Giant enhancement in thermoelectric performance of copper selenide by incorporation of different nanoscale dimensional defect features

We report a simple experimental strategy for enhancing the figure-of-merit (ZT) of thermoelectric materials by introducing different kinds of defect features, including nano-porosity, in a range of nano to meso-scale dimensions, employing spark plasma assisted (SPS) reaction sintering of mechanically alloyed nanopowders. This strategy has been experimentally demonstrated in a well known thermoelectric compound, Cu2Se, which is shown to yield a high ZT of 2.1 at 973 K, which is among the highest reported value for this material and shows 40% increase over its bulk melt-processed counterpart. The main contribution to the enhanced ZT, despite moderate values of power factor, primarily originates from a very small value of thermal conductivity of 0.34W m(-1) K-1. This low thermal conductivity owes its origin primarily to the enhanced low-to-high wavelength phonon scattering by different kinds of defects, in a wide spectrum of nano to meso-scale dimensions, involving microstructural defects generated during high-energy ball milling, abundant nanocrystalline grain boundaries due to very low crystallite size, and more importantly the nano-to-meso scale residual porosity created due to SPS at optimized process parameters. The role of SPS in enhancing the ZT has been discussed and this strategy can also be applied to other thermoelectric materials. (C) 2015 Elsevier Ltd. All rights reserved.