MICROSTRUCTURES AND DISSOCIATED DISLOCATIONS IN YBA2CU3O7-X PREPARED BY A GRAIN-COATING TECHNIQUE

Microstructures of YBCO prepared by a ''grain-coating'' technique were observed through transmission electron microscopy. The coating materi al of Ag or Bi2O3 is detected by EDS analysis only at grain boundaries and not inside grains in which abundant dislocations are found. Most of the dislocations are dissociated into partial dislocations with sta cking faults. Two types of stacking fault are observed: One has a larg e width and is terminated by straight or smooth partial dislocations, the other is terminated by curved dislocations of which the separation is alternately large and small. The stacking fault vector is found to be 1/6[0 $($) over bar$$ 31], being consistent with an extra CuO laye r in the 123 matrix. The coating material improves the weak-link at gr ain boundaries and increases the J(c), while plenty of dislocations as sociated with stacking faults act as effective pinning centers and con tribute to increasing the J(c) in a high magnetic field.