The Study of Solvothermal Synthesis of Nano-Engineered CoSb3 Skutterudite Thermoelectric Materials
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The Study of Solvothermal Synthesis of Nano-Engineered CoSb3 Skutterudite Thermoelectric Materials Xiaohua Ji1, Jian He1, Paola N. Alboni1, Terry M. Tritt1, and Joseph W. Kolis2 1 Department of Physics and Astronomy, Clemson University, Clemson, SC, 29634 2 Department of Chemistry, Clemson University, Clemson, SC, 29634 Abstract Nanostructured materials have been shown to enhance phonon scattering and improve the figure of merit of thermoelectric materials. Solvothermal syntheses of nano-engineered CoSb3 skutterudite have been studied in the present work in which CoCl2 and SbCl3 were used as precursors and NaBH4 as a reductant. Elemental, structural and morphology characterization techniques including: XRD, SEM, TEM and EDAX were used to identify and characterize the products. NaBH4 was found to be a necessary factor in forming cobalt antimonide. It was detected the products’ phase transited from Sb2Co to CoSb3 in conjunction with the amount increase of NaBH4. The change of synthesis time and temperature contributed little on the products’ phases under the present experimental routes. Single-phased CoSb3 skutterudites was obtained from the solvothermal syntheses combined with an acid wash. The as-prepared CoSb3 powders consist of irregular nanoparticles with 15~20 nm in size. A possible chemical mechanism was also discussed. Keyword: CoSb3, skutterudite, thermoelectric, nano, NaBH4, Sb2Co, reduction and oxidation *Corresponding Author: Xiaohua Ji, email [email protected]
1. Introduction & Background Skutterudite compounds are of increasing interest and have been extensively studied as potential high-efficiency thermoelectric materials in recent years [1,2]. Due to their special crystal structures (b.c.c. structure with space group Im3, containing large voids which can accept exotic guest atoms and these guest atoms are loosely bounded and scatter phonons thus reducing the lattice thermal conductivity), skutterudites exhibit novel electrical and thermal transport properties, which was classified as “Phonon-Glass and Electron-Crystal” (PGEC) materials [3,4]. CoSb3-based skutterudites have particularly been a focal point of research efforts mainly because of their favorable electrical and thermal properties coupled with the abundance of the constituent elements. Despite their excellent electronic properties, the thermal conductivity, κ, of the parent CoSb3 is too high (κ ~ 10Wm-1K-1at room temperature) to compete with state-of-the-art thermoelectric materials [5]. Therefore, filled skutterudites, which have rattling atoms introduced into the cages, have been intensively investigated in pursuit of a lower thermoelectric conductivity and thus a high figure of merit ZT [6-10]. The performance of thermoelectric materials can be enhanced dramatically through engineering and processing the materials at the nano-scale, which were named as nano-engineered thermoelectric materials (NETEMs) [11]. NETEMs can be envisioned as composites that are fabricated of the parent’s material (eg. CoSb3) intermixed with simila
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