Identification and correlation of microstructural defects with flux pinning in Ni-doped melt textured YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]]

Microstructural examination using transmission electron microscopy has been conducted on melt textured Ni-doped and pristine YBaCu[sub 3]O[sub 7[minus][delta]]. Magnetization hysteresis suggests that the observed microstructural imperfections strongly influence flux pinning behavior. The investigation reveals a considerable difference in the density and distribution of stacking faults, especially near the grain boundaries. Dislocation nets and tangles were also observed in the Ni-doped samples. It is proposed that the addition of Ni creates an excess of Cu which diffuses into the subgrains during oxygenation to be incorporated as stacking faults. Fine inclusions (25--50 nm) of Y[sub 2]BaCuO[sub 5] were observed, suggesting that Ni refines the microstructure.