Study On The Interface Morphology And The Mophology Evolution Rules Of The YBCO Crystal Growth During The Unidirectional Solidification

It is important that a superconductor with a kind of orientation crystal must be obtained so that it has an available critical current density because of the anisotropism of the YBCO crystal structure. This technology can make the microstructure of material to be aligned exactly along with the preferential orientation and then can obtain unidirectional domains or single crystal, so the research, which is preparing high temperature superconductor with stronger anisotropism by the unidirectional solidification method, is being paid more attention.In the thesis, we investigated the the stopped growth mechanism of YBCO crystal growth during the peritectic reaction moment of the directional solidification, and analyzed the morphology and the chemical composition ahead of the interface of the YBCO bulk. We found that the higher technology temperature and pulling velocity will influence the macroscopical surface. It was found that YBCO crystal will cease growing when yttrium and barium are depleted and copper becomes rich element in the liquid phase at the YBCO crystal growth front. For maintaining the continuous growth of YBCO, the composition of Y, Ba and Cu in raw sample has to be adjusted so as to make yttrium and barium enrichments in the liquid phase at the YBCO crystal growth front during the melt growth process.In this thesis, the YBCO crystal growth characteristics during the uidirectional solidification was analyzed detailed based on the interface stability and morphology evolution rules of the crystal growth. The interface stability and the morphology evolution rules of the metalic crystal growth during the traditional unidirectional solidification is not applicable to the analysis of the YBCO crystal growth interface during the same process. The interface stability theory and the morphology evolution rules of the YBCO crystal growth during the traditional unidirectional solidification decided mainly by the crystallology feature of the YBCO crystal itself;The YBCO crystal growth morphology is decided by the anisotropism between the different YBCO crystal facet growth velocity. The state of the interface, growth mechanismand the driving force of the growth influence the growth of the YBCO crystal. The YBCO crystals will grow steady if the kinetic anisotropism of the YBCO crystal compensate for the non-homogeneous concentration distribution ahead of the interface of the YBCO crystal, otherwise, the phenomenon of interface instability will occur.