Concentration Dependence of the Ionic Conductivity in Superionic Conductors

Abstract

The dependence of the ionic conductivity on the mobile ion concentration in superionic conductors is studied by making use of the lattice gas model with a hopping term and Kubo's formula. The ionic conductivity has symmetry with respect to concentration ρ=1/2, and has a minimum value at ρ=1/2 and a maximum value at ρ ≈ 0.3 and ρ ≈ 0.7. The ionic conductivity first increases with the increasing mobile ions, and has the maximum and then decreases with the further increase of mobile ion concentration by increasing the repulsive interaction among the mobile ions. At 50% concentration, it is understood that the ionic conductivity has the minimum because the mobile ion and the vacancy occupy the lattice sites alternatively.