Synthesis, crystal structure, and transport properties of quaternary tetrahedral chalcogenides
Quaternary chalcogenides with tetrahedral zinc-blend structure types continue to be of interest for thermoelectrics applications. We report on the synthesis, crystal structure, and high temperature transport properties of Cu2.1Fe0.9SnSe4, Cu2.2Fe0.8SnSe4 and Cu2.2Zn0.2Fe0.6SnSe4. The identity and compositions for each specimen were established using a combination of Rietveld refinement and elemental analysis and indicate that all compositions are homogeneous with the stannite crystal structure. Excess Cu reduces the electrical resistivity, ρ, by an order of magnitude compared with Cu2FeSnSe4 with no significant degradation of the Seebeck coefficient, S. The energy band gaps were estimated from the high temperature S values and indicate that Cu2.1Fe0.9SnSe4 and Cu2.2Fe0.8SnSe4 possess narrow band gaps, 0.18 eV and 0.25 eV, respectively, as compared to most other quaternary chalcogenides. The power factor (PF = S2/ρ) increases with decreasing Fe content. Although Cu2.2Fe0.8SnSe4 possesses a smaller PF than that of Cu2.2Zn0.2Fe0.6SnSe4, a ZT of 0.45 was obtained at 750 K for Cu2.2Fe0.8SnSe4 due to its low thermal conductivity.
- This article is part of the themed collection: The Chemistry of Thermoelectric Materials