Enhanced thermoelectric properties of Mn Cu1.8S via tuning band structure and scattering multiscale phonons

Digenite (Cu1.8S) as a potential p-type thermoelectric (TE) material has attracted extensive attention due to its environmental benign, abundant resources and low cost of component elements. In this study, the TE properties of MnxCu1.8S bulk samples prepared by mechanical alloying (MA) combined with spark plasma sintering (SPS) were investigated. Doping Mn would initially substitute Cu and tune the band structure of Cu1.8S with an enlarged band gap Eg. However, if Mn content is beyond the solubility limit of x = 0.01 in Cu1.8S will cause the formation of MnS, which contributes to the formation of Cu-rich phases at 0.02 ≤ x ≤ 0.08. Benefiting from the synergetic scattering effect of point defects (MnCu•, VS••) and MnS, Cu1.96S, Cu1.97S, Cu2S phases, the lowest thermal conductivity κ value of 0.75 W m−1K−1 was obtained at 773 K for Mn0.08Cu1.8S. Along with the decreased κ, the highest figure of merit ZT value of 0.92 at 773 K achieved in Mn0.08Cu1.8S bulk sample. A maximum engineering ZTeng of 0.3 and its efficiency ηmax of about 6% were obtained at 323–773 K, which is almost 3 times than that of the pristine Cu1.8S (ηmax = 2.2%). Introducing Mn in Cu1.8S is an effective and convenient strategy to improve TE performance.