Enhanced thermoelectric performance of spark plasma sintered copper-deficient nanostructured copper selenide

•Cu-deficient Cu2Se synthesized by nanostructuring and spark plasma sintering.•Nanostructured Cu1.98Se had a high ZT of ~1.4 at 973 K.•Nanostructuring significantly reduced the lattice thermal conductivity.•Atomic/nanoscale features were characterized by HRTEM after sintering.

We report the thermoelectric properties of nanostructured Cu-deficient Cu2Se, which was synthesized by high energy ball milling followed by spark plasma sintering. Our method obtained a significant enhancement in the thermoelectric figure of merit (ZT), i.e., ~1.4 at 973 K, which was ~30% higher than its bulk counterpart. This enhancement in the thermoelectric performance was due mainly to a significant reduction in the lattice thermal conductivity, which was attributed to enhanced phonon scattering at various length scales by nanoscale defects as well as abundant nanograin boundaries. The nanoscale defects were characterized by transmission electron microscopy of the nanostructured Cu2−xSe samples, which formed the basis of the ZT enhancement.