Vacancy controlled nanoscale cation ordering leads to high thermoelectric performance

Abstract

High thermoelectric performance is generally achieved in solid-solution alloyed or heavily doped semiconductors. The consequent atomic disorder has a trade-off in the thermoelectric figure of merit, zT: lattice thermal conductivity decreases with increasing disorder, but charge carrier mobility also reduces simultaneously. Herein, we demonstrate a strategy to optimize disorder rooted in the thermodynamic phase diagram and achieve a maximum zT = 2.3 in Ag vacant Ag_1−xSbTe₂. The formation of AgSbTe₂ in the Ag₂Te–Sb₂Te₃ pseudo-binary phase-space causes the precipitation of Ag₂Te impurities due to thermodynamic instabilities. We show that Ag vacancies partially remove the disorder from the cation sub-lattice along with the suppression of the secondary Ag₂Te impurities. Consequently, the electrical conductivity and power factor increase, while the concomitant formation of nanoscale superstructures (2–6 nm) due to local cation ordering reduces the lattice thermal conductivity. We obtained a high output power density of ∼268 mW cm⁻² for ΔT = 325 K in a double-leg thermoelectric device. Our demonstration provides a pathway to optimize intrinsic atomic disorder using vacancy formation and optimize thermoelectric performance.