In this Article, we elucidate the structural and thermoelectric properties of stannite-kuramite solid solutions, Cu2+xFe1-xSnS 4-y (x = 0-1), with sulfur defects (y) ≤ 0.4. Structural analysis revealed that anisotropy decreases and Cu/Sn disorder increases with an increase in x. The samples with x = 0.8-1 exhibit degenerate conduction, whereas the Seebeck coefficient (S) remains relatively high, S ≈ 100 μV K-1 for x = 0.8 at 300 K. Thermal conductivities (κ) of the solid solutions are in the range 10-3-10-2 W cm-1 K -1, which is close to the κ value of silicon dioxide. The dimensionless figure of merit (ZT) reaches 0.044 for x = 0.8 at 300 K. The ZT is enhanced significantly by an increase in temperature and is doubly larger than that of x = 0 at 300 K. These findings allow us to attain higher ZT values through optimization of chemical composition.
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