固溶体・溶液の溶存化学種の化学結合のXANESスペクトルによる研究

点击翻译按钮获取中文摘要

XANES (X-ray Absorption Near-Edge Structure) is sensitive to chemical states and local structures around photoexcited atoms in materials. We have obtained theoretical spectra by first-principles DV-Xα molecular orbital method with continuum basis functions in the frame work of the LィイD12ィエD1 method. Some developments and improvements of the software were performed in the present work. A number of basis functions were utilized for two steps of the continuum calculations. First, an extended basis set consisting of continuum wave functions and a minimal set of atomic orbital were used to obtain self-consistent charge density. Then a further extended basis set was used to represent the states in the continuum. The obtained wave functions were also utilized for understanding characters of the peaks in XANES.Most of the conclusions drawn from the XANES for the lanthanoid compounds were concerned with the chemical states and characteristics of the electronic structures. Theoretical XANES spectra for CeOィイD22ィエD2 and vacancy-including CeOィイD22ィエD2 ・LaィイD22ィエD2OィイD23ィエD2 solid solution were obtained in the present work. Peaks in the Ce LィイD23ィエD2 X-ray absorption spectra were assigned to quasi-bound states which were generated by the cage effect due to the oxygen atoms surrounding the Ce atom. A spectral change originating from the oxygen vacancy of the solid solution was analyzed. It is found that valence fluctuation of Ce, possibly caused by the vacancy formation, is undistinguishable in the spectra. Theoretical and experimental spectra of the sulfur K absorption for SOィイD24ィエD2ィイD12-ィエD1 and SOィイD23ィエD2ィイD12-ィエD1 ions are compared. The peaks in the spectra are assigned to atomic pairs of scattering such as S-O and S-Na for NaィイD22ィエD2SOィイD24ィエD2. Theoretical XANES of Li compounds revealed characters of each peak in the spectra. Charge transfer from the Li ion to the halogen ions due to exciton and scattering between Li-halogen were clarified.