The Irradiation Behavior of 2M, 3O and 4M Polytypes Zirconolite Solid Solutions Under α Particles

The long-term irradiation stability of high-level radioactive waste forms is one key indicators for the safety evaluation of deep geological disposal. In this work, 500 keV He²⁺ ion beams irradiation of zirconolite-2M, zirconolite-3O and zirconolite-4M three-type solid solutions were performed to study the structure damage behavior from long-term α decay irradiation. All samples were synthesized through conventional high-temperature solid-state reaction (sintering at 1400 °C for 48 h twice). The grazing incidence x-ray diffraction (GIXRD), Raman and X-ray photoelectron spectroscopy (XPS) results indicated that zirconlite-2M sample experienced crystalline phase evolution from zirconolite-2M to zirconolite-4M, and then to pyrochlore during the amorphization process by α particles irradiation. zirconolite-3O phase partially transformed to perovskite at 5×10¹⁵ ions/cm² dose, and perovskite quickly transformed to disordered pyrochlore at dose above 1×10¹⁶ ions/cm². Zirconolite-4M sample still retained the main phase of zirconolite-4M at a dose of 1×10¹⁷ ions/cm², with secondary disordered pyrochlore or defect fluorite phase. In summary, the irradiation damage resistance of zirconolite-2M and zirconolite-3O was similar, and slightly lower than that of zirconolite-4M from the perspective of maintaining crystal structure stability.