Effect of Copper Additions on the Thermoelectric Properties of a Layered Calcium Cobaltite Prepared by Hot Pressing

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

“…The activation energy of the electrical conductivity of the samples that was calculated in the temperature range 700−1100 K varies within the range 0.086−0.117 eV (except the Ca 3 Co 4 O 9 + δ + x wt % Cu composites sintered at 1373 K and the Ca 3 Co 4 O 9 + δ + 3 wt % Cu material sintered at 1473 K, Table 1). This is close to the published [13,[20][21][22]28] values for Ca 3 Co 4 O 9 + δ composites and suggests a common mechanism of electrical conductivity, which is determined by the charge transfer in the matrix phase, layered calcium cobaltite.…”

“…Hence, it follows that the introduction of copper particles to the Ca 3 Co 4 O 9 + δ ceramics with subsequent two-step sintering gives coarser-grained ceramics. Interestingly, the modification of the hot-pressed Ca 3 Co 4 O 9 + δ ceramics with copper nanoparticles gave the opposite result, namely, a decrease in the grain size of the ceramics [22]. The plate size of the ceramics increased with increasing its sintering temperature from ~2-5 μm for the Ca 3 Co 4 O 9 + δ + 3 wt % Cu sample sintered at 1173 K to ~5-10 μm for the material that had the same composition but was sintered at higher temperatures (1273-1473 K) (Figs.…”

“…Theoretical density ρ t (g/cm 3 ), apparent density ρ a (g/cm 3 ), porosity Π (%), electrotransport parameters (E A,⊥ , E A,|| , meV), and thermoelectric characteristics (σ 1100,⊥ , S/cm; S 1100,⊥ , μV/K; P 1100, ⊥ , μW/(m K 2 )) of the Ca 3 Co 4 O 9 + δ + x wt % Cu composites sintered at various temperatures (T sint , K) [3-13, 22, 27]. S of the Ca 3 Co 4 O 9 + δ + x wt % Cu composites is typically higher than that of the Ca 3 Co 4 O 9 + δ matrix samples, which is due to the phase heterogeneity of the composites [5,13,22,23].…”

“…oxides [15,16], semiconductors [17], noble metals (Ag) [3,18,19], and transition metals (Fe, Co, Ni, Cu) [20][21][22] and also to create phase heterogeneity in them by their self-doping, i.e., using of the initial reaction mixture with the composition beyond the homogeneity region of the compound Ca 3 Co 4 O 9 + δ [13,23]. Such a modification of ceramics significantly increases their electrical conductivity σ [3,[16][17][18][19]22] or Seebeck coefficient S [13,23], and, as a result, improves such functional (thermoelectric) characteristics of the ceramics as the power factor P = σS 2 and the dimensionless thermoelectric figure of merit ZT = σS 2 T/λ = PT/λ, where T is absolute temperature.…”

“…The introduction of Fe, Co, or Ni particles to Ca 3 Co 4 O 9 + δ [20,21] considerably decreased the porosity of the ceramics, but did not lead to a essential improvement of their electrotransport and functional properties. We previously determined [22] that the addition of Cu nanoparticles to hot-pressed Ca 3 Co 4 O 9 + δ ceramics substantially decreases their porosity and increases their electrical conductivity and power factor of the produced nanocomposites.…”