Influence of S and Te substitutions on the thermoelectric properties of the cluster compound Ag3.8Mo9Se11
Résumé
We report on a detailed study of the influence of S and Te substitutions for Se on the thermoelectric properties of the cluster compound Ag3.8Mo9Se11. Two series of polycrystalline samples Ag3.8Mo9Se11-ySy (0 ≤ y ≤ 0.5) and Ag3.8Mo9Se11-zTez (0 ≤ z ≤ 0.5) were synthesized by a combination of conventional powder metallurgy technique followed by spark plasma sintering. Powder X-ray diffraction and wavelength dispersive spectroscopy indicate that both S and Te successfully substitute for Se and exhibit a low solubility limit of y ≈ z ≈ 0.5. Measurements of the thermoelectric properties between 2 and 800 K show that S and Te substitutions tend to lead to a more pronounced heavily-doped character with respect to Ag3.8Mo9Se11. The very low lattice thermal conductivity of these compounds (κL ≈ 0.5 W m−1 K−1) can be attributed to the large thermal displacement parameters of the Ag atoms. Despite the heavily-doped nature of the samples, the charge carriers conduct less heat than expected by the Wiedemann-Franz law resulting in significantly lower Lorenz numbers than predicted by the degenerate limit above 300 K. The combination of favourable electronic properties and low thermal conductivity leads to interesting dimensionless thermoelectric figures of merit ZT of 0.7 near 800 K. © 2017 Elsevier B.V.
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