Thermoelectric Properties of Ca(3)Co(2−x)Mn(x)O(6) (x = 0.05, 0.2, 0.5, 0.75, and 1)

High-temperature instability of the Ca(3)Co(4−y)O(9+δ) and CaMnO(3−δ) direct p-n junction causing the formation of Ca(3)Co(2−x)Mn(x)O(6) has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca(3)Co(2−x)Mn(x)O(6) with x = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca(3)CoMnO(6) (x = 1) demonstrated a large positive Seebeck coefficient of 668 μV/K at 900 °C, but very low electrical conductivity. Materials with compositions with x < 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 ± 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1−x. The conductivity reached about 11 S·cm(−1) at 900 °C for x = 0.05. The material Ca(3)Co(1.8)Mn(0.2)O(6) (x = 0.2) yielded a maximum zT of 0.021 at 900 °C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca(3)Co(2−x)Mn(x)O(6) layers between Ca(3)Co(4−y)O(9+δ) and CaMnO(3−δ) open for new geometries and designs of oxide-based thermoelectric generators.