Journal of Alloys and Compounds 437 (2007) 39–46 Band energy and thermoelectricity of filled skutterudites LaFe 4 Sb 12 and CeFe 4 Sb 12 K. Nouneh a,d , Ali H. Reshak b , S. Auluck b , I.V. Kityk c,∗ , R. Viennois d , S. Benet a , S. Charar d a Laboratoire de Physique Appliqu´ ee et Automatique, Universit´ e de Perpignan, 52 Av. Paul Alduy, Perpignan, France b Physics Department, Indian Institute of Technology, Roorkee, Uttaranchal 247667, India c Institute of Physics, J. Dlugosz University of Czestochowa, Al. Armii Krajowej 13/15, Czestochowa, Poland d Groupe d’Etude des Semiconducteurs, CNRS-UMR 5650, Universit´ e Montpellier II, Pl. Eug` ene Bataillon, 34095 Montpellier Cedex 5, France Received 20 July 2006; received in revised form 26 July 2006; accepted 26 July 2006 Available online 1 September 2006 Abstract Complex density functional theory (DFT) calculations of band energy structure and density of states for two principal representatives of the filled skutterudites LaFe 4 Sb 12 and CeFe 4 Sb 12 have been performed using the tight-binding, linear muffin-tin orbital (TB-LMTO) and full potential linear augmented plane wave (FP-LAPW) methods to clarify origin of thermoelectricity. Both methods were used within a framework of the LDA approach. We have found that both methods show similar band energy dispersion features with minor differences. Particularly, LaFe 4 Sb 12 is metallic with a band crossing two times the Fermi level with direct energy gap equal to about 0.81 eV. Whereas CeFe 4 Sb 12 is a semiconductor with indirect energy gap equal to about 0.66eV. Our calculations performed for density of electronic states near the Fermi energy level show that the large thermopower at room temperature originates from the d Fe states hybridized with the p states of Sb and that there is no contribution from the Ce states in the case of CeFe 4 Sb 12 . Because these two compounds are strongly correlated fermions systems, during calculations of thermoelectric properties, this factor may play several roles. Role of spin fluctuations in the observed thermopower dependencies is also discussed. © 2006 Elsevier B.V. All rights reserved. Keywords: Thermoelectric alloys; Electronic structure 1. Introduction The potential of materials for thermoelectric applications [1] is determined by the figure of merit, Z = S 2 ·σ /κ where S is the Seebeck coefficient, σ the electrical conductivity, and κ is the thermal conductivity. Better thermoelectric properties are determined by a combination of high mobilities (for higher σ with reasonable carrier concentrations), higher band masses (to obtain higher values of S), and lower lattice thermal conduc- tivities, κ = κ e + κ 1 which include both electronic and phonon contributions, respectively. The last requirement leads to the consideration of complex (i.e. many atoms per unit cell) solids since this is necessary to achieve very low thermal conductivi- ties. Therefore most of the efforts here are focused on reducing of lattice thermal conductivity κ l during filling of the empty ∗ Corresponding author. E-mail address: i.kityk@ajd.czest.pl (I.V. Kityk). icosahedral cages (2a) site in the skutterudite structure with rare earth atoms and formation of solid solutions and alloys. To do the desirable changes in the materials it is necessary to have reli- able band energy structure parameters determining both electron mobility as well as occupation of electrons near the Fermi energy level. Moreover information about the relative position of Fermi energy level with respect to principal point of the crystalline BZ (so called van Hove singularities) and general distribution of the upper valence DOS usually are main criteria for design and synthesis of materials possessing promising thermoelectric properties. This one should clarify main strategy of materials design, particularly using appropriate cationic substitution and forming of the desirable number of vacancies. So in the present work we present complex investigations of band energy structure for two principal representatives of the skutterudites. Principal question is how replacement of the particular cationic RE influ- ences the principal parameters of the skutterudites, particularly crucial is the density of states (DOS) near the energy Fermi level N(E F ) for determining thermoelectric coefficients. 0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.07.114