Electronic properties of CeOs 4 Sb 12
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Electronic properties of CeOs4 Sb12 D. H. Galvan Centro de Ciencias de la Materia Condensada-UNAM, Apartado Postal 2681, CP 22800, Ensenada, B. C., México Abstract CeOs4 Sb12 is a very interesting material due to the diversity of physical properties which could be dedicated to industrial applications. With this goal in mind, electronic structural calculations were performed in order to provide more information regarding its properties. The energy bands yielded information regarding its semiconductor behavior as well as a mini gap of the order of o.45 eV between the valence and conduction bands. Moreover, total and projected density of states yielded information of a possible hybridization between Ce f-, Os d- and p-, with Sb p- orbitals. Hence, this compound could be considered a likely candidate as a thermoelectric material. Introduction Filled skutterudites [1] are a family of compounds with general formula RT4 X12 (where R = alkaline earth, rare earth, actinides; T = Fe, Ru, Os; X = pnictogen: P, As, Sb) and crystallize [1,2] in the cubic skutterudite structure. These materials show a variety of interesting physical properties such as: superconductivity [3,4], magnetic order [5], small hybridization gap semiconductivity [6], valence fluctuation and heavy Fermion behavior [7,8], non-Fermi liquid behavior [9] and metal insulator transition [10]. Furthermore, lately these compounds have attracted attention toward thermoelectric applications [11]. Computational details The electronic structure calculations reported in this study were performed using the tight-binding method [12] within the extended Huckel [13] framework using YAeHMOP [14] computer package including f-orbitals [15]. More details about the mathematical formulation of the method has been described elsewhere [16] and are omitted here for brevity.
Figure 1 Unit cell for CeOs4 Sb12 . Large spheres represent Ce, medium size spheres correspond to Os and small spheres are Sb. Results and Discussion The structure for CeOs4 Sb12 used through out the calculations is illustrated in Fig. 1, from P. –C. Ho et al. [17]. Large spheres represent Ce atoms, while medium size spheres represent Os and smaller spheres depict Sb atoms. This material is characterized by the
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space group Im-3-Th5 , No. 204 with primitive vectors a = 0.93106 nm. The Ce atoms are located in the position (2a), The Os located at (8c) and the Sb located at (24g). The atomic parameters employed in our calculations were provided by Alvarez et al. [18]. The band structure for CeOs4 Sb12 is depicted in Figure 2 and was calculated using 51 kpoints sampling the first Brillouin zone. The Fermi level is indicated by a horizontal dotted line. The inset in Fig. 2 depicts the Wigner-Seitz cell for a base center cubic configuration. The most important features in the dispersion diagrams for the filled skutterudite under study, is a tendency to form a pseudo gap that appears above the Fermi level (see Fig. 2), which is a typical characteristic of skutterudites, specially when a
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