X-ray photoelectron spectroscopic investigation on the elemental chemical shifts in multiferroic BiFeO 3 and its valence band structure

Abstract

A phenomenological rule based on the charge transfer, exists to predict the ionic/covalent character of the bonds in mixed oxides and is widely used to explain the binding-energy shifts of cations in mixed oxides compared to their simple oxides. Here, we have verified the above rule in the multiferroic BiFeO 3 and have applied the same to explain the X-ray photoelectron spectra of BiFeO 3 and its parent oxides Fe 2O 3 and Bi 2O 3. Ionic charges on Fe, Bi and O were calculated from density functional theory (DFT) within the local density approximation. Measured chemical shifts of O 1s, Fe 2p 3/2 and Bi 4f 5/2 were compared with the chemical shifts evaluated theoretically considering different contributions such as charge transfer, Madelung potential (initial state effect) and extra-atomic relaxation (final state effect). The chemical shift in the binding energy of O 1s photoelectron was used to build a covalence scale among Fe 2O 3, Bi 2O 3 and BiFeO 3. The effect of charge transfer on the valence band spectra of BiFeO 3 was also investigated.