Abstract
Over-stoichiometric BaRCo4O7+δ phases have been investigated by powder XRD, TG-DTA, and high resolution TEM. Three ordered structures of excess oxygen atoms were confirmed. In the case of Lu compound with the oxygen composition of δ = 0.80, an orthorhombic superlattice with the triple periods, 3ao, based on the fundamental orthorhombic structure of stoichiometeric phase. In the case of Y compound with the oxygen composition of δ = 0.96 equilibrated in the 1 atm O2 at 364℃, we observed the 2ao superlattice, which agrees with the results of recent neutron diffraction study. For the Y compound slowly cooded down to room temperature, a superlattice with a = 5ao was observed although the superlattice period is heavily disordered.
