OBSERVATION OF A SCREW DISLOCATION IN THE HG-1223 SUPERCONDUCTOR UNDER A TRANSMISSION ELECTRON-MICROSCOPE

Screw dislocations were observed in a Hg-1223 sample under the transmi ssion electron microscope. A typical dislocation reported here, was ob served on the (110) plane of the Hg-1223 unit cell. The angle between the Burger's vector and the [001] crystal direction of the Hg-1223 uni t cell is 26 degrees, and the magnitude of the Burger's vector is 17.6 3 Angstrom. 2D and 3D diagrams showing this dislocation are presented in order to explain its configuration. A simple semi-quantitative mode l is also proposed to describe the occurrence of the screw dislocation based on an analysis of the shear stress along the (110) plane. It is believed that the formation of this screw dislocation is due to the i ntergrowth of different Hg superconducting phases during the special s olid state reaction of the Hg superconductor. These intergrowth struct ures generate a stress field inside the lattice of the Hg sample, whic h indicates various kinds of microdefects such as the screw dislocatio n.