High temperature transport and thermoelectric properties of Ca3−xErxCo4O9+δ

Ca3−xErxCo4O9+δ (x=0, 0.05, 0.15, 0.3 and 0.5) samples were prepared using a sol–gel method followed by hot-pressing sintering technique. Powder X-ray diffraction analysis showed the single-phases of Ca3−xErxCo4O9+δ were obtained up to x=0.3 and the crystallinity of the samples decreased with increasing Er-doping amount. The high-temperature (323–1073 K) thermoelectric properties of the samples were investigated. The substitution of Er3+ for Ca2+ resulted in the decrease of electrical conductivity, thermal conductivity and the increase of Seebeck coefficient for all the samples except the x=0.05 one. The dimensionless figure of merit ZT reached 0.28 at 1073 K for Ca2.7Er0.3Co4O9+δ, indicating the thermoelectric properties of CaCo4O9+δ can be enhanced by doping Er in the system.

Research Highlights
► Thermoelectric materials Ca3−xErxCo4O9+δ (x=0–0.5) were synthesized by sol–gel process.
► High high-textured ceramic samples were fabricated by the hot-pressing method.
► The effect of Er3+ doping on thermoelectric property and transport mechanism were discussed.
► The results indicated that Ca3−xErxCo4O9+δ are potential oxides for thermoelectric applications.