High field O-17 NMR study of defects in doped zirconia and ceria

The local coordination structure around oxygen ions in CeO ₂-Y₂O₃ (YDC) and Y₂O ₃-ZrO₂ (YSZ) binary has been investigated by solid-state O-17 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy at high magnetic field of 21.8 T. Compositional dependence of the spectrum was observed and compared with the previous Y-89 MAS NMR results. The O-17 MAS NMR spectra of YSZ showed a line shape with overlapped peaks which did not allow straightforward peak separation. On the other hand, O-17 MAS NMR of YDC showed clearly resolved peaks depending on the local coordination environments of oxygen sites. By the peak separation, the relative amount of oxygen tetrahedra with different numbers of cations, O^T(4Ce), O^T(3Ce + 1Y) and O^T(2Ce + 2Y) can be determined. O^T(4Ce) was dominant compared to O^T(3Ce + 1Y) and O^T(2Ce + 2Y) at Y contents below 25%. The distribution of oxygen species deviated from a value expected from a random distribution. Therefore, the thermodynamic stability of oxygen species was considered, assuming an equilibrium constant between O ^T(4Ce), O^T(3Ce + 1Y) and O^T(2Ce + 2Y). A preferential decrease of O^T(3Ce + 1Y) species was found to reproduce the experimental values. The degree of the oxygen sites preference on composition was quantitatively determined for YDC for the first time.