Pressure-induced increase in the ionic conductivity of Li, Na, and K zeolites of type A

The effect of pressure on the ionic conductivity of hydrated A-zeolites containing Li, Na, and K cations was investigated. Room-temperature experiments at pressures to 4.8 GPa show an increase in the conductivity, which attains its maximum value in the range of 1.7–1.8 GPa for the three zeolites. Further compression leads to a drastic decrease in the conductivity at 2.5–3.5 GPa. The decrease in the conductivity is associated with the pressure-induced transition to the amorphous state, as follows from previously reported IR spectroscopy data. It is believed that the increase in the conductivity with pressure and the subsequent transition to the amorphous state follow one or several of the following mechanisms: (1) cation conductivity involving hydroxyls, (2) hydroxyl-proton conductivity, and (3) enhanced cation mobility due to pressure-induced change in the degree of hydration. With decreasing pressure, the conductivity does not follow the compression curve. For pressure-cycled samples, the low-pressure conductivity during decompression is two orders of magnitude higher than its value at the same pressure during compression. Compression provides a new way for conductivity optimization in hydrated A-zeolites.