Extended interfacial structure between two asymmetrical facets of a Σ = 9 grain boundary in copper

The presence of an extended structure in a = 9 grain boundary of copper has been highlighted by high-resolution transmission electron microscopy. The phase, located in a grain boundary region between two different asymmetrical facets, may be described as a three dimensional phase with a hexagonal structure. A detailed analysis of the defects at the limits between the phase and the two copper crystals allows us to propose an interpretation for the occurrence of this local phase transformation.