LOW-ANGLE AND SPECIAL BOUNDARIES IN SINTERED YBA2CU3O7-DELTA

Low angle and special boundaries have been observed in the YBa2Cu3O7-d elta compound prepared by cold isostatic pressing and sintering by hig h resolution electron microscopy. The structures of some 90 degrees ro tation twin boundaries, low angle tilt boundaries and a Sigma 17 bound ary have been presented. A 90 degrees rotation domain with (001) plana r interface is found to have steps and has been observed as a conseque nce of domain growth process. It is shown by geometrical consideration s that the grain boundary dislocations with Burger's vector [001] in t he low angle [100] tilt boundaries can dissociate into only three part ials. In the low angle boundaries parallel to [100], the misorientatio n is accomodated by 1/3[001] shifts over about 3c distances perpendicu lar to the (001) planes, at intervals of about 12 nm along the (001) p lanes. The orientational difference between grains forming low angle t ilt boundaries with both [100] and [010] tilts are accommodated by a r eorientation of the (001) planes and misfit dislocations. A grain boun dary close to Sigma 17 CSL orientation is shown to be perpendicular to the (001) planes which are continuous across the boundary and forms b y an a-b inplane rotation about the c-axis by approximately 30 degrees .