Crystal Growth Mechanism And Orientation Control Of YBCO Superconductors Prepared By Unidirectional Solidifucation Method

Since the unidirectional solidification technology has made a great success in improving the critical current density of YBa₂Cu₃O_7-8 ( YBCO or Y123 ) superconductor, a lots of researchers have been engaged in this kind of works with a budget. By the unidirectional solidification technology, the paper studied the preparation processing of the YBCO high temperature superconductor, discussed the formation mechanism of YBCO, and analyzed the microstructures obtained by different experiment parameters on theory and experiment.We investigated technical process of YBCO superconducting rods by unidirectional solidification. It includes preparation method of pioneer power and preparation of pioneer rod. The materials grown by these methods show a highly aligned structure and few weak links. We studied the dependence of microstructure on the traveling rate. The results show that the lower traveling rate is benefit for the growth of crystal. We analyzed the microstructure of YBCO. It was discovered that both kinds of bulks and the layer crystal was anisotropic. By the means of systematical study on the unidirectional solidification YBCO with different inclusions, important roles of dispersive distributed 211 particles on suppression microcracks, affecting the crystal growth. There were cracks and holes concurrence in the crystal. The holes were the objections for blocking the current and also the sources of cracks creating. The micro-crack was as scale to the size of 211 particles. The more 211 particle was fine, the more the space between cracks was small.We have studied the nucleation and growth mechanisms of textured YBCO. Our data confirm a crystallization of Y123 directly from a liquid as a peritectic reaction where a major part is played by yttrium diffusion in the liquid. Y atoms are supplied by the diffusion of 211 particles. We investigated the YBCO crystal's interface theoretically. The smoothing interface of a-b plane has been proved by calculation of Jackson's factor α while also by experimental analyses. It was concluded that there was two-dimension nucleation mechanism and layer growing along c-axial on a-bplane and the growing formation was as extending along a or b direction.