Correlated ion hopping in single-crystal yttria-stabilized zirconia

A study of the effect of correlated ion motion on the electrical conductivity relaxation in single-crystalline yttria-stabilized zirconia is presented. Complex admittance in the radio frequency range show power-law dependencies in the real part of the conductivity at high frequencies of the form omega(n) and asymmetric electric modulus plots as a result of correlations. An analysis of the frequency dependence of the electric modulus is conducted to obtain time decay functions of the form exp[-(t/tau)(beta)] from an analytical distribution of relaxation times. Correlation times, and parameters n and beta characterizing the relaxation in time and frequency domains are compared to show the equivalence of time and frequency representations. The common origin of ac and dc processes is discussed in view of the frequency dependence of the complex conductivity. From a macroscopic activation energy for ion motion E = 1.16 eV and a beta value of 0.43, a single-ion microscopic activation energy E(a) = 0.5 eV is obtained as beta E according to Ngai's coupling model. The microscopic activation energy is related to the association energy of oxygen vacancies.