Intrinsic nanostructure induced ultralow thermal conductivity yields enhanced thermoelectric performance in Zintl phase Eu2ZnSb2.

The Zintl thermoelectric phase Eu2ZnSb2 has a remarkable combination of high mobility and low thermal conductivity that leads to good thermoelectric performance. The key feature of this compound is a crystal structure that has a Zn-site with a 50% occupancy. Here we use comparison of experimental thermal conductivity measurements and first principles thermal conductivity calculations to characterize the thermal conductivity reduction. We find that partial ordering, characterized by local order, but Zn-site disorder on longer scales, leads to an intrinsic nanostructuring induced reduction in thermal conductivity, while retaining electron mobility. This provides a direction for identifying Zintl compounds with ultralow lattice thermal conductivity and good electrical conductivity. Understanding mechanisms for obtaining low thermal conductivity without degraded electrical properties remains a challenge. Here, the authors reveal a mechanism for thermal conductivity reduction in a Zintl phase thermoelectric based on length scales for disorder in Eu2ZnSb2.