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

摘要

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 photoelectronwas 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.