Electro-Thermo-Magnetic\nEffect-Induced Large Thermoelectric\nPerformance of Calcium Cobaltite Nanocomposites

As attractive thermoelectric oxides, Ca<sub>3</sub>Co<sub>4</sub>O<sub>9</sub>-based materials have been intensively studied\nfor their\napplications in recent years. However, their thermoelectric performance\nis enormously limited due to the contradiction of electrical resistivity\nand thermal conductivity. Herein, BaFe<sub>12</sub>O<sub>19</sub> nanospheres\nwere introduced into the Ca<sub>3</sub>Co<sub>4</sub>O<sub>9</sub> matrix. The metallic Ag, ferrites, and matrix phase survived together,\nand a high density of nanoscale BaFe<sub>12</sub>O<sub>19</sub> precipitation\nwas observed. The reduction of work function could lead to band bending\nand form an interface potential due to the electro-thermo-magnetic\neffect contributing to the hole migration. As a result, a huge ZT\nvalue of 0.51 for the 8 wt % BaFe<sub>12</sub>O<sub>19</sub>/Ca<sub>3</sub>Co<sub>4</sub>O<sub>9</sub> nanocomposites was obtained at\n1073 K, accompanied by a low electrical resistivity of 6.7 mΩ·cm\nand a high Seebeck coefficient of 217.5 μV/K. In addition, a\nsignificant reduction of thermal conductivity (1.11 W/(m·K))\noccurred, which was due to the nanoscale ferromagnetic phase effectively\nscattering the mid- and short-wavelength heat-carrying phonons. The\nsynergistic enhancement of thermoelectric performance confirmed that\nthe electro-thermo-magnetic effect is an effective way to solve the\nchallenging problem of performance deterioration in oxide thermoelectric\nmaterials.