Abstract <p>The structure of a single crystal of a molybdenum–niobium–oxygen alloy after high-temperature stretching has been analyzed by transmission electron microscopy. Two important effects have been detected in the fracture region: the formation of grain boundaries and a change in the NbO₂ oxide shape from cuboid to spindle (the raft process). It is shown that this transformation of the dispersed structure can be implemented via diffusion and only under the extremely high superequilibrium and permanent supersaturation of the alloy with vacancies generated by dislocation reactions during their slip.</p>