Abstract
Microstructures of YBa2Cu3O7-γ a ceramics deformed at room temperature were characterized by transmission electron microscopy. Dislocations with <100> Burgers vectors gliding in the (001) plane, which have been found to control plastic deformation, interact strongly with mirror twin boundaries (MTBs) in the orthorhombic phase. The mechanisms of interaction between these dislocations and MTBs are discussed. A model is proposed which explains these interactions as well as the observed shapes of dislocations.