The effect of ionic group rotations on proton orderings in super-ionic crystals

The various proton orderings occurring in crystals are investigated in the framework of a lattice-gas-type model with account taken of the interactions of the proton subsystem with the orientations of the ionic groups. In particular, it is shown that the orientational ordering of ions is strongly involved in the I-II-III-IV phase transitions which take place in and appears to be the basic mechanism determining the observed phase sequence. The phase diagram obtained together with the microscopic parameter values calculated for agree with the experimental data for the phase orderings.

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