Study on the Low-temperature Sintering of Thermoelectric Material CaMnO₃

It is Proposed to fabricate a thermoelectric generator with P－N structure by sintering the N－type CaMnO₃ together with the P－type Ca₃Co₄O₉ directly. It is necessary to sinter CaMnO₃ ceramic below the phase transition temperature of Ca₃Co₄O₉, 926 ℃. In this paper, CaMnO₃ powder wsa synthesized using the solid reaction method, then mixed with Bi₂O₃ and pressed into pellet. Sintering was carried out in air at 900℃ for 12h. The microstructure and thermoelectric properties of prepared sample were also investigated. As a result, there was no detectable secondary phase caused by additional Bi₂O₃; the average electrical conductivity increased and the approximate Seebeck coefficient decreased with increasing adding of Bi₂O₃; the average electrical conductivity and the approximate Seebeck coefficient increased with increasing temperature. The addition of Bi₂O₃ promoted the sintering process and decreased the sintering temperature, and effectively improved the thermoelectric properties of CaMnO₃ sample as well.