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

TL;DR

This study maps the hydration phase diagram of sodium cobalt oxyhydrate, revealing humidity thresholds for hydration, dehydration, and stability of various phases, crucial for understanding its superconducting properties.

Contribution

It provides the first detailed hydration phase diagram of Na0.3CoO2*yH2O as a function of relative humidity at 298K.

Findings

Complete hydration requires >75% RH.

Stable superconducting phase at 43% RH.

Intermediate hydrate stable between 10-50% RH.

Abstract

The hydration phase diagram for sodium cobalt oxyhydrate, Na0.3CoO2*yH2O (y=0, 0.6, 1.3), was determined as a function of relative humidity at 298K. 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% to 0% relative humidity on dehydration.