Transformations to amorphous and X-type phases in swift heavy ion-irradiated Ln2O3 and Mn2O3

The intense, highly localized electronic excitation resulting from swift heavy ion irradiation induces phase transformations in many materials including lanthanide sesquioxides (Ln2O3). To explore the effects of chemical composition on radiation-induced transformations, the structural responses of several related sesquioxides to swift heavy ion irradiation were compared. Polycrystalline Nd2O3, Eu2O3, Yb2O3, and Mn2O3 were irradiated by 946 MeV Au ions to a range of ion fluences up to 2 × 1013 cm−2, and structural modifications were characterized using beamline-based in situ x-ray diffraction and Rietveld refinement. Amorphization was induced in Nd2O3, Eu2O3, and Mn2O3 with the extent of induced transformation following a clear dependence on cation ionic radius. Nd2O3 and Eu2O3, having the largest cations, were rapidly amorphized, whereas Mn2O3, having the smallest cation, experienced only a slight loss of crystallinity at the highest fluences studied. The radiation response was different for Yb2O3, which underwent a sluggish transformation to a nonequilibrium X-type phase. The crystalline-to-amorphous transformations were proceeded by direct-impact mechanisms, while the C-to-X transformation was proceeded by a multi-impact mechanism.