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    题名: 利用X光吸收光譜研究單晶結構的YBaCuFeO5
    其它题名: X-ray absorption studies of YBaCuFeO5 single crystal
    作者: 邱顯勝;Qiu, Xian-Sheng
    贡献者: 淡江大學物理學系碩士班
    彭維鋒
    关键词: 吸收光譜;X光吸收之線二向性;YBCFO;XLD;XANES;EXAFS
    日期: 2016
    上传时间: 2017-08-24 23:38:18 (UTC+8)
    摘要: 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.
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