Empirical research of electron-phonon interaction on transition-metal oxides

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K05604
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Kanazawa University
• Principal Investigator: Okudera Hiroki 金沢大学, 地球社会基盤学系, 准教授 (50401881)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 鉱物物理 / 電子フォノン相互作用 / Mn-doped magnetite / Ni-doped magnetite / trimeron / 格子歪み

Outline of Final Research Achievements

The author successfully prepared two series of heteroatom-doped magnetite specimens with compositions Ni(x)Fe(3-x)O(4)(x: 0.0 ~ 0.5) and Mn(x)Fe(3-x)O(4)(x: 0.0 ~ 1.0) (total 14). Changes in interatomic distances, absolute values of atomic displacements and their anisotropy were examined on those specimens with single-crystal X-ray diffractometry and successive structure refinements. As a result, not only an abrupt weakening of cation-anion bonds but also disappearance of a particular lattice vibration mode (dynamic) were observed on heteroatom-doped specimens. By comparing the reported atomic displacements (static) in the low temperature phase and the lattice mode which should be unique on the high temperature phase, the author confirmed that the atomic displacements in the low temperature phase is a “frozen” phonon which is unique in the high temperature, semimetallic phase of magnetite.

Free Research Field

結晶学

Academic Significance and Societal Importance of the Research Achievements

磁鉄鉱（Fe3O4）は同じ構造を取る金属酸化物中で唯一高い電気伝導性を示すことと、低温で絶縁体に転移することが知られており、それらの理由は固体物理学上の難問である。申請者は伝導に関与すると見られる原子の変位もまたユニークな事を見いだし、これが電子（遍歴電子系）-フォノン（格子振動）相互作用の顕れとの仮説を立てた。本研究では電気伝導度の異なる一連の試料を準備し解析することで、伝導相に固有なフォノンが存在することと、高温相から低温相への一次相転移がこのフォノンの凍結により生じることを示した。