As attractive thermoelectric oxides, Ca3Co4O9-based materials have been intensively studied
for their
applications in recent years. However, their thermoelectric performance
is enormously limited due to the contradiction of electrical resistivity
and thermal conductivity. Herein, BaFe12O19 nanospheres
were introduced into the Ca3Co4O9 matrix. The metallic Ag, ferrites, and matrix phase survived together,
and a high density of nanoscale BaFe12O19 precipitation
was observed. The reduction of work function could lead to band bending
and form an interface potential due to the electro-thermo-magnetic
effect contributing to the hole migration. As a result, a huge ZT
value of 0.51 for the 8 wt % BaFe12O19/Ca3Co4O9 nanocomposites was obtained at
1073 K, accompanied by a low electrical resistivity of 6.7 mΩ·cm
and a high Seebeck coefficient of 217.5 μV/K. In addition, a
significant reduction of thermal conductivity (1.11 W/(m·K))
occurred, which was due to the nanoscale ferromagnetic phase effectively
scattering the mid- and short-wavelength heat-carrying phonons. The
synergistic enhancement of thermoelectric performance confirmed that
the electro-thermo-magnetic effect is an effective way to solve the
challenging problem of performance deterioration in oxide thermoelectric
materials.