Ionic conductivity and the mixed alkali effect inLixRb1−xPO3glasses

Abstract

The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the alkali ions in the glass structure, that is, a strong mixed alkali effect on the dc conductivity was observed. The results show that the mixed alkali effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity mixed alkali effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of alkali ions [Phys. Rev. B 63, 132202 (2001)].