Thermoelectric properties of nano-grained CoSb3 skutterudites doped with Ni and Te
L. Bertini1, K. Billquist2, M. Christensen3, C. Gatti1, L. Holmgren4, B. Iversen3, E. Mueller5, M. Muhammed2, G. Noriega6, A. Palmqvist7, D. Platzek5, D.M. Rowe8, A. Saramat7, C. Stiewe5, M. Toprak2, S.G.K. Williams8, Y. Zhang2
1Istituto di Scienze e Tecnologie Molecolari (ISTM), Via Camillo Golgi 19, 20133 Milano, Italy
2Royal Institute of Technology, Materials Chemistry Division, SE-10044 Stockholm, Sweden
3University of Aarhus, Department of Chemistry, DK-8000 C Aarhus, Denmark
4LEGELAB, SE-451 44 Uddevalla, Sweden
5German Aerospace Center (DLR), Institute of Materials Research, D-51170 Cologne, Germany
CIDETE Ingenieros SL, E-08800 Vilanova (Barcelona), Spain
7Chalmers University of Technology, Dept. Applied Surface Chemistry, Goteborg, Sweden
8NEDO Laboratory for Thermoelectric Engineering (NEDO), Cardiff, UK
Skutterudites have been identified as promising materials for thermoelectric applications due mainly to the reduced thermal conductivity k caused by filling the large voids within the crystal lattice by "rattling atoms" (usually rare earth elements).
CoSb3 skutterudites were prepared by a novel chemical method of co-precipitating the constituents from aqueous solution and subsequent heat treatment at comparably low temperature. The precipitated nano-grained powder results in a very high concentration of grain boundaries. Under certain conditions grain boundary scattering is expected to be more effective on heat carrying phonons than on charge carriers , therefore achieving an increased s /k ratio.
To overcome the expected reduction of the electrical conductivity by grain boundary scattering, skutterudites with various substitution of Co by Ni, Sb by Te and combined substitutions have been prepared by KTH and their thermoelectric properties investigated by DLR and NEDO, i.e. electrical and thermal conductivity as well as Seebeck coefficient and figure-of-merit. ZT values of up to 0.67 at 723 K have been measured on these still unfilled skutterudites. To assure reliability of measured data, standardisation and round robin measurements were performed by both laboratories.