Rare earth ferrites LuFe2O4±x polymorphism, polytypism and metastable phases

• LuFe2O4±x: structural relationships between five polymorphs and polytypes.
• Transitions through complex commensurate and incommensurate modulations.
• Models for oxygen insertion.
• Fascinating remarkable 3D flexibility of the Lu ferrite vs. T, P and oxygen content.

This work is a compendium of the structural properties of layered LnFe2O4±x ferrites, focussed on recently discovered polymorphs and their transitions through five complex commensurate and incommensurate modulated structures. These phases are obtained varying the oxygen content (reversibly from O4.0 to O4.5) or applying high pressure (up to 15 GPa). The relationships between the different structures are discussed and models are proposed. These ferrites, which contain magnetic cations and exhibit remarkable 3D flexibility, open the road for magnetic, electric, catalytic or energy materials.

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