Ionic conductivity of high-temperature phases of alkaline metal perchlorates was studied. It was found that the conductivity passes through a minimum with increasing radius of cation, and KClO4 exhibits the lowest conductivity. This was explained by a decrease in the relative size of conduction channel, which hampers the cation transfer, and an increase in the relative free volume. The free-volume increase promoted the perchlorate anion reorientation and reduces the activation energy for ion transfer by the so-called paddle-wheel mechanism; as a result, the conductivity increased.

Conductivity of Alkali Perchlorates at High Temperatures. A.S.Ulihin, N.F.Uvarov, B.E.Mellander: Solid State Ionics, 2008, 179[1-6], 228-30