| Project/Area Number |
17K05518
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Hiroshima University |
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Principal Investigator |
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Project Status |
Completed (Fiscal Year 2019)
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| Budget Amount *help |
¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000)
Fiscal Year 2019: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Fiscal Year 2018: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2017: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000)
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| Keywords | インバー合金 / 高圧力 / X線吸収分光法 / 磁気体積効果 / X線吸収スペクトル / インバー効果 / 元素選択的な体積弾性率 / 圧力下EXAFS / 負の熱膨張 |
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| Outline of Final Research Achievements |
This study experimentally investigated the origin of the anomalous thermal expansion of Fe-based alloys from the viewpoint of interatomic bonds by using X-ray absorption spectroscopy. We focus on the zero thermal expansion of Fe65Ni35 alloy and the negative thermal expansion of Fe72Pt28 alloy. In the latest theory of the Invar effect, it is reported that the magnetic fluctuation of Fe plays an important role for the anomalous thermal expansion. Therefore, the bond length and its pressure-induced change were determined element-selectively. We experimentally demonstrate characteristic behavior of Fe that the interatomic distance around Fe is longer than that of Ni, and the bulk modulus around Fe is significantly small. Three-dimensional visualization of the arrangement of atom pairs in the alloy are carried out by the inverse Monte Carlo simulation.
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| Academic Significance and Societal Importance of the Research Achievements |
インバー合金のほぼゼロの熱膨張は，1897年の発見から120年以上が経過したが原子レベルでのその原因が分かっていなかった．理論的にはFeの磁気体積効果の重要性が以前より報告されたが，その実験は未達成であった．本研究のX線吸収分光を用いた元素選択的な局所構造解析により，今回初めてインバー合金の特異な磁気体積効果がFe-Fe間の原子間距離の伸長・収縮によって生じていることを見出した．面心立方格子中のFeの磁気状態には大きな磁気体積効果が期待されていたが，その特長が構造が乱れた合金中においても実現していることを見出しており，意義ある結果といえる．
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