Abstract
In this thesis, the X-ray Absorption Near Edge Structure (XANES), Extended X-Ray Absorption Fine Structure (EXAFS), X-Ray Emission Spectroscopy (XES) and Resonant Inelastic X-Ray Scattering (RIXS) have been investigated the following two topics. In the first part, the superconductor, SC, (K1.9Fe4.2Se5) and non-superconductor, NS, (K2Fe4Se5) samples have been synthesized by quenching from various temperatures, 820 0C (SC-820 and NS-820) and 750 0C (SC-750 and NS-750). Fe K-edge EXAFS show enhanced Fe vacancy disorder in SC samples as compared to the NS samples, suggesting the Fe vacancy disorder strongly associated with the superconductor. The RR factor analysis by using Fe Lα, β-edge RIXS spectra, the SC-sample revealed the lower magnetic spin state, suggesting increasing in the low spin state enhance the superconducting behavior. Fe L3,2-edge and Se K-edge XANES suggested that the lower charge transfer effect from Fe 3d to Se 4p state in SC-group, which resulted in the lower spin state in SC-sample. These observations clearly elucidate that the spin state of Fe atom, charge transfer effect and Fe vacancy disorder are closely associated with the superconducting behavior in K2-xFe4+ySe5. In the second part, the evolution of a series of satellite peaks below the anomalous resistivity transition (T*~147 K) have been observed in Sr3Ir4Sn13 (SIS) single crystal by using X-ray scattering experiment, indicating the formation of possible charge density wave (CDW) in the (110) plane, and consistent with Sn K-edge EXAFS results. XANES spectra at the Ir L3-edge and Sn K-edge demonstrated that the Ir 5d states are closely related to the anomalous resistivity transition, rather than the Sn 5p state. Accordingly, a close relationship exists between local electronic and atomic structures and the CDW-phase in the SIS.