High-Temperature Transport Properties of Yb4−xSmxSb3

Polycrystalline L4Sb3 (L = La, Ce, Sm, and Yb) and Yb4−x Sm x Sb3, which crystallizes in the anti-Th3P4 structure type (I-43d no. 220), were synthesized via high-temperature reaction. Structural and chemical characterization were performed by x-ray diffraction and electronic microscopy with energy-dispersive x-ray analysis. Pucks were densified by spark plasma sintering. Transport property measurements showed that these compounds are n-type with low Seebeck coefficients, except for Yb4Sb3, which shows semimetallic behavior with hole conduction above 523 K. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4Sb3 up to 0.7 at 1273 K

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

Étude des équilibres des phases dans le système Ag-Sn-In à 280 °C

The Ag-Sn system is among the most studied ones in the prospective of the abandon of the lead containing alloys. On the other hand the temperatures of these alloys are higher than those of the now used Pb-Sn eutectic alloys. Consecutively the addition of In – a low melting element is interesting from the new materials’ development. The isothermal section of the Ag-Sn-In system at 280°C was studied by using optical and scanning electron (SEM) microscopies, X-ray diffraction, differential scanning calorimetry (DSC) and Vickers’ microhardness measurements. The microhardness values of $\alpha$(Ag), $\epsilon$(Ag$_4$Sn) and $\zeta$ phases were measured. The ternary eutectic‘s position reported in the literature was confirmed. The respective third element’s solubilities were determined.Le système Ag-Sn est parmi les systèmes les plus étudiés dans la perspective de l'abandon des alliages à base de Pb. D'autre part les températures de fusion de ces alliages sont plus élevées que celle de l'eutectique Pb-Sn actuellement employé. Consécutivement, l'addition d'indium, un élément ayant température de fusion relativement basse, est un moyen intéressant pour la mise au point de nouvelles brasures. La coupe isotherme du système Ag-Sn-In à 280°C a été construite à l'aide des microscopies optique et électronique à balayage (MEB), de la diffraction des rayons X, de mesures de microdureté Vickers et de calorimétrie différentielle à balayage (DSC). Les microduretés des phases $\alpha$(Ag), $\epsilon$(Ag$_4$Sn) et $\zeta$ ont été mesurées. La position de l'eutectique ternaire rapportée antérieurement dans la littérature a été confirmée. Les solubilités du troisième élément respectif ont été déterminées

Étude expérimentale du système Sn-Ti-Zn à 600 °C

The interest towards the new lead-free solders becomes important in view of the prohibition of lead solders. Multiple substituting materials are presently at study. Tin and zinc are often constituents of various potential solders. Further, the additions of Ti in the binary systems improve the mechanical properties and alloys’ wetting. The isothermal section of the Sn-Ti-Zn system was studied using scanning electron microscopy, X-ray diffraction, and metallographic methods. An important result of this work is the discovery of a formerly unknown ternary compound. The statistical treatment of the obtained data gives compositions between Sn$_4$Ti$_5$Zn$_11$ and SnTiZn$_2$.L'intérêt des alliages de brasure sans plomb devient important dans la perspective d’interdiction des brasures au plomb. De nombreux matériaux de substitution sont actuellement à l'étude. L'étain et le zinc sont souvent utilisés dans les alliages de brasures potentiels. Par ailleurs, en général, les additions de Ti dans les systèmes binaires entraînent une amélioration des propriétés mécaniques et de la mouillabilité des alliages. La coupe isotherme du système Sn-Ti-Zn a été étudiée, en utilisant la diffraction des rayons X, la microscopie électronique à balayage et les méthodes métallographiques. Un résultat important de cette étude est la découverte d'un composé ternaire, inconnu auparavant. Le traitement statistique des données situe la composition entre Sn$_4$Ti$_5$Zn$_11$ et SnTiZn$_2$

3-dimensional methylammonium and ammonium templated lithiumberyllofluoro frameworks

Two three-dimensional lithiumberyllofluoride materials, of the same framework stoichiometry but different topologies, have been synthesized using hydrothermal pressure conditions and ammonium/methylammonium cations as structure-directing species. Compound I, [Li2Be2F7] [NH4], and compound II, [Li2Be2F7][CH3NH3], both crystallize in orthorhombic space groups: Pca2(1) for I and Cmcm for II. Single crystal analysis reveals that the materials have slightly different 3-D framework topologies for the [Li2Be2F7] framework composed of [LiF4] and [BeF4] tetrahedra connected through doubly and triply bridging fluorides. Both networks can be viewed as sheets formed of 3- and 4-nets that link perpendicular to the sheet, through a bridging fluoride, to form six-membered interlayer pores. The six-membered channels contain the amine species hydrogen-bonded to framework fluoride ions surrounding the interior of the pore. The thermal stability, spectroscopic properties, and both powder X-ray and neutron data of these compounds are reported, along with the single-crystal analysis used to solve the structures