  Layered Sr0.35CoO2 has been synthesized by means of an ion exchange reaction
from Na0.7CoO2. Resistivity measurements show that this material can be either
metallic or semiconducting depending on the annealing conditions. Magnetic
susceptibility, following the Curie-Weiss law, increases with lowering
temperature and shows a small anomalous kink at around 30 K.
Transmission-electron-microscopy observations reveal the presence of two
superstructures arising respectively from the intercalated Sr-ordering (a
compositional modulation) with q1 = a* / 3 + b* / 3 and a periodic structural
distortion (a transverse structural modulation) with q2 = a* / 2.
