Preparation And Properties Of Top Seed Infiltrated Law Of Single Domain YBCO Superconductor

Seeded infiltration and growth technique (SIG) , based on conventional infiltration and seeding technique, has been developed by many laboratories in recent years. An important feature of the SIG process is that it is very convenient to produce large samples of designed shape without distortion or microcracks. In this process, the liquid source infiltrates into a porous Y₂BaCuO₅ (Y211) pellet when the temperature is higher than the peritectic temperature of Y123, which react with Y211 and form Y123 during the cooling process. The reaction is as following: Y₂BaCuO₅+ (3BaCuO₂+2CuO)â†'2YBa₂Cu₃0_x. In this paper, we report the studies on the fabrication process, microstructure and superconducting properties of the sample by seeded infiltration and growth technique in detail.The effects of the formation pressure of Y₂BaCuO₅(Y211) pellet and its ratio to liquid source on the growth morphology of YBCO bulk superconductors have been investigated. It is found that single domain YBCO bulks can be fabricated with the optimal weight ratio of Y211 to liquid source(1:1.25),which corresponding to molar ratio of Y: Ba: Cu is about 0.26: 0.31: 0.43. The optimal pressure of Y211 pellet is around 110MPa.We also optimized the parameters of heat treatment process. Base on these work, single domain YBCO bulk superconductor of up toΦ30mm have been fabricated by seeded infiltration and growth (SIG) technique.The microstructure of superconducting Y123 phase is rather homogeneous, the average particles size of Y211 phase is less than 2μm and in spherical shape, but Y211 distribution in the Y123 phase matrix rather inhomogeneous. The concentration of Y211 particles in the c-GS is lower than that in a-GSs, this inhomogeneity increases with Y211 particle refinement. The factors that influence the microstructure of the single domain YBCO bulk sample is discussed.It is found that the maximum trapped field increases first and then decreases with the magnetization intensity increasing at liquid nitrogen temperature under zero field cooling condition, the samples show a multi-magnetic domain last. It is also found that the maximum levitation force and the stiffness of the force-distance curve are increasing first and then decreasing with the increasing of the approaching speed and, there is a optimal speed to get the maximum levitation force.The driving force for the liquid infiltration is mainly controlled by the capillary force or the chemical potential, while gravity does not play a significant role and may be neglected.The liquid infiltration velocity is only in a short time, it is not need to keep a long time at T_p. This SIG method is very important for maintaining the sample's original dimensions and preventing the size coarsening of Y211 particles during the fabrication of YBCO bulk superconductors.