Boosting the Thermoelectric Performance of Calcium Cobaltite Composites through Structural Defect Engineering.

Misfit-layered Ca3Co4O9 as a p-type semiconductor is difficult to commercialize because of its relatively poor performance. Here, Ca2.7-xLaxAg0.3Co4O9/Ag composites prepared by spark plasma sintering were systematically investigated in terms of La3+ dopant levels and nano-sized Ag compacts. Multiscale microstructures of stacking fault, dislocation, and oxygen vacancy-linked defects could be recognized as an effective strategy for tuning the transport of charge carriers and phonon scattering. An increasing concentration of charge carriers was caused by the introduction of nano-sized Ag particles at the grain boundary. The multiscale structural defects served as phonon scattering centers to reduce the thermal conductivity. Finally, the Ca2.61La0.09Ag0.3Co4O9/Ag sample exhibited a maximum ZT of 0.35 at 1073 K. The results suggest that the interplay of structural defects provides an impetus for a huge improvement in thermoelectric performance.