High-resolution electron microscopy images of a Σ3/(111) bicrystal produced by heavy cold rolling and annealing show a multiplicity of grain boundary core structures. Two grain boundary states are separated by a partial grain boundary dislocation with Burgers vector b = 1 2 b1 (where b1 = 1 6 is the Burgers vector of a secondary dislocation). This implies a change in translational state. All other structures are related through continuous transport of atoms from one grain to the other resulting in  grain boundary steps. Calculations of the energy associated with the observed structures indicate that the two perfect twin states t = 0 and 2b1 are stable, while all other grain boundary translational states are metastable.
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