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The pressure-induced anomalously high AC conductivity of zeolite NaA mixed with water was measured by impedance spectroscopy at various water/zeolite ratios. The conductivity reaches a maximum value at 0.9–1.4 GPa with increasing water content of up to 20 wt.% in NaA + water. The high ionic conductivity of NaA compressed in water is interpreted to result from cation diffusion in the quasi-liquid Na+–H2O intra-channel system enhanced by the filling of additional H2O sites. The pressure range of anomalously high AC conductivity in NaA enlarges towards higher pressures with decrease of the water/zeolite ratio. An abrupt drop in conductivity observed at P > 1.5 GPa appears to be associated with freezing of intra-channel water. After pressure release, the overhydrated state of the zeolite kept in a closed container can be preserved for a long time, providing abnormally high conductivity which is comparable with that of Na+ β-alumina.

Edingtonite is a ferroelectric material of the Rochelle salt (RS) class and shows large anomalies of different properties in the temperature range of −53 to −133 °C. Classical RS exhibits the low-temperature phase transition P21212–P2111, whereas ammonium RS shows the phase transition P21212–P11211. According to our data, edingtonite blocks this possible symmetry lowering by the phase transition P21212–P112. Edingtonite, similarly to RS crystals, has two sub-lattices of water molecules and exhibits a complex low-temperature behavior. There are at least three anomalies in the low-temperature dependence of the generation of the second optical 0.53-micron harmonics, excited by the 1.06-micron line of a Nd pulse laser. Edingtonite also exhibits significant anomalies in the low-frequency range of its IR spectrum at low temperatures. The maximum IR anomaly is observed in natural edingtonite at −124 °C, whereas in the deuterated sample the same anomaly occurs at −113 °C. The most intense anomalous broad band at 220 cm−1 did not shift due to deuteration. According to the presented lattice-dynamical calculations, this vibration corresponds to a strong deformation of the cavity around the water molecules during the phase transition. Raman study of edingtonite under high pressure in a diamond anvil cell (DAC) at room temperature shows that there is no pressure-induced phase transition up to 6.4 GPa. No amorphization was observed at this pressure range.