Synthesis and high temperature thermoelectric properties of calcium and cerium double-filled skutterudites Ca_0.1Ce_xCo ₄Sb₁₂

The thermoelectric properties of double-filled skutterudites Ca _0.1Ce_xCo₄Sb₁₂ (x = 0.05, 0.10 and 0.15) were investigated at temperatures ranging from 300 to 775 K. The results showed that the addition of Ca and Ce as filler atoms into CoSb₃ led to a substantial decrease in lattice thermal conductivity. The minimum lattice thermal conductivity of 2.76 W K^-1 m^-1 was observed in the sample Ca_0.1Ce_0.15Co₄Sb₁₂ at 323 K. This is a 69% reduction as compared with pristine CoSb_3. Moreover, filling the voids of the skutterudite crystal lattice with Ca and Ce atoms led to a transition from semiconducting-like behaviour (i.e. dρ/dT < 0) to metallic behaviour (i.e. dρ/dT > 0) as well as a change in the sign of the Seebeck coefficient. The highest dimensionless figure of merit, ZT, was obtained for the sample Ca_0.1Ce_0.15Co₄Sb ₁₂. Specifically, it reached ZT of 0.83 at 677 K, which is double that of single-filled Ca_0.2Co₄Sb₁₂ reported in the literature.