NaSe 2 Yb, trigonal, R3m (No. 166), a = 4.0568(8) Á, c = 20.772(6)Á, V = 296.1 Â 3 , Z= 3, R gt (F) = 0.051, wR K f(F 2 ) = 0.110, Γ =298 Κ. Source of materialCrystals of NaYbSe2 were formed from a molten chalcogenide flux reaction of 51.5 mg Yb, 21.8 mg Ge, 94.0 mg Se, and 40.6 mg Na2Se2.The reactants were combined in a fused silica ampoule in an inert atomosphere glovebox, sealed under vacuum, and heated to 998 Κ at a rate of 35 Κ / hour.After 72 hours of heating, the ampoule was cooled at 4 Κ / hour to room temperature.Dimethylformamide was added to dissolve remaining sodium selenide flux, resulting in well-formed hexagonal red-orange plates of NaYbSe 2 .
Near-monodisperse microscopic nanostructures of MoS2 were prepared by thermal decomposition of two different ammonium thiomolybdate molecular precursors, (NH4)2MoS4 and (NH4)2Mo3S13, within the confined voids of a porous aluminum oxide membrane template. Our low-temperature (450 °C) synthetic route yielded large quantities of hollow tubules of MoS2 of uniform size and shape that were ∼30 μm long with diameters of 50 nm and wall thicknesses of about 10 nm. More irregularly shaped, mainly solid fibers of MoS2 with diameters of about 200 nm were synthesized by changing the template to one with larger pores. The morphology of the fibers or tubules was studied with respect to the choice of precursor, the characteristics of the precursor solutions, the incorporation methods, the template characteristics, and the heat treatment during firing. The MoS2 structures were characterized by scanning and transmission electron microscopies, energy dispersive spectroscopy, electron and X-ray diffraction, and optical absorption spectroscopy. This template-assisted growth process yielded large quantities of MoS2 tubules or fibers that could be isolated from the template. However, under the growth conditions studied, the formation of HxMoS2 "bronzes" could not be discounted.
Films of tantalum pentoxide (Ta2O5) with thickness of 10–100 nm were deposited on Si wafers and have been compared using spectroscopic ellipsometry (SE) and x-ray reflectivity (XRR). (Ta2O5) was chosen for comparison work based on various criterions for material selection outlined in this article. Measurements were performed at six positions across the sample area to take into consideration thickness and composition inhomogeneity. SE and XRR fitted curves required the incorporation of a linearly graded interface layer. SE systematically measured higher values of film thickness as compared to XRR. A linear equation was established between the thickness measurements using SE and XRR. The slope of the linear equation established was found to be 1.02±0.01. However, the intercepts were found to be 1.7±0.2 and 2.6±0.3 when the interface was excluded and included, respectively. These differences in the values of intercepts were attributed to the uncertainties in the determination of the interface layer.
The Cottrell Scholars Collaborative (CSC) Academic Leadership Team (ALT) staged its first leadership workshop in February 2016. Its objective is to provide teacher-scholars with the theory and tools for effective leadership as well as exposure to the practice of being a leader in academia. Academic leadership is here defined to include research center directors, department heads, deans, or related institutional administrators. Our hypothesis is that this intentional approach to train future leaders will enable them to be more effective in such roles. In this article, we report the details of the first workshop, and its effectiveness as determined from pre- and post- assessments.
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A new compound, Na1.515EuGeS4, has been synthesized at 750 °C from a reaction of elemental europium, germanium, and sulfur and Na2S. The compound crystallizes in the trigonal system with Z = 18 and the R3c space group with a = 23.322(3) Å, c = 6.838(1) Å, and V = 3221.2(9) Å3. Na1.515EuGeS4, which is isostructural with Na2EuSiSe4, contains quasi-infinite nanoscale ∞[EuGeS4]2– tubules that are held together by sodium cations through electrostatic interactions. The tubules consist of a complex network of monoface-capped EuS7 trigonal prisms and GeS4 tetrahedra. The most striking structural feature of Na1.515EuGeS4 is the absence of sodium cations inside the tubules, an absence that is balanced by the presence of mixed valence europium(II/III) ions. This mixed valence is confirmed by europium-151 Mössbauer spectroscopy, which indicates discrete mixed-valence europium ions at least up to 295 K. The stoichiometry has been determined by a fit of χMT measured between 20 and 300 K with a combination of europium(II) ions, with a Curie constant of 7.877 emu K/mol, and europium(III) ions whose contribution to χMT has been fit by using the Van Vleck expression for its molar susceptibility. The best fit corresponds to 51.5% of europium(II), 48.5% of europium(III), a stoichiometry of Na1.515(5)EuGeS4, and a splitting, E, between the J = 0 and the first excited J = 1 state of europium(III) of 360(6) cm–1. The field dependence of the 1.8 K magnetization is in perfect agreement with a S = 7/2 Brillouin function with g = 2.00 and yields a saturation magnetization of 7 Nβ at 5 T.
This chapter contains sections titled: Introduction The Building-block Approach Quaternary Rare-earth Metal Chalcophosphates Quaternary Rare-earth Metal Chalcoarsenites and Antimonites Quaternary Rare-earth Metal Chalcotrielates and Tetrelates Summary References
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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