Synchrotron X-ray Absorption Spectroscopy Study of Local Structure in Al-Doped BiFeO3 Powders

The Al-doped BiFeO3, i.e., BFA(x)O powder samples with x = 0, 0.025, 0.05, and 0.1, were prepared via the hydrothermal route. The effects of Al substitution on the structural, electrical, and optical properties of BFA(x)O samples were investigated. It is found that the substitution of Al ions at B-site of BiFeO3 did not cause structural change and it still retains the rhombohedral perovskite structure with R3c symmetry, which was confirmed by the X-ray diffraction (XRD) and Raman measurements. X-ray absorption fine structure (XAFS) above the Fe K-edge and Bi L-3-edge in BFA(x)O powders was also measured and analyzed. Fe ions exhibit mixed valence states (Fe2+/Fe3+) while Bi ions keep the +3 valence state in all the samples. Fe K-edge XAFS also indicated that there was a competition between hybridization of Fe 3d and Al 3d with O 2p orbitals and occurrence of the more 4p orbitals with Al doping. The Bi L-3-edge XAFS revealed that transition from 2p(3/2) to 6d state increased, so did the energy of 6d state. Besides, Al ion doping affected both the nearest-neighbor and next-nearest coordination shells of Fe atom and nearest-neighbor shells of Bi atom. Ultraviolet-visible (UV-Vis) spectroscopy results show the BFA(x)O prepared by hydrothermal method could be an appropriate visible-light photocatalytic material.