Thermoelectric properties and electronic structure of the Zintl phase Sr₅In₂Sb₆ and the Ca_(5−x)SrxIn₂Sb₆ solid solution

Abstract

The Zintl phase Sr₅In₂Sb₆ is isostructural with Ca₅In₂Sb₆—a promising thermoelectric material with a peak zT of 0.7 when the carrier concentration is optimized by doping. Density functional calculations for Sr₅In₂Sb₆ reveal a decreased energy gap and decreased valence band effective mass relative to the Ca analog. Chemical bonding analysis using the electron localizability indicator was found to support the Zintl bonding scheme for this structure type. High temperature transport measurements of the complete Ca_(5−x)SrxIn₂Sb₆ solid solution were used to investigate the influence of the cation site on the electronic and thermal properties of A₅In₂Sb₆ compounds. Sr was shown to be fully miscible on the Ca site. The higher density of the Sr analog leads to a slight reduction in lattice thermal conductivity relative to Ca₅In₂Sb₆, and, as expected, the solid solution samples have significantly reduced lattice thermal conductivities relative to the end member compounds.

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