三角格子系鉄複合酸化物LuFe_2O_4における電荷秩序構造と誘電特性 Charge Ordered Structure and Dielectric Properties in LuFe_2O_4
Recent works revealed that a ferroelectric polarization in the charge-frustrated system LuFe<SUB>2</SUB>O<SUB>4</SUB> originates from an emergence of the charge ordering, which is characterized by a regular arrangement of Fe<SUP>2+</SUP> and Fe<SUP>3+</SUP> ions on the frustrated triangular lattice. In this work, we have investi-gated both the charge ordered (CO) structure and charge ordering processes mainly by means of the transmission electron microscopy (TEM) . Both the CO structure and charge ordering processes depend strongly on the amount of the oxygen deficiency (δ) involved in LuFe<SUB>2</SUB>O<SUB>4-δ</SUB>. In the case of δ-0, the three-dimensional CO structure with the modulation vector of <I>q</I>= [1/3 1/3 1/2] was formed at room temperature. On the other hand, as δ was increased, the three-dimensional CO structure changed into the two-dimensional CO one and the coherent length becomes shorter along the  direction. For proper understanding of the dielectric and magnetic properties in LuFe<SUB>2</SUB>O<SUB>4</SUB> and related materials, it should be essential to prepare LuFe<SUB>2</SUB>O<SUB>4-δ</SUB> samples with properly controlled oxygen-concentration and elucidate the physical properties in LuFe<SUB>2</SUB>O<SUB>4-δ</SUB> with δ-0.
日本結晶学会誌 50(2), 150-154, 2008-04-30
The Crystallographic Society of Japan