On the Conversion of Bulk Polycrystalline Y2O3 into the Nanocrystalline State

A reversible phase transformation (RPT) process is observed that converts fully dense polycrystalline Y2O3 directly into the nanocrystalline state. The process involves a forward transformation from cubic-to-monoclinic symmetry under a high pressure and a reverse transformation from monoclinic-to-cubic symmetry under a lower pressure. An example is given of a reduction in grain size of cubic-Y2O3 from 300 to 0.1 mu m in a single pressure-induced RPT at 1000 degrees C.