Walker, A.M.; (2010) Simulation of screw dislocations in wadsleyite. Physics and Chemistry of Minerals , 37 (5) pp. 301-310. 10.1007/s00269-009-0334-y.

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Abstract

The structure and energies of the cores of [100] and [001] screw dislocations in wadsleyite \left(\beta-Mg{_2}SiO{_4}\right) are calculated using a cluster-based combined elastic-atomistic method and a new parameterized interatomic potential model. For a core radius of 10 \dot{A}, core energies are found to be 2.5 and 4.4 eV/\dot{A} for the [100] and [001] dislocations, respectively. Both dislocations are associated with signicant non-elastic displacement elds extending beyond the core with a radial component towards the dislocation line. The core of the [100] dislocation contains tetrahedrally coordinated magnesium, has a simple 2D structure and is spread parallel to (011) in a manner that suggests high mobility. In contrast, the core of the [001] dislocation has an extended and complex 3D structure involving the formation a large Si{_6}O{_1_9} unit twisted around the dislocation line. This implies that movement of the [001] dislocation will be inhibited by the need to cleave Si-O bonds. These observations, combined with the anomalously low core energy of the [100] dislocation, explain the regular occurrence of [100] dislocations and very rare observation of [001] dislocations in experimentally deformed wadsleyite samples.

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