Hydration phase diagram for sodium cobalt oxide Na0.3CoO2·yH2O

The hydration phase diagram for sodium cobalt oxhydrate, Na0.3CoO2·yH2O (y = 0, 0.6 and 1.3), was determined as a function of relative humidity at 298 K It is found that greater than 75% relative humidity is needed for complete hydration of anhydrous Na0.3CoO2 to the superconducting phase Na0.3CoO2·1.3H2O. Dehydration studies show that a minimum of 43% relative humidity is needed to maintain the stability of the fully hydrated superconducting phase. The intermediate hydrate, Na0.3CoO2·0.6H2O, is stable between 10 and 50% relative humidity on hydration, and 35 and 0% relative humidity on dehydration.