The atomic structure of the Σ = 13( θ = 22.6°)[001] twist boundary in gold determined using quantitative X-ray diffraction techniques

Abstract

Quantitative X-ray diffraction techniques have for the first time determined the complete three-dimensional atomic structure of a grain boundary. The structure of a large angle Σ = 13( θ = 22.6°)[001] twist boundary in Au was obtained with a resolution of ±0.06 Å or better normal to the interface and ±0.02 Å or better parallel to the interface. The atomic coordinates were determined by fitting a model structure to the intensity observations from large portions of the three-dimensional reciprocal lattice using a χ 2 analysis. Details of the atomic structure of the grain boundary, including the magnitude of the decrease in density at the interface, are presented. The grain boundary structure was shown to consist of arrays of distorted octahedra that bridge the interface in the regions of good fit between the two misoriented crystals, and special configurations of distorted tetrahedra, octahedra and Archimedean antiprisms located between the regions of good fit within the interface. The polyhedral construct is used to predict sites for, and concentrations of solute atoms that segregate to interstitial positions within the boundary, without causing appreciable distortion of the boundary structure.