Variations of ferroelectric off-centering distortion and 3d-4p orbital mixing in La-doped BiFeO3 multiferroics
Variations of ferroelectric off-centering distortion and 3d-4p orbital mixing in La-doped BiFeO3 multiferroics
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DOI：
10.1103/physrevb.82.045113
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发表时间：
2010-07-16
影响因子：
3.7
通讯作者：
Jang, Hyun Myung
中科院分区：
文献类型：
--
作者：
Lee, Jung-Hoon;Choi, Hyoung Joon;Jang, Hyun Myung
镧（La）改性可以改善BiFeO 3（BFO）的介电和磁性能，BiFeO 3是一种有前途的室温多铁性氧化物。结合第一性原理密度泛函理论（DFT）计算，实验研究了La掺杂对BFO的偏心畸变和轨道混合的影响. La的掺杂显著降低了FeO 6-八面体笼中Fe-O键的各向异性和沿[001]（h）h的偏心铁电极化沿着。这些DFT预测同意从高分辨率的X射线粉末衍射数据获得的结构细化的结果。我们已经表明，极化场响应的明显改善不是内在的，可以归因于由La掺杂的漏电流降低。X射线吸收近边结构（XANES）谱研究进一步表明，La的掺杂降低了Fe的3d-4p轨道混合程度。从XANES研究中得出的结论与轨道分辨态密度的预测，La掺杂的p轨道的未占态的数目增加，但在Fe 3d轨道的未占态的数目抑制相关。
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 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 FeO6-octahedron cage and the off-centering ferroelectric polarization along the hexagonal [001](h) 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 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.