Structure and properties of vacancy and interstitial clusters in α-zirconium

The structure and properties of planar interstitial and vacancy clusters in α-zirconium containing up to ≈300 defects were studied by atomic-scale computer modelling. Clusters of different shape and habit plane have been simulated at zero temperature. Vacancy clusters were constructed as close-packed platelets of vacancies in (0 0 0 1), {1 1 2¯ 0} and {1 1¯ 0 0} planes. Clusters of self-interstitial atoms were formed as planar arrays of 〈1 1 2¯ 0〉 crowdions (the most stable configuration for the model potential used) in a {1 1 2¯ 0} plane. The most favourable shape for both types in the {1 1 2¯ 0} and {1 1¯ 0 0} prism planes is rectangular and clusters relax to perfect dislocation loops with Burgers vector b = 1/3〈112¯0〉. Their stability is increased by dissociation of the sides in basal planes. Vacancy clusters in the (0 0 0 1) basal plane form hexagonal loops enclosing an extrinsic stacking fault with b = 1/2[0 0 0 1]. Quantitative information is provided on the energy and structure parameters of the clusters.