Pitfalls in crystallographic analysis of doped skutterudite materials

L. Bertini1, M. Christensen2, C. Gatti1, L. Holmgren3, B. B. Iversen2, M. Muhammed4,

E. Müller5, G. Noriega6, A. E. C. Palmqvist7, D. Platzek5, D. M. Rowe8, A. Salimat7,

C. Stiewe5, M. Toprak4, S. G. K. Williams8, Y. Zhang4

1 Istituto di Scienze e Tecnologie Molecolari (ISTM), Via Camillo Golgi 19, 20133 Milano, Italy

2 Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark

3 LEGELAB, Klevåsvagen 3, 45155 Uddevalla, Sweden

4 Department of Materials Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden

5 German Aerospace Center (DLR), Linder Hoehe, D-51147 Cologne, Germany

6 CIDETE INGENIEROS S. L. Anselmo Clave 98, 08800 Villanova I la Geltru, Spain

7 Department of Applied Surface Chemistry, Chalmers University of Technology, SE-412 96 Göteborg, Sweden

8 NEDO Laboratory for Thermoelectric Engineering, University of Wales, Cardiff, UK

The main problem in X-ray structural analysis of Ni and Fe containing CoSb3 samples is the very similar scattering power of the transition metals. In case of neutron diffraction there is a much larger contrast with scattering lengths of 2.49 fm, 10.3 fm and 9.45 fm for Co, Ni and Fe respectively. For samples studied on conventional powder diffractometers equipped with CuKa radiation sources there is an added problem of fluorescence due to Fe and Co, which leads to very high background counts. Furthermore, Sb dominates the scattering relative to the transition metals an potential oxide impurity phases. Taken together this can make it difficult to detect sample impurities. We present neutron and synchrotron powder diffraction investigations of nano-structured CoSb3 skutterudites having partial Ni substitution (NixCo1-xSb3) as well as doping with Fe (FexCoSb3). The study serves as a case story for the determination of fine structural details of thermoelectric skutterudites by diffraction methods.