Abstract
In a recent Letter, Roling et al. [Phys. Rev. Lett. 78, 2160 (1997)] proposed a novel scaling approach, requiring no arbitrary parameters, for the analysis of the ac conductivity resulting from ionic motion in glasses. However, this approach cannot be applied to alkali germanate glasses whose alkali content varies by more than a decade, since changes which occur in the ion hopping length that accompany the changing alkali content are not incorporated. Here, I show that these changes can be incorporated into a universally valid approach which successfully scales the ac conductivity of sodium germanate glasses as well as two additional ionic systems without the introduction of arbitrary parameters.