The fabrication and characterization of ybco single crystals for levitation applications

In this study, (% 75 Y123 ve % 25 Y211) + % 0,.5 CeO2 (YBCO) superconductors with the diameters of 13, 20, 32 and 40 mm were fabricated by Top-Seeded-Melt-Gwroth (TSMG) method. The single crystal YBCO superconductor with a diameter of 40 mm is the largest single crystal produced in Turkey. Vertical force (Fz) - vertical movement (z), lateral force (Fx) - lateral movement (x), vertical force (x) at low temperatures (T = 37, 47, 57, 67 and 77 K) Fz - time (t) and vertical force (Fz) - temperature (T) measurements of YBCO single grain with a diameter of 20 mm were made under ZFC and FC regime. Y20 sample was cut symmetrically to obtain specimen at different positions. It was seen that the critical transition temperature value of the specimen 5 mm below from center of seed is 0,2 K lower than that of the specimen of below 3 mm and 4.5 mm right direction of seed. It was found that specimen 4.5 mm right direction of seed has the highest critical current density. It was observed that the critical current density increased as temperature of the sample decreased. Multi-seeded YBCO superconductors (with different seed distances (d) and structures) was fabricated as same as YBCO single grain compound by TSMG. The seed structure of fabricated multi-seeded samples were chosen d = 0, 1, 4, 12 and 16 mm for (100) // (100) alignment and d = 0, 4 and 12 mm for (100) // (010) alignment. Fz - z measurements of these samples were performed at 83, 80 and 77 K under the ZFC and FC regime and d value increases as magnetic levitation force decreases. Trapped field measurements on the top and bottom surfaces of the (100) // (100) aligned samples were measured and as the value of d increases, the increase of the melt phase is seen to decrease the magnetic field trapping.