Department of Chemistry

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,

ABSTRACT Various powerful oxygenation approaches were tested in order to find the limits of the oxygen-storage capability of YBaCo4O 7+δ. By means of extreme solid-medium high-pressure oxygenation employing KClO3 as an oxygen generator the phase was successfully loaded with excess oxygen up to δ ≈ 1.56.

ABSTRACT Here we show that the high-temperature phase stability of the highly potential oxygen-storage material YBaCo4O7 + δ is substantially enhanced by replacing part of cobalt by gallium. Our systematic investigation of the YBa(Co1-xGax)4O7 + δ system reveals that with increasing Ga-substitution level x the temperature where the phase starts to decompose under oxygen-containing atmospheres gradually increases such that for x ≥ 0.20 no indication of phase decomposition is seen upon heating in 1 atm O2 up to 1000 °C. At the same time, the low-temperature oxygen-storage capability of the phase is somewhat affected by the Ga-for-Co substitution. With increasing x, the oxygen absorption rate gets slower but the amount of excess oxygen tolerated by the structure is little affected such that e.g. under 100 atm O2 pressure the x = 0.20 sample could be loaded with excess oxygen up to δ ≈ 1.2. We discuss the Ga-substitution effects in the present system comparing to those previously observed in the YBa(Co,Al)4O7 + δ system.