(Bi2-xPbx)(Sr2-yRy)CuOZ (R = La, Pr)之結構、氧計量與超導性研究

Structure, Oxygen Stoichiometry and Superconductivity of (Bi2-xPbx)(Sr2-yRy)CuOZ (R = La, Pr)

洪勝男(Shan-Nan Hong)

指導教授 ： 高惠春

淡江大學/理學院/化學學系碩士班/碩士(2009年)

https://doi.org/10.6846/TKU.2009.00177

摘要

本實驗是利用固態法製備了三系列(Bi2-xPbx)(Sr2-yRy)CuOZ (R = La, Pr) 取代量0 ≤ x ≤ 0.1 的單相樣品與一系列(Bi2.2-xPbx)(Sr2-y Lay)CuOZ 取代量0 ≤ x ≤ 0.2 的單相樣品，透過X-光繞射光粉末繞 射圖譜與SEM 鑑定為單相，樣品結構為層狀堆疊。Pb2+會減少過量 的氧原子進入Bi2O2 2+雙層，受到Pb 摻雜的影響，造成madulation peak 減少。四系列樣品透過Rietveld 精算的結果，所有系列樣品皆 為正交晶相。Pr3+、La3+離子半徑比Sr2+離子半徑小，會使c 軸晶胞 參數隨取代量增加而縮短；在Bi2O2 平面上，有過量的氧原子掺入， 造成結構上的破壞，同時也撐大了a、b 方向的軸長。導電度的量 測結果，La18 系列在低溫下(0-30 K)具有半導性，取代量y = 0，在 低溫下(0-50 K)為半導體；La16、Pr16 與Pr18 系列均具有超導性； 在所有樣品中，Pr02 系列取代量y = 0.05 時有著最大超導轉移溫度 Tc(onset) = 15.5 K。Bi-L edge、Pb-L edge 及Cu-L edge XANES 吸收光 譜可知道，樣品中所含的元素Bi、Pb 與Cu 皆有混價的情形發生。 Bi 的平均價數小於三價，Pb 的平均價數等於三價；樣品所含的電 洞濃度，則隨著取代量的增加而呈現減少的趨勢，為電洞填充效 應。碘滴定法得知，四系列的氧計量隨著取代量的增加而增加，電 子轉移量隨著取代量增加而下降，由此推論，四系列的電洞濃度隨 取代量增加而呈現下降的趨勢。

關鍵字

正交晶系 ； 超導性 ； 吸收光譜 ； 電洞填充效應

並列摘要

Three series of single phase (Bi2-xPbx)(Sr2-yRy)CuOZ (R = La, Pr) oxides
with 0 ≤ x ≤ 0.1 and a series of single phase (Bi2.2-xPbx)(Sr2-y La y)CuOZ
oxides with 0 ≤ x ≤ 0.2 were prepared by a solid state reaction method.
They all have the orthorhombic symmetry and laminar structure observed
under SEM. Pb substitution for Bi is quite effective to the suppression of
the modulation structure. For these calcultions we use Rietveld method.
The a and b cell dimensions increased with R (R = rare-rarth) doping
while the c cell dimensions deccreased with R doping. The decrease in c
with increasing R content is explained primarily by the substitution of
smaller R ion for the larger Sr. The smaller increase in a and b with
increasing R content is probably caused by the added oxygen which is
accommodated in the Bi2O2 slab of the structure. Most of sample are
superconductors at low temperature. The series of (Bi2.2-xPbx)(Sr2-y La
y)CuOZ oxides showed semiconducting properties at low temperature.The
maximum Tc (15.5 K) is found in the R = Pr , x = 0.2 and y = 0.050
sample. The valence states of the Bi and Pb, and Cu, and the hole
concentration of the all Bi2201 superconductors were studied by theXANES spectroscopy in the NSRRC of Taiwan. The L-absorption edge
of the Bi atom shows that the Bi ions in all the samples have mixed
valence states. The oxidation states of Bi which one state smaller then
3.The L-absorption edge of the Pb atom shows that the Pb ions in all the
samples have mixed valence states. The oxidation states of Pb which one
state to be equal to 3. 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. Oxygen content (z) increasd with
increasing y. Number of electron transfer decreased with increasing y.
Hole concentration decreased with increasing y, showing a hole filling
effect.

並列關鍵字

hole concentration ； doping ； superconductivity ； XANES

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