Preparation and electrical characterization of ruthenia-doped yttria-stabilized zirconia ceramics

Samples belonging to the [(ZrO2)0.92(Y2O3)0.08]1-x(RuO2)x system, where 0 ≤ x ≤ 0.1 (mol), have been synthesized by a polymeric sol-gel route and sintered in air at 1400 C for 2 h. The RuO2-YSZ solid solution limit is found at x = 0.05 at 1400 C by X-ray diffraction and electrochemical impedance spectroscopy measurements. The electrical conductivity of the studied materials decreases with ruthenia additions. At high temperature (700--850 C) and low oxygen partial pressure, these materials behave as mixed oxygen ion-electronic conductors. The electronic conductivity as a function of PO2 shows a dependence of -1/4 and an activation energy of 0.98 eV. The electronic contribution is explained on the basis of redox equilibrium between trivalent Ru3+ and divalent Ru2+. The EPR spectra of polycrystalline sintered samples confirm the presence of Ru3+