The projected atomic structure of a large angle [001] Σ = 5 ( θ = 36.9°) twist boundary in gold: Diffraction analysis and theoretical predictions

Abstract

The projected atomic structure of a large angle [001] Σ = 5 ( θ = 36.9°) twist boundary in Au was determined using X-ray diffraction techniques. The extra reflections resulting from the periodic structure of the boundary were studied using synchrotron radiation. The observed structure factor rules are consistent with the boundary existing in the exact (no translation away from) coincidence configuration. The projected structure was determined using a variable coordinate and reliability factor analysis which was simplified by the low value of Σ, the boundary symmetry and the assumption of a thin boundary region. The structure thus determined consists of groups of atoms which have undergone large rotations about “0”-elements in the planes immediately adjacent to the boundary. The structure is made up of separate patches of median f.c.c. structure in analogy with small angle boundaries. Various structures calculated by computer relaxation techniques using interatomic potentials are also presented and compared with the diffraction results. These structures also show rotational relaxations about “0”-elements but the degree of the rotation is much smaller than was determined by diffraction leading to a distortion of the median f.c.c. structure. Consequently, there is only limited correspondence between the computer results and experimental observations.