Study of atomic structure and electronic structure of an AA'_3B_4O_(12) double-perovskite CaCu_3Ir_4O_(12) using STEM imaging and EELS techniques

摘要

A newly discovered 1:3 A-site-ordered AA'_3B_4O_(12) perovskite oxide CaCu_3Ir_4O_(12) 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 CaCu_3Ru_4O_(12) and CaCu_3Ru_4O_(12) 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 L_(2.3) core loss and O-K edges show that the electronic structure of CaCu_3Ru_4O_(12)is very close to that of CaCu_3Ru_4O_(12), but different from CaCu_3Ru_4O_(12). The O-K near edge fine structures show extensive hybridization of Ir 5d and O 2p band. Cu L2.3 peaks indicate Cu in CaCu_3Ru_4O_(12) has 2+ valence, though Cu~(2+) electrons mainly localized, they might have strong interactions with Ir~(4+) Sd electrons through Ir-O-Cu, similar to the strong coupling of Ru with Cu in CaCu_3Ru_4O_(12).