Determination of the charge-ordered phases in LuFe2O4

Abstract

High-resolution synchrotron powder diffraction and Fe K-edge x-ray resonant scattering (RXS) have been combined to determine both the magnitude and sequence of the Fe charge segregation in LuFe2O4. Two phases with different charge disproportionation were found below the so-called charge ordering transition temperature T CO 320 K. The crystal structure between 320 K and 200 K shows a symmetry where four non-equivalent iron sites with different valences were determined (Fe2.77+,Fe2.63+, Fe2.36+ and Fe2.26+ ). Below 200 K the structure further changes to the symmetry and six crystallographic sites for the iron atoms were found. The simplest valence distribution corresponds to a tri-modal one, where the six Fe atoms are grouped in couples with three valences Fe2.8+, Fe2.5+ and Fe2.2+. Both polar and anti-polar charge sequences have been discarded. © EPLA, 2014.