Abstract :
The layered sodium cobalt oxyhydrate superconductor Na0.3CoO2·1.4H2O is shown through X-ray diffraction and thermogravimetric studies to be one of the series of hydrated phases of Na0.3CoO2. Further, it is shown that the material is exceptionally sensitive to both temperature and humidity near ambient conditions, easily dehydrating to a non-superconducting lower hydrate. The observation of this stable lower hydrate with c=13.8 Å implies that the superconductivity turns on in this system between CoO2 layer spacings of 6.9 and 9.9 Å at nominally constant chemical doping.
