Thermoelectric Properties and Electronic Structure of the Zintl‐Phase Sr3AlSb3

Abstract

The Zintl-phase Sr3 AlSb3 , which contains relatively earth-abundant and nontoxic elements, has many of the features that are necessary for good thermoelectric performance. The structure of Sr3 AlSb3 is characterized by isolated anionic units formed from pairs of edge-sharing tetrahedra. Its structure is distinct from previously studied chain-forming structures, Ca3 AlSb3 and Sr3 GaSb3 , both of which are known to be good thermoelectric materials. DFT predicts a relatively large band gap in Sr3 AlSb3 (Eg ≈1 eV) and a heavier band mass than that found in other chain-forming A3 MSb3 phases (A=Sr, Ca; M=Al, Ga). High-temperature transport measurements reveal both high resistivity and high Seebeck coefficients in Sr3 AlSb3 , which is consistent with the large calculated band gap. The thermal conductivity of Sr3 AlSb3 is found to be extremely low (≈ 0.55 W mK(-1) at 1000 K) due to the large, complex unit cell (56 atoms per primitive cell). Although the figure of merit (zT) has not been optimized in the current study, a single parabolic band model suggests that, when successfully doped, zT≈ 0.3 may be obtained at 600 K; this makes Sr3 AlSb3 promising for waste-heat recovery applications. Doping with Zn(2+) on the Al(3+) site has been attempted, but does not lead to the expected increase in carrier concentration.