淡江大學機構典藏:Item 987654321/32835
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    題名: Bi2(Sr2-xAx)CuOy (A = Pr、Nd、Sm、Eu) 化合物之結構、氧計量與超導性研究
    其他題名: Structure, oxygen stoichiometry and superconductivity of Bi2(Sr2-xAx)CuOy (A = Pr, Nd, Sm, Eu)
    作者: 朱禹臻;Chu, Yu-chen
    貢獻者: 淡江大學化學學系碩士班
    高惠春;Kao, Huey-chuen I.
    關鍵詞: 正交晶系;超導體;吸收光譜;電洞填充效應;hole concentration;doping;Superconductivity;XANES;Bi2(Sr2-xAx)CuOy
    日期: 2006
    上傳時間: 2010-01-11 02:49:55 (UTC+8)
    摘要: 本實驗是利用固態法製備了四系列Bi2(Sr2-xAx)CuOy (A= Eu、Sm、Nd、Pr) 取代量0≦x≦0.25的單相樣品， X-光繞射圖譜顯示所有樣品皆屬正交晶系的金屬化合物，隨著離子半徑減小，樣品的製備溫度亦隨之下降。電阻率的量測結果，發現 Eu、Sm、Nd、Pr取代Sr的系列樣 品皆有超導性。其電阻率隨著溫度呈現緩慢的下降。在Pr = 0.050取代有著最高的超導轉變溫度39 K。隨著取代元素的半徑越大超導轉變溫度越高，這是因為小原子造成的結構空隙大，電子的傳導不易所造成的。在電洞濃度方面，我們是以三價的 Eu、Sm、Nd、Pr來取代二價的Sr，屬於電洞填充效應，電洞濃度隨取代量增加而呈現先增後減的趨勢，在x = 0.025取代時有一個最大值。而氧含量則是呈現一個上升的趨勢，這是由於氧原子為了要平衡電荷，所以才會隨著取代量增加而上升。以Cu-K edge 及 Bi-L edge吸收光譜分析發現 Cu 元素有混價態而 Bi元素則沒有。O-K edge及 Cu-L edge吸收光譜分析 Eu、Sm、Nd、Pr 摻雜樣品發現隨著取代量增加，Cu及Cu-O平面上的電洞濃度減少，這是電洞填充效應所造成的結果。而SEM圖形觀察每個樣品都是層狀的。而片狀表面上的小白點則為其主要成份為 Bi和 Sr元素。Bi元素在製備過程中有較明顯的逸失，這是由於Bi元素熔點較低所致。而Sr及取代元素則無改變。
    Four series of single phase Bi2(Sr2-xRx)CuO4 (R = Pr, Nd, Sm, Eu)
    oxides with 0≦x≦0.25 were prepared by a solid state reaction method.
    They all have the orthorhombic symmetry and laminar structure observed
    under SEM. Most of the R doped Bi-2201 are superconductors at low
    temperature. The maximum Tc (42.6 K) is found in the R = La and x =
    0.050 sample. The maximum Tc found for each series is either in the x
    = 0.050 or 0.075 samples, indicating the optimal substitution amount is in
    between 0.050 and 0.075 that is dependent on the ionic radius of R, the
    bigger is the higher. No anomalous is observed in the Pr series, which
    shows the same trend as other samples. The valence states of the Bi and
    Cu, and the hole concentration of the Bi2(Sr2-xRx)CuO4 (R = Pr, Nd, Sm,
    Eu) superconductors were studied by the XANES spectroscopy in the
    NSRRC of Taiwan. The L-absorption edge of the Bi atom shows that the
    Bi ions in all the samples haven，t mixed valence states, The K- absorption
    edge of the Cu shows that the Cu ions in all the samples have mixed
    valence states.The L-absorption edge of the Cu and The pre-edge of the
    K- absorption edge of the O atom is related to the hole concentration of
    these superconductors. Hole concentration decrease with increasing
    x,showing a hole filling effect. The optimal hole is deduced in the 0.050≦x≦0.075 for Bi2(Sr2-xRx)CuO6+δ superconductors . EDS shows that the
    amount of Bi existing in the samples is less than its nominal composition,
    indicating that Bi is more volatile than the other constituents.
    DOI: 10.6846%2fTKU.2006.00026
    顯示於類別:[化學學系暨研究所] 學位論文

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