Abstract
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Sulphur doping effects on the crystal structures, thermoelectric properties, density-of-states, and
effective mass in Cu1.98SxSe1−x were studied based on the electrical and thermal transport property
measurements, and first-principles calculations. The X-ray diffraction patterns and Rietveld refinements
indicate that room temperature Cu1.98SxSe1−x (x=0, 0.02, 0.08, 0.16) and Cu1.98SxSe1−x (x=0.8, 0.9,
1.0) have the same crystal structure as monoclinic-Cu2Se and orthorhombic-Cu2S, respectively. Sulphur
doping can greatly enhance zT values when x is in the range of 0.8≤×≤1.0. Furthermore, all doped
samples show stable thermoelectric compatibility factors over a broad temperature range from 700
to 1000K, which could greatly benefit their practical applications. First-principles calculations indicate
that both the electron density-of-sates and the effective mass for all the compounds exhibit nonmonotonic
sulphur doping dependence. It is concluded that the overall thermoelectric performance of
the Cu1.98SxSe1−x system is mainly correlated with the electron effective mass and the density-of-states.