Nanostructured Cu12+Sb4S13 tetrahedrites prepared by solvothermal synthesis in 1-(2-aminoethyl)piperazine for efficient thermal energy harvesting

Intrinsically low lattice thermal conductivity and the earth-abundant nature of elements make tetrahedrites very promising sulfur-based materials for thermoelectric applications. Although the thermoelectric performance of lightweight sulfides is usually restricted due to high lattice thermal conductivity, nanoengineering may effectively enhance the energy conversion performance of tetrahedrites by disturbing phonon transport. In this work, we modified our unique solvothermal synthesis method with 1-(2-aminoethyl)piperazine as a solvent and pure elements as reagents to obtain both copper-rich and copper-poor tetrahedrites with nanometric grain sizes ranging from 40 to 300 nm. The powders obtained were densified by the PECS method at T = 573 K and p = 40 MPa. The structural and thermal properties of the fabricated materials were systematically investigated as a function of temperature to revisit the phase evolution of the Cu-Sb-S system in the vicinity of the tetrahedrite compounds. The Seebeck coefficient of the investigated materials changes from 150 µVK ⁻¹ up to 400 µVK ⁻¹ at 300 K due to the effective tuning of the carrier concentration. In turn, the nanocrystalline nature of the prepared tetrahedrites, which influences the strong phonon scattering at grain boundaries, results in an ultralow lattice thermal conductivity of around 0.25 Wm ⁻¹K ⁻¹ at 300 K. As a result of the tuned electronic transport and ultralow lattice thermal conductivity, the highest ZT parameter of 0.9 at 596 K was achieved for the nominal composition Cu ₁₃Sb ₄S ₁₃ . This is one of the best values reported to date for low-cost and environmentally friendly tetrahedrites at this temperature. The resultant nanomaterials can be used as components in novel inorganic and organic-inorganic composites for direct conversion of heat to electricity.