YBa2Cu3O7- delta single-crystal microstructure related to transport critical current density

The structure of YBa2Cu3O7- delta crystals has been investigated by means of high-resolution electron microscopy. The cooperative growth of a number of spirals causes the 'interference' of stresses and the formation of microblocks. It is suggested that the screw dislocations inside the growing spirals as well as the edge dislocations on subgrain boundaries are responsible for the high Jc values. Actually, the highest transport critical current density Jc(77 K) and Jc(H) have been measured on these YBa2Cu3O7- delta single crystals.