  Semiconducting half- and, to a lesser extent, full-Heusler compounds are
promising thermoelectric materials due to their compelling electronic
properties with large power factors. However, intrinsically high thermal
conductivity resulting in a limited thermoelectric efficiency has so far
impeded their widespread use in practical applications. Here, we report the
computational discovery of a class of hitherto unknown stable semiconducting
full-Heusler compounds with ten valence electrons ($X_2YZ$, $X$=Ca, Sr, and Ba;
$Y$= Au and Hg; $Z$=Sn, Pb, As, Sb, and Bi) through high-throughput $ab-initio$
screening. These new compounds exhibit ultralow lattice thermal conductivity
$\kappa_{\text{L}}$ close to the theoretical minimum due to strong anharmonic
rattling of the heavy noble metals, while preserving high power factors, thus
resulting in excellent phonon-glass electron-crystal materials.
