Unlocking the thermoelectric potential of the CaAlSb structure type.

YbMnSb and YbMgSb are among the best p-type high-temperature (>1200 K) thermoelectric materials, yet other compounds of this CaAlSb structure type have not matched their stability and efficiency. First-principles computations show that the features in the electronic structures that have been identified to lead to high thermoelectric performances are present in YbZnSb, which has been presumed to be a poor thermoelectric material. We show that the previously reported low power factor of YbZnSb is not intrinsic and is due to the presence of a YbZnSb impurity uniquely present in the Zn system. Phase-pure YbZnSb synthesized through a route avoiding the impurity formation reveals its exceptional high-temperature thermoelectric properties, reaching a peak of 1.2 at 1175 K. Beyond YbZnSb, the favorable band structure features for thermoelectric performance are universal among the CaAlSb structure type, opening the possibility for high-performance thermoelectric materials.