Effect of Buffer Layer on the Physical Properties of Single Domain YBCO Bulk Superconductors

The buffer layer can play an important role in the fabrication of high quality REBCO bulk superconductors, because it can not only prevent the YBCO crystal from contaminating by the NdBCO seeds, but also can improve the successful rate of single domain YBCO bulk superconductors. However, the key problem is how to optimize the buffer layer for fabrication of single domain YBCO bulks, so in this paper, a group of YBCO bulks of 30 mm in diameters have been fabricated by NdBCO crystal seeds assisted with cylindrical buffer layers of diameter D = 13 mm and height H mm, H = 1, 2, 3, 4, 5, 6, 7, 8 mm. Both the levitation force and the trapped field of the samples are increasing first and decreasing then as H increases from 1 mm to 8 mm. The largest levitation force and the trapped field are achieved in the sample fabricated with the buffer layer of height H = 4 mm; The optimal ratio of H/R is about 0.615, nearly equal to the ratio of the YBCO crystal growth rate along the a-axis and c-axis directions. Based on this result, single domain YBCO bulks of φ93 mm have been fabricated by the Y+011 TSIG method. The results indicate that this is effective method for fabrication of high-quality single domain REBCO bulk superconductors.