Point Defects and Swelling Induced in Yttria-Stabilized Zirconia by Swift Heavy Ion Irradiations
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Point Defects and Swelling Induced in Yttria-Stabilized Zirconia by Swift Heavy Ion Irradiations Jean-Marc Costantini1 and François Beuneu2 1
CEA, SRMA, 91191 Gif-sur Yvette Cedex, France.
2
LSI, CEA-CNRS-Ecole Polytechnique, 91128 Palaiseau Cedex, France.
ABSTRACT We present a study of point-defect creation in yttria-stabilized zirconia (ZrO2: Y) or YSZ exposed to various heavy ions (from C to U) covering an energy range from 100 MeV to several GeVs. It is concluded that F+-type centers (involving singly-ionized oxygen vacancies) are produced by elastic-collision processes. The ion-induced out-of-plane expansion is found to be small (< 0.2%) and to increase linearly as a function of the average F+-type center concentration with a large slope compatible with small oxygen vacancy clusters. The large defect volume and axial symmetry of the F+-type centers hint that these color centers might actually be divacancies (i.e. F2+ centers). INTRODUCTION Cubic-stabilized zirconia (ZrO2) is considered as a suitable refractory host for actinide transmutation in high-temperature breeders. In this case, it is expected that radiation damage may be induced by ionization processes upon fission-fragment irradiation. By using RBS/channeling spectrometry and X-ray diffraction (XRD), we have previously shown that the YSZ single crystals are not amorphized even with heavy ions at high stopping power [1, 2] in agreement with older data [3]. We concluded that polygonization might occur above a threshold electronic stopping power ∼ 20 keV nm-1. On this basis, we have undertaken a study of the point defects induced by swift heavy ion irradiation by using ion beams ranging from 100-MeV C to 2.6-GeV U ions using EPR spectroscopy. EXPERIMENTAL PROCEDURES We have used yttria-stabilized zirconia (YSZ) (with 9.5 mol% Y2O3) (100) and (110) single crystal plates with 500-µm thickness (provided by Crystal GmbH, Berlin, Germany). Reduced (R) samples were also obtained by thermal annealing in vacuum for 24 h at 1100°C. The asreceived (AR) samples are colorless and transparent, whereas the R-ones are yellowish due to the charge-compensating T centers induced by thermo-chemical reduction (TCR) [4]. Heavy-ion irradiations were carried out at GANIL in Caen (France) for the irradiation with C ions, at the VIVITRON in Strasbourg (France) for S, Ni, Br, I, Au ions, and at GSI/UNILAC in Darmstadt (Germany) for U ions. The 145-MeV C ions were also transmitted through 100-µm thick samples. Irradiations were performed under high vacuum with low particle fluxes (∼ 108-1010 cm-2 s-1) in order to prevent sample heating. The temperature during irradiations was thus near RT, except for the carbon beams which were applied at LNT. The irradiation parameters computed with the SRIM/TRIM code [5] are listed in Table I. Electron irradiations have also been performed previously at the Van-de-Graaff accelerator of the LSI in Palaiseau under helium
gas at around 310 K with energy of 2.5 MeV and flux around 1014 cm-2 s-1. Electrons were transmitted through t
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