Protonic conductivity at the superionic phase transitions in the M3H(XO4)(2) crystal group

A microscopic model for the description of the proton subsystem dynamics in superionic crystals with hydrogen bonds is developed. Besides the inclusio n of the proton-transport mechanism, the effect of the displacement of the nearest oxygens during hydrogen-bond formation is taken into account. The l atter effect is the cause of the strong proton-phonon coupling that leads t o the polaronic effect. Using the occupation number formalism, the virtual (in superionic phases) or ordered (in low-temperature phases) character of the hydrogen-bonded system is taken into account on the basis of the proton -ordering model. Protonic conductivity studies are carried out in the frame work of the Kubo theory for the cases of superionic phases as well as low-t emperature phases with different types of proton ordering (as an example th e M3H(XO4)(2) class of crystals is considered). The temperature dependencie s of the conductivity are analysed. The activation energies for the static conductivity are determined; for this case the influence of the internal fi eld which appears as a result of the proton ordering is investigated.