Suppressing Ag₂Te nanoprecipitates for enhancing thermoelectric efficiency of AgSbTe₂

Thermoelectrics are a class of materials that provide interconversion between heat and electricity, with desirable traits such as low thermal conductivity and low electrical resistivity. AgSbTe₂ has emerged as one of the leading materials in recent years due to its ultra-low thermal conductivity. However, one major hindrance in undoped AgSbTe₂ is its high electrical resistivity and low Seebeck coefficient due to the presence of Ag₂Te nanoprecipitates. In this work, we leverage on the combination of an off-stoichiometric composition and a non-equilibrium process to simultaneously enhance the properties of AgSbTe₂ and its thermoelectric device performance. Microscopically, the Ag₂Te-deficient starting composition combined with a non-equilibrium thermal process suppresses the Ag₂Te nanoprecipitates in the material. In addition, it is evident from the density functional theory (DFT) electronic structure that Ag₂Te deficiency results in a smaller lattice and higher density-of-states near the Fermi level, which simultaneously lower the electrical resistivity and increase the Seebeck coefficient. As a result, zT as high as 1.7 was achieved at 573 K. Additionally, when combined with a high room temperature zT of 0.75, a power conversion efficiency of 7.3% was achieved at a ΔT of 290 K. Crucially, the strategy in this work can inspire application in other ABX₂ material systems to achieve improved thermoelectric performances.