It was noted that the origin of the high ionic conduction in superionic conductors could be attributed to the double minimum potential produced by strong third- and fourth-order terms of the phonon displacements. Such terms were derived from the low energy and low dispersion of the optical and acoustic phonon modes that originated from the enhanced electronic polarization of superionic conductors. Based upon the double minimum potential, an attempt was made to explain why dielectric parameters correlated closely with the ionic activation energy and transition temperature, and to describe the effects of the low-energy phonon mode, large phonon damping and heavy atomic mass of the framework ion upon high ionic conduction.

Interpretation of High Ionic Conduction in Superionic Conductors based on Electronic and Phonon Properties. K.Wakamura: Solid State Ionics, 2004, 171[3-4], 229-35