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

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. Yb14-xRExMnSb11 (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)(4)Sb-3 is apparent after synthesis. After consolidation and measurement, (Yb, RE)Sb and (Yb,RE)(11)Sb-10 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 Yb14-xRExMnSb11 is x = 0.55, however, (Yb,RE)(11)Sb-10 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. Yb13.82Pr0.18Mn1.01Sb10.9(has the best maximum zT value of similar to 1.2 at 1275 K, while Yb13.80Sm0.19Mn1.00Sb11.02 has its maximum zT of similar to 1.0 at 1275 K, respectively, similar to 45% and similar to 30% higher than Yb14MnSb11 prepared in the same manner.