Dielectric relaxation strength in ion conducting glasses caused by cluster polarization

A model for interpreting the dielectric relaxation strength Δε observed in ionic glasses is proposed. The model relates the dielectric strength to the polarization of nanometric structures formed by energetic clustering. The calculation of Δε relies exclusively upon equilibrium arguments, and its results are in agreement with previous derivations of the dc conductivity made from percolation approaches. The expression of Δε shows that its temperature and alkali content dependence is very sensitive to the underlying ion statistics so that no universal trend is expected. The model prediction is evaluated on the test case system of sodium conducting borate glass. The large variety in the dielectric strength dependences on modifier content is discussed in light of the inherent glassy structural complexity.