Heavy ion irradiation effects in the rare-earth sesquioxide Dy2O3

Abstract Polycrystalline pellets of the rare-earth sesquioxide Dy 2 O 3 with cubic C -type rare-earth structure were irradiated with 300 keV Kr 2+ ions at fluences up to 5 × 10 20  Kr/m 2 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 ( Ia 3 ¯ ) to a monoclinic, B -type ( C 2/ m ) rare-earth structure in Dy 2 O 3 during Kr 2+ ion irradiation at a fluence of less than 1 × 10 20 Kr/m 2 . 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 ( P 6 3 / mmc ) rare-earth structure when the irradiation fluence is increased to 5 × 10 20  Kr/m 2 ; 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 Dy 2 O 3 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.