  The ionic conductivity of mixed alkali glasses exhibits a deep minimum as a
function of the relative concentrations of the two alkali ions. To study this
behaviour we consider a simple one-dimensional model for asymmetric diffusion
of two kinds of particles. Different particles are assumed to repulse each
other. We consider two versions of the model: with or without overtaking of
particles. For the case of perfect repulsion we find exact expressions for the
stationary current. The model with weaker repulsion is studied by means of
numerical simulations. The stationary current as a function of the ratio of
particle concentrations is found to exhibit a minimum, related to correlations
existing in this system.
