Radiation effects in Gd2Ce2O7: role of anion sublattice in disordering and limitations of Gibbons model for damage evolution in disordered systems.
Résumé
Disordering in ternary oxide systems derived from the parent fluorite structure has attracted significant attention with a particular interest in correlating the crystal chemistry and ordering of metal cations and oxygen anions to their radiation tolerance, ionic and thermal conductivity. Radiation effects in these systems have been mainly focused on the role of cations in the disordering and amorphization while the role of anion sublattice is not well understood due to the unavailability of the model system which allows deconvoluting the effect of both cation and anion sublattices. The current work will discuss the role of anions in a specific system (Gd2Ce2O7) when subjected to Swift Heavy Ion irradiations and characterized using quantitative X-ray diffraction analysis. Our results show that the topological disorder on the anion sub- lattice grows faster than that on the cation sub-lattice. In addition, radiation damage descriptions are usually binary, in that they model damage evolution as a transition from an initial, pristine unirradiated structure to a new, final irradiated structure, this final state is often an amorphous phase: these models track the relative proportions of the two phases i.e. amorphous or crystalline, at any time during irradiation, as well as the rate of the transformation from the initial state to the final state. Here, we develop a different approach wherein we describe at the atomic scale the homogeneous and coherent materials’ response to irradiation before amorphization takes place. The material response can then be understood with greater mechanistic insight, compared to the conventional, binary response where the latter approach simply addresses the question, “Does the material amorphized or not?”.
Acknowledgment: This work was supported in part by the French Grant ANR-10-LABX-0039-PALM.