We performed polarization-dependent x-ray absorption spectroscopy studies on epitaxially grown Bi4-xLaxTi3O12 thin films at the 3p→6s edges to find the La substitution site. Our results show a clear difference between the absorption spectra taken with parallel and perpendicular polarizations, which is consistent with the view that La replaces Bi in the layer rather than at the perovskite site. Calculated absorption spectra also support the interpretation. We therefore conclude that some, if not all, La atoms replace the Bi atoms in the layer.
Bibliographical noteFunding Information:
This work is supported (in part) by the Korean Science and Engineering Foundation through the Center for Strongly Correlated Materials Research. One of the authors (B.H.P.) was supported by the National Research Program for the 0.1 Terabit Non-volatile Memory Development sponsored by the Korea Ministry of Science and Technology. SSRL is operated by the DOE Office of Basic Energy Sciences, Divisions of Chemical Sciences and Materials Sciences. FIG. 1. Bi 4 Ti 3 O 12 crystal structure. One may replace Bi atoms by La to make Bi 4 − x La x Ti 3 O 12 . FIG. 2. (a) Photoexcitation of an electron from 3 p to 6 s orbitals in an isotropic environment (at the perovskite site). The 6 s orbital is symmetric due to the isotropic crystal field. (b) Excitation from 3 p to 6 s at the layer site. The 6 s orbital is deformed due to the anisotropic crystal field. FIG. 3. The La 3 p → 6 s XANES spectra for (a) small and (b) wide energy ranges. Corresponding energy window for the data in panel (a) is shown in panel (b) as a dotted rectangle. (c) Experimental configurations. The TEY was measured by taking the sample current through the LSCO layer. Definition of the polarization angle is also shown. θ = 0 ° (normal incidence) corresponds to the polarization in the a b plane. FIG. 4. La 3 p → 6 s XANES spectra calculated by FEFF 8.0 for (a) the perovskite and (b) the layer sites.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)