  Single crystals of NaxCoO2 with beta-phase (x=0.55, 0.60 and 0.65),
alpha'-phase (x=0.75) and alpha-phase (x=0.9, 1.0) have been grown by the
floating zone technique. The Na-extraction and hydration were carried out for
the alpha'-sample to get superconducting phase of NaxCoO2.yH2O (x~0.3, y~1.3).
Hydrated single crystals exhibit cracked layers perpendicular to the c-axis due
to a large expansion when the water is inserted into the structure. A study of
intercalation/deintercalation was performed to determine the stability of the
hydrated phase and effects of hydration on the structure of the compound. X-ray
diffraction and Thermogravimetric experiments are used to monitor the process
of water molecules accommodated in and removed from the crystal lattice. The
initial intercalation process takes place with two-water molecules
corresponding to y=0.6) inserted in a formula unit, followed by a group of four
(y=1.3) to form a cluster of Na(H2O)4. Thermogravimetric analysis suggests that
the deintercalation occurs with the removal of the water molecules one by one
from the hydrated cluster at elevated temperatures of approximately 50, 100,
200 and 300 C, respectively. Our investigations reveal that the hydration
process is dynamic and that water molecule inter- and deintercalation follow
different reaction paths in an irreversible way.
