Thermoelectric properties of n-type Cu(4)Sn(7)S(16)-based compounds.

Copper-based chalcogenides have ultralow thermal conductivity and ultrahigh thermoelectric performance, but most of them are p-type semiconductors. It is urgent to develop n-type counterparts for high efficiency thermoelectric modules based on these copper based-chalcogenides. Cu(4)Sn(7)S(16) is an intrinsically n-type semiconductor with complex crystal structure and low thermal conductivity. However, its thermoelectric properties have not been well studied when compared to the well-known n-type CuFeS(2). In this work, high-quality Cu(4)Sn(7)S(16)-based compounds are fabricated and their thermoelectric properties are systematically studied. Using Ag and Sb as dopants, the carrier concentration is tuned over a wide range. The electrical transport properties can be well described by the single parabolic band model with carrier acoustic phonons scattering. It is revealed that Cu(4)Sn(7)S(16) exhibits a low effective mass and relatively high mobility. The thermal conductivity is lower than 0.8 W m(-1) K(-1) from 300 to 700 K and shows a weak dependence on temperature. A maximum zT of 0.27 is obtained in Cu(3.97)Ag(0.03)Sn(7)S(16) at 700 K. Further enhancement of thermoelectric performance is possible when a more efficient n-type dopant is used.