Synthesis and structure determination of a new layered compound: V2P4S13

V₂P₄S₁₃ was prepared from the elements taken in stoichiometric proportions and heated in an evacuated Pyrex tube for 10 days at 450°C. The crystal symmetry is triclinic, space group P1¯ with the parameters: a = 9.112(1) Å, b = 9.680(1) Å, c = 11.620(1) Å, α = 72.15(1)°, β = 110.82(1)°, γ = 110.13(1)°, V = 879.5(1) ų, and Z = 2. The structure was solved from 3052 independent reflections and 173 parameters, the least-squares refinement yielding R = 0.033. The building units of the structure are made up of two distorted (VS₆) octahedra and four distorted (PS₄) tetrahedra sharing edges to form (V₂P₄S₁₆) groups. These share sulfur atoms through their four (PS₄) tetrahedra with the same neighbor groups. Infinite (V₂P₄S₁₃) planes parallel to (101) are thus obtained, with no bonds other than van der Waals' ones between them. Within the slabs, the layered phase presents the following average distances: d_V-S = 2.471(1) Å, d_P-S = 2.050(1) Å, d_V-V = 3.715(2) Å. From the various oxydation states of the atoms, the developed formula can be written V^III₂P^V₄S^?II₁₃. The phase is semiconducting and magnetic susceptibility measurements show a Curie behavior with the occurrence of high spin d² vanadium. Antiferromagnetic ordering is observed below 10 K.     

Structure cristalline et propriétés physiques électriques et magnétiques des phases M0.50NbSe2 (M = Ti,V, Cr)

The structure of M_0.50NbSe₂ (M = Ti, V, Cr) phases is reported. A detailed crystal structure analysis has been performed on Cr_0.50NbSe₂. Large single crystals were grown by chemical transport reaction with bromine as the transport agent. Electrical and magnetic properties have been measured in the 4.2–300°K range. Susceptibilities of both Cr_0.50NbSe₂ and Ti_0.50NbSe₂ follow the Curie-Weiss law. At low temperature (T < 53°K) an antiferromagnetic ordering is observed for Cr_0.50NbSe₂. V_0.50NbSe₂ exhibits a temperature-independent paramagnetism. Transport properties of M_0.50NbSe₂ phases are consistent with their metallic behavior and show several transitions at low temperature. The physical properties are discussed along with the reported crystal structure.     

Preparation et structure cristalline de I0.33NbSe4(I4Nb12Se48)

Single crystals with I_0.33NbSe₄ composition are grown, along with NbSe₂ crystals, by iodine vapor transport from NbSe₃. Single phase powder is obtained by heating the elements in corresponding proportions at 700°C. The structure has been studied by X-ray diffraction on a single crystal. The symmetry is tetragonal with the following parameters of the unit cell a = 9.489 Å, c = 19.13 Å. The space group is $\text{P4}\text{mnc}$ with Z = 12. The structure is built up with chains of rectangular [NbSe₈]-antiprisms. Iodine atoms are located between these chains.     

Les conducteurs ioniques NaxYxZr1−xS2

Results about new ionic conductors Na_xY_xZr_1?xS₂ are presented. The electronic conductivity normally induced by sodium intercalation layered chalcogenides has been suppressed by performing at the same time a substitution of zirconium by yttrium in the slabs of the host structure. Electrical measurements using the complex impedance technique lead to the activation energy of the ionic conduction. This energy was found to present a marked minimum around x = 0.50. A NMR study showed quadrupole coupling to prevail in relaxation process. Electrical field gradient is maximum for x = 0.50. The activation energy of the local motion remains practically constant throughout the composition range. The above results are compared to others obtained from compounds having the same structure.     

Indentation response of glass with temperature

The mechanical response of different glasses to a Vickers indentor has been investigated between room temperature and T_g+50 °C. The permanent deformation, from which hardness is estimated, as well as the brittle fracture characteristics, allowing for an evaluation of the fracture toughness, were measured and analysed. Comparison between a standard float glass and advanced glasses such as chalcogenide (with mainly covalent bonding) and metallic glasses was made to get a more general insight into high temperature indentation behaviour. As temperature increases, the glass response becomes more and more time-dependent, and in the vicinity of T_g the permanent deformation was observed to increase rapidly for all glasses. Further, while the standard float glass showed an enhanced apparent toughness at elevated temperatures due to a brittle to ductile transition, almost no change in apparent toughness was revealed in the GeAsSe glass emphasizing the time-dependent response of glass at elevated temperature.     

Fabrication of toughened plastic using styrene butadiene rubber-poly (methyl methacrylate) interpenetrating polymer networks

A standard set of interpenetrating polymeric networks (IPNs) has been contrived using an elastomer-styrene butadiene rubber and a thermoplastic poly (methyl methacrylate) through sequential polymerization protocol. This low-cost material can be hopefully engaged as a toughened plastic with co-continuous morphology. Different morphological protocols including Raman imaging are effectively utilized to envisage the effect of blend ratio in IPN fabrication. The different mechanical properties of IPNs revealed that the cross-linking in phases have their own impact. Thermogravimetric analysis is used as an efficient tool to prove the extra thermal stability of IPNs. Of seven different composites theoretical models, the Davies model showed better fit to the experimental data. The etiquette of characterization adopted in this work including mechanical, morphological, and thermal protocols and their correlation with theoretical predictions can definitely be act as a platform for the synthesis of low-cost toughened plastic.     

The influence,on lithium electrochemical intercalation,of bond ionicity in layered chalcogenophosphates of transition metals

In the course of lithium electrochemical intercalation in the host structure of layered M∥PX₃ phases (M = V, Mn, Fe, Co, Ni, X = S, Se), it was shown that the best energy yield was obtained from low ionicity bond materials. The absorption edge energy, along with the free energy of the intercalation reactions have been correlated in a satisfactory way to the ionicity fi of the M-X bonds. These diagrams indicate which phases have to be looked at to obtain the maximum electrochemical yields.     

Surface oxidation and thin film preparation of AlCuFe quasicrystals

This paper reviews the work carried out over the last decade by the Nancy team on surface oxidation and thin film preparation of AlCuFe icosahedral quasicrystals. After discussing the problems linked with the surfaces of these quasicrystals, this review addresses the issue of the preparation of quasicrystalline surfaces and the first steps of oxidation under very low pressure of oxygen. This paper compares the nucleation and growth of oxide on i-AlCuFe quasicrystal and on a classical crystalline phase of this alloy: ω-AlCuFe. Aluminium diffusion is studied through the aluminium segregation on the surface that occurs during exposure to oxygen. Some surface properties of quasicrystals are reviewed with regard to oxidation. The evolution of physical parameters such as surface energy, friction coefficient and optical emissivity is described. This review also deals with the preparation of i-AlCuFe thin films. Two protocols to make i-AlCuFe thin films with free surfaces are described and discussed. The mechanical resistance and the tribological behaviour of these thin films, the oxygen and carbon influence on the final crystalline structure, and the quasicrystallization kinetics are presented.