STUDIES OF IRIDIUM SURFACES AND GRAIN-BOUNDARIES

We have used local volume potentials to study surfaces and grain boundaries in Ir. We found that (110), (210) and (310) surfaces reconstruct in a 1 x 2 missing-row fashion. The (110) surface reconstruction is consistent with experimental observations, while the predictions of 1 x 2 reconstructions on (210) and (310) surfaces need to be tested experimentally. The grain boundaries have high grain boundary energies and fracture at a much lower strain than the bulk. This behaviour is consistent with intergranular brittleness of polycrystalline Ir. We propose an intrinsic grain boundary fracture map to sort materials into categories with distinct fracture behaviours according to their physical quantities and grain boundary cohesion.