Effect of growth anisotropy on the morphology and property of directionally solidified RE123

The REBa2Cu3Oy (RE123: RE = Y, Sm, Gd etc.) superconducting current lead is a favorable application due to the high Jc properties and low thermal conductivity. Since the RE123 crystal shows the anisotropy in the Jc properties as well as the mechanical properties, the ab-plane of the crystal parallel to the growth direction is preferable. The preferential growth direction during directional solidification is determined by the growth anisotropy in the early stage of the growth. In order to get the fundamental information to control the growth orientation, we investigated the growth rates of the Gd123 and Sm123 crystals against the undercooling and the continuous growth condition of Sm123 in directional solidification process. The growth rates of Sm123 and Gd123 were found to be about 5-10 times larger than that of Y123 at the same undercooling. The Sm123 showed the continuous growth structure up to 15 mm/h for fiber samples and up to 10 mm/h for 2 mm∅ rods by the zone melting process. These pulling rates for continuous growth are larger than those of Y123 although the difference in growth rates between Sm123 and Y123 is much larger than this difference.