Thermoelectric properties in Ca₃Co_4−xMn_xO_y ceramics

Abstract

Ca₃Co_4−xMn_xO_y 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 ∼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°C, ∼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.

Keywords:

• Ceramics
• Cobaltites
• Electrical properties
• Thermopower