利用X光吸收光譜 (X-ray Absorption Spectroscopy, XAS)，研究其以3d過渡金屬摻雜其釔錳氧化物 (YMnO3)-YMn2/3Tm1/3O3 (Tm= Co, Ni and Cu)之電子及原子結構。Mn L3-edge及K-edge結果顯示Tm2+取代了部分Mn3+，而使得Mn離子電荷價數增加。Tm2+的摻雜使得Mn 3d未佔據態變寬而不侷限其局部區域性，進而增進其導電性。由局域密度近似 (Local Spin Density Approximation + Hubbard U parameter，LDA+U)計算電子態密度與X光吸收譜圖比較得知，YMn2/3Ni1/3O3中，造成Mn L3-edge未佔據態改變的是Mn 3d↑-spin eg而不是一般認為的Mn 3d t2g。且O K-edge第二吸收峰為O 2p與Ni 3d↓-spin eg之混成 (hybridized)。

X-ray absorption spectroscopy measurements have been performed to elucidate local electronic and atomic structures of 3d-transition metal doped yttrium manganites (YMnO3) with chemical formula YMn2/3Tm1/3O3 (Tm= Co, Ni and Cu). The Mn L3-edge and K-edge XANES results indicate the direct substitution of Tm2+ for Mn3+, so that the positive effective charge of Mn ions are increased. Tm-doping is also found to induce substantial broadening of the Mn L3-edge feature, which suggests enhancement of the delocalization of Mn 3d eg subbands and conductivity. Local spin density approximation (LDA) + U (Hubbard U parameter) calculation shows that the leading features in the Mn L3-edge XANES spectra of YMn2/3Tm1/3O3 are due to majority-spin Mn eg subband rather than the Mn t2g subband commonly assigned. The comparison between O K-edge XANES spectrum of YMn2/3Ni1/3O3 and the LDA+U calculation shows significant contribution of O 2p and minority-spin Ni 3d eg hybridized states to the second feature of the O K-edge XANES spectra.

第一章　緒論..........................................1
(一) 雙交換機制 (Double exchange，DE).................2
(二) 楊泰勒晶格形變 (Jahn-Teller distortion)..........5

第二章　X光吸收光譜簡介及ＬＤＡ＋Ｕ 近似..............7
(一) 吸收邊緣與E0值...................................9
(二) X光吸收近邊緣結構................................10
(三) 延伸X光吸收精細結構..............................11
(四) 實驗方法.........................................15
(五) 數據分析.........................................19
(六) 局域密度近似 (Local Spin Density 
     Approximation + Hubbard U parameter ，LDA+U).....23

第三章　樣品之電子及原子結構研究......................25
(一) 研究目的.........................................25
(二) 樣品製備與量測...................................25
(三) 實驗數據分析與討論...............................26

第四章　結論..........................................44

參考文獻..............................................45
 
圖表目錄
圖1-1 鈣鈦礦結構 (Perovskite Structure)示意圖.........3
圖1-2 錳(Mn)離子電子組態示意圖........................3
圖1-3 雙交換機制 (Double exchange，DE)電子傳遞示意圖..4
圖1-4 楊泰勒晶格形變 (Jahn-Teller distortion)示意圖...6
圖2-1 光子能量與典型物質吸收截面關係圖................8
圖2-2 XANES與EXAFS分界圖..............................13
圖2-3 光電子平均自由路徑與能量關係圖..................13
圖2-4 單一散射與多重散射之圖像........................14
圖2-5 射出電子受鄰近原子的背向散射而產生干涉現象......14
圖2-6 X光吸收光譜實驗示意圖...........................16
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.......................19
圖2-9 選擇能量底限E0值的不同方法......................20
圖3-1 樣品的X光繞射譜圖...............................27
圖3-2 樣品原子結構示意圖..............................28
圖3-3 Mn K-edge及Tm (Tm= Co, Ni and Cu) K-edge 
      EXAFS k3χ傅利葉轉換圖...........................30
圖3-4 歸一化後樣品的Mn K-edge XANES...................33
圖3-5 歸一化後樣品的Mn L3,2-edge XANES................37
圖3-6 利用第一原理LDA及LDA+U近似法對YMn2/3Ni1/3O3
      所作之理論計算電子態密度分佈狀況................38
圖3-7 歸一化後樣品的O K-edge XANES....................39
圖3-8 利用第一原理LDA及LDA+U近似法對YMn2/3Co1/3O3
      所作之理論計算電子態密度分佈狀況................42
圖3-9 利用第一原理LDA及LDA+U近似法對YMn2/3Cu1/3O3
      所作之理論計算電子態密度分佈狀況................43

表3-1 原子半徑比較....................................29

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