Comparative Study of Indium as a Filler or as a Substitute in Yb-Filled Ni-Doped CoSb3

Abstract

CoSb _3 with an open structure that can accommodate several fillers has been extensively studied due to its PGEC character. It is known that partial substitution of Ni with Co generates more free electron and alter the CoSb _3 into a stable n-type skutterudite. In this work, we used In as a filler with Yb and as a partial substitution of Sb in Co _3.85 Ni _0.15 Sb _12. All alloys have been synthesized by solid-state reaction method and hot press processes. The Seebeck coefficient varies from 160 μ VK ^−1 to 200 μ VK ^−1 in Yb _0.3 Co _3.85 Ni _0.15 Sb _11.5 In _0.5; however, it exhibits the highest charge carrier concentration. Yb _0.3 Co _3.85 Ni _0.15 Sb _11.5 In _0.5 exhibits the highest power factor of 3.9 mW ^−1 K ^−2 at 723 K, which is 20% and 15% larger than a single-filled and double-filled Ni-doped system respectively. The suitable amount of In doped with Sb in a Ni-doped single-filled skutterudite system resulted is not only an improvement of the thermopower but also a decrease of the thermal conductivity due to enhanced point-defect scattering and increased electron-phonon interaction. Hence Yb _0.3 Co _3.85 Ni _0.15 Sb _11.5 In _0.5 exhibits a maximum zT of 1.25 which is 25% higher than Yb _0.2 In _0.2 , Co _3.85 Ni _0.5 Sb _12 . Therefore, indium is also a good option to use as a substitution, n-type skutterudite compared to use as a filler.