Effect of n-type Dopants on CoSb3 Skutterudite Thermoelectrics Sintered by Spark Plasma Sintering

Abstract

<TEX>$CoSb_3$</TEX> Skutterudites materials have high potential for thermoelectric application at mid-temperature range because of their superior thermoelectric properties via control of charge carrier density and substitution of foreign atoms. Improvement of thermoelectric properties is expected for the ternary solid solution developed by substitution of foreign atoms having different valances into the <TEX>$CoSb_3$</TEX> matrix. In this study, ternary solid solutions with a stoichiometry of <TEX>$Co_{1-x}Ni_xSb_3$</TEX> x = 0.01, 0.05, 0.1, 0.2, <TEX>$CoSb_{3-y}Te_y$</TEX>, y = 0.1, 0.2, 0.3 were prepared by the Spark Plasma Sintering (SPS) system. Before the SPS synthesis, the ingots were synthesized by vacuum induction melting and followed by annealing. For phase analysis X-ray powder diffraction patterns were checked. All the samples were confirmed as single phase; however, with samples that were more doped than the solubility limit some secondary phases were detected. All the samples doped with Ni and Te atoms showed a negative Seebeck coefficient and their electrical conductivities increased with the doping amount up to the solubility limit. For the samples prepared by SPS the maximum value for dimensionless figure of merit reached 0.26, 0.42 for <TEX>$Co_{0.9}Ni_{0.1}Sb_3$</TEX>, <TEX>$CoSb_{2.8}Te_{0.2}$</TEX> at 690 K, respectively. These results show that the SPS method is effective in this system and Ni/Te dopants are also effective for increasing thermoelectric properties of this system.