Radiation damage effects in zirconia

The evolution of radiation-induced damage in fully-stabilized, cubic zirconia (FSZ) (Y, Ca and Er dopants acting as stabilizers) and in pure, unstabilized, monoclinic zirconia, was investigated using Rutherford backscattering spectrometry and ion channeling (RBS/C), along with X-ray diffraction and transmission electron microscopy (TEM). FSZ crystals were irradiated with 340-400 keV Xe⁺⁺ ions and at temperatures ranging from 170 to 300 K, or with ¹²⁷I⁺ ions (72 MeV) at temperatures ranging from 300 to 1170 K. No amorphization of zirconia was found under any irradiation condition, though in the case of 72 MeV I⁺ ion irradiations, the irradiation-induced defect microstructure was observed to produce dechanneling effects in RBS/C measurements that reach the `random' level. Damage accumulation in Xe-ion irradiation experiments on FSZ crystals was found to progress in three stages: (1) formation of isolated defect clusters; (2) a transition stage in which damage increases rapidly over a small range of ion dose, due to the linking of dislocations and defect clusters; and (3) a `saturation' stage in which damage accumulation is retarded or increases only slowly with ion dose. The FSZ crystal composition does not seem to alter significantly the dose-dependence of these damage stages. Unstabilized, monoclinic ZrO₂ was observed to transform to a higher symmetry, tetragonal or cubic phase, upon 340 keV Xe⁺⁺ ion irradiation to Xe fluences in excess of 5×10¹⁸ m^-2 (dose equivalent, approximately 2 displacements per atom or dpa) at 120 K. This transformation was accompanied by a densification of the ZrO₂ phase by approximately 5%. No amorphization of the pure ZrO₂ was observed to a Xe⁺⁺ ion fluence equivalent to a peak displacement damage level of about 680 dpa.