We have successfully conducted B site Mn substitution on oxygen storage material YbFe2O4 to form YbMnxFe2-xO4 (x=1, 0.75, 0.5, 0.25) solid solutions. High resolution Synchrotron X-ray Diffraction (SXRD) shows, same as their parent structure, YbMnxFe2-xO4 (x=1, 0.75, 0.5, 0.25) can uptake oxygen (being oxidized) and undergo a structure transition from R-3m to P-3 symmetry, showing their potential as oxygen storage materials. X-ray Photoelectron Spectroscopy (XPS) implies the oxidation of Mn2+ and Fe2+ into Mn3+ and Fe3+ after the structure transition. Thermogravimetric analysis (TGA) as well as in-situ SXRD measurement at elevated temperature show YbMnxFe2-xO4 series started to uptake oxygen at 200 °C but undergo structure transition at 300 °C. Their structure evolution under methane and air atmosphere were monitored with in-situ SXRD, showing promising reversibility and structure stability. By performing Rietveld structure refinement, we discovered that the Mn substitution has an opposite influence on the lattice parameters (a and c) of the reduced phases YbMnxFe2-xO4 (R-3m) and oxidized phases YbMnxFe2-xO4.5 (P-3). We proposed that such an interesting phenomenon can be attributed to the different influence of Mn substitution on the B site (Mn/Fe) d electron filling under the triangular bipyramid crystal field for reduced phases and oxidized phases. In addition, we measured the magnetic susceptibility of both reduced phases and oxidized phases. Their very different magnetic behaviors were briefly discussed.

Structure study of oxygen storage material YbMnxFe2-xO4 before and after oxygen uptake

ACS Fall 2021

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