Thermodynamic and direct-current electrical conductivity measurements were performed on non-stoichiometric CeO2-x in order to characterize its electrical behavior and defect structure near to the n-to-p transition. By using the mass action approach, activation energies of 2.57, 1.15 and 0.63eV were deduced for the electron, hole and ionic partial conductivities, respectively (at temperatures ranging from 600 to 1000C, and O partial pressures [P] of between 0.0001 and 1atm). Thermodynamic data which were obtained from 4N-purity material, by means of electrochemical coulometric titration, furnished expressions for the point defect concentration per cm3 and the non-stoichiometry in the impurity-dominated region at 800C: [CeCe'] = (7.08 x 1016)P-¼/cm3; [h.] = (9.26 x 1018)P¼/cm3; x = (2.03 x 10-23)(7.08 x 1016P-¼ - 9.26 x 1018P¼). The measurements revealed a decrease in the partial molar enthalpy (from -10eV) with decreasing stoichiometry when x was less than 10-2.8. This decrease was attributed to the effect of defect reactions which involved both holes and electrons.

M.A.Panhans, R.N.Blumenthal: Solid State Ionics, 1993, 60[4], 279-98