Elastic models of symmetrical < 002 > and < 011 > tilt grain boundaries indiamond

The disclination-structural units model (DSUM), which was previously applie d to grain boundaries in metals and a limited number of structures in the d iamond cubic lattice, is extended to treat more complicated metastable stru ctures of [001] and [011] symmetric tilt boundaries in diamond. These struc tures are described in terms of flat and faceted disclination dipole walls and screw dislocation dipole walls, with the energies of these defects calc ulated from anisotropic elasticity theory. Disclination-dislocation models are constructed for [001] tilt boundaries in the complete misorientation ra nge and for [001] tilt boundaries in the range 0 less than or equal to thet a less than or equal to 70.5 degrees, and the energy versus misorientation curves are calculated using input structures and energies of key grain boun daries obtained from atomistic modeling. Quantitative agreement with atomis tic predictions is obtained for the most stable grain-boundary structures. while predictions of the DSUM for higher-energy metastable structures an qu alitatively consistent with atomic studies.