The role of electronegativity on the thermoelectric performance of GeTe - I-V-VI2 solid solutions

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.