Diluted effect on the charge ordered (CO) structure in dielectric materials LuFeMO4 (M = Cu, Co) were investigated by an energy-filtered transmission electron microscopy (TEM), in combination with a conventional TEM. It is revealed that partial substitution of Cu2 + and Co2 + for Fe2 +in LuFe2O4 destabilized the CO structure. In LuFeCuO4, there exist characteristic zigzag-shaped diffuse streaks and diffuse spots at the h/3-δ h/3-δ 0-type positions (h: integer, δ = 0.06) in reciprocal space, which originate from static cationic ordering of Fe3 + and Cu2 + ions in the triangular lattice. Moreover, real-space images by the energy-filtered TEM revealed that nanometer-sized domain structures with the 5∼10 nm size are formed. In contrast, honeycomb-shaped diffuse streaks were found in LuFeCoO4, in which no domain structures are observed in real-space images.
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