Type II Magnetic Levitation on Sinter‐Forged YBa 2 Cu 3 O x Superconductor

Submicrometer powder of singlephase YBa 2 Cu 3 O x (YBC), prepared from nitrate salts, were free‐sintered and sinter‐forged at 1223 K. The levitation force on magnets exerted by the superconductor was found to depend on the thickness of the superconductor, the shear strain imposed during sinter‐forging, and the time and temperature of the high‐pressure oxygen anneal after sinter‐forging. The first result is direct proof of the type II nature of the YBC superconductor. In the second experiment a shear strain of 300% increased the levitation force by a factor of 3. The third result confirmed that YBC transforms to the tetragonal structure at 1223 K, which must be restored to the orthorhombic structure by annealing at lower temperature. Optimum results were obtained when the specimens were annealed in pressurized oxygen (3 MPa) for 50 h at 673 K.