Thermoelectric properties in single crystals of Ca-Co-O system

Single crystals of Co-based layered oxide, Ca/sub 3/Co/sub 4/O/sub 9/ (Co349), were grown using a flux method and their electrical and thermal properties were investigated. Values of thermoelectric power S are quite large above 773 K and reach almost 250 /spl mu/V/spl middot/K/sup -1/ at 973 K, and their thermal conductivity /spl kappa/ is nearly 3 W/spl middot/m/sup -1//spl middot/K/sup -1/, as determined by mathematical extrapolation. The relatively low /spl kappa/ is likely the result of a misfit structure between the CoO/sub 2/ layers and the Ca/sub 2/CoO/sub 3/ slabs. The figure of merit for (Ca,Sr,Bi)/sub 2/Co/sub 2/O/sub 5+0/ with Co349 structure can be estimated as greater than 1.1. Co349 should be a promising material for thermoelectric power generation.