STATE OF ORDER IN ALPHA-AGI

The disorder entropy of α-AgI as determined from the latent heat of the β→α transition is used to analyze the state of order in α-AgI. The experimental data are consistent with a configurational model of disorder based on a nearly random occupation of the tetrahedral 12d sites by the silver ions excluding nearest-neighbor site occupation. It is argued that the diffuse x-ray scattering of α-AgI is dominated by thermal scattering yielding practically no information about the static state of order. As a consequence of this analysis the elementary transport process in a superionic conductor is a transition from one equilibrium configuration into another equilibrium configuration; an adequate description of superionic conduction should therefore be based on a lattice-gas model. © 1979 The American Physical Society.