Thermoelectric properties in Ca3Co4-xMnxOy ceramics

Ca3Co4-xMnxOy polycrystalline thermoelectric ceramics with small amounts of Mn have been prepared by the classical solid state method. X-ray diffraction data have shown that Ca3Co4O9 is the major phase, with small amounts of the Ca3Co2O6 one. Moreover, they show that the Mn has been incorporated into these two phases. Electrical resistivity decreases, compared with the values for undoped samples, with Mn content until a minimum for the 0.03 doped ones, increasing for higher Mn substitution. Seebeck coefficient does not change in all the measured temperature range, independently of Mn content. The improvement in electrical resistivity leads similar to 30% higher power factor values for the 0.03 Mn doped samples than that obtained in the undoped ones. The maximum power factor at 800 degrees C, similar to 0.28 mW K-2 m(-1), is close to that obtained in much higher density samples, clearly indicating the good thermoelectric properties of these samples.