Characterization of nano-composite M-2411/Y-123 thin films by electron backscatter diffraction and in-field critical current measurements

Thin films of nano-composite Y-Ba-Cu-O (YBCO) superconductors containing nano-sized, non-superconducting particles of Y2Ba 4CuMOx (M-2411 with M = Ag and Nb) have been prepared by the PLD technique. Electron backscatter diffraction (EBSD) has been used to analyze the crystallographic orientation of nano-particles embedded in the film microstructure. The superconducting YBa2Cu3O7 (Y-123) phase matrix is textured with a dominant (001) orientation for all samples, whereas the M-2411 phase exhibits a random orientation. Angular critical current measurements at various temperature (T) and applied magnetic field (B) have been performed on thin films containing different concentration of the M-2411 second phase. An increase in critical current density J c at T < 77 K and B < 6 T is observed for samples with low concentration of the second phase (2 mol % M-2411). Films containing 5 mol % Ag-2411 exhibit lower Jc than pure Y-123 thin films at all fields and temperatures. Samples with 5 mol % Nb-2411 show higher Jc(B) than phase pure Y-123 thin films for T < 77 K

The effect of seed orientation and separation on the field trapping properties of multi-seeded, melt processed Y-Ba-Cu-O

The size of large, individual bulk Y-Ba-Cu-O (YBCO) grains fabricated by top seeded melt growth (TSMG) determines fundamentally both the sample growth time and the homogeneity of microstructure more distant from the seed. Multiple seeds have been used in the TSMG process with their ab planes aligned to provide controlled multiple nucleation sites to promote grain orientation and improve the bulk microstructure. This study reports the influence of the angle of intersection of ab plane growth sector boundaries on trapped field and compares the results with those obtained for samples fabricated from perfectly-aligned seeds. The trapped field profiles on the surface of YBCO multi-seeded samples were measured using scanning Hall probe apparatus, and their microstructure investigated using high-resolution optical microscopy. It was observed that the homogeneity of adjacent, multi-seeded grains is related to the angle between the intersecting ab planes, with larger angles of mis-orientation producing significant minima in the trapped field profile. This suggests that the grain boundaries form weak links to the flow of current in multi-seeded samples. A single inverted parabolic flux profile, on the other hand, was observed for large grains fabricated from perfectly-aligned seeds. This preliminary study demonstrates the feasibility of fabricating strongly-coupled multiple grains by a multi-seeding technique and identifies seed alignment as a key parameter in achieving this processing aim

High-performance single grain Y-Ba-Cu-O bulk superconductor fabricated by seeded infiltration and growth

Large single grains of Y-Ba-Cu-O (YBCO) bulk superconductor of up to 32 mm in diameter have been fabricated by a seeded infiltration and growth (IG) technique. Small Y2BaCuO5 (Y-211) particles are observed in the seeded IG sample microstructure, albeit with a rather inhomogeneous distribution in the superconducting YBa2Cu3Oy (Y-123) phase matrix. Values of magnetic critical current density, Jc, measured in self-field along the a and c growth sectors of the bulk samples prepared by seeded IG appear higher than the corresponding values for samples fabricated by conventional top seeded melt growth (TSMG), despite the inhomogeneous distribution of Y-211 particles in the former. A maximum trapped field of 0.42 T at 0.2 mm above the sample surface was observed at liquid nitrogen temperature (the actual mean temperature during measurement was around 78 K) in samples fabricated by seeded IG due to the increased Jc, despite the relatively small YBCO grain size (25 mm diameter · 7.4 mm thickness). This value of trapped field is almost two times greater than that of samples fabricated by TSMG and of a similar size