ABSTRACT
Atoms located at the boundary between crystals must in general be displaced from positions they would occupy in the undisturbed crystal. Nevertheless, it is now well established that many interfaces have a periodic structure. In such cases, the misfit between the crystals connected by the boundary is not distributed uniformly over every element of the interface; it is localized periodically into discontinuities which separate patches of the boundary where the fit between the two crystals is good or perfect. Stress-free coherent interfaces can exist only between crystals which can be related by a transformation strain which is an invariant-plane strain. Low-angle boundaries contain interface dislocations whose role is to localize and accommodate the misfit between adjacent grains, such that large areas of the boundary consist of low-energy coherent patches without mismatch. These intrinsic interface dislocations are called primary dislocations because they accommodate the misfit relative to an ideal single crystal as the reference lattice.
