Abstract
We compare the dielectric response of ionic glasses and dipolar liquids near the glass transition. Our work is divided into two parts. In the first section we examine ionic glasses and the two prominent approaches to analyzing the dielectric response. The conductivity of ion-conducting glasses displays a power law dispersion σ(ω)∝ωn, where n≈0.67, but frequently the dielectric response is analyzed using the electrical modulus M*(ω)=1/ɛ*(ω), where ɛ*(ω)=ɛ(ω)-iσ(ω)/ω is the complex permittivity. We reexamine two specific examples where the shape of M*(ω) changes in response to changes in (a) temperature and (b) ion concentration, to suggest fundamental changes in ion dynamics are occurring. We show, however, that these changes in the shape of M*(ω) occur in the absence of changes in the scaling properties of σ(ω), for which n remains constant. In the second part, we examine the dielectric relaxation found in dipolar liquids, for which ɛ*(ω) likewise exhibits changes in shape on approach to the glass transition. Guided by similarities of M*(ω) in ionic glasses and ɛ*(ω) in dipolar liquids, we demonstrate that a recent scaling approach proposed by Dixon and co-workers for ɛ*(ω) of dipolar relaxation also appears valid for M*(ω) in the ionic case. While this suggests that the Dixon scaling approach is more universal than previously recognized, we demonstrate how the dielectric response can be scaled in a linear manner using an alternative data representation.