Space-charge relaxation in ionicly conducting oxide glasses. I. Model and frequency response

Abstract

A mathematical model for space-charge relaxation is presented which takes account of both field drift and diffusion of unipolar ions between plane parallel blocking electrodes. The model has been applied to alkali ion-conducting silicate and borosilicate glasses. The results are plotted against the reduced logarithmic frequency scale, log(ωτD), where τD is the relaxation time for the bulk glass obtained from the dielectric modulus peak. For small signal conditions and thick specimens, the conductivity relaxation in the bulk, the space-charge relaxation, and high-field recharging processes appear in quite different frequency ranges. The space-charge relaxation is characterized by a constant conductivity and a permittivity varying as ω−2 in approximate agreement with the experimental data. A more exact agreement with the experiment is found by the inclusion of a constant phase angle element to model the behaviour of rough electrode interfaces. The theory presented for space charge relaxation is also applicable to any isotropic unipolar ionic conductor.