Control of grain alignment to fabricate long Y-Ba-Cu-O superconductors with high current density

A directional solidification method has been developed to grow YBa₂Cu₃O_x samples in excess of 55 mm in length with uniform grain alignment and a-b planes oriented parallel to the sample length. Using a furnace configuration that yields a negative lateral gradient, the YBa₂Cu₃O_x grains have been forced to nucleate and grow along the axis instead of at an angle to the sample length. X-ray pole figures analyses along the entire length at different sections show that the a-b planes are aligned parallel to the sample length with deviations less than 5° along the growth direction. Transport critical current density (J_c) measurements over the entire length and at different sections of the sample reveal a uniform current density in excess of 7000 A/cm² at 1.5 T and 77 K.