Enhanced thermoelectric figure of merit in stannite-kuramite solid solutions Cu_2+xFe_1-xSnS_4-y (x = 0-1) with anisotropy lowering

In this Article, we elucidate the structural and thermoelectric properties of stannite-kuramite solid solutions, Cu_2+xFe_1-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.