Modeling the ac conductivity dispersion of mixed alkali germanate glasses

The ac conductivity and permittivity of mixed alkali, (Li₂O)_x(Na₂O)_1-x: 9GeO₂, glasses are reported. An analysis of the scaling properties is performed which indicates the ac conductivity and permittivity at different temperatures but fixed glass composition can be collapsed to a master curve. However, these master curves exhibit systematic changes with cation mixing which include a decrease in the conductivity dispersion exponent and substantial increase of dielectric loss at low frequencies. A simple model, based upon the dynamic structure model of Ingram and coworkers, is introduced in an attempt to understand these changes. A key feature of the model is the assumption that the cation's local conduction space is modified by mixing of the two cation species.