Stability and oxygen-storage characteristics of Al-substituted YBaCo4O7+δ

A series of Al-substituted YBa(Co1−xAlx)4O7+δ samples was synthesized and characterized with respect to the capability to store large amounts of oxygen at low temperatures (at 200–400 °C) and the phase decomposition upon heating under oxidizing conditions at higher temperatures (above 550 °C). It was revealed that increasing the Al-substitution level up to x≈0.10 boosts up the phase-decomposition temperature from ∼550 to ∼700 °C, while the unique oxygen absorption/desorption characteristics remain nearly the same as those of the pristine YBaCo4O7+δ phase. The maximum amount of excess oxygen absorbed by the Al-substituted YBa(Co1−xAlx)4O7+δ samples was determined to be as large as δ≈1.45 for x=0.10 (in 100 atm O2 at 320 °C). Isothermal annealing experiments carried out for the same x=0.10 phase at 300 °C revealed that it could be reversibly charged and discharged with 1.2 oxygen atoms per formula unit by switching the gas flow from N2 to O2 and vice versa.