Pressure-induced disorder in hydrated Na-A zeolite

We report on pleasure-induced disorder in hydrated Na-A zeolite at pressures up to 4.8 GPa. Room temperature ionic conductivity measurements show anomalous conductivity increase with pressure up to similar to 1.8 GPa, signifying progressive disordering as found in Li-A zeolites, followed by rapid decrease in conductivity consistent with a collapse of the local environment around the Na+ ions. X-ray diffraction patterns on recovered samples show reduced diffraction line intensities suggesting incomplete reversion to the ordered state. Conductivity values at the lowest pressure on de-pressurization are higher than equivalent pressures on pressurization by a factor in the range 3-7. The partially disordered structural state of the recovered sample may thus confer transport properties on Na-A zeolite that may be useful for specific applications. (C) 1999 Elsevier Science Ltd. All rights reserved.