Accommodation of coherency strain by interfacial disconnections at a 90° ⟨110⟩ grain boundary in gold

The structure of interfacial disconnections (i.e. line defects possessing both step and dislocation character) at a 90° d 110 ¢ tilt boundary in gold has been investigated. High-resolution transmission electron microscopy observations identify these defects separating short (40-60 Å) d 111 ¢ - d 112 ¢ terraces along the boundary. Because the ratio of the periodic length in the d 111 ¢ direction to that in the d 112 ¢ direction is irrational (2 1/2 ), the crystallography of this boundary is incommensurate. By measuring the dislocation content of the disconnections, it is shown how the defects accommodate the 5.7% 'misfit' in the directions parallel to the interface and thereby enable coherency to be achieved across the d 111 ¢ - d 112 ¢ terraces. This structural relaxation is markedly different from that at d 100 ¢ - d 110 ¢ grain boundary facets in this same system, for which previous observations have found an incoherent structure with no strain localization.