Enhanced thermoelectric properties from pore design via adjustment and elimination of residual stresses for Yb0.2(CoSb2.875Te0.125)4

The CoSb3-based skutterudite, as a medium-temperature thermoelectric material, shows excellent thermoelectric performance, but intrinsic high thermal conductivity suppresses enhancement of the ZT value. Here, the Yb0.2(CoSb2.875Te0.125)4 sample was synthesized by the melting reaction, high energy ball milling and the spark plasma sintering, which followed by different processes in order to obtain proper porous structures and eliminate undesirable phases. Elimination of residual stress via annealing results in the formation of micro- and nanopores. The Seebeck coefficient of the S4 sample with the micro- and nanopores is greatly enhanced due to the reduction of the carrier concentration induced by the energy filtering effect of the micro- and nanopores. The power factor achieves 3310 µW m−1 K−2 at 773 K for the sample prepared by pickling and spraying gold particles. The annealed S4 sample with the micro- and nanopores presents a greatly reduced thermal conductivity (~ 1.4 W m−1 K−1) due to the existing abundant the irregularly shaped pores and grain boundaries. Eventually, reasonable porous structures improve the thermoelectric merit (ZT) by 56%.