Propagation of short-range order in the lattice gas

The lattice gas model is examined to make a comparison between the superposition approximation and one which is free from the approximation as long as the three-body distribution is concerned. The formulation is applied to the type I superionic conductor, AgI, in which Ag-ions can move like the atoms in liquid and give rise to a strongly correlated Ag-ion distribution over available lattice sites. The oscillatory behavior of the radial distribution function is found up to the seventh neighbor distances including three maxima and three minima. The degree of disordered arrangement is then examined by calculating the latent heat of transition from the ordered β-phase to disordered α-phase of the superionic conductor.