The earth-abundant natural mineral chalcopyrite CuFeS2 is a potential n-type thermoelectric material because of its large Seebeck coefficient at high carrier concentrations. For a long time, the large Seebeck coefficient of CuFeS2 has been attributed to a large electron effective mass, but the reasons for this and the unusual carrier concentration dependent behavior have rarely been discussed. Here, we systematically investigated the special transport behavior of CuFeS2 and found the classical parabolic band model to be inadequate in explaining it. Our experimental and theoretical studies indicate that there are two flat electronic pockets at the Γ and Z points of the Brillouin zone near the conduction band edge of CuFeS2 that dominate the charge transport. These electronic pockets result from nonparabolic quasilinearly dispersing bands that give rise to a linear wave vector dependent energy (E∼k) and a carrier density dependent effective mass (m∗∼m0n1/3). Such a strong carrier concentration dependent carrier effective mass results in the high Seebeck coefficient of CuFeS2 compound under a large carrier density. The work demonstrates that quasilinearly dispersing bands can give strongly enhanced Seebeck coefficient, and could be useful in optimizing the properties of thermoelectric materials.
ASJC Scopus subject areas
- Materials Science(all)
- Physics and Astronomy (miscellaneous)