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

Single crystals of (Ca2CoO3)(0.7)CoO2 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 (5x10x0.05 mm(3)). At 973 K, thermoelectric power S and electrical resistivity rho of the specimens are approximate to240 muV K-1 and approximate to2.3x10(-5) Omega m, respectively, and their thermal conductivity kappa is nearly 3 W m1 K-1, as determined by mathematical extrapolation. The figure of merit ZT=(ST)-T-2/rhokappa derived therefrom is approximate to0.87 at 973 K. The relatively low kappa is likely the result of a misfit structure between the CoO2 layer and the Ca2CoO3 slab. (C) 2003 American Institute of Physics.