Recent research on image crystals; Discovery of shape-controllable cavities surrounded by facets in ceramics

Serizawa, Hiroyuki  

My investigation on cavities in ceramics was triggered by the unexpected discovery of a polyhedral cavity in a UO matrix. The SEM image that attracted my attention was a cavity observed in the fracture surface of a single-crystal of UO that was heat-treated in helium at 90 MPa, followed by annealing at high temperature for 1 h. The cavity was the so-called negative crystal which is sometimes seen in a broken mineral casually. The negative crystal was formed by the precipitation of helium during heat treatment after Hot Isostatic Pressing (HIP) injection. In a series of experiments, I noticed that the shape of the negative crystal changes depending on the heat-treatment history. We also confirmed that nanosized image crystals can be formed in CeO matrix.