MICROSTRUCTURE OF MELT-TEXTURED YBA2CU3O7-DELTA

The microstructure of stoichiometric Bridgman melt-textured YBa2Cu3O7- delta was investigated by transmission electron microscopy and electro n diffraction. Crystal defects like twins, dislocations, small second- phase inclusions and lattice distortions are observed. The density of the dislocations is extremely high (1.7X10(10)/cm(2)) and the average diameter of the second-phase inclusions (BaCuO2) of 35 nm is rather sm all. The density of the inclusions amounts to 6X10(19)/m(3). The forma tion of the microstructural defects and their influence on flux pinnin g is discussed. It is supposed that the observed lattice distortions a re possible defects which cause the fish-tail effect.