Influence of preforming pressure on the morphology and properties of single-grain Y–Ba–Cu–O superconductors by the 011-type infiltration growth technique

Abstract

Using the 011-type infiltration growth (011-IG) technique, the influence of preforming pressure on the morphology and superconducting properties of the Y–Ba–Cu–O (YBCO) bulks was investigated. The solid preforms of composition Y2O3 + BaCuO2 (011) containing embedded NdBCO/YBCO/MgO film seed were pressed at different pressures (100 MPa, 200 MPa and 300 MPa). The results indicate that, YBCO single grains can be successfully grown for these pressures. But some macro-defects (such as pores, cracks) were observed on the surface of the samples pressed at 300 MPa. Superconducting property measurements prove that, the 200 MPa pressed sample shows significantly enhanced levitation force and trapped field properties than the 100 MPa pressed sample, indicating that the preforming pressure is a very critical factor for appearance of high bulk performance. While three 300 MPa pressed samples exhibit rather varying properties related to their macro-defects. Magnetization measurements show that, the preforming pressure has no effect on the onset Tc of the samples, and the samples pressed at 200 MPa and 300 MPa display comparable Jc properties, which are both higher than that of 100 MPa pressed sample. Taking into account both of the sample morphology and the bulk property, the preforming pressure of 200 MPa can be considered as an optimum condition for steadily fabricating macro-defect-free YBCO single grains with excellent trapped field and levitation force properties, when a conventional mould for pressing cylindrical pellet is used.