High-temperature transport properties of complex antimonides with anti-Th3P4 structure

Polycrystalline samples of R4Sb3 (R = La, Ce, Smand Yb) and Yb4-xR¢xSb3 (R¢ = Sm and La) have been quantitatively synthesized by high-temperature reaction. They crystallize in the anti-Th3P4 structure type (I ¯43d, no. 220). Structural and chemical characterizations have been performed by X-ray diffraction and electron microscopy with energy dispersive X-ray analysis. Powders have been densified by spark plasma sintering (SPS) at 1300 ◦C under 50 MPa of pressure. Transport property measurements show that these compounds are n-type with low Seebeck coefficient except for Yb4Sb3 that shows a typical metallic behavior with hole conduction. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4-xR¢xSb3 up to 0.75 at 1000 ◦C

Effect of doping on the thermoelectric properties of thallium tellurides using first principles calculations

We present a study of the electronic properties of Tl5Te3, BiTl9Te6 and SbTl9Te6 compounds by means of density functional theory based calculations. The optimized lattice constants of the compounds are in good agreement with the experimental data. The band gap of BiTl9Te6 and SbTl9Te6 compounds are found to be equal to 0.589 eV and 0.538 eV, respectively and are in agreement with the available experimental data. To compare the thermoelectric properties of the different compounds we calculate their thermopower using Mott's law and show, as expected experimentally, that the substituted tellurides have much better thermoelectric properties compared to the pure compound.Comment: PTM2010 Conferenc

Physical properties of Thallium-Tellurium based thermoelectric compounds using first-principles simulations

We present a study of the thermodynamic and physical properties of Tl5Te3, BiTl9Te6 and SbTl9Te6 compounds by means of density functional theory based calculations. The optimized lattice constants of the compounds are in good agreement with the experimental data. The electronic density of states and band structures are calculated to understand the bonding mechanism in the three compounds. The indirect band gap of BiTl9Te6 and SbTl9Te6 compounds are found to be equal to 0.256 eV and 0.374 eV, respectively. The spin-orbit coupling has important effects on the electronic structure of the two semiconducting compounds and should therefore be included for a good numerical description of these materials. The elastic constants of the three compounds have been calculated, and the bulk modulus, shear modulus, and young's modulus have been determined. The change from ductile to brittle behavior after Sb or Bi alloying is related to the change of the electronic properties. Finally, the Debye temperature, longitudinal, transverse and average sound velocities have been obtained

Physical properties of thermoelectric zinc antimonide using first-principles calculations

We report first principles calculations of the structural, electronic, elastic and vibrational properties of the semiconducting orthorhombic ZnSb compound. We study also the intrinsic point defects in order to eventually improve the thermoelectric properties of this already very promising thermoelectric material. Concerning the electronic properties, in addition to the band structure, we show that the Zn (Sb) crystallographically equivalent atoms are not exactly equivalent from the electronic point of view. Lattice dynamics, elastic and thermodynamic properties are found to be in good agreement with experiments and they confirm the non equivalency of the zinc and antimony atoms from the vibrational point of view. The calculated elastic properties show a relatively weak anisotropy and the hardest direction is the y direction. We observe the presence of low energy modes involving both Zn and Sb atoms at about 5-6 meV, similarly to what has been found in Zn4Sb3 and we suggest that the interactions of these modes with acoustic phonons could explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the most stable defects and this explains the intrinsic p-type conductivity of ZnSb.Comment: 33 pages, 8 figure

Phase stability of nickel and zirconium stannides

International audienceNi-Sn-Zr alloys have many interests in different fields of application going from nuclear material applications to functional materials (such as thermoelectrics). This wide application range requires a good knowledge of the stability of the phases. In the present study, first principles calculations are used to determine the enthalpies of formation of intermediate phases and of the structural defects in some structures. Based on these data and on the literature, the stability of the phases is discussed at low and high temperatures. Finally, for the first time the complete ternary system is described in the whole temperature range

Détermination de la structure cristalline du fluorobéryllate de cupritétrammine monohydraté : Cu [(NH3)4] H2O Be F4

Cu[(NH₃)₄ H₂O] BeF₄ crystalizes in the orthorhombic space group Pnma : the unit cell dimensions are : a = 23.942 ; b = 7.030 ; c = 20.979 Å. There are sixteen formulae per unit cell. The structure is built up from copper coordination polyedron and discrete fluoroberyllate tetraedra connected by hydrogen bonds. Copper coordination polyedron is a square based pyramid. The pyramidal based-plan is built by four nitrogen atoms and the water molecule is situed on the axis perpendicular to this plane.Cu[(NH₃)₄ H₂O] BeF₄ cristallise dans le système orthorhombique groupe spatial Pnma ; les paramètres de la maille sont : a = 23,942 ; b = 7,030 ; c = 20,979 Å. Il y a seize motifs par maille. La structure est formée de polyèdres de coordination du cuivre et de tétraèdres BeF₄²⁻ reliés par liaison hydrogène. Le polyèdre de coordination du cuivre est une pyramide à base carrée déformée. Le plan de base de la pyramide est formé par les quatre atomes d'azote et la molécule d'eau se trouve sur l'axe perpendiculaire à ce plan.Tédenac Jean-Claude, Philippot Etienne, Maurin Maurice. Détermination de la structure cristalline du fluorobéryllate de cupritétrammine monohydraté : Cu [(NH3)4] H2O Be F4. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 98, 1, 1975. pp. 36-42

Sur quelques nouveaux fluorobéryllates complexes du cuivre. Étude cristallographique

Tédenac Jean-Claude, Cot Louis, Maurin Maurice. Sur quelques nouveaux fluorobéryllates complexes du cuivre. Étude cristallographique. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 95, 4, 1972. pp. 525-528

Calphad assessment of the Ni-Sn-Ti system

International audienceThe ternary phase diagram Ni–Sn–Ti has been assessed by a general Calphad procedure. Ab-initio calculations using the VASP code have been made to obtain the enthalpies of formation of the compounds and the enthalpies of mixing along two key sections. Phase modeling provides a complete description of the system. Three phases exist in this system: NiTiSn, Ni2TiSn and Ni2Ti2Sn. Moreover the NiTi5Sn3 phase resulting from the filling with Ni of the 2b Wyckoff sites in the Ti5Sn3 binary phase has been considered as an ordered structure. Isotherm sections are shown in order to understand the stabilities of phases and some isopleth sections are drawn together with the experimental data of liquidus arrests