Low thermal conductivity and enhanced thermoelectric performance of Gd-filled skutterudites

With Fe compensation, the heavy rare earth element Gd-filled GdyFexCo4−xSb12 (x<2) skutterudites have been successfully synthesized by melting-annealing approach. Fe substitution on the Co site brings two contrary effects on Gd filling: charge compensation which enhances the filling fraction of Gd, and Lattice expansion which is deleterious for the stability of filled compounds that contain smaller atoms. When Fe content is less than 1.7, pure GdyFexCo4−xSb12 compounds are obtained and the Gd maximum filling fraction (ymax) increases with Fe content. The power factor (S2σ) of the GdyFexCo4−xSb12 increases with Fe content. The lattice thermal conductivity is significantly depressed by Gd filling. The sample Gd0.41Fe1.48Co2.52Sb12 has a lattice thermal conductivity as low as 1.1 W m−1 K−1 at room temperature, and its figure of merit (ZT) reaches a maximum value of 0.83 at 700 K. At high temperature, thermal conductivity shows significant increase due to bipolar diffusion, which obstructs obtaining higher ZT.