Nanostructures in LuFe2O4+δ

• Absence of intergrowth and extended defects in LuFe2O4+δ.
• Existence of original nanometric defects associated with gliding mechanisms.
• Charge ordering responsible for the monoclinic distortion.
• Symmetry lowering creates additional structural complexity.
• General character of these phenomena in these layered ferrites.

A LuFe2O4+δ sample, previously characterized by X-ray synchrotron and neutron diffraction, has been studied by electron microscopy techniques, in order to get a precise description of its micro- and nanostructures at room temperature. The X-ray synchrotron data vs. temperature show that the monoclinic distortion is associated with the charge ordering; this distortion results in elongated twinning domains, which enhance the complexity of the microstructural state at room temperature. The structural modulation associated with oxygen excess is observed in large domains inside a non modulated matrix, in contrast with the modulations associated with the charge ordering of the Fe2+ and Fe3+ species, which are mostly short-range. The investigation of the nature and density of defects in the sample shows that they are nano-scaled, preserving the regularity of the layer stacking mode, and limited to the formation of one- or two-units large stacking faults, associated with gliding mechanisms. Based on these observations, an original description of the LuFe2O4 ferrite structure, through puckered [LuO4]∞ sandwiching [Fe2]∞ layers, is proposed.

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