Visualizing the Mg atoms in Mg3Sb2 thermoelectrics using advanced iDPC-STEM technique

Abstract

Mg3Sb2-based Zintl phase compounds have attracted considerable attention as promising thermoelectric materials in recent years. Mg defects are generally thought to play an important role in the n-type conduction of Mg3Sb2, and obtaining atomic occupancy of Mg and Sb is important for understanding the relationship of atomic defects and transport properties. However, the high angle annular dark-field (HAADF) and annular bright-field (ABF) in scanning transmission electron microscopy (STEM), which were commonly used to reveal the atomic information of other thermoelectric materials, failed to visualize the Mg atoms of Mg3Sb2, giving an illusion of the disappearance of Mg. In this work, the advanced integrated differential phase contrast (iDPC) technique is used, which clearly visualize the Mg and Sb atoms simultaneously in Mg3Sb2 single crystal. We found that Mg and Sb occupancy the real lattice sites without observing the interstitial Mg atoms. Our results highlight the importance of the iDPC technique in revealing the accurate atomic occupancy of light-element-based thermoelectrics, which will pave the way for understanding the microstructure-properties relationship.