Thermoelectric properties of Bi-based Zintl compounds Ca1−xYbxMg2Bi2†
Bi-based Zintl compounds, Ca1−xYbxMg2Bi2 with the structure of CaAl2Si2, have been successfully prepared by mechanical alloying followed by hot pressing. We found that the electrical conductivity, Seebeck coefficient, carrier concentration, and thermal conductivity can be adjusted by changing the Yb concentration. All Ca1−xYbxMg2Bi2 samples have low carrier concentrations (∼2.4 to 7.2 × 1018 cm−3) and high Hall mobility (∼119 to 153 cm2 V−1 s−1) near room temperature. The partial substitution of Ca with Yb causes structural disorders, which lowers the thermal conductivity. The highest figure of merit of ∼1.0 is observed in Ca0.5Yb0.5Mg2Bi2, and ∼0.8 in the unsubstituted CaMg2Bi2 and YbMg2Bi2. A small amount of free Bi was found in all the samples except YbMg2Bi2. By reducing the initial Bi concentration, we succeeded in obtaining phase pure samples in all compositions, which resulted in a much better thermoelectric performance, especially much higher (ZT)eng and a conversion efficiency near 11%. Such a high efficiency makes this material competitive with half-Heuslers and skutterudites.