[10p-M116-1~22] 9.1 誘電材料・誘電体

[10p-M116-21] 強誘電体における酸素空孔分布制御―遷移金属イオンとの相互作用を利用した欠陥設計

〇野口 祐二¹、松尾 拓紀²、宮山 勝¹ (1.東大院工、2.東大新領域)

キーワード：強誘電体、点欠陥、酸素空孔

Here, we report a practical route to designing oxygen-vacancy distributions by utilizing the interaction with transition-metal dopants. Our thin-film experiments combined with ab-initio theoretical calculations for BiFeO₃ demonstrate that isovalent dopants such as Mn³⁺ with a partly or fully electron-occupied e_g state can trap oxygen vacancies, leading to a complete polarization switching. For TM = Ti, V, and Cr, V_O^·· does not find an energetically favourable site inside the lattice; the vacancies in the vicinity of the bottom electrode are pulled toward its interface owing to a strong depolarization field arising from the discontinuity of P_s, suggesting a formation of an V_O^··-rich layer. This defective layer has been reported for non-doped BiFeO₃ films. By contrast, the cells with TM = Mn, Co, Ni, and Cu provide a stable position of V_O^··, i.e., the 1^st NN site adjacent to the TMs. Provided that the concentration of TMs is higher than that of V_O^·· and also that the attractive interaction between V_O^·· and TMs is sufficiently strong, V_O^·· is trapped by TMs in an equilibrium state.