  The infrared conductivity of NaxCoO2 is studied as a function of doping and
temperature for x between 0.5 and 1. Charge localization in CoO2 layers shows
up through a far-infrared peak (FIP) in the infrared conductivity which
coexists with a small Drude contribution. Long-range ordering at x = 0.5 is
confirmed to create a far-infrared gap, in addition to the FIP. At high x, the
formation of a Spin-Density Wave reported below 22 K dramatically shifts the
FIP to higher energy when x is incommensurate with the lattice, indicating an
abrupt deepening of the localizing potential. The in-plane E1u phonon lifetime
is shown to be sensitive to both "freezing" and ordering of the mobile Na+
ions. A comparison with the behavior of the FIP shows that such "freezing" is
not the only origin of charge localization in the CoO layers.
