Electronic structure and transport in thermoelectric compounds AZn(2)Sb(2) (A = Sr, Ca, Yb, Eu)

TheAZn(2)Sb(2)(P (3) over bar m1, A = Ca, Sr, Eu, Yb) class of Zintl compounds has shown high thermoelectric efficiency (zT similar to 1) and is an appealing system for the development of Zintl structure-property relationships. High temperature transport measurements have previously been conducted for all known compositions except for SrZn2Sb2; here we characterize polycrystalline SrZn2Sb2 to 723 K and review the transport behavior of the other compounds in this class. Consistent with the known AZn(2)Sb(2) compounds, SrZn2Sb2 is found to be a hole-doped semiconductor with a thermal band gap similar to 0.27 eV. The Seebeck coefficients of the AZn(2)Sb(2) compounds are found to be described by similar effective mass (m* similar to 0.6 me). Electronic structure calculations reveal similar m* is due to antimony p states at the valence band edge which are largely unaffected by the choice of A-site species. However, the choice of A-site element has a dramatic effect on the hole mobility, with the room temperature mobility of the rare earth-based compositions approximately double that found for Ca and Sr on the A site. This difference in mobility is examined in the context of electronic structure calculations.