Material design and developments of uniaxially oriented polycrystalline materials with multivalent cationic conductivity

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K22051
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 26:Materials engineering and related fields
• Research Institution: Nagoya Institute of Technology
• Principal Investigator: FUKUDA Koichiro 名古屋工業大学, 工学(系)研究科(研究院), 教授 (90189944)
• Project Period (FY): 2019-06-28 – 2022-03-31
• Keywords: セラミックス / 構造・機能材料 / 環境材料

Outline of Final Research Achievements

Bond valence method is a powerful technique for exploring new ion conductors. Using this technique, we have discovered that Ca ions conduct along <101> in grossite-type compounds CaAl4O7 and CaGa4O7. The randomly grain-oriented polycrystals were prepared to evaluate the conductivity. With increasing temperature from 723 to 1073 K, the bulk conductivity of CaGa4O7 steadily increased from 1.26 × 10&#8211;7 to 4.40 × 10&#8211;5 S cm&#8211;1, which was 2.7&#8211;4.0 times higher than that of CaAl4O7 when compared at the same temperatures. These conductivities were compared with those of NASICON-type compounds in which Ca ions conduct in three dimensions. The total conductivities were superior to that of CaZr4(PO4)6, while the bulk conductivities were inferior to that of (Ca0.05Hf0.9)4/3.9Nb(PO4)3. The polycrystals with the constituent grains aligned in the conduction direction and/or single crystals cut in the relevant orientations can be expected to further improve the conductivity.

Free Research Field

無機結晶化学

Academic Significance and Societal Importance of the Research Achievements

多価陽イオン伝導体に関する研究成果が現在までに多数報告されているが、それらは全てランダム配向多結晶体に注目しており、イオン伝導の異方性に着目してこなかった。その結果、二次元または三次元方向に比較的高いイオン伝導度を示す化合物だけが選択的に研究されてきた。本研究では、Ｃａ２＋イオンが＜１０１＞方向に高速伝導する複合酸化物を世界で初めて発見した。