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-type layered manganese dioxide岡本 範彦*; 吉迫 大輝*; 市坪 哲
Energy Storage Materials, 61, p.102912_1 - 102912_9, 2023/08
被引用回数：1 パーセンタイル：52.07(Chemistry, Physical)Layered manganese dioxide (birnessite) that contains K cations and water molecules at interlayers exhibits reversible heat storage properties via a water-intercalation mechanism (0.5 mol H
O per K
MnO). However, a certain amount of an irreversible capacity of water intercalation is observed after the initial thermal cycle, which limits the reversibly available energy density of the material for the subsequent cycles. In this study, crystal structures of the K-containing birnessite, KMnO, was analyzed before and after heat treatment, by electron diffraction and atomic-resolution scanning transmission electron microscopy, to elucidate the origin of the initial irreversible capacity (0.83 mol per KMnO).
Wei, D.*; Wang, L.*; Zhang, Y.*; Gong, W.; 都留 智仁; Lobzenko, I.; Jiang, J.*; Harjo, S.; 川崎 卓郎; Bae, J. W.*; et al.
Acta Materialia, 225, p.117571_1 - 117571_16, 2022/02
被引用回数：59 パーセンタイル：99.75(Materials Science, Multidisciplinary)Recently-developed high-entropy alloys (HEAs) containing multiple principal metallic elements have ex-tended the compositional space of solid solutions and the range of their mechanical properties. Here we show that the realm of possibilities can be further expanded through substituting the constituent metals with metalloids, which are desirable for tailoring strength/ductility because they have chemical interactions and atomic sizes distinctly different from the host metallic elements. Specifically, the metalloid substitution increases local lattice distortion and short-range chemical inhomogeneities to elevate strength, and in the meantime reduces the stacking fault energy to discourage dynamic recovery and encourage defect accumulation via partial-dislocation-mediated activities. These impart potent dislocation storage to improve the strain hardening capability, which is essential for sustaining large tensile elongation. As such, metalloid substitution into HEAs evades the normally expected strength-ductility trade-off, enabling an unusual synergy of high tensile strength and extraordinary ductility for these single-phase solid solutions.
Nb with the L1
structure岡本 範彦*; 竹本 昌平*; Chen, Z. M. T.*; 山口 正剛; 乾 晴行*
International Journal of Plasticity, 97, p.145 - 158, 2017/10
被引用回数：11 パーセンタイル：49.82(Engineering, Mechanical)The deformation behaviour of IrNb with stoichiometric and off-stoichiometric compositions has been investigated as functions of crystal orientation and deformation temperature. The critical resolved shear stress (CRSS) for (111)[
01] slip in stoichiometric IrNb exhibits a marginal temperature dependence at all temperatures with neither strong negative temperature dependence at low temperatures nor positive (anomalous) temperature dependence at high temperatures. The CRSS for (111)[01] slip exhibits orientation dependence, neither. The [01] dislocation dissociates into the anti-phase boundary (APB)-type scheme and is observed to be smoothly curved on the (111) slip plane at all temperatures, indicating the planar core structure. This is exactly what is known for the perfect dislocation in many pure FCC metals and is the reason for the observed FCC metal-like deformation behaviour of IrNb. The absence of yield stress anomaly in IrNb is discussed in terms of anisotropy in planar fault energies and elastic constants calculated by first principles calculations and experimentally determined in the present study.
Co NMR測定中堂 博之; 鈴木 和也; 岡本 範彦*; 市坪 哲; 高梨 弘毅
no journal, ,
ハイエントロピー合金(HEA)とは、5成分以上の元素を含み、主要元素が定まらないにも関わらず単相の不規則固溶体となる合金である。元素の組み合わせと混合割合の多さから、HEAには広大な物質探索領域があると期待され、精力的に研究されている。HEAには大きさの異なる多様な元素を固溶する性質があるため、格子ひずみが大きくなるということから主に構造材料としての性質が注目されている。また、磁気モーメントを持つ元素も固溶できることから磁気的性質も研究されており、バルク試料の帯磁率といった巨視的性質が測定されている。本研究では微視的測定手法である核磁気共鳴法(NMR)を用いて、等組成FeCoNiCrPdの多結晶試料におけるCo NMR測定を行い、当試料における固溶体の均一性を微視的に検証する。
