Dimension changes due to aligned Vkcentres and H centres in ionic crystals

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Abstract
When anisotropic defects are aligned, the dimensions of the host crystal parallel and perpendicular to the defect axis are changed, an effect observed previously for H centres and Vk centres in KCl. The authors have calculated the effect for H centres and Vk centres in several crystal structures. The contribution from long-range Coulomb interactions has been obtained in all cases, with less-detailed estimates of short-range repulsion and covalency effects in special cases. The predictions are in good agreement with experiment for H centres in KCl, but agree only poorly for Vk centres in the same host. The discrepancy appears to arise from modifications of the local repulsive forces near the defect. Measurements of dimension changes show great promise for studies of such interatomic forces.