Microstructural Analysis of the Bismuth-2212 High T sub c Superconductor Prepared From the Melt Quenched Precursor by Transmission Electron Microscopy

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Título:
Microstructural Analysis of the Bismuth-2212 High T sub c Superconductor Prepared From the Melt Quenched Precursor by Transmission Electron Microscopy
Autor: Zhang, Z-P
Notas: SourceType-Dissertations & Theses-1
ObjectType-Dissertation/Thesis-1
content type line 16
Descrição: Three phases are known to be responsible for the superconductivity in the Bi--Sr--Ca--Cu--O high Tc superconductor. They are: the n = 1, n = 2, and n = 3 phases. The Bi sub 2 Sr sub 2 Ca sub 1 Cu sub 2 O sub 8+ delta (Bi-2212) superconductor in the present study is made by the melt quenching method. Its superconducting property is a function of the subsequent annealing condition. The microstructural development in Bi-2212 system, under annealing temperature between 500-865 deg C, is studied by transmission electron microscopy (TEM) and X-ray powder diffraction. Electrical resistivity of samples, which is the main indicator of the superconductivity, is measured as a function of temperature. From X-ray powder diffraction, one can obtain the average structural information of the material. The growth characteristics of the superconducting phases are investigated by TEM. It is found that at low annealing temperature (T < 600 deg C) the n = 1 phase and a newly discovered phase, the "cubic" phase, grow with annealing time. The growth of the n = 2 phase is suppressed. The majority of the n = 1 phase has extremely small grain size ( approx 200 A). A few large grains of the n = 1 phase are detected and the modulation found in these large grains is found to be incommensurate both in the b and c directions. In addition, the 180 deg twist boundary is also found to exist in these grains. The hypothesis that the "cubic" phase is a new superconducting phase is further explored.In the mid annealing temperature range (650 deg C < T < 750 deg C), the n = 1 and the "cubic" phases are no longer dominant in the material. The n = 2 phase grows very slowly and with many defects. In the high annealing temperature range (T > 800 deg C), the n = 2 phase grows exclusively. Its preferential growth direction is its basal plane. The n = 2 phase grown at high temperature has fewer defects. It is found that the n = 1 phase nucleates first out of the amorphous precursor. The n = 2 phase grows out of the n = 1 phase. A number of impurity phases are also discovered. Their crystal structures and compositions are determined by electron diffraction and energy dispersion spectrometry (EDS) respectively. (DA9215704).
Data de criação/publicação: 1992
Formato: 178
Idioma: Inglês

Microstructural Analysis of the Bismuth-2212 High T sub c Superconductor Prepared From the Melt Quenched Precursor by Transmission Electron Microscopy

Zhang, Z-P

1992

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