  Motivated by recently reported experimental phase diagrams, we study the
effects of CoO6 distortion on the electronic structure in NaxCoO2.yH2O. We
construct the multiband tight-binding model by employing the LDA result.
Analyzing this model, we show the deformation of band dispersions and
Fermi-surface topology as functions of CoO2-layer thickness. Considering these
results together with previous theoretical ones, we propose a possible
schematic phase diagram with three successive phases: the extended s-wave
superconductivity (SC), the magnetic order, and the spin-triplet SC phases when
the Co valence number s is +3.4. A phase diagram with only one phase of
spin-triplet SC is also proposed for the s=+3.5 case.
