Investigating the Role of Vacancies on the Thermoelectric Properties of EuCuSb‐Eu₂ZnSb₂ Alloys

Abstract

AMX compounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on the M‐site in the planar MX‐layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu1−xZn0.5xSb solid solution. The transition from a fully‐occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn0.5Sb) leads to non‐linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on the M and Sb‐sites, and significant lattice softening. This, combined with a rapid increase in point defect scattering, causes the lattice thermal conductivity to decrease from 3 to 0.5 W mK−1 at 300 K. The effect of vacancies on the electronic properties is more nuanced; we see a small increase in effective mass, large increase in band gap, and decrease in carrier concentration. Ultimately, the maximum zT increases from 0.09 to 0.7 as we go from EuCuSb to EuZn0.5Sb.

Alloying-Induced Structural Transition in the Promising Thermoelectric Compound CaAgSb

“…AMX compounds form several closely related crystal structures, making them an excellent space to study structure–property relationships. Of the various crystal structures, the cubic half-Heusler structure is the most extensively studied. , The most common Zintl AMX structure is that of ZrBeSi, which forms a covalently bonded hexagonal M–X sublattice, separated by A cations. , In addition to TE applications, the hexagonal AMX compounds like SrAgSb, EuCuSb, Eu 2 ZnSb 2 , etc. are being extensively studied as potential topological insulators , and frustrated magnets …”

“… 16 , 17 The most common Zintl AMX structure is that of ZrBeSi, which forms a covalently bonded hexagonal M–X sublattice, separated by A cations. 18 , 19 In addition to TE applications, the hexagonal AMX compounds like SrAgSb, 20 EuCuSb, 21 Eu 2 ZnSb 2 , 22 etc. are being extensively studied as potential topological insulators 23 , 24 and frustrated magnets.…”

High thermoelectric performance in p-type ZnSb upon increasing Zn vacancies: an experimental and theoretical study

“…34 In this context, intrinsically occurring vacancies in semiconductors, typically point defects that are seen to be thermodynamically stable, generally contribute to more, charge carriers and heat-carrying phonon scattering centres, thereby assisting in altering the electrical and thermal transport properties. In recent years, thermoelectric properties of various class of materials, such as GeTe, 35 PbSe, 36 EuCuSb, 37 and AgSbTe 2 (ref. 38) have been tremendously enhanced by carefully engineering the vacancies.…”