic performance. Molten phases of metal vanadates, which are used for solar thermochemical cycles of sulfur, are another example of PGM-free catalysts. These examples highlight the critical roles of each metal element and their combination for obtaining synergy, which are required to further understand the ways to simultaneously achieve catalytic activity and thermal/corrosion stability.
Full Paper
published : vol. 129, no. 5, May 2021
Yoshihito SHIMABUKURO, Tetsuto WATANABE and Shiro KAMBE
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Although Pb2+ substitution for Bi3+ increases the hole concentration, p, in Pb-substituted Bi-based superconductors, the Pb substitution effect has yet to be studied in detail. Herein the Pb substitution effect on the electronic properties of Bi2201, 2212, and 2223 superconductors is investigated to elucidate the role of Pb on the correlation between p and formal valence, v. Consistent with Mott-Hubbard theory, p increases as v increases in the Pb-free Bi2201 and Pb-free Bi2212 phases. In contrast, p decreases with increasing v for the Pb-substituted Bi2201 phase, which contradicts Mott-Hubbard theory but can be explained by the increase in Pb4+. For the Pb-substituted Bi2212 phase, p increases with increasing v from 2.0 to 2.2, and then remains constant at p = 0.10–0.20 from v 2.2 to 2.63. When v increases from 2.0 to 2.2, the hole is doped at a Cu site, which is the same behavior as that of the Pb-free Bi2212 phase. As v increases from 2.2 to 2.63, the hole is doped in a Pb site and not a Cu one. For the Pb-substituted Bi2223 phase, p decreases with increasing v, and a mixed-valence state between Pb2+ and Pb4+ may coexist. As the v increases, the Pb valence increases and the Cu valence decreases. These results indicate two factors influence p. One is correlated with the substitution of Sr2+ for La3+ or Y3+ for Ca2+, which obeys Mott-Hubbard theory. The other is correlated with the substitution of Pb2+/4+ for Bi3+, which does not obey Mott-Hubbard theory. The results strongly suggest that Pb substitution for Bi does not necessarily dope a hole but decreases the hole concentration.
Full Paper
published : vol. 129, no. 5, May 2021
Hiroki ITO, Akira MIURA, Yosuke GOTO, Yoshikazu MIZUGUCHI, Chikako MORIYOSHI, Yoshihiro KUROIWA, Nataly Carolina ROSERO-NAVARRO and Kiyoharu TADANAGA
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The magnetic and electronic properties of CeOInS2 and their influence on phase transition were analyzed in this study. High-temperature XRD measurements of CeOInS2 revealed that orthorhombic CeOInS2 transformed into tetragonal CeOInS2 at a high temperature of 636 K. The transport properties of CeOInS2 showed semiconducting behavior, with a larger temperature dependence of electronic resistivity in the tetragonal phase compared to that in the orthorhombic phase. Unlike structurally similar Ce(O,F)BiS2 superconductors that show long-range magnetic ordering, CeOInS2 neither exhibited superconductive transition nor long-range magnetic ordering at temperatures between 2 and 300 K.
Full Paper
published : vol. 129, no. 5, May 2021
Yutaka OHYA, Hiroaki KANAOKA, Souma IWATA, Chika TAKAI-YAMASHITA and Takayuki BAN
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The electrical conductivity of porous and high-purity β-Ga2O3 ceramics was measured as a function of oxygen partial pressure, po2, at 700 to 900 °C. In the high po2 range, the conductivity was proportional to about −1/4th power of po2, while in the lower po2 range less than about 10−5 atm its exponent was −0.1 to −0.13. This suggests that different types of defects were formed at high and low po2. The point defect of doubly ionized interstitial gallium ion causes the exponent of −1/4, the same value of the experiment in high po2. When po2 was changed, the electrical conductivity first changed sharply, followed by a slow change, suggesting some migrations and/or formation of crystalline defects, and so on. In the Ga2O3 samples, many dislocations, with density of about 1012 cm−2, were observed. As the source of carriers, line defects, such as dislocations, should be considered as well as point defects.
Full Paper
published : vol. 129, no. 5, May 2021
Yuichi HAMAZAKI and Hiromichi TAKEBE
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The dissolution behavior of calcium aluminosilicate (CAS) glasses with various CaO and Al2O3 concentrations was investigated at 180 °C in NaOH aqueous solutions with an initial pH of 13.2–14.0. A CaO–Na2O–Al2O3–SiO2–H2O (C–N–A–S–H) layer was formed on the immersed glass surface due to the dissolution and penetration of the glass and solution constituents. An excellent alkali durability was achieved by the minimization of Al2O3 addition and a [CaO]/[SiO2] molar ratio of 1.10–1.20 for the glass composition design. The results of the infrared spectroscopy indicated that the C–N–A–S–H layer contained H2O and CO32− species from the ambient atmosphere and consisted of the network structure of SiO4–AlO4 tetrahedra. The hydrothermal reactions between the CAS glasses and NaOH solution promoted the formation of the C–N–A–S–H layer and precipitation of Ca(OH)2 with an immersion time. Stable Al-substituted tobermorite and hillebrandite phases were finally formed on the immersed glass surfaces due to the hydrothermal reactions.
Technical Report
published : vol. 129, no. 5, May 2021
Takashi AKATSU, Masashi UNNO and Tomotsumi FUJISAWA
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Prestress in alumina-strengthened porcelain, caused by the mismatch in thermal shrinkage between the porcelain matrix and alumina particles during porcelain cooling, is estimated using Raman spectroscopy by monitoring the frequency shift of Raman band at 417 cm−1, which is assigned to the A1g vibrational mode of α-alumina. This spectroscopic estimation supports the validity of prestress which is expected to accumulate during porcelain cooling beginning at ∼850 °C.
Full Paper
published : vol. 129, no. 4, April 2021
Son Thanh NGUYEN, Tsuyoshi TAKAHASHI, Ayahisa OKAWA, Hisayuki SUEMATSU, Koichi NIIHARA and Tadachika NAKAYAMA
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In the emerging era of aircraft industry, silicon carbide (SiC) is regarded as an appropriate material for gas turbine engine blades. In order to protect this ceramic component against the oxidation and volatilization in hot steam environments, environmental barrier coating should be utilized. The composite of SiC/Yb2Si2O7–Yb2SiO5 with self-healing ability is a candidate for the top layer of this coating. In this study, the crack-healing behavior of SiC/Yb2Si2O7–Yb2SiO5 nanocomposites is investigated by pre-cracking followed by annealing in oxidizing environments. Comparing to previous studies, the healing time and healing temperature can be reduced to 15 min and 800 °C by increasing the volume fraction of SiC to 20 %. In addition, nanocomposites with both self-healing ability and superior strength were created in this research by combining two types of SiC filler (whiskers and nanoparticulates). The self-healing mechanism in these composites is the SiC oxidation and silicate transformation associated with their volume expansion, which is evidenced by X-ray diffraction and scanning electron microscope. According to the results, the best volume ratio between whisker and nanoparticulate is determined as 1/3.
Full Paper
published : vol. 129, no. 4, April 2021
Yoshihiro KAWAKAMI
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In this paper, the results of evaluating vibration power generation by increasing the area of the BaTiO3 (BT) film formed on a stainless-steel substrate by aerosol deposition (AD) is presented. Fe–Cr–Al-based heat-resistant stainless steel with a thickness of 0.1 mm was used as the substrate. BT films with a thickness of about 10 µm were formed on the substrate of six different shapes with different widths and lengths and BT films were annealed at 1000 °C. Electrodes were formed on the surface of these samples, and the poling process with a voltage of 60 V was applied to prepare samples for evaluation. A weight was attached to the tip of these samples and set up in a cantilever state. A damped vibration under the same stress condition was applied to the BT film by pushing and snapping the tip of samples one time. The generated voltage on the load resistance connected in parallel to the BT film was measured and the generation energy was evaluated. As a result, it was confirmed that the generation energies of the samples with areas of 15 × 3 and 30 × 40 mm2 were 0.17 and 39 µJ, respectively. About 230 times as much energy was obtained by increasing the film area about 20 times. This result indicates that increasing the film area using AD method effectively increases the generation energy.
Note
published : vol. 129, no. 4, April 2021
Susumu NAKAYAMA
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In this study, phosphors based on Srx(La9.2−xTb0.8)(SiO4)6Oα (x = 2, 3, 4, 5, and 6) ceramic powders were prepared and their photoluminescence (PL) spectra were investigated. The phosphors show green emission at approximately 545 nm when excited by 378 nm UV light. X-ray photoelectron spectroscopy suggests that Tb in the Tb3+ and Tb4+ valence states coexist in phosphors at a Tb3+/Tb4+ atomic ratio of unity. [Sr2−x(La,Tb)x]SiOα was confirmed to exist in addition to Srx(La9.2−xTb0.8)(SiO4)6Oα at x = 4, 5, and 6. The PL intensity increased with increasing Sr(x) content, which is considered to be due increasing Srx(La9.2−xTb0.8)(SiO4)6Oα particle size. The strongest PL intensity was observed at x = 6, where the absorptivity, internal quantum efficiency, and external quantum efficiency were 20, 50, and 10 %, respectively.
Note
published : vol. 128, no.11, November 2020
Hiroya OKAZAKI, Ryota KOBAYASHI, Rei HASHIMOTO, Emiko FUKUSHI and Junichi TATAMI
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We successfully fabricated dense aluminum nitride (AlN) ceramics containing AlN whiskers by low-temperature pressureless sintering and evaluated their microstructures, thermal conductivities, and mechanical strengths. Furthermore, the anisotropy of thermal conductivities caused by the orientation of AlN whiskers was also evaluated. The thermal conductivities of the samples measured in parallel and perpendicular to the longer direction of AlN whiskers were 98 and 67 W m−1 K−1, respectively. The bending strengths of the samples without and with AlN whiskers were 147 and 235 MPa, respectively. From the observation of the fracture surface of the samples, AlN whiskers in the samples probably withstand the fracture originating from weak grain boundaries.