A high-resolution electron microscopy study of structural defects in YBa 2Cu 4O 8 superconductor

Abstract

Structural defects in YBa 2Cu 4O 8 have been observed by means of high-resolution electron microscopy, coupled with multi-slice image simulations. The as-synthesized crystals contained several types of structural defects, as follows: (i) Planar defects consisting of a local structure of YBa 2Cu 5O 9 with triple CuO chains resulting from the insertion of one extra CuO chain at the location of the original double CuO chains. (ii) Planar faults consisting of thin 90° rotation twins about the c-axis. The layer thickness of the a– c plane domain in the b– c plane domain was 1 2 unit cell along the c-axis of YBa 2Cu 4O 8. (iii) The coexistence of YBa 2Cu 4O 8 layers and YBa 2Cu 3O 7− y layers within one crystal. (iv) an edge dislocation with Burgers vector of either b = b〈010〉 or a〈100〉 on a single CuO chain layer, and dislocations with a Burgers vector b = 1 2 [110] on double CuO chain layers, which exist at the boundary of the 90° twins.