M. Tang

Order-disorder phase transformation in ion-irradiated rare earth sesquioxides

An order-to-disorder (OD) transformation induced by ion irradiation in rare earth (RE) sesquioxides, Dy2O3, Er2O3, and Lu2O3, was studied using grazing incidence x-ray diffraction and transmission electron microscopy. These sesquioxides are characterized by a cubic C-type RE structure known as bixbyite. They were irradiated with heavy Kr++ ions (300keV) and light Ne+ ions (150keV) at cryogenic temperature (∼120K). In each oxide, following a relatively low ion irradiation dose of ∼2.5 displacements per atom, the ordered bixbyite structure was transformed to a disordered, anion-deficient fluorite structure. This OD transformation was found in all three RE sesquioxides (RE=Dy, Er, and Lu) regardless of the ion type used in the irradiation. The authors discuss the irradiation-induced OD transformation process in terms of anion disordering, i.e., destruction of the oxygen order associated with the bixbyite structure.

Irradiation‐Induced Amorphization and Order‐Disorder Transformation in the Tungsten δ‐phase Oxides Yb6W1O12 and Y6W1O12

Poly crystalline Yb6W1O12 and Y6W1O12 samples, which possess rhombohedral symmetry (structure known as the δ‐phase, closely related to cubic fluorite structure), were irradiated with 280 keV Kr++ ions to fluences up to 2×1020 ions/m2 at cryogenic temperature (100 K). Ion irradiation damage effects in these samples were examined using grazing incidence X‐ray diffraction (GIXRD) and cross‐sectional transmission electron microscopy (TEM). Irradiation‐induced amorphization in both compounds has been observed by GIXRD and TEM, while the amorphization dose for Yb6W1O12 is lower than that for Y6W1O12. Experimental results also revealed that both irradiated samples experience an ordered rhombohedral to disordered cubic fluorite (O‐D) transformation before amorphization. Factors influencing the irradiation damage response of these two compounds will be discussed in terms of cation radius ratio and cation antisite formation energy calculated by density functional theory (DFT).