Electrical conductivity of the system ThO2-Er2O3

ThO2-Er2O3 systems containing 3, 6, 9 and 12 mol% Er2O3 were found by X-ray diffraction to be solid solutions. The lattice parameters were obtained by various diffraction-angle analysis methods and these values increased with increasing dopant level. The electrical conductivities measured as a function of temperature from 520 to 11000C and of oxygen partial pressure from 1 x 10-4 to 2 x 10-1 atm, increase with increasing temperature, and show a maximum with increasing dopant level. The calculated activation energies (Esub(a)) decrease with increasing dopant level, but an abrupt increase in Esub(a) appears in the 12 mol% sample. The phenomenon of the maximum in the conductivity occurring simultaneously with the maximum in the Esub(a) can be explained by the ordering of free dopant ions and charged associates. The exponential dependence of the conductivity on the oxygen pressure (σ ∝ Psub(O2)sup(1/n)) is 1/n = 1/4, and the main defect is an oxygen vacancy for oxygen pressures above 10-3 atm. Below 10-3 atm, the conductivity no longer has linearity. The conduction mechanism suggested for this system is mixed ionic and electronic conduction due to oxygen ions and holes. (author)