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 L3,2-, Fe L3,2-, and Cu L3,2-edges demonstrate the reversal of orbital symmetry in CaCu3Ti4O12 on Fe3+ions substitution. The study of Cu L3,2- and Fe L3,2-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 3d(t2g) and 3d(eg) 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 3d and O-2p orbitals and a weakening of the hybridization of Ti 3d, Fe 3d, and O-2p orbitals.