Role of cation choice in the radiation tolerance of pyrochlores

We have used atomistic computer simulations to study anion diffusion coefficients and the response to swift heavy ion irradiation of Gd2TixZr2-xO7 pyrochlore for x values of 0, 0.5, 1, 1.5 and 2. In Gd2Ti2O7, a thermal energy deposition per unit length of 12 keV nm(-1) results in a cylindrical amorphous track of radius 2 nm in good agreement with experiment. The volume swelling of the track is 4%, which suggests that it is partially amorphous. Gd vacancies and Ti interstitials along with cation exchange play a role in damage accumulation in the titanate. In sharp contrast, Gd2Zr2O7 does not swell and merely transforms from pyrochlore to fluorite under the same conditions. The activation energy barrier for oxygen hopping by the vacancy mechanism in these pyrochlores is 0.26-0.44 eV. The radiation tolerance of gadolinium zirconate pyrochlore is related to the efficient annihilation of cation Frenkel pairs, the low energy cost and negligible volume expansion associated with the resulting cation exchange, and efficient annealing of anion sublattice damage.