Heavy ion irradiation effects in the rare-earth sesquioxide Dy2O3

Polycrystalline pellets of the rare-earth sesquioxide Dy2O3 with cubic C-type rare-earth structure were irradiated with 300 keV Kr2+ ions at fluences up to 5 × 1020 Kr/m2 at cryogenic temperature. Irradiation-induced microstructural evolution is characterized using grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). In previous work, we found a phase transformation from a cubic, C  -type (Ia3¯) to a monoclinic, B-type (C2/m) rare-earth structure in Dy2O3 during Kr2+ ion irradiation at a fluence of less than 1 × 1020 Kr/m2. In this study, we find that the crystal structure of the top and middle regions of the implanted layer transform to a hexagonal, H-type (P63/mmc) rare-earth structure when the irradiation fluence is increased to 5 × 1020 Kr/m2; the bottom of the implanted layer, on the other hand, remains in a monoclinic phase. The irradiation dose dependence of the C-to-B-to-H phase transformation observed in Dy2O3 appears to be closely related to the temperature and pressure dependence of the phases observed in the phase diagram. These transformations are also accompanied by a decrease in molecular volume (or density increase) of approximately 9% and 8%, respectively, which is an unusual radiation damage behavior.