Nearly constant dielectric loss of glasses containing different mobile alkali ions

Recently, Rivera et al. [Phys. Rev. Lett. 88 (2002) 125902] found that the magnitude of the nearly constant dielectric loss (NCL) in alkali triborate glasses decreases as m−1/3 with increasing alkali ion mass m. We have carried out conductivity measurements on aluminosilicate and aluminogermanate glasses containing different mobile alkali ions, and we show that the magnitude of the NCL does not follow a m−1/3 relation. Instead, we find a strong correlation between the magnitude of the NCL, the dc conductivity, and the dielectric relaxation strength which is valid for various ionic glasses at temperatures above 173 K.