Low angle and special boundaries in sintered YBa 2Cu 3O 7−δ

Abstract

Low angle and special boudaries have been observed in the YBa 2Cu 3O 7 − δ compound prepared by cold isostatic pressing and sintering by high resolution electron microscopy. The structures of some 90° rotation twin boundaries, low angle tilt boundaries and a Σ17 boundary have been presented. A 90° rotation domain with (001) planar interface is found to have steps and has been observed as a consequence of domain growth process. It is shown by geometrical considerations that the grain boundary dislocations with Burger's vector [001] in the low angle [100] tilt boundaries can dissociate into only three partials. In the low angle boundaries parallel to [100], the misorientation is accomodated by 1 13 [001] shifts over about 3 c distances perpendicular to the (001) planes, at intervals of about 12 nm along the (001) planes. The orientational difference between grains forming low angle tilt boundaries with both [100] and [010] tilts are accommodated by a reorientation of the (001) planes and misfit dislocations. A grain boundary close to Σ17 CSL orientation is shown to be perpendicular to the (001) planes which are continuous across the boundary and forms by an a- b inplane rotation about the c-axis by approximately 30°.