Electrical and thermal properties of single-crystalline (Ca2CoO3)0.7CoO2 with a Ca3Co4O9 structure

Single crystals of (Ca2CoO3)0.7CoO2 were grown using a modified strontium chloride flux technique, and their electrical and thermal properties were determined. Growth conditions were established for obtaining plate-like single crystals of a relatively large size (5×10×0.05 mm3). At 973 K, thermoelectric power S and electrical resistivity ρ of the specimens are ≈240 μV K−1 and ≈2.3×10−5 Ω m, respectively, and their thermal conductivity κ is nearly 3 W m1 K−1, as determined by mathematical extrapolation. The figure of merit ZT=S2T/ρκ derived therefrom is ≈0.87 at 973 K. The relatively low κ is likely the result of a misfit structure between the CoO2 layer and the Ca2CoO3 slab.