Abstract
Soon after the discovery of LaO1-xFxFeAs with superconductivity transition Tc ~ 26 K, the Tc of iron-based superconductor was quickly raising up to 56 K. More iron-based superconductors, e.g., (Ba,K)Fe2As2, LiFeAs and Fe1+yTe1-xSex were discovered subsequently. Among of that, Iron-chacogenides series, i.e. FeSex, has triggered great interest because of its simplest crystal structure and superconductivity below 8 K without any carrier doping. It do not involve arsenic but share several common features with iron-pnictides. The simplest structure of FeSe-superconductors might be able to provide important clues to the mechanism of superconductivity in iron-based superconductors. In this thesis, we present the growth method of the FeSex crystals by using KCl flux, the measurements of magnetic properties and X-ray absorption sprectroscopy (XAS), especially the Near edge structure of XAS. FeSex crystals can be easily grown with KCl flux, which need to annealing in-situ at low temperature after the growth process immediately to stabilize the tetragonal phase and improve the crystalinity. Our crystal tends to prefer in (101) direction. Low temperature X-ray measurements reveals that FeSex posses a structure transformation below 100 K which may play an important roles to the superconductivity. Due to the layered structure, the magnetic measurement reveal that FeSex posses an anisotropy magnetic behavior, which the Fe – Se layered may contribute to the anisotropy behavior. The XANES measurement reveal that a lattice distortion observed in the XAS Fe K-edge spectra of Se-deficient FeSex crystals that may produce itinerant electrons in the Fe – Se hybridization bond seen in the Se K-edge spectra.