Study of atomic structure and electronic structure of an AA′3B4O12 double-perovskite CaCu3Ir4O12 using STEM imaging and EELS techniques

A newly discovered 1:3 A-site-ordered AA′3B4O12 perovskite oxide CaCu3Ir4O12 which has unusual electrical and magnetic properties was investigated using STEM imaging and EELS techniques in a probe corrected microscope. The target sample was compared with the other two iso-structural oxides of CaCu3Ru4O12 and CaCu3Ti4O12 with dissimilar physical properties. It has been found by STEM HAADF imaging that Ca and Cu on A and A′ sites are ordered as expected. Oxygen atoms are imaged with STEM ABF imaging. The fine structures of the Cu L2,3 core loss and O–K edges show that the electronic structure of CaCu3Ir4O12 is very close to that of CaCu3Ru4O12, but different from CaCu3Ti4O12. The O–K near edge fine structures show extensive hybridization of Ir 5d and O 2p band. Cu L2,3 peaks indicate Cu in CaCu3Ir4O12 has 2+ valence, though Cu2+ electrons mainly localized, they might have strong interactions with Ir4+ 5d electrons through IrOCu, similar to the strong coupling of Ru with Cu in CaCu3Ru4O12.