本論文主要以同步輻射相關實驗研究類鈣鈦礦單晶結構的YBaCuFeO5電子、原子結構的相關性。實驗包含在不同溫度下X光吸收之線二向性(XLD)、X光吸收近邊緣結構(XANES)、延伸X光吸收精細結構(EXAFS)。YBaCuFeO5隨著溫度從室溫降至低溫我們觀察到電阻率急遽增加，沿著樣品不同的方向上(AB平面)和(C軸)測量到(110K)及(125K)不同的相變溫度。從XLD實驗結果中發現位於晶格結構中心的Fe 3d eg電子從室溫降到相變溫度時，電子軌域由x2-y2轉向3z2-r2軌域；同樣位於晶格結構中心的Cu 3d eg電子在變溫過程中卻沒有任何明顯的變化，從X光延伸吸收精細結構的實驗中，可以觀察到降溫過程時Cu-O鍵沒有明顯的變化；而Fe-O鍵在相變溫度時會發現樣品不同平面的鍵結縮短及拉長，導致電阻變大。

We report the x-ray absorption study of the single crystal YBaCuFeO5 (YBCFO) to investigate the role of charge, orbital and local structure around the associated Fe/Cu cations on the electrical transport behavior of YBCFO. A resistivity transition is observed ~125K. X-ray linear dichroism (XLD) at Fe L3,2-edge shows different preferential occupation of eg-orbitals below (3d3z2-r2) and above (3dx2-y2) the transition temperature (125K). Larger resistivity along c-axis as compared to the ab-plane is argued in terms of direction dependent hybridization of Fe/Cu 3d - O 2p states as evident by the temperature dependent O K-edge XANES spectra and larger Fe - Oapical bond length compared to Fe - Obasal. Unusual increase in Debye-Waller Factor for Fe at 125K, accompanied by an increase in Fe – O bond distance, is observed, with expected temperature evolution of DWF for Cu. These findings reveal the distortion in square pyramidal sublattice associated with iron square pyramid. Fe/Cu K-edge spectra of YBCFO single crystal reveal the existence of Fe and Cu in Fe3+ and Cu2+ oxidation states, respectively.

目錄
目錄..........................................................................................................IV
圖表目錄..................................................................................................VI
第一章、緒論............................................................................................1
1-1. 多鐵材料.....................................................................................1
1-2. 文獻回顧.....................................................................................2
第二章、實驗技術.......................................................................4
2-1. X光吸收光譜簡介 ......................................................................4
2-1-1. 吸收邊緣與E0值.............................................................6
2-1-2. X光吸收近邊緣結構(XANES)........................................7
2-1-3. 延伸X光吸收精細結構(EXAFS)..................................8
2-1-4. 實驗方法.........................................................................13
2-1-5數據分析...........................................................................17
2-2. X光吸收之線二向性簡介 ........................................................21
(X-ray Linear Dichroism、XLD) ...................................................21
第三章、實驗數據分析與討論.......................................................25
3-1.樣品製備與基本量測.................................................................25
3-2. X光吸收近邊緣結構(X-ray Absorption Near Edge Structure、XANES) 之分析..........................................................30
3-3. X光吸收之二向性能譜(X-ray Linear Dichroism、XLD) 之分析....................................................................................................34
3-4. 延伸X光吸收精細結構(Extended X-ray Absorption Fine Structure、EXAFS) 之分析...........................................................39
第四章、結論....................................................................................44
參考文獻...................................................................................................46

圖表目錄
圖1-1 YBa2Cu3O7與YBaCuFeO5單位晶胞........................................3
圖2-1光子能量與銅吸收截面關係圖.....................................................5
圖2-2XANES與EXAFS分界圖..........................................................10
圖2-3光電子平均自由路徑與能量關係圖...........................................10
圖2-4單一散射與多重散射之圖像.......................................................11
(a)為單一散射路程示意圖...............................................................11
(b)為多重散射路程示意圖...............................................................11
圖2-5射出電子受鄰近原子的背向散射，而產生干涉現象...............12
(a)建設性干涉(b)破壞性干涉........................................................12
圖2-6X光吸收光譜實驗示意圖............................................................14
圖2-7 三種光譜量測方法......................................................................16
圖2-8 X光吸收光譜之數據分析流程...................................................17
圖2-9 eg軌域的壓縮或拉伸改變能階...................................................23
圖2-10 θ= 0º 和70º Fe L3,2-edge吸收譜.............................................24
圖2-11 (0º -70º) Fe L-edge XLD譜圖..................................................24
圖3-1樣品生長方向與背向勞厄X射線衍射圖..................................27
圖3-2 YBaCuFeO5X光繞射圖.............................................................27
圖3-3 YBaCuFeO5變溫電阻率和變溫磁化率.....................................29
圖3-4(a)、(b)Fe θ= 0⁰及70⁰時K-edge XANES能譜........................32
(c)、(d)Cu θ= 0⁰及70⁰時K-edge XANES能譜.........................32
圖3-5(a)、(b)Fe受到不同的位能差影響激發填入的軌域.................32
(c)Cu d軌域只剩單一空缺可以填入............................................32
圖3-6 Fe3+與O2-超交互作用示意圖......................................................33
圖3-7(a) Fe (b) Cu L3,2-edge及XLD譜圖..........................................36
圖3-8(a) 變溫O K-edge吸收光譜.......................................................38
(b) O 2px,y和Fe、Cu 軌域混成積分...........................................38
圖3-9 Fe 0º和70º EXAFS傅立葉轉換圖............................................41
圖3-10 Cu 0º和70º EXAFS傅立葉轉換圖.........................................41
圖3-11 Fe和Cu各個溫度下的鍵長和第白-華勒因子.......................42
表格3-1: Fe K-edge Fitting....................................................................43
表格3-2: Cu K-edge Fitting...................................................................43

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