Elastic models of symmetrical Š001‹ and Š011‹ tilt grain boundaries in diamond

The disclination-structural units model ~DSUM!, which was previously applied to grain boundaries in metals and a limited number of structures in the diamond cubic lattice, is extended to treat more complicated metastable structures of ^001& and ^011& symmetric tilt boundaries in diamond. These structures are described in terms of flat and faceted disclination dipole walls and screw dislocation dipole walls, with the energies of these defects calculated from anisotropic elasticity theory. Disclination-dislocation models are constructed for ^001& tilt boundaries in the complete misorientation range and for ^011& tilt boundaries in the range 0<u<70.5°, and the energy versus misorientation curves are calculated using input structures and energies of key grain boundaries obtained from atomistic modeling. Quantitative agreement with atomistic predictions is obtained for the most stable grain-boundary structures, while predictions of the DSUM for higher-energy metastable structures are qualitatively consistent with atomic studies.