Effect of the Addition of Copper Particles on the Thermoelectric Properties of the Ca3Co4O9+δ Ceramics Produced by Two-Step Sintering

Composite thermoelectric materials based on layered calcium cobaltite Ca3Co4O9 + delta doped with copper particles were synthesized by two-step sintering, and their microstructure, and electrotransport and thermoelectric properties were studied. It was determined that the introduction of copper particles into the ceramics improves their sinterability at moderate sintering temperatures ( T-sint <= 1273 K), leading to a decrease in the porosity of the samples and an increase in their electrical conductivity and power factor, whereas the oxidation of copper to less conductive copper(II) oxide significantly decreases the electrical conductivity and power factor of the ceramics sintered at elevated temperatures (T-sint >= 1373 K). The power factor is maximum for the Ca3Co4O9 + delta + 3 wt % Cu ceramic sintered at 1273 K (335 mu W/(m K-2) at a temperature of 1100 K), which is by a factor of 2.3 higher than the power factor of the base material Ca3Co4O9 + delta with the same thermal history (145 mu W/(m K-2) at 1100 K) and more than 3 times higher than the power factor of the Ca3-Co4O9+delta ceramic synthesized by the conventional solid-phase method.