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    題名: 利用X光吸收譜研究RMnO3 (R= Y, Ho, Tb與Eu) 電子與原子結構
    其他題名: Electronic and atomic structures of RMnO3 (R= Y, Ho, Tb and Eu) studied by X-ray absorption spectroscopy
    作者: 吳嘉祥;Wu, Chia-hsiang
    貢獻者: 淡江大學物理學系碩士班
    彭維鋒;Pong, Way-faung
    關鍵詞: X光吸收光譜;X光輻射光譜;X光延伸精細吸收光譜;錳氧化物;XAS;XES;EXAFS;manganites
    日期: 2009
    上傳時間: 2010-01-11 02:15:55 (UTC+8)
    摘要: 在本篇論文中,利用X光吸收光譜來研究 RMnO3 (R= Y, Ho, Tb與Eu)的電子結構和原子結構,我們也會使用理論計算局域自旋態密度模擬[Local Spin Density Approximate (LSDA+U)]來驗證實驗上取得的數據。從氧X光吸收能譜(X-ray absorption spectroscopy)和LSDA+U我們可以發現氧和錳之間有很強的p-d混成,我們推測這類的錳氧化物為電荷傳遞絕緣體(charge-transfer insulator)。從文獻可以發現在六角形錳氧化物中其電阻大於正菱形錳氧化物106(Ω cm),並且從氧X光吸收能譜和Kα輻射能譜(X-ray emission spectroscopy),發現此系列樣品之能隙並沒有太大的變化,推測影響這類錳氧化物的電阻大小,能隙並不是主要的因素,可能與樣品中之載子濃度有關。經由錳延伸X光吸收能譜[Extended X-ray Absorption Fine Structure (EXAFS) ]的傅立葉轉換,與擬合的結果發現,原子結構的對稱性會影響到晶格場與第白-華勒因子(Debye-Waller factor)。
    In this study, the X-ray absorption spectroscopy (XAS) results from the study on RMnO3 (R= Y, Ho, Tb, and Eu) manganites were then compared with the theoretical calculations using Local Spin Density Approximate (LSDA+U). The O K-edge XAS results showed that the Mn 3d states have strong hybridization with the O 2p states, which is consistent with the theoretical calculations. We have therefore suggested that manganese oxides with strong Mn3d-O2p hybridizations are charge-transfer insulators. Although the resistances of hexagonal manganites (HM) are in the order of 106 (Ω-cm) larger than those of the orthorhombic manganites (OM), their bandgap measurements did not differ greatly based from the combined analysis of the O K-edge and O Kα emission spectra. The large difference in their resistances is probably related to their carrier concentrations. The Mn K-edge Fourier Transforms (FT) of the Extended X-ray Absorption Fine Structures (EXAFS) and their fitting results show that the symmetry of atomic structures profoundly affects the crystal fields and Debye-Waller factors of HM and OM.
    顯示於類別:[物理學系暨研究所] 學位論文

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