  The specific heats of three samples of Na0.35CoO2,1.3H2O show an evolution of
the superconductivity, and its ultimate disappearance, with increasing sample
age. An overall increase in pair-breaking action, which occurs preferentially
in an electron band with a small energy gap, produces a shift in the relative
contributions of two electron bands to the superconducting condensation. The
similarity of the time scale for these changes to that recently reported for
structural changes in the CoO2 layers and the formation of O vacancies suggests
a relation between the two effects and an explanation for the strong sample
dependence of the properties of this material more generally. The onset of the
transition to the vortex state is independent of magnetic field, suggesting the
presence of unusually strong fluctuation effects.
