Optimization of the thermoelectric performance of Cu22Sn10S32-based composites†

Cu₂₂Sn₁₀S₃₂, a type of Cu–Sn–S (CTS) compound, is known for its super-high carrier concentration, which is unfavorable for thermoelectric applications. In this work, nanostructured In₂O₃ was incorporated into a Cu₂₂Sn₁₀S₃₂ matrix (CTS-x wt% In₂O₃, x = 0, 1, 2, 3, 4, 5, 6, 7) through high-energy ball milling in conjunction with spark plasma sintering. Microstructure analysis reveals that the introduced nano-In₂O₃ reacts with Cu₂₂Sn₁₀S₃₂, with In being uniformly doped in the matrix. At higher In₂O₃ contents (x ≥ 5), a SnO₂ secondary phase appears. The incorporation of nano-In₂O₃ leads to a substantial decrease in carrier concentration by one order of magnitude. At the same time, the carrier mobility shows a clear increase due to the suppressed carrier–carrier scattering. This ultimately lowers the electrical conductivity, which also contributes to a significant decrease in electronic thermal conductivity. Additionally, the lattice distortion caused by the substitution of In for Cu also leads to a significant reduction in lattice thermal conductivity. Ultimately, a maximum zT of 0.6 at 723 K was achieved for the CTS-5 wt% In₂O₃ sample, which shows a 60% increase compared to the Cu₂₂Sn₁₀S₃₂ matrix. Our study illustrates that the introduction of nanoparticles into a CTS matrix can effectively lower its carrier concentration and lattice thermal conductivity, thereby optimizing its thermoelectric performance.