The effect of light rare earth element substitution in Yb14MnSb11 on thermoelectric properties

Abstract

After the discovery of Yb₁₄MnSb₁₁ as an outstanding p-type thermoelectric material for high temperatures (≥900 K), site substitution of other elements has been proven to be an effective method to further optimize the thermoelectric properties. Yb_14−xRE_xMnSb₁₁ (RE = Pr and Sm, 0 < x < 0.55) compounds were prepared by powder metallurgy to study their thermoelectric properties. According to powder X-ray diffraction, these samples are iso-structural with Yb₁₄MnSb₁₁ and when more than 5% RE is used in the synthesis the presence of (Yb,RE)₄Sb₃ is apparent after synthesis. After consolidation and measurement, (Yb,RE)Sb and (Yb,RE)₁₁Sb₁₀ appear in the powder X-ray diffraction patterns. Electron microprobe analysis results show that consolidated pellets have small (Yb,RE)Sb domains and that the maximum amount of RE in Yb_14−xRE_xMnSb₁₁ is x = 0.55, however, (Yb,RE)₁₁Sb₁₀ cannot be distinguished by electron microprobe analysis. By replacing Yb²⁺ with RE³⁺, one extra electron is introduced into Yb₁₄MnSb₁₁ and the carrier concentration is adjusted. Thermoelectric performance from room temperature to 1275 K was evaluated through transport and thermal conductivity measurements. The measurement shows that Seebeck coefficients initially increase and then remain stable and that electrical resistivity increases with substitutions. Thermal conductivity is slightly reduced. Substitution of Pr and Sm leads to enhanced zT. Yb_13.82Pr_0.18Mn_1.01Sb_10.99 has the best maximum zT value of ∼1.2 at 1275 K, while Yb_13.80Sm_0.19Mn_1.00Sb_11.02 has its maximum zT of ∼1.0 at 1275 K, respectively, ∼45% and ∼30% higher than Yb₁₄MnSb₁₁ prepared in the same manner.