Pressure-induced disorder in hydrated Na-A zeolite

We report on pleasure-induced disorder in hydrated Na-A zeolite at pressure s up to 4.8 GPa. Room temperature ionic conductivity measurements show anom alous conductivity increase with pressure up to similar to 1.8 GPa, signify ing progressive disordering as found in Li-A zeolites, followed by rapid de crease in conductivity consistent with a collapse of the local environment around the Na+ ions. X-ray diffraction patterns on recovered samples show r educed diffraction line intensities suggesting incomplete reversion to the ordered state. Conductivity values at the lowest pressure on de-pressurizat ion are higher than equivalent pressures on pressurization by a factor in t he range 3-7. The partially disordered structural state of the recovered sa mple may thus confer transport properties on Na-A zeolite that may be usefu l for specific applications. (C) 1999 Elsevier Science Ltd. All rights rese rved.