R-Site Substitution Effect on the Oxygen-Storage Capability of RBaCo4O7+δ

Here we show that the low-temperature oxygen-storage capability of RBaCo4O7+delta (R = Y, Dy, Ho, Er, Tm, Yb, and Lu) depends on the size of the rare earth constituent R. For all these R constituents the RBaCo4O7+delta phase can be charged and discharged with large amounts of oxygen in a narrow temperature ran-e below 400 degrees C. With decreasing ionic radius, r(R-III). the oxygen-release temperature (T-R) decreases while the temperature where the phase decomposes (T-D) increases such that the "safety window" between TR and TD widens. On the other hand, the maximum amount of excess oxygen taken by the RBaCo4O7+delta lattice in 1 atm O-2 decreases from delta approximate to 1.4 (for R = Dy) to similar to 1.0 (for R = Lu) with decreasing r(R-III). Hence the optimum oxygen-storage characteristics are found about R = Tin in terms of r(R-III). We also discuss the crystal structures of the oxygen-annealed RBaCo4O7+delta samples.