X-ray diffraction study of the structure of large-angle [001] twist grain boundaries in gold

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Abstract
The structures of several large-angle [001] twist grain boundaries with widely different values of Σ in gold bicrystal specimens have been studied using X-ray diffraction techniques (Σ is the reciprocal of the fraction of lattice sites in one crystal in good coincidence across the boundary plane). New reflections in addition to gold reflections were observed from all the boundaries studied, indicating that low-, medium- and high-Σ boundaries all have periodic structures. The positions of the reflections are consistent, with one exception, with the coincidence site-lattice unit cell corresponding to the particular Σ value of the boundary. The observed reflections can be classified into two groups depending on their indices and intensities. These structure factor rules are related to the form of the displacement field of the grain boundary. Specifically, these rules are linked with the existence of a displacement field that varies (falls off) with distance from the boundary plane. An initial attempt, which had limited success, was made to understand the absence or presence of various grain-boundary reflections, by comparison to the structure factors associated with the van der Merwe displacement field. It is pointed out that the experimentally observed structure factors can be used to check the validity of computer-generated structural models of twist boundaries