Analytical distributions of relaxation times for the description of electrical conductivity relaxation in ionic conductors

Electrical conductivity relaxation was measured in three different ionic conductors (yttria-stabilized zirconia, Li0.5La0.5TiO3 and Li0.5.5Na0.5La(Cr04)2), using the admittance spectroscopy technique. A study of the frequency dependence of the dielectric modulus is presented, which shows that the Havriliak-Negami dielectric functions describe the relaxation process accurately. This allows the use of an analytical distribution of relaxation times to determine the time decay function from admittance data in the frequency domain. Electrical conductivity relaxation of the measured ionic conductors has been analysed using this method showing strong non-Debye frequency behaviour and ‘stretched’-exponential Kohlrausch-Williams-Watts time decay functions. The results obtained are interpreted in terms of cooperative effects or correlation among ions. Activation energies for long- and short-range ion motion are deduced.