Radiation damage in YSZ simulated by single and double beam ion irradiation

YSZ (yttria-stabilized zirconia) with cubic phase is a promising nuclear material. YSZ has excellent radiation resistance and chemical stability and can be applied for the inter matrix layer of fuel cells or for the covering and storage of nuclear waste. The effect of irradiation on YSZ has been intensively investigated in recent years via single beam implantation.[1,2] Most of experimental works were performed to simulate the radiation damage from alpha particles by He+ implantation [2] or to simulate the neutron radiation damage and the damage introduced from alpha recoils by implantation of heavy ions. [1] In fact, the radiation damages created by the simultaneous dual beam implantation of Zr+ and He+ ions is much more adequate to reflect the real irradiation conditions. However this case is rarely reported in the literature due to the experimental restrictions. In this work the dual beam facility in Rossendorf is used for the investigation of the radiation damage in YSZ created either by simultaneous implantation of Zr+ & He+ or by separate single beam implantation. The samples were analyzed by a variety of methods such as Rutherford backscattering spectrometry in channeling mode, high resolution x-ray diffraction, positron annihilation spectroscopy, nanointendation and transmission electron microscopy.
The results show that the excitation by the additional Zr+ implantation can activate and enhance the out diffusion of the simultaneously implanted He. The release of He.from YSZ substrate, instead to be trapped by implantation induced vacancies generated by the heavy Zr+ ions, avoids the formation and growth of He bubbles. Such bubbles make the material hard and brittle. In this way the ability of YSZ for the stable inclusion of nuclear waste in the long term is verified. Possible mechanisms are discussed.

[1] S. Moll et al., Journal of Applied Physics 105, 023512 (1999).
[2] G. Velisa et al., Journal of Nuclear Materials 402, 87 (2010).