Transmission electron microscopy of dislocations in YBa2Cu3O7−xdeformed plastically at high temperatures

Dislocation structures in single crystals of YBa2Cu3O7−x with a tetragonal structure, deformed by indentation at 650 and 850°C, have been studied in detail using transmission electron microscopy. The Burgers vectors of the dislocations were determined by standard contrast experiments. At 850°C, perfect dislocations with Burgers vectors (100) were dominant; occasionally 〈110〉 dislocations were observed when two types of 〈100〉 dislocation, that is [100] and [010] dislocations, reacted with each other. At 650°C 〈100〉 dislocations were dissociated into two partial dislocations. Contrast experiments revealed that a 〈100〉 perfect dislocation is dissociated into two 1/2(100) partial dislocations, leaving a stacking fault in between. The stacking-fault energy decreases with decreasing temperature. This is explained by a model in which the stress-induced ordering of oxygen vacancies takes place.