X-ray photoelectron spectroscopic investigation on the elemental chemical shifts in multiferroic BiFeO3 and its valence band structure

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 BiFeO3 and have applied the same to explain the X-ray photoelectron spectra of BiFeO3 and its parent oxides Fe2O3 and Bi2O3. 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 2p3/2 and Bi 4f5/2 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 Fe2O3, Bi2O3 and BiFeO3. The effect of charge transfer on the valence band spectra of BiFeO3 was also investigated.

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