Unconventional Oxygen Storage/Release Properties of Melilite-Type Ba₂MnGe₂O_7+ Associated with Complex Structural Transformation

Kosaku Ohishi, Satoshi Ogawa, Hisanori Yamane, Saburo Hosokawa, Zi Lang Goo, Kunihisa Sugimoto, Miwa Saito, Teruki Motohashi

Here, we report the synthesis and characterization of melilite-type A2MnC2O7 (A = Sr, Ba; C = Si, Ge) and the discovery of its unconventional oxygen storage and release properties. Unlike conventional Mn-containing oxygen storage materials driven by the Mn2+/Mn3+ redox couple, Ba2MnGe2O7+δ (BMG) does not require highly reducing atmospheres for oxygen release and exhibits reversible oxygen storage/release under oxygen-rich conditions at moderate temperatures (200–500 °C). Comprehensive compositional and structural analyses utilizing X-ray absorption spectroscopy, synchrotron in situ powder X-ray diffraction, single-crystal X-ray diffraction, and powder neutron diffraction revealed that the oxygen storage/release processes involve changes in the local coordination environment. Specifically, MnO4 tetrahedra in the reduced phase change into MnO5 trigonal bipyramids in the oxidized phase, accompanied by a distinct transformation from the fundamental melilite-type structure of Ba2MnGe2O7 (tetragonal, space group P4̅21m) to a 5a × 5a × 1c superstructure of Ba2MnGe2O7.455(4) (tetragonal, P4̅). BMG exhibits a maximum oxygen storage capacity of δ ≈ 0.45 and, notably, develops a distinctive blue color upon oxygen storage. This characteristic response suggests promising potential for various oxygen-related applications, such as oxygen sensors and oxygen-sensitive inorganic pigments.

Chem. Mater. 2026, 38, 3, 1084-1093. (DOI: 10. 10.1021/ acs.chemmater.5c02228)

プレスリリース（神奈川大学）