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S4.1.1

Effect of Ni in new skutterudite compounds CaxCo4Sb12 Matthieu Puyet, Bertrand Lenoir, Anne Dauscher, Hubert Scherrer, Moukrane Dehmas1, Jiri Hejtmanek2, Christian Stiewe3, Eckhard Müller3 Laboratoire de Physique des Materiaux, UMR 7556, Ecole National supérieure des Mines de Nancy, Parc de Saurupt, 54042 Nancy cedex, France 1 Laboratoire de Science et Génie des Matériaux et de Métallurgie, UMR 7584, Ecole National supérieure des Mines de Nancy, Parc de Saurupt, 54042 Nancy cedex, France 2 Institute of Physics Academy of Sciences of the Czech Republic, Cukrovarnicka 10, CZ-162 53 Praha 6, Czech Republic 3 German Aerospace Center (DLR), Institute of Materials Research, Linder Hoehe, 51147 Cologne, Germany. ABSTRACT The transport properties of the partially filled CaxCo4-yNiySb12 skutterudite compounds have been investigated in the 300 - 800 K temperature range. We underline the positive influence of the Ni substitution on the electrical resistivity and thermopower while the thermal properties – thermal conductivity – remains almost unaffected. These results suggest again a beneficial effect of Ni atoms on the dimensionless figure of merit in CoSb3 based compounds. INTRODUCTION Over the past few years there has been renewed interest in the field of thermoelectrics. The research was accompanied by the development of synthetic semiconductors that possess Seebeck coefficients reaching hundreds of microvolts per Kelvin which, consequently, can provide a useful amount of electrical power. The improvement of the efficiency of thermoelectric generators by means of the improvement of material thermoelectric properties was the leitmotiv during the past five decades. More recently, efforts were focused on one of the most promising families of materials envisaged for thermoelectric applications at moderated temperatures, namely the skutterudite type [1,2]. The operation of such generators requires the use of both ntype and p-type legs. In this respect, the importance is also in the fact that both types of conduction are obtained in partially filled skutterudites and that the properties of respective materials appear to be far superior to the current standard represented by the widespread Si-Ge alloys [1-24]. One of the key features of this family of materials is that atoms may be inserted in the voids offered by the crystal structure where they can “rattle”. Consequently, the lattice thermal conductivity is significantly reduced by the rattling motion of the filler atom while the electrical properties of the material remain interesting [1-17]. Many kinds of atoms were used to fill the voids of the structure. The best p-type skutterudite material was found in the CexFeyCo3ySb12 family [25]. Good n-type skutterudite material was obtained by Chen et al. [24] who used the barium atom to fill the voids of the binary skutterudite CoSb3. Dick et al. [26] found later on that the thermoelectric properties of BaxCo4Sb12 compounds can be significantly improved by

S4.1.2

replacing small amount of Co by Ni. The positive influence