- 學位論文
正交結構硒化鐵之晶體成長、磁性性質與近緣吸收光譜研究
Investigation of the crystal growth, magnetic properties and X-ray absorption Near Edge Structure of Tetragonal FeSex
摘要
在擁有超導轉變溫度26 K的氟(F)摻雜砷化鐵基超導體(LaO1-xFxFeAs)發現後, 鐵基超導體的轉變溫度在短短數年內迅速的提升至56 K. 同時, 更多的鐵基超導體接著被研究出來, 包括了(Ba,K)Fe2As2, LiFeAs 和Fe1+yTe1-xSex等等. 不同於其它鐵基超導體, 硒化鐵在鐵基超導體中擁有最簡單的晶體結構, 它的超導轉變溫度在8 K. 同時, 其結構中不含砷, 但與砷化鐵又有很多共同的物理特性. 其簡單的層狀結構, 提供了人們對高溫超導體超導機制的暸解一個有用的方向, 特別在結構與超導之間的關連. 在此論文中, 我們將呈現硒化鐵晶體的成長方法, 硒化鐵的磁性及吸收光譜的量測結果. 硒化鐵晶體可以很容易的使用KCl當溶劑的助溶劑生長成取得. 成長之後的晶體需馬上降至低溫長時間退火以助於正交結構硒化鐵的穩定與改善其晶體結晶性. 我們成長出的硒化鐵晶體皆呈現(101)的優選方向. 低溫的X光量測顯示, 硒化鐵在約100 K左右會有一個結構相變, 其與超導呈現了重要的關連. 硒化鐵因其層狀的特性, 在磁性量測上我們得到其異向性的磁性超導行為, 其中Fe-Se層提供了它主要的磁性異向性來源. 根據吸收光譜的量測, 硒化鐵中硒缺陷所造成的結構變異會提供鐵-硒混成軌域的自由電子機率, 這可能與超導生成的機制有關.
並列摘要
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.
參考文獻
延伸閱讀
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