Irradiation-induced amorphization of Cd2Nb2O7 pyrochlore - art. no. 104109

Several investigations have recently been undertaken in order to achieve a more complete understanding of the radiation-damage mechanisms in A(2)B(2)O (7) pyrochlore-structure compounds. The present work represents the first s ystematic study of the irradiation-induced amorphization of a pyrochlore wi th A- and B-site cation valences of +2 and +5, respectively. Relatively lar ge single crystals of Cd2Nb2O7 were grown for these experiments. In situ io n-irradiation experiments were carried out in a transmission electron micro scope in conjunction with ex situ Rutherford backscattering measurements of ion-irradiated Cd2Nb2O7 single crystals. Cd2Nb2O7 can be amorphized in sit u by Ne or Xe ions at temperatures up to 480 and 620 K, respectively. At ro om temperature, the amorphization fluence was 36 times higher for 280 keV N e+ than for 1200 keV Xe2+, corresponding to a displacement dose that was hi gher by a factor of 3. Disordering of Cd and Nb over the available cation s ites occurs at intermediate ion doses prior to amorphization. The temperatu re dependence of the amorphization dose is modeled, and the results are com pared to those of a previous model. The bulk-sample Rutherford backscatteri ng spectroscopy (RBS) results were generally consistent with the in situ TE M measurements. Effects of crystallographic orientation and ion charge stat e had relatively little effect on the damage accumulation in bulk crystals. The RES data are consistent with a defect-accumulation, cascade-overlap mo del of amorphization of Cd2Nb2O7, as are the in situ TEM observations.