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(Ti1−xZrx)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 940MeV Pb or 870MeV 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.