Structural properties determining the ionic conductivity ofCsI-dopedAgPO3glasses

Abstract

The conductivity and structure of ${(\mathrm{CsI})}_{x}\text{\ensuremath{-}}{({\mathrm{AgPO}}_{3})}_{1\ensuremath{-}x}$ glasses, where $0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.2$, were investigated by means of dielectric spectroscopy, x-ray and neutron diffraction, and reverse Monte Carlo modeling. Evidence was found for a partial dissociation of $\mathrm{Ag}$ ions from oxygen sites into iodine-rich environments upon addition of $\mathrm{CsI}$. A similar dissociation effect, although stronger, has previously been found in ${\mathrm{PbI}}_{2}$-doped ${\mathrm{AgPO}}_{3}$ glasses, where it, together with network expansion, was considered to cause a much higher dc conductivity of ${\mathrm{PbI}}_{2}$-doped ${\mathrm{AgPO}}_{3}$ glasses as compared to $\mathrm{AgI}$-doped ${\mathrm{AgPO}}_{3}$ glasses [Phys. Rev. B 60, 12 023 (1999)]. However, the dc conductivity is much lower in the present $\mathrm{CsI}$-doped glasses than in ${\mathrm{Pbl}}_{2}$-doped glasses. This is explained on the basis that the conductivity in salt-doped ${\mathrm{AgPO}}_{3}$ is determined by three effects: (i) network expansion, (ii) partial $\mathrm{Ag}$ dissociation, and (iii) a mixed mobile ion effect. The last effect, which reduces the conductivity, is present when the salt cations, here cesium ions, are mobile.