On diffusion hindered by dimers, site percolation and the mixed alkali effect
Abstract Mixed alkali effects in solid ionic conductors are investigated from the point of view of percolation theory. We assume basically that there exists a strong effective attractive interaction between the two different species of alkali ions, which causes the unlike ions to form immobile dimers. The excess ions are considered as hard-core particles. Using two-dimensional Monte Carlo simulations we show that the conductivity and the tracer diffusion constant are strongly affected by the existence of two characteristic percolation thresholds. This leads to the observed nonlinear behaviour of transport properties in the mixed alkali systems.