Correlation between local structure and electrical response of Rb and (Rb,Ag) germanate glasses: dc conductivity

Abstract

The relationship between ionic conductivity and local structure (interatomic distance, coordination number, structural disorder around the various cations and the fraction of non-bridging oxygen) is determined for xRb 2O · (1 - x)GeO 2 binary glasses with x = 0.01−0.20, and 0.2(Ag,Rb) 2O · 0.8GeO 2 mixed mobile ion glasses. The composition dependence of activation energy for dc conductivity is explained by the existence of an ‘unoccupied volume’. The cooperative ion movement model proposed for alkali silicate glasses is found inappropriate for describing ionic conduction in Rb germanate glasses, probably because elastic interactions in the latter are not duly accounted. The mixed (Rb,Ag) germanate glass series shows the classical mixed mobile ion effect in dc conductivity. The distance of the mobile cation from oxygen and the disorder around it are not important for the development of this effect.