The Peierls mechanism in MgO

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Abstract
The Peierls mechanism for dislocation movement based on the formation and motion of double kinks has been investigated for a/2〈110〉 edge dislocations in MgO. Characteristic parameters of this mechanism, such as the activation energy and volume, have been calculated as a function of the applied resolved shear stress (R.S.S.) from the shape and height of the Peierls barrier. This barrier was determined using a novel atomistic calculation. The theoretical results are critically compared to the experimental results based on dislocation velocity measurements of Singh and Coble (1974) and the Bordoni peak measurements of Chang (1961) and Ikushima and Suzuki (1963). It is concluded that the dislocation velocity results may be explained on the basis of a Peierls mechanism when the R.S.S. is greater than about 5 MPa and the crystal contains less than 20 μmg/gFe3+ impurities. However, below this value of R.S.S. and above a concentration of 5 μmg/gFe3+, the controlling mechanism may be the interaction of non-centrosymmetric defects with the dislocations. Finally, our calculations suggest that the Bordoni peaks determined by Chang (1961) and Ikushima and Suzuki (1963) cannot be explained by the Peierls mechanism and, hence, Peierls stresses derived from these data are incorrect.