臺灣博碩士論文加值系統

本文利用X光吸收近邊結構(XANES)、延伸Ｘ光吸收精細結構(EXAFS)、X光發射能譜 (XES)和非彈性共振X光散射能譜術(RIXS)來研究以下兩個主題。在第一部分，利用製程中不同的冷卻溫度(820 0C和750 0C)來合成，不同的超導體K1.9Fe4.2Se5 (SC-820和SC-750)與非超導體K2Fe4Se5 (NS-820和NS-750)。Fe K-edge EXAFS證明在超導的樣品(SC)中的鐵缺陷亂度比非超導樣品(NS)較大，藉此說明鐵缺陷的亂度與超導有很大的關係。利用Fe Lα, β-edge RIXS 來分析RR factor，發現到超導樣品(SC)具有較低的磁自旋態，說明較多的低自旋態可以增加超導之特性。在Fe L3,2-edge 和 Se K-edge XANES中，發現在超導的樣品中(SC)，由Fe 3d到Se 4p的電荷轉換現象較微弱，此即導致超導樣品(SC)有較低磁自旋態之原因之一。這些現象說明了在K2-xFe4+ySe5中鐵的自旋態、電荷轉移、鐵缺陷亂度與超導特性有強烈的關係。
在第二部分中，利用X光散射實驗發現到當Sr3Ir4Sn13 (SIS)單晶溫度低於不規則的電阻轉變T<147 K (T*)時，會演化出一系列的衛星峰，說明了當溫度低於T*時，電荷密度波(CDW)可能形成在(110)平面且此結果也與EXAFS結果相吻合。在Ir L3 -edge 和 Sn K-edge XANES中，證實在溫度接近T*時，不規則的電阻變化與Ir 5d態有強烈的關係而並非與Sn 5p態有關。根據以上的結果，在SIS單晶中局域性的電子、原子結構和CDW有著密不可分的關係。

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.

Abstract.....................................................................................................................1
Contents....................................................................................................................3
List of figures............................................................................................................5
1. Introduction........................................................................................................10
1-1. Strongly Correlated Electron System............................................................10
1-2. Necessity of spectroscopic studies................................................................12
2. Experimental techniques...................................................................................15
2-1. Synchrotron radiation....................................................................................15
2-2. X-Ray Diffraction (XRD).............................................................................16
2-3. X-Ray Absorption Spectroscopy (XAS).......................................................19
2-4. Normal/Resonant X-ray Emission Spectroscopy (N/RXEX).......................23
3. Mechanism of Superconductor K2-xFe4+ySe5....................................................29
3-1.Introduction....................................................................................................29
3-2. Experimental.................................................................................................34
3-3. Results and Discussion..................................................................................35
3-4 Conclusion.....................................................................................................59
4. Electronic and atomic structures of Sr3Ir4Sn13 single crystal: A possible charge density wave material ...............................................................................60
4-1. Introduction...................................................................................................60
4-2. Experimental.................................................................................................63
4-3. Results and Discussion..................................................................................64
4-4 Conclusion.....................................................................................................84
5. Summary.............................................................................................................86
Reference.................................................................................................................88

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