Structure and mechanical properties of swift heavy ion irradiated tungsten-bearing delta-phase oxides Y ₆W ₁O ₁₂ and Yb ₆W ₁O ₁₂

We report on the relationship between structure and mechanical properties of complex oxides whose structures are derivatives of fluorite, following irradiation with swift heavy ion (92 MeV Xe) which approximately simulates fission product irradiation, where the electronic energy loss dominates. The two compounds of interest in this paper are Y ₆W ₁O ₁₂ and Yb ₆W ₁O ₁₂. These compounds possess an ordered, fluorite derivative crystal structure known as the delta (δ) phase, a rhombohedral structure belonging to space group R3̄. Structural changes induced by irradiation were examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD investigations indicated an irradiation-induced amorphization in these compounds. This result is consistent with our previous study on Y ₆W ₁O ₁₂ under displacive radiation environment in which the nuclear energy loss is dominant. High resolution TEM also revealed that individual ion tracks was amorphized. The mechanical properties of both irradiated compounds, were determined by cross-sectional nano-indentation measurements as a function of ion penetration depth. The decreases in Young's modulus, E, and hardness, H (both by about 40% at the irradiated surface) suggest amorphization beyond simple defect accumulation occurs under this irradiation condition.