Control of phase transition of the rare earth oxyfluorides

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05077
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 26020:Inorganic materials and properties-related
• Research Institution: Osaka University
• Principal Investigator: TAMURA Shinji 大阪大学, 大学院工学研究科, 准教授 (80379122)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: フッ化物イオン / 固体電解質 / 希土類 / 相転移

Outline of Final Research Achievements

In this study, RO1-xF1+2x (R: rare earths) with intentionally varied anion ratios (O / F) in the samples were synthesized in order to clarify structural properties of rare earth oxyfluorides and their ionic conductivity.
Phase transition of LaO1-xF1+2x can be suppressed at compositions of x higher than equal to 0.1. The maximum conductivity was obtained at x = 0.4. The suppression of the phase transition was also achieved by partial substitution of La sites with divalent cations, and the conductivity increased with increasing the amount of partial substitution. For a series of ROFs, it was found that the formation phase differs depending on the type of rare earths, and that the composition at which the phase transition can be suppressed varies, and that relatively high conductivity can be obtained in ROFs with a tetragonal crystal structure.

Free Research Field

無機材料化学

Academic Significance and Societal Importance of the Research Achievements

本研究で明らかとなった希土類オキシフッ化物の結晶相と相転移、さらには結晶相とフッ化物イオン伝導性との関係に関する知見は、これまで未解明であったオキシフッ化物の物性を理解する上で極めて重要な基礎的知見を与えた。本知見は、上記学術的な意義のみならず、今後開発が活発となるフッ化物イオン電池への有力候補となる金属オキシフッ化物材料の開発にも多いに貢献できる知見となる。