Ac conductivity in ionically conducting crystals and glasses

Abstract

The ac conductivity behavior has been studied for crystalline oxygen-ion conductors: CeO 2:Gd 3+ and CaTiO 3:Al 3+ as well several silicate and borate glasses over a wide range of temperature. In all cases, Jonscher's universal power law behavior: σ( ω)= σ(0)+ Aω s is observed, where σ(0) is the dc conductivity and s the power law exponent. Furthermore, there are three regions of behavior. At the higher temperatures, s is a constant (usually≈0.6) independent of T. In this range σ can be written in the form suggested by Almond and West: σ( ω)= σ(0)[1+( ωτ) s ]. We find that τ has the same activation energy as σ(0) and a pre-exponential ≈10 −14 s. However, the quality of the activation energies does not imply that all carriers are unassociated, as Almond and West have claimed. Rather, it suggests that the ac and dc parts of the conductivity are manifestations of a single hopping process involving ion-ion interactions. At lower temperatures, the exponent s increases as T decreases, finally leveling off at s=1.