Insights into the radiation response of pyrochlores from calculations of threshold displacement events

We have used molecular-dynamics simulations to examine the displacement threshold energy (E-d) surface for cations and anions in Gd2Ti2O7 and Gd2Zr2O7 pyrochlores. In both pyrochlores, the E-d surface is highly anisotropic and it requires less energy to displace anions than cations. Both anion and cation E-d values are higher in the titanate compared to the zirconate. Titanium displacement energies are in excess of 170 eV for all directions examined, because cation exchange is less energetically favorable in Gd2Ti2O7 compared to Gd2Zr2O7. These high-energy Ti displacements result in the formation of defect clusters that may prevent efficient defect recovery. This provides an explanation for the difference in susceptibility to amorphization between titanate and zirconate pyrochlores.