Comprehensive Study of Oxygen Storage in YbFe2O4+x (x ≤ 0.5): Unprecedented Coexistence of FeOn Polyhedra in One Single Phase

The multiferroic LuFe 2.5+ 2 O 4 was recently proposed as a promising material for oxygen storage due to its easy reversible oxidation into LuFe 3+ 2 O 4.5 . We have investigated the similar scenario in YbFe 2 O 4+x , leading to a slightly greater oxygen storage (OSC) capacity of 1434 μmol O/g. For the first time, the structural model of LnFe 2 O 4.5 was fully understood by high-resolution microscopy images, and synchrotron and neutron diffraction experiments, as well as maximum entropy method. The oxygen uptake promotes a reconstructive shearing of the [YbO 2 ] sub-units controlled by the adaptive Ln/Fe oxygen coordination and the Fe 2/3+ redox. After oxidation, the rearrangement of the Fe coordination polyhedra is unique such that all available FeO n units (n = 6, 5, 4 in octahedra, square pyramids, trigonal bipyramids, tetrahedra) were identified in modulated rows growing in plane. This complex pseudo-ordering gives rise to short-range antiferromagnetic correlation within an insulating state.