RELAXATION DISPERSION OF IONIC-CONDUCTIVITY IN A ZR0.85CA0.15O1.85 SINGLE-CRYSTAL

The dynamic behavior of the oxygen ion conductivity of a cubic Zr0.85C a0.15O1.85 single crystal has been investigated with AC impedance spec troscopy and a dynamic pulse method as a function of both temperature and frequency between 450 and 1200 K and 20 and 10(8) Hz. This is the frequency-temperature range where the relaxation dispersion of the ion ic conductivity can be observed. From the temperature dependence of th e relaxation frequency, the diffusion coefficient and the mobility of oxygen vacancies were determined. In the entire temperature range inve stigated, the temperature dependence of the ionic conductivity of a Zr 0.85Ca0.15O1.85 single crystal arises exclusively from the temperature dependence of the mobility of oxygen vacancies, the concentration of which remains constant with temperature and is equal to the concentrat ion of all extrinsic oxygen vacancies created by calcia stabilizing. N o transition in the Arrhenius plot of the ionic conductivity due to a gradual dissociation o oxygen vacancy-defect cation associates, as pro posed in the literature, has been observed. A simple model for the tem perature dependence of the ionic conductivity of solid electrolytes in terms of the parallel and serial combination of RC-elements is given.