Mixed alkali effect in galliogermanate glasses

The relaxation of alkali ions in 20(Li2O-Cs2O)-15Ga2O3-65GeO2 glasses is investigated in both the ac conductivity and the electric modulus formalisms. The power law exponents that are obtained from ac conductivity are close to one at relatively low temperatures and decrease with increasing of temperatures. The coupling parameters obtained from the electric modulus decrease with increasing temperatures. However, for samples with pronounced mixed alkali effect, the coupling parameters are less sensitive with temperature changes. In those samples, the ion–ion coupling and the coupling between ion and structural-relaxation are both important for ionic relaxation. The near constant loss found at low temperatures is originated from the vibrational relaxation of ions within their cages. This may also be the origin of the ion and structural-relaxation coupling. The dc conductivities indicate that the mixed alkali effect is most pronounced in the sample containing 8 mol% of Li2O.