HIGH-PERFORMANCE IN A BULK MELT-TEXTURED YBA2CU3O7-DELTA CERAMIC

In the present work a YBa2Cu3O7-delta Melt-textured growth (MTG) sample was used to achieve grain orientation in a thermal gradient over a large domain using 211 bars as support. Starting from a YBa2Cu3O7-delta precursor sintered at 950-degrees-C, we were able to obtain unidirectional orientation over a large area, 22 x 8 x 7 mm, using a 20-degrees-C cm-1 gradient and a very slow cooling rate, 1-degrees-C h-1. The so-obtained microstructure has been characterized. The study of cleaved surfaces using diffraction and Laue patterns shows widespread development of a-b planes parallel to the thermal gradient and to the bar axis. Moreover, microstructural observations point out that the texturization may extend to the 211 support. Polarized optical microscopy observations show large twinning domains all over the sample which confirm orthorhombicity and thus good reoxygenation of the sample. Magnetic and electrical characteristics were investigated. Large magnetic hystereses were obtained, even at 77 K, revealing the presence of strong pinning centres. Transport critical current density higher than 3.5 x 10(4) A CM-2 at 77 K in zero field and 2.6 x 10(4) A CM-2 at 77 K in a 7 T magnetic field were measured.