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Keywords:

  • density functional calculations;
  • electronic transport;
  • thermal transport;
  • zintl phases

Abstract

The Zintl-phase Sr3AlSb3, which contains relatively earth-abundant and nontoxic elements, has many of the features that are necessary for good thermoelectric performance. The structure of Sr3AlSb3 is characterized by isolated anionic units formed from pairs of edge-sharing tetrahedra. Its structure is distinct from previously studied chain-forming structures, Ca3AlSb3 and Sr3GaSb3, both of which are known to be good thermoelectric materials. DFT predicts a relatively large band gap in Sr3AlSb3 (Eg≈1 eV) and a heavier band mass than that found in other chain-forming A3MSb3 phases (A=Sr, Ca; M=Al, Ga). High-temperature transport measurements reveal both high resistivity and high Seebeck coefficients in Sr3AlSb3, which is consistent with the large calculated band gap. The thermal conductivity of Sr3AlSb3 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 Sr3AlSb3 promising for waste-heat recovery applications. Doping with Zn2+ on the Al3+ site has been attempted, but does not lead to the expected increase in carrier concentration.