Rapid microwave-assisted calcination and doping-driven enhancement of n-type CaMnO3-based thermoelectrics

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.