Strontium ordering, structural modulation in layered hexagonal Sr xCoO2 and physical properties of Sr0.35CoO2

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. The magnetic susceptibility of the sample increases with decreasing temperature, showing a Curie-Weiss behavior in high temperatures. Transmission electron microscopy observations reveal the presence of two superstructures arising respectively from the intercalated Sr-ordering (a compositional modulation) with q 1 = a*/3 + b*/3 and a periodic structural distortion (a transverse structural modulation) with q 2 = a*/2