Correlating crystal structure and oxygen storage properties in mixed-metal layered oxides

Abstract

We investigate the relationship between crystal structure and oxygen storage properties in hexagonally layered AB2O4-type oxides. The research begins with a deep-dive investigation into LuMnGaO4. Using a combination of neutron and synchrotron X-ray diffraction alongside thermogravimetric analysis, the study characterizes the topotactic transition from the reduced phase (R-3m) to the oxidized phase (P-3). A reversible colorimetric transition from greenish-grey to black upon oxygen uptake is observed, suggesting LuMnGaO4 as a candidate for optical oxygen sensing. The scope is expanded to the AMnGaO4 series (A = Lu, Yb, In) to examine A-site substitution effects. While the Yb-analogue mirrors the oxygen storage behavior of LuMnGaO4, the In-analogue exhibits a rigid lattice that suppresses oxygen insertion due to stronger In–O bonding. Magnetic characterization further reveals complex magnetic behaviors, including a transition into a frustrated spin-glass state in the oxidized Yb-based phases. Finally, a comprehensive study across the AFe2O4, AMnFeO4, and AMnGaO4 (A = Lu, Yb, Er, Y) series reveals a divergent structural response to oxidation driven by B-site occupancy. While AFe2O4 undergoes typical lattice expansion upon oxygen intercalation, Mn-substituted analogues exhibit an unconventional contraction of the c-lattice parameter and unit cell volume. This phenomenon is correlated with the changing coordination environment and effective ionic radii of manganese (Mn2+ to Mn3+). These findings demonstrate that strategic cation selection at both A and B sites can affect the structural stability and oxygen capacity in the lattice. Future research should focus on the long-term cycling stability and kinetic performance of these oxides under industrial operating conditions.