Valence control of charge and orbital frustrated system YbFe2O4 with electrochemical Li+ intercalation

Abstract We report a trial of the valence control for mixed valence iron triangular oxide YbFe2O4 in order to develop an effective technique to control the frustration of charges in strongly correlated electron systems. The electro-chemical doping of Li + into YbFe2O4 was examined on the cell type sample similar to the Li-ion secondary battery cell. Systematic change of the lattice constant, Fe–Fe and Fe–Yb distance were observed with Li doping. Maximum value of the doping was over 300 mAh/g. An EXAFS experiment indicated that Li positioned between Yb octahedron layer (U-layer) and Fe-bipyramidal layer (W-layer). However, detailed change of iron valence state of YbFe2O4was not clearly observed because of the superimpose of the signal from iron metal nano particles in XANES observation. We discuss that the uncertainty might arise from the inhomogeneous distribution of the sample particle size, which might prevent the homogeneous doping of Li because the doping occurs on the surface of each nano-particles.