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.