Wulff shape of microscopic voids in UO2 crystals -: art. no. 235411

UO2 single crystals with a size of around 1 cm(3) are created in a process involving a period of spectacular grain growth. (111) cleavage cross sections through these crystals expose voids that are typically of mum dimensions. Low voltage scanning electron microscopy of the voids reveals that they are bound by {111} and {001} facets, and some appear to have reached their thermodynamic equilibrium shape (Wulff shape). An analysis of the facet areas shows that the smaller voids are closer to the Wulff shape, and have a surface energy ratio epsilon(001)/epsilon(111)=1.42+/-0.05. The larger voids show step bunching at the facet intersections which typically gives rise to ordered step structures of 10s of nm periodicity and produces nanoscale staircases and amphitheatres. Evidence of void ripening by way of connecting channels is also observed.