Diagramatic mapping of key factors for controlling the structure and formation of complex alloy crystals

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K04677
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 26010:Metallic material properties-related
• Research Institution: Tohoku University
• Principal Investigator: Fujita Nobuhisa 東北大学, 多元物質科学研究所, 講師 (70431468)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 準結晶 / 近似結晶 / 複雑合金 / 合金状態図 / 構造安定性 / 構造解析

Outline of Final Research Achievements

By synthesizing many alloy samples with different choices of elements and mixing ratios, the formation behaviors of complex alloy phases, namely, icosahedral quasicrystals and their approximants, in the Al-Pd-TM (=transition metal) and Cd-Mg-RE (=rare earth element) systems were studied in detail. A few novel complex alloy crystals including an unconventional 1/1 approximant in the Cd-Mg-Ce system were discovered. Moreover, the crystal structures were determined for some of the approximants using single-crystal X-ray diffraction technique. Meanwhile, a new mapping method was examined in order to reveal any universal trends in the formation behaviors irrespective of TM species. In this method, compositions of related phases were projected onto a planar map in which the mean number of valence electrons per atom and the vacant fraction of d-orbitals as calculated from the composition were used as the orthogonal coordinate axes.

Free Research Field

金属物性、結晶学、物性基礎

Academic Significance and Societal Importance of the Research Achievements

準結晶や様々な近似結晶の相形成挙動に関する調査は、準結晶の発見から長きにわたり世界中で行われてきた。これらの新規複雑合金相の探索指針として固溶合金に対するヒュームロザリー則が適用されてきたが、元素置換による構造変化には電子の干渉効果に加えて軌道混成効果の影響も無視できず，その詳細なメカニズムの理解は道半ばである。本研究では元素の部分置換による相形成挙動の変化を系統的に調査するとともに、平均価電子濃度やd軌道空席率等を座標軸とするマッピング法を考案することで、準結晶や近似結晶の普遍的な形成挙動を部分的にあぶりだした。この試みをさらに進めれば、構造変化の支配因子を解明できると期待できる。