Probing reversal of orbital symmetry in CaCu3-xTi4-xFe2xO12 (x = 0.0–0.7) by X-ray absorption spectroscopy

The electronic properties studied using the X-ray absorption near-edge structure (XANES) spectroscopy performed in the vicinity of O K -, Ca L 3,2 -, Fe L 3,2 -, and Cu L 3,2 -edges demonstrate the reversal of orbital symmetry in CaCu 3 Ti 4 O 12 on Fe 3+ ions substitution. The study of Cu L 3,2 - and Fe L 3,2 -edges confirms that the valence states to be +2 and +3 for Cu and Fe ions, respectively. The O K -edge XANES spectra show a very systematic change leading to a reversal of relative intensities of the spectral features assigned to 3 d (t 2g ) and 3 d (e g ) peaks. This implies that Fe substitution induces the tilted octahedral to the square planar symmetry transformation. This is well supported by the cation distribution and also indicates that there is a strong hybridization of Cu-Fe 3 d and O-2 p orbitals and a weakening of the hybridization of Ti 3 d , Fe 3 d, and O-2 p orbitals.