Nanostructured CuFeSe<inf>2</inf> Eskebornite: An efficient thermoelectric material with ultra-low thermal conductivity

Bulk and nanoparticles of CuFeSe2 eskebornite have been synthesized using vacuum-sealed tube melting and facile hydrothermal method, respectively. The phase purity of bulk and nano-CuFeSe2 is confirmed through powder X-ray diffraction. Field emission-SEM micrographs of nano-CuFeSe2 depict the randomly distributed plate-like agglomerated particles. Further, TEM studies reconfirm the plate-like CuFeSe2 nanoparticles with an average particle size of ∼ 102 nm. The electronic states of Cu1+, Fe3+, and Se2- in CuFeSe2 are confirmed using XPS analysis. VSM measurements depict the weak ferromagnetic behavior in both bulk and nano-CuFeSe2 samples. The electrical conductivity of bulk CuFeSe2 is ∼ 0.6x104 S/m, and it reduces to 0.07x104 S/m at 300 K for nano-CuFeSe2, whereas the Seebeck coefficient increases from ∼ 12 µV/K to ∼ 48.4 µV/K at 300 K. Intriguingly, an ultra-low thermal conductivity of ∼ 0.73 W/mK at 300 K has been achieved for nano-CuFeSe2, which leads to the maximum figure of merit, zT of ∼ 0.02 at 645 K.