Matthew Janish1 Terry Holesinger1 Blas Uberuaga1

1, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

Pyrochlores are a class of materials with the general formula A2B2O7, and they have attracted considerable interest both as nuclear waste forms as well as fast ion conductors. The relevant material properties for these applications, namely radiation hardness and ionic conductivity, have been related to disorder on the cation sublattice. Cation disorder may be introduced in a variety of ways: mixing of A and B atoms by heating or ion irradiation, or by the presence of grain boundaries.

In this work we describe the effects of ion irradiation on the cation sublattice of Gd2Ti2O7 (GTO). Single crystals of GTO were grown by the floating zone method, oriented at the <110> pole by Laue diffraction, then sectioned and polished for irradiation. Light ion irradiation (He, 200 keV) was used to gradually introduce disorder into the material as a function of dose. TEM specimens were prepared from the irradiated crystals in the plan-view orientation using traditional dimpling and ion-milling techniques, giving a {110}-type foil plane. The irradiated samples were then examined using high-resolution TEM in a monochromated, image-corrected FEI Titan 80-300 operated at 300 kV. Additionally, the recrystallization and recovery of damage in the irradiated regions of the GTO were examined in these specimens by heating them in-situ using a Gatan double-tilt heating holder. From these experiments, a quantitative understanding of changes in the local cation environment with induced disorder is expected to better inform models of how cation structure imparts functionality to this class of materials.