Nouveaux thiochlorures de molybdène(II): Mo6Cl10Y (Y = S,Se, Te): Structure et propriétés magnétiques et électriques

The thiochlorides Mo₆Cl₁₀Y (Y = S, Se, Te) have been prepared; they are isostructural with Nb₆I₁₁, space group Pccn, and have four formula units per unit cell. The X-ray structure of Mo₆Cl₁₀Se has been determined from three-dimensional single-crystal counter data and refined to a final R value of 0.053 for 3350 independent reflections. The most important result concerning this structure is a statistical distribution of the Se atom on the unit (Mo₆X′₈) with $\text{X′ ?}\text{7}\text{8}\text{Cl}\text{+}\text{1}\text{8}\text{Se}$: so the compound Mo₆Cl₁₀Se must be formulated $\text{(Mo}{}_6\text{Cl}{}_7\text{Se)Cl}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}\text{Cl}{}_{\mathrm{<mtext>2</mtext><mtext>2</mtext>}}$. The diamagnetic and dielectric behavior of these new thiochlorides is discussed.     

Sur de nouvelles phases séléniées ternaires du molybdène

The synthesis and the crystal properties of new selenides of formula M_xMo₃Se₄ are described. If M = Zn, Ag, Cd, Sn and Pb, they are stoichiometric with x = 0.6; if M = Fe, Mn, Cr, V, Ti, triclinic solid solutions are observed with 0.5 < x < 0.7; if M = Cu, Co, Ni, rhombohedral solid solutions are obtained with 0 < x < 1.4 for M = Cu, 0 < x < 0.7 for M = Co and 0 < x < 0.8 for M = Ni All these phases can be deduced from the Mo₃Se₄ structure by introducing metal atoms into the tunnels between the “Mo₆Se₈” metal atom cluster configuration.     

Crystallochemistry of some new niobium bromides with (Nb6Br18) units: Structures of CsErNb6Br18 and Cs2EuNb6Br18

Two new series of Nb₆ bromides, CsRENb₆Br₁₈ (RE = all the lanthanides excepted Eu and Yb, + Y) (type H ) and M₂RENb₆Br₁₈ (M = Cs, Rb, Tl; RE = Eu, Yb) (type R ) have been isolated. The crystal structures of CsErNb₆Br₁₈ and Cs₂EuNb₆Br₁₈, isotypic with the corresponding chlorides, have been determined by single crystal X-ray diffraction data. The (Nb₆Br₁₈) intra-unit strength is related to the nature and the charge of the counter cation. A comparison between the corresponding chlorides and bromides series, based on the chemical properties and the size of the halogen is discussed.     

Transport and percolation in a low-density high-mobility two-dimensional hole system

We present a study of the temperature and density dependence of the resistivity of an extremely high quality two-dimensional hole system grown on the (100) surface of GaAs. For high densities in the metallic regime (p > or approximately4x10;{9} cm;{-2}), the nonmonotonic temperature dependence ( approximately 50-300 mK) of the resistivity is consistent with temperature dependent screening of residual impurities. At a fixed temperature of T=50 mK, the conductivity versus density data indicate an inhomogeneity driven percolation-type transition to an insulating state at a critical density of 3.8x10;{9} cm;{-2}.     

Degradation Thermique des Polystyrenes et du Polychlorure de Vinyle : Application d'une Matrice d'experiences a l'etude de l'influence des Parametres de l'analyse Thermomanometrique. Partie I : Exploitation des résultats par traitement mathématique

Thermal degradation of polystyrene and polyvinylchloride was studied by thermomanometric analysis. A design of experiments was used to quantify the influence of 8 physico-chemical parameters on the responses of the analyser and on the different types of degradation compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interpretation dü spectre RMN-3H du PK-11195 (3H)

(1D-³H NMR) of PK 11195 ³H gives a complex spectrum. Homonuclear 2D-³H NMR (COSY and J. Resolved) gives useful information such as tritium chemical shifts, ³H-³H and ³H-¹H coupling constant, percentage of isotopomers and specific activity.