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41.
42.
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) Å3, 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: dV-S = 2.471(1) Å, dP-S = 2.050(1) Å, dV-V = 3.715(2) Å. From the various oxydation states of the atoms, the developed formula can be written VIII2PV4S?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. 相似文献
43.
The structure of M0.50NbSe2 (M = Ti, V, Cr) phases is reported. A detailed crystal structure analysis has been performed on Cr0.50NbSe2. 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 Cr0.50NbSe2 and Ti0.50NbSe2 follow the Curie-Weiss law. At low temperature (T < 53°K) an antiferromagnetic ordering is observed for Cr0.50NbSe2. V0.50NbSe2 exhibits a temperature-independent paramagnetism. Transport properties of M0.50NbSe2 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. 相似文献
44.
Single crystals with I0.33NbSe4 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 with Z = 12. The structure is built up with chains of rectangular [NbSe8]-antiprisms. Iodine atoms are located between these chains. 相似文献
45.
Results about new ionic conductors NaxYxZr1?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. 相似文献
46.
The mechanical response of different glasses to a Vickers indentor has been investigated between room temperature and Tg+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 Tg 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. 相似文献
47.
J. James G.V. Thomas D. Rouxel M. Strankowski N. Kalarikkal S. Thomas 《Materials Today Chemistry》2021
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. 相似文献
48.
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. 相似文献
49.
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. 相似文献
50.