Dipolar dielectric relaxation in CeO2-YO1,5 solid solutions

The dielectric properties of yttrium oxide-doped cerium oxide solid solutions have been studied by using a.c. techniques. Frequency and temperature respectively range from 10 to 10⁵ Hz and from 70 to 200°C. Both a complex impedance plot (Z″ vs Z′) and a conductance plot (G at fixed frequency vs inverse of temperature T^?1) are shown to be complementary for an accurate determination of the bulk resistance and of the dielectric loss. For the three investigated concentrations of yttrium oxide (m/% YO_1,5:0.001, 0.01 and 0.1), the activation energies for conduction are equal to 0.86, 0.75 and 0.75 eV, while the activation energy for dipole reorientation is found to be concentration independent (0.75 eV; angular frequency preexponential factor: 6.0 × 10¹², 1.43 × 10¹³ and 3.05 × 10¹³ s^?1). Moreover, the dipolar relaxation rates are found to be of the same order of magnitude as that of the migration rate. Interpretation is given on the basis of Wachtman's model and of previous results obtained by Nowick et al. from ITC (ionic thermo-current) investigations. The observed dielectric peak appears to be due to the redistribution of oxyygen vacancies between charged (Y_Ce-V₀) pairs and fixed charged Y_Ce defects.