Ion transport in salts orientationally disordered in anionic sublattice

A short review of transport properties of orientationally disordered phases (ODP) of alkali nitrates and perchlorates is presented. Analysis of the data shows that the conductivity, the activation energy and the pre-exponential factor do not change trivially with the increase of the cation size. It may be explained by two mechanisms: a classic one and a cooperative mechanism involving reorientation of anions, the latter becomes dominant in systems with a large free volume. Among nitrates ODP RbNO3-III is the most conducting and its stability range may be controlled via cationic and anionic substitutions. The mechanism of the ionic transport in RbNO3 seems to be different from those in perchlorates. According to the results of MD simulation conductivity is limited by the defect formation rather than the cation migration which proceeds via vacancy mechanism. Correlation times for the anion reorientation process correlate with ionic conductivity values thus suggesting that the cation diffusion and anion reorientation are closely interrelated.