Rapid microwave‐assisted calcination and doping‐driven enhancement of n‐type CaMnO ₃ ‐based thermoelectrics

Abstract Ca 1‐ x Y x MnO 3 and Ca 1‐ x Y x Mn 1‐ y Nb y O 3 (0 ≤ x , y ≤ 0.07) thermoelectric ceramics were fabricated via microwave‐assisted calcination followed by conventional sintering. The effects of substituting Ca with Y and Mn with Nb on the microstructure and power factor ( PF ) were systematically investigated. The results indicate that the crystal structure of CaMnO 3 remains unchanged upon doping. Electrical conductivity increases, while the absolute value of the Seebeck coefficient decreases with increasing dopant concentration in both series of compounds. Consequently, the PF for Ca 1‐ x Y x MnO 3 increases continuously within the range of doping amount (0 ≤ x ≤ 0.07), whereas that of Ca 1‐ x Y x Mn 1‐ y Nb y O 3 initially increases with x = y ≤ 0.02, and then decreases for 0.02 < x = y ≤ 0.06. In addition, the PF increases for all samples as the temperature increases. The maximum PF achieved are 127 µW m −1 K −2 for Ca 1‐ x Y x MnO 3 ( x = 0.07), and 154 µW m −1 K −2 for Ca 1‐ x Y x Mn 1‐ y Nb y O 3 ( x = y = 0.02). These results demonstrate that the co‐doping of CaMnO 3 with Y/Nb is more effective in improving the electronic transport characteristics than single Y‐doping.