CRYSTALLINITY OF YBA2CU3O7-X SINGLE-CRYSTALS GROWN BY THE PULLING METHOD

Large YBa2Cu3O7-x (Y123) single crystals (larger than 13 mm cubed) hav e been grown along the c-axis reproducibly by the modified pulling met hod. The crystallinity of Y123 single crystal was investigated by x-ra y diffraction and x-ray topography. Crystals grown from an MgO single crystal seed had some low angle subgrain boundaries which tilted 0.1-0 .8 degrees from each other. These grain boundaries originated from the seed crystal, and the subgrains were extended along the growth direct ion from the seed crystal. Y123 single crystals with no marked subgrai ns in the whole area were obtained by using Y123 single subgrain cryst al seeds. FWHM of the x-ray rocking curve for the crystal so produced was about 0.14 degrees, which was much better than the spectrum consis ting of several separated peaks obtained from the previous crystals. T -c onset of the annealed sample was about 93.6 K, and the transition w idth was about 0.9 K. The low angle subgrain boundaries did not seem t o be effective pinning centers for the magnetic flux.