Abstract
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 1000 K, 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 non-monotonic 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.
Highlights
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
Cu2−xSe and Cu2−xS compounds show high thermoelectric performance, even though there still are some issues that need to be resolved before practical applications can be considered[16]
We investigated sulphur doping effects on the thermoelectric properties of the Cu2−xSe system based on the following considerations: (1) At high temperature, α-Cu2S has the same crystal structure as β-Cu2Se, and sulphur should be very easy to substitute into the lattice and replace Se. (2) S2− has the same valence as Se2−, which should result in good electron balance in this system
Summary
The temperature dependence of the dimensionless figure-of-merit shown in Fig. 4d reveals that the selenium doping does not improve the overall thermoelectric performance of the Cu1.98S system, with the Cu1.98S having the highest zT values around 0.86 at 850 K among all the orthorhombic structured samples, even though certain thermoelectric parameter is enhanced. This observation is in good agreement with our previous reports on the tellurium and iodine doped Cu2−xSe system[21], which provides further evidence of the distinctiveness of superionic thermoelectric materials in comparison with the conventional thermoelectric materials. Has non-monotonic effects on the DOS and m*, with the Cu15S6Se2 and Cu15S4Se4 having the highest DOS value, ~0.69 states/eV/f.u., and the highest m*, ~0.336 me, respectively
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