Structure, Oxygen Stoichiometry and Superconductivity of Bi2(Sr2-xAx)CuOy (A = Pr, Nd, Sm, Eu)
| Autor: | YU-CHEN CHU, 朱禹臻 |
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| Rok vydání: | 2004 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 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. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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