Mechanical properties of fluorite-related oxides subjected to swift ion irradiation: Pyrochlore and zirconia

The modifications of the mechanical properties of related-fluorite oxides (cubic zirconia [c-ZrO₂] and pyrochlores [Gd₂(Ti_1−xZr_x)₂O₇ with x = 0.5 and x = 1]) induced by swift heavy ion irradiation are investigated. Polycrystalline pellets of both materials were irradiated at room temperature with 940 MeV Pb or 870 MeV Xe ions at the GANIL accelerator in Caen at fluences ranging from 2 × 10¹¹ to 10¹³ cm⁻². Residual macroscopic stresses induced by irradiation were determined using X-ray diffraction and the sin²ψ method. The microhardness and the fracture toughness of irradiated samples were studied by Vickers micro-indentation. Amorphization occurs in Gd₂TiZrO₇ and not in Gd₂Zr₂O₇ and c-ZrO₂. The mechanical behavior of materials is found to be closely related to the residual stresses induced in the surface layer by irradiation. Compressive stresses are generated in c-ZrO₂ and Gd₂TiZrO₇ (leading to an increase of fracture toughness), whereas tensile stresses (inducing a large decrease of fracture toughness) are observed in Gd₂Zr₂O₇ due to the lattice contraction related to a pyrochlore fluorite→transition.