Nanocomposite Y-Ba-Cu-O superconductors containing a wide range of Y 2 Ba 4 CuMO y (Y-2411), where M = Nb, Ta, Mo, W, Zr, Hf, Ru, Ag, Sb, Sn and Bi, embedded in the YBa 2 Cu 3 O 7−δ matrix, have been fabricated successfully. The Y-2411 phase typically has dimensions in the range 20-50 nm and it is observed to form effective flux pinning sites even at higher magnetic fields. A direct correlation between the Y 2 Ba 4 CuMO y phase inclusion content in the YBa 2 Cu 3 O 7−δ matrix and increased magnetic flux pinning has been observed. The critical current density increases by an order of magnitude for a nanocomposite compared to that of Y-123 without inclusions.

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A multi-seeding process has been developed to fabricate single Y-Ba-Cu-O (YBCO) grains containing strong artificial grain boundaries. Multi-seeding of heterogeneous YBCO grains with controlled orientation was achieved using large Sm-Ba-Cu-O (SmBCO) single crystal seeds of rod-like geometry with slots of various widths (up to 13 mm) cut into their bottom surface (i.e. parallel to the c-axis of the seed) to produce a bridge-like structure. Several YBCO grains with artificial grain boundaries were fabricated from these seed crystals and used to investigate the effect of varying the distance between the individual grain nucleation sites and the grain orientation (in-plane and out of plane) on the nature of grain boundaries. The measured local magnetic critical current density (J c) and the magnitude of the trapped field across these artificial grain boundaries indicate that seed alignment is a key parameter in achieving strongly-coupled grain boundaries in multi-seeded grains.

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