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An extremely large levitation force of as high as 30 N at a height of 1 mm was achieved in Ag-doped YBaCuO fabricated by the Melt-Powder-Melt-Growth process using a repulsive force against a 0.4 T rare-earth magnet at 77 K. The combination of a large J c value and large shielding current loop is the source of such a large levitation force.

Microstructures of two MPMG processed YBaCuO materials with and without Y2BaCuO5 (211) inclusions were investigated by transmission electron microscopy. Using the MPMG process, it is possible to change the quantity of the 211 inclusions in the YBa2Cu3O7 (123) matrix. We prepared two YBaCuO samples with 0 and 30 vol. % 211 and with respective critical current density values of 2000 and 30 000 A/cm2 at 77 K and 1 T (magnetic field parallel to the c-axis). As possible pinning centers, we found stacking faults in the 123 matrix. However, we observed no appreciable change in their number and structure by introducing the 211 inclusions. Therefore, the difference in Jc values can be attributed to the 211 inclusion itself.

The fracture toughness of melt-powder-melt-growth(MPMG)-processed YBaCuO samples was measured and the beneficial effect of the dispersed 211 particles in the 123 superconducting phase on toughening the material was confirmed. Preferred fracture planes were (100), (010) and (001) planes, and the fracture toughness of the (001) plane was lower than that of the (100) and (010) planes.