Correlation between the metal-insulator transition and the electronic density of states near the Fermi level in oxygen-deficient perovskite-type NdBaCo2O5.5

Autor: M. Soda, Nark Eon Sung, Min Gyu Kim, Sun Hee Choi, Masanori Hidaka, M. Soejima, Masatoshi Sato, Jay Min Lee
Rok vydání: 2005
Předmět:
Zdroj: physica status solidi (b). 242:1422-1430
ISSN: 1521-3951
0370-1972
DOI: 10.1002/pssb.200440031
Popis: X-ray absorption spectra near the absorption edges of Nd, Ba, and Co ions have been taken to study the metal–insulator (M–I) transition occurring at about 360 K (TMI) in NdBaCo2O5.5. In the metallic and insulating phases, the electronic density of states (DOS) just above the Fermi level (EF) consists of the high-density unoccupied bands of Nd–5dσ and Ba–5dσ. The narrow charge-transfer Co–3d7(eg)L band and the broad charge-transfer Co–3d(t2g)nLm bands occupy positions just below and near EF, respectively, where L represent a hole in the O–2p valence band. The negative charge-transfer Nd–4dnL′m and Ba–4dnL′m hybridized bands are also just below EF, where L′ represent a hole in the fully occupied 4d band of the Nd and Ba ions. It is suggested that the metallic conductivity above TMI arises from the itinerant (p–d) hybridized holes having an 3d(eg)-symmetry in the top of the O–2p valence band. The structural deformation localized around the Ba ions but not the Nd and Co ions affects the crystal-field splitting of the Co–3d orbitals in the CoO polyhedra and the hybridization between the outer orbitals of the cations (Nd, Ba, Co ions) and the O–2p orbitals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Databáze: OpenAIRE
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