The role of electronegativity in the thermoelectric performance of GeTe–I–V–VI2 solid solutions

Abstract

GeTe-based solid solutions, exemplified by GeTe–AgSbTe₂ (TAGS), have revealed superior thermoelectric performance in the past few decades. Recently, alloying GeTe with other compounds in the I–V–VI₂ family has been employed as an effective means to further enhance figures-of-merit. The following work has systematically investigated the alloying effect of I–V–VI₂ compounds (I = Cu and Na; V = Sb and Bi; VI = Te) on the thermoelectric performance of GeTe. It has been found that all these alloying compounds can synergistically optimize the carrier concentration and reduce lattice thermal conductivity, which boosts the figure-of-merit for GeTe. More importantly, this work has demonstrated that the electronegativity difference between group I elements and Ge determines the alloy scattering potential and thus carrier mobility. As a result, compounds with nominal compositions of (GeTe)_0.92(NaSbTe₂)_0.08 and (GeTe)_0.92(CuSbTe₂)_0.08 have achieved zTs of ∼1.30 and 1.58 at 773 K, respectively. Our work highlights the importance of electronegativity in thermoelectric GeTe-based solid solutions and thus provides valuable guidance for designing novel thermoelectric materials.