Ga-for-Co substitution in YBaCo4O7+δ: Effect on high-temperature stability and oxygen-storage capacity

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.