Secondary grain boundary dislocations in [001] twist boundaries in MgO I. Intrinsic structures

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Abstract
Intrinsic secondary grain boundary dislocation (GBD) structures were observed by weak-beam transmission electron microscopy in a variety of [001] twist boundaries in MgO prepared by a welding technique. Square networks of intrinsic screw GBDs were found in boundaries possessing twist deviations from the exact ∑ = 1, 6, 13, 17, 25, 29 and 53 coincidence site lattice (CSL) misorientations. (∑ ≡ fraction of lattice sites in coincidence.) These GBDs were all perfect GBDs with Burgers vectors given by the primitive vectors of the corresponding DSC lattice except in the case of ∑ = 13 where a square array of apparently partial screw GBDs was observed. Arrays of screws GBDs were not detected in a number of high. ∑ boundaries. Superimposed arrays of edge-type intrinsic GBDs were observed in all boundaries when a small tilt component was present. The structures were similar in many respects to those observed in an earlier study of corresponding [001] twist boundaries in gold. All results appeared consistent, with the CSL model for grain boundaries. suggesting that this model therefore holds for grain boundaries in ionic solids.