Abstract

The lanthanum
La modification is known to improve dielectric and magnetic properties of BiFeO3
BFO,
a promising room-temperature multiferroic oxide. The effects of La doping on the variations of the offcentering distortion and the orbital mixing of BFO are experimentally studied, in conjunction with firstprinciples density-functional theory
DFT calculations. Both the Fe-O bond anisotropy in the FeO6-octahedron
cage and the off-centering ferroelectric polarization along the hexagonal 001h 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
Fe 3d-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 Fe 3d orbital.