The lanthanum (La) modification is known to improve dielectric and magnetic properties of ${\text{BiFeO}}_3$ (BFO), a promising room-temperature multiferroic oxide. The effects of La doping on the variations of the off-centering distortion and the orbital mixing of BFO are experimentally studied, in conjunction with first-principles density-functional theory (DFT) calculations. Both the Fe-O bond anisotropy in the ${\text{FeO}}_6$-octahedron cage and the off-centering ferroelectric polarization along the hexagonal ${\left[001\right]}_{\text{h}}$ are predicted to be substantially reduced by the La doping. These DFT predictions agree with the structural-refinement results obtained from high-resolution x-ray powder-diffraction data. We have shown that the apparent improvement of the polarization-field response is not intrinsic and can be attributed to the reduced leakage current by the La doping. X-ray absorption near-edge structure (XANES) spectroscopy study further indicates that the degree of $\text{Fe}3d\text{−}4p$ orbital mixing decreases with the La doping. The conclusion deduced from XANES study correlates well with the orbital-resolved density of states which predicts that the La doping increases the number of unoccupied states in the $p$ orbital but suppresses the number of unoccupied states in the $\text{Fe}3d$ orbital.

• Received 23 April 2010

DOI:https://doi.org/10.1103/PhysRevB.82.045113