Dielectric relaxation properties of dehydrated and hydrated Na-mordenite are measured by means of thermally stimulated depolarization current (TSDC) spectroscopy. TSDC spectroscopy allows us to determine two characteristic terms which depend on the hydration state: on one hand, the site selectivity of sodium ions and water molecules and on the other hand, the sodium/network interaction energy. Upon hydration, half of the Na+ ions remain embedded in site A, whereas the other Na+ ions are extracted from the main channel sites (sites D and E). Besides, according to the water content, we show that water molecules are adsorbed in different sites, first in sites H or F, then in sites B, C, or G, and finally in sites G. Furthermore, it is pointed out that the interaction energy (Na+/zeolite) value depends on the sodium localization following the sequence: E site A > E site D > E site E. Finally, it is shown that the interaction energy decreases as the water content increases (typically from 0.79 eV to 0.44 eV). This evolution is successfully described by using a qualitative model referring to electronegativity and charge-transfer concepts.

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The evolution of conduction and polarization phenomena is studied as a function of dehydration temperature (TT varying from 100 up to 400 °C) on a faujasite Y zeolite. The measurements are carried out as a function of frequency at different temperatures. In all cases, the conductivity is ascribed to the migration of cations in large cages involving energies varying from 0.61 to 0.85 eV. Two relaxation domains are observed. It is assumed that they are due to the movement of cations of sites III‘ and II. The existence of these two domains is confirmed by the technique of the thermally stimulated currents. The spreading domain of relaxation depends on the dehydration state of the zeolite.

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