Paramagnetic defects in electron-irradiated yttria-stabilized zirconia: Effect of yttria content

We have studied the effect of the yttria content on the paramagnetic centers in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol % or 18 mol % Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0, and 2.5 MeV. The paramagnetic center production was studied by X-band electron paramagnetic resonance (EPR) spectroscopy. The same paramagnetic centers were identified for both chemical compositions, namely two electron centers, i.e., (i) F+-type centers (involving singly ionized oxygen vacancies), and (ii) so-called T centers (Zr3+ in a trigonal symmetry site), as well as hole-centers. A strong effect is observed on the production of hole-centers that is strongly enhanced when doubling the yttria content. However, no striking effect is found on the electron centers (except the enhancement of an extra line associated with the F+-type centers). It is concluded that hole-centers are produced by inelastic interactions, whereas F+-type centers are produced by elastic collisions with no effect of the yttria content on the defect production rate. In the latter case, the threshold displacement energy (E-d) of oxygen is estimated from the electron-energy dependence of the F+-type center production rate, with no significant effect of the yttria content on E-d. An E-d value larger than 120 eV is found. This is supported by classical molecular dynamics (MD) simulations with a Buckingham-type potential that show E-d values for Y and O are likely to be in excess of 200 eV. Due to the difficulty in displacing O or Y atoms, the radiation-induced defects may alternatively be a result of Zr atom displacements for E-d = 80 +/- 1eV with subsequent defect rearrangement. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3666062]