Ge-Induced Cation Ordering for Enhanced Thermoelectric Performance in AgSbTe2

Abstract

Waste heat recovery through thermoelectric conversion is a promising route toward sustainable energy utilization. AgSbTe₂ is a notable mid-temperature thermoelectric material owing to its inherently low thermal conductivity. However, its performance is limited by Ag₂Te precipitates and cation disorder. In this study, Ge doping is introduced as an effective approach to promote Ag/Sb cation ordering and suppress Ag₂Te formation, as evidenced by synchrotron XRD, pair distribution function (PDF) refinements, and TEM/SAED analyses. The improved structural coherence mitigates grain-boundary scattering and optimizes carrier transport, leading to enhanced parameters such as weighted mobility (μ_W), quality factor (B), and electronic transport coefficient (σ_E0). Hall measurements confirm an increase in carrier concentration alongside an optimized effective mass, indicating partial decoupling of the Seebeck coefficient and electrical conductivity. The optimized composition achieves a nearly temperature-independent power factor of 1.15 mWm^-1K^-1 between 300 – 675 K, with a peak zT of 1.31 at 673 K and an average ZT of 0.97 across the same range. A single-leg device generates 25 mW output power (ΔT = 370 K), underscoring AgSb_0.94Ge_0.06Te₂’s promise for practical mid-temperature energy conversion. Single parabolic band (SPB) analysis suggests further enhancement of zT is possible through tailored thermal conductivity reduction.