Synthesis of YBaFe4O7 and its spontaneous oxidation in air to YBaFe4O8.5

What is it about?

Conditions for YBaFe4O7 synthesis from oxide/carbonate amorphous precursors are investigated versus temperature and partial pressure of oxygen at high-temperature equilibrium with the sample in flowing atmosphere of humidified Ar and H2 gas mixtures. When exposed to ambient air, the completely cooled-down pellet oxidizes topotactically into YBaFeIII4O8.5 in a couple of minutes upon warming to some 200 °C. Neutron powder diffraction suggests that the added oxygens enter octahedral holes in the cubic closest packing of O and Ba atoms of YBaFe4O7. Up to two oxygen atoms add to some Fe coordination tetrahedra in the kagome-like layer of YBaFe4O7 in a disordered distribution described as partially occupied crystal-structure sites. The thus oxidized YBaFe III4O8.5 is metastable and decomposes at high temperatures into Fe III oxides of barium or yttrium. The synthesized YBaFe4O7 is a powerful room-temperature O2 getter that can be reverted by annealing in the above gas mixture. The crystal structure parameters are reported, the crystal structure of the oxidized phase with partially random distribution of the added oxygens is solved from neutron powder diffraction data.

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Why is it important?

The unique tendency of YBaFe4O7 to rapidly oxidize in air to a YBaFe4O8.5 of trivalent Fe lends it an ability of a room-temperature getter to suck up traces of O2 in a gas. One mole of YBaFe4O7 absorbs 3/4 mole of O2.