Metallurgical and thermoelectric properties in Co1−xPdxSb3 and Co1−xNixSb3 revisited

Polycrystalline thermoelectric Co1−xMxSb3 (M = Ni, Pd) skutterudites have been synthesized by melting, annealing, and spark plasma sintering. The solubility limit of Pd and Ni are determined to be respectively xmax = 0.03 and xmax = 0.09. The density of states effective masses range between 2.0m0 and 4m0 in Co1−xPdxSb3 and Co1−xNixSb3. These values are consistent with the effective band mass (0.3m0) and the degeneracy number Nv = 36 derived from band structure calculations. Power factor measurements and calculations in Co1−xPdxSb3 show that at 300 K, the optimum electron concentration would be [n]opt = 1.4 × 1020 cm−3, slightly beyond the electron concentration (1.1 × 1020 cm−3) of the solubility limit composition Co0.97Pd0.03Sb3. The maximum power factor is effectively obtained for the composition Co0.97Pd0.03Sb3 and reaches 4.3 mW m−1 K−2 at 700 K. An activation energy, which can correspond to the intrinsic gap εG = 0.13 eV, is determined in Co0.98Ni0.02Sb3. Co1−xNixSb3 displays smaller electronic mobilities than in Co1−xPdxSb3 leading to smaller power factors. Best properties (3.4 mW m−1 K−2) are observed at 700 K in Co0.95Ni0.05Sb3-Co0.94Ni0.06Sb3.