HREM studies of stacking faults in HoBa2Cu3O7-δ superconductors

Abstract High resolution transmission electron (HREM) has been used to reveal directly the structure of the metal lattice and its defects in HoBa 2 Cu 3 O 7−δ high- T c superconductors. Columns of Ho, Ba and Cu atoms can be discriminated by their differences in image contrast depending on the atomic scattering factors, while the colunms of oxygen atoms and voids appear as white (“tunnels”). Twins have been observed as well as several types of extrinsic planar fults which have been studied through comparison between the experimental HREM images and different structural model. Besides the displacement vectors R = 1 6 [0,0,1], R = 1 6 [3,0,1], R = 1 6 [0,3,1], proposed previously for translation faults in YBa 2 Cu 3 O 7−δ materials, an new fault model having a displacement vector R = 1 6 [3,3,1] is discussed here. Other new structural model have been constructed by adding a rotation operation to the models mentioned above, which correspond to permutation planar faults. The transformation from mirror to glide character along such faults, as well as the dislocations produced by the difference between lattice parameters a and b across the interferences which have been observed on the HREM micrographs, confirm the structure of the permutation faults proposed in the present work.