Structural properties determining the ionic conductivity of CsI-doped AgPO3 glasses

The conductivity and structure of (CsI)x-(AgPO3)1−x glasses, where 0⩽x⩽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 Ag ions from oxygen sites into iodine-rich environments upon addition of CsI. A similar dissociation effect, although stronger, has previously been found in PbI2-doped AgPO3 glasses, where it, together with network expansion, was considered to cause a much higher dc conductivity of PbI2-doped AgPO3 glasses as compared to AgI-doped AgPO3 glasses [ Phys. Rev. B 60 12 023 (1999)]. However, the dc conductivity is much lower in the present CsI-doped glasses than in Pbl2-doped glasses. This is explained on the basis that the conductivity in salt-doped AgPO3 is determined by three effects: (i) network expansion, (ii) partial 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.