Thermoelectric properties of the Bi- and Na- substituted Ca3Co4O9 system

Bi- and Na-substituted Ca3Co4O9 polycrystalline samples have been prepared using a hot-pressing technique and their thermoelectric properties were carefully studied in air from room temperature to 1000 K. The substitutions of Bi3+ and Na+ for Ca2+, as well as Bi3+ and Na+ double substitution, cause both the electrical conductivity (sigma) and thermoelectric power (S) to increase simultaneously. The double substitution has also been demonstrated to be effective to decrease the thermal conductivity (kappa). The dimensionless figure of merit ZT (=S(2)sigmaT/kappa) reaches 0.32 at 1000 K in the double-substituted sample. (C) 2002 American Institute of Physics.