Imaging the nanospace
of dislocations in layered materials.
Malcolm I Heggie,
Department of Chemistry,
The formation and movement
of dislocations control the plastic behaviour of materials. In materials such
as the cores of graphite moderated nuclear reactors, direct observation of
material properties with time and neutron dose is impossible – due to constraints
of space, heat, irradiation and reactor safety in
general. Extrapolation from materials test reactor data is necessary and such
extrapolation must have sound theoretical foundations. First principles total
energy calculations and computer visualisation afford
a privileged view of irradiated graphite that has radically altered our
understanding of the dramatic changes that occur on irradiation. The biggest
single factor in this change is the revelation that basal dislocations, and not
point defect migration and clustering, are responsible for most property
changes. The effects are, by and large, unique to layered materials and
illustrate the need for clear symbolic/diagrammatic descriptions of
dislocations as well as for clear physical representations .
The observations should
provide insight for layered materials in general from clays to ceramic
superconductors under irradiation and under mechanical deformation.