Anelastic and dielectric relaxation of scandia-doped ceria

Of all the trivalent dopants which may be added to ceria (CeO₂) to make it an oxygen-ion conductor, Sc³⁺ appears to be unique in producing unusually low conductivity due to a relatively high vacancy-dopant association energy. In order to better understand the defect structure of Sc³⁺-doped ceria, the present work was undertaken using both anelastic and dielectric relaxation. A number of relaxation peaks were found. Most strikingly, a new low temperature relaxation with activation enthalpy near 0.2 eV was observed; it was shown to be due to a low-symmetry off-center configuration of an isolated Sć_Ce defect. At higher temperatures the relaxation due to Sc-V_o pairs (where v_o = oxygen vacancy) was found to have an activation enthalpy of 0.41 eV (much lower than that of larger dopant ions, e.g. Y³⁺ and Gd³⁺. In addition, complex relaxation spectra are observed even for concentrations as low as 0.3mol% Sc₂O₃, showing that higher clustered defects readily form in this system.