Crystal Structure and Thermoelectric Properties of Cu₂Fe_1–xMn_xSnSe₄ Diamond-like Chalcogenides

Quaternary diamond-like chalcogenides have attracted great attention for thermoelectric application in the past decade. The electrical and thermal transport properties of quaternary diamond-like chalcogenides are sensitively related with their crystal structures. In this work, a series of Cu2Fe1–xMnxSnSe4 solid solutions has been synthesized, and the relation between crystal structure and thermoelectric properties were investigated. Significantly varied carrier concentration, mobility, effective mass, and lattice thermal conductivity were observed with increasing Mn-alloying content in Cu2Fe1–xMnxSnSe4, which were attributed to the modifications of the crystal structure, such as the enlarged lattice parameters, increased Cu–Se bond length, and strengthened internal structure distortion. On the basis of the deep understanding of these Cu2Fe1–xMnxSnSe4 solid solutions, we further doped Cu in Cu2Fe0.5Mn0.5SnSe4 to tune the carrier concentration. A peak dimensionless figure-of-merit of 0.6 was achieved for Cu2.1(Fe0.5Mn0.5)0.9SnSe4 at 800 K, about 71% and 33% higher than those for Cu2FeSnSe4 and Cu2MnSnSe4, respectively.