Transmission electron microscopy of dislocations in YBa₂Cu₃O_7−x deformed plastically at high temperatures

Abstract

Dislocation structures in single crystals of YBa₂Cu₃O_7−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.