In Situ TEM Studies of Nanostructured Thermoelectric Materials: An Application to Mg-Doped Zn₄ Sb₃ Alloy

We demonstrate an advanced approach using state of the art in situ transmission electron microscopy (TEM) to understand the interplay between nanostructures and thermoelectric (TE) properties of high-performance Mg-doped Zn₄ Sb₃ TE systems. By using the technique, microstructure and crystal evolutions of TE material have been dynamically captured as a function of temperature from 300 K to 573 K. On heating, we have clearly observed precipitation and growth of a Zn-rich secondary phase as nanoinclusions in the matrix of primary Zn₄ Sb₃ phase. Elemental mapping by STEM-EDX spectroscopy reveals enrichment of Zn in the secondary Zn₆ Sb₅ nanoinclusions during the thermal processing without decomposition. Such nanostructures strongly enhances phonon scattering, resulting in a decrease in the thermal conductivity leading to a zT value of 1.4 at 718 K.