Micro-structure Research Of Bi-system Superconductors Using Analytical Electron Microscope

Bi-system superconductors have more advantages than Y-system superconductors, for example higher transition temperature (T_c) and not containing rare earth elements and easily producing tapes or wires. But practical applications of these materials have been hampered by themselves intrinsically shortcoming, such as the low critical current density (J_c) and the weak-link behavior between grain boundaries. In addition, owing to Bi-system superconductors in the structure are more complex, these questions are still disputed for the symmetries and the details of the modulation structure especially. Considerable effort is being focused on understanding the structure, processing and the mechanisms responsible for the properties involved. In the thesis, the microstructure and the modulation of the Bi-system superconductors have been investigated systematically using analytical electron microscope, including conventional analysis methods, convergent beam electron diffraction (CBED), high-resolution electron microscopy (HREM) and other techniques, which is aimed at understanding the microstructure characteristics and the phase transformation law of Bi-system superconductors. These research results will be very useful for improving production technology and probing into superconducting properties and mechanisms of high Tc superconductors.According to a vast amount of TEM observation results, a diffusion model through dislocation pipe about Bi-2223 phase transformation first has been proposed. Combining dislocation dynamics with diffusion theory, the nucleation energy and the growth rate of the Bi-2223 phase have been calculated at the same time. The calculation results: (1) Requisite force for the Bi-2223 phase growth in the diffusion...