Abstract
The structural, electronic, and magnetic properties of Sr0.75Y0.25CoO2.625 system are reported based on the density-functional calculation within the GGA + U method. The structural properties show that the CoO6 and the CoO4.5 sites show the elongation and the compression of Jahn-Teller distortions, respectively, in which more evident distortion at the CoO4.5 sites is shown. The distortions are strongly induced by the Y3+-doping-assisted oxygen vacancies and lifts the degeneracy of Co 3d and O 2p orbitals. The system shows the half-metallic ferromagnetic properties with a local ferrimagnetism at the CoO6 sites. The Co3+ ions exhibit mixed intermediate-high and low-high spin states at the CoO6 and the CoO4.5 sites, respectively. The principle of centroids of DOS peaks is then used to provide accurate energy positions of sub-Co 3d orbitals under the distortion. It is shown that the bonding level of the valence band comes from Co 3d at the CoO6 and the CoO4.5 sites hybridized with 8i-site O 2px/2py and 16m-site O 2pz orbitals, respectively, via σ bond, while π and σ* bonds between all-site O 2p and Co 3d orbitals are implied at the non-bonding and the anti-bonding levels. This study reports the essential properties to guide future experiments.
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