High-resolution electron microscopy at the atomic scale has been applied to study the edge dislocation redistribution between interfaces in Ge/Ge0.5Si0.5/Si(001) heterostructures. It is demonstrated that such heterostructures relax in two stages: a network of edge dislocations is formed on the Ge/GeSi interface during heterostructure growth; after that, during additional annealing, some of these edge dislocations move through the volume of initially elastically strained GeSi to the GeSi/Si interface. Our results provide a direct explanation that plastic relaxation of the GeSi buffer layer proceeds owing to motion of Lomer-type dislocation complexes consisting of a pair of complementary 60 degrees dislocations with the ends of the {111} extra planes being located at a distance of similar to 2-12 interplanar spacings from each other. (C) 2016 Elsevier B.V. All rights reserved.