Prismatic Configuration Research Articles

Crystal structure of neodymium(III)-diethylene glycol complex

The title complex was crystallized from a diethylene glycol (DEG) solution containing 0.2 M neodymium trichloride hexahydrate. The X-ray structural analysis of the complex showed that [Nd(DEG) 3] 3+ cation consists of a central neodymium atom coordinated with nine oxygen atoms from the three DEG ligands with the approximate tricapped-trigonal prismatic configuration. There was a slight difference in conformation among the three DEG chains: one DEG ligand exhibited a zig-zag chain, while the other two were approximately planar due to disordering of the zig-zag conformations. The unequivalence of the conformation among the DEG ligands could be explained by an asymmetric arrangement of Cl − anions surrounding the [Nd(DEG) 3] 3+ cation.

Lithium-ion battery for electronic applications

Lithium-ion (rocking-chair) batteries with lithiated metal oxide cathodes and carbon anodes are finding use in many emerging electronic applications with current drains ranging from a few microamperes (e.g., memory backup, real-time clock, bridge function) to many milliamperes (e.g., laptop computers, phones, etc.). The majority of these applications (e.g., coin, cylindrical, prismatic cell configuration) require a steady low current with periodic high drain pulses. We have found that lithium-ion systems based on lithiated nickel oxide cathodes (LiNiO 2) and carbon anodes can be tailored for high capacity moderate rate or moderate capacity high rate applications. In the first instance, a graphitic carbon anode and ethylene carbonate-based electrolyte (e.g., ethylene carbonate-dimethyl carbonate (EC-DMC)) has proven effective while in the second case a petroleum coke anode and propylene carbonate-based electrolyte (e.g., propylene carbonate-dimethoxyethane (PC-DME)) look best. An unoptimized, experimental LiNiO 2/LiPF 6, EC-DMC/graphitic carbon, AA-cell has delivered 620 mAh at 0.1 mA cm −2 but the capacity then dropped to 535 mAh at 1 mA cm −2 and 375 mAh at 3 mA cm −2. Efforts are under way to improve the rate capabilities of cells incorporating graphitic carbon anodes. Initial results indicate that microfiber graphite, special electrolytes and in-house prepared LiM x Ni 1− x O 2 compounds will achieve the desired performance levels.

An EXAFS Study on the Ni and W Environment in Carbon-Supported, Sulfided W and Ni-W Catalysts

The structure of sulfided W/C and Ni-W/C catalysts was studied by means of EXAFS on the W LIII-edge and Ni K-edge. In the W/C catalyst the tungsten is present as small WS2 particles consisting of 5 to 14 W atoms, while the higher W-W coordination number in the Ni-W/C catalysts points to a larger WS2 particle size and/or crystallinity. Also, the W-S coordination number increased, which can be explained by a more pronounced sulfidation combined with a larger particle size. Up to a Ni/W atomic ratio of 0.5 all Ni was found to be present in a Ni-W-S-like structure, which strongly resembles the Ni-Mo-S structure in Ni-Mo/C catalysts. A difference is that in the Ni-W/C catalysts Ni is coordinated by six sulfur atoms, probably in a trigonal prismatic configuration. Four of these sulfur atoms are located at a distance of 2.22 Å from the Ni atom, and two at 2.35 Å. The intrinsic catalytic activity of the Ni atoms in the Ni-W-S structure for thiophene hydrodesulfurization turned out to be the same as in Ni-Mo/C catalysts, which suggests that the Ni atoms are the catalytically active sites.

Kinetics of Intercalation of Lithium into NbSe3 and TiS2 Cathodes

Titanium disulfide and niobium triselenide are two well‐studied candidate materials for positive electrodes in rechargeable lithium cells. A comparative study of the kinetics of intercalation of lithium in both the cathodes is made here based on various electrochemical techniques, i.e., linear polarization, potentiodynamic polarization, and ac impedance under different experimental conditions such as prismatic or disk configuration of fresh, partially discharged, or cycled electrode. Further, the diffusion coefficients of lithium ions in these cathodes are estimated under these conditions using conventional techniques, i.e., ac impedance, chronocoulometry, chronoamperometry, and current pulse relaxation. Based on the values of the diffusion coefficients, the applicability of these methods for the determination of diffusion coefficients is discussed.

Raman study and lattice dynamics of single molecular layers of MoS2.

A valence-force-field model has been used to study the lattice dynamics of molybdenum disulfide single molecular layers. A comparison between the room-temperature Raman spectra of aqueous suspensions and the calculated phonon-dispersion curves for single layers of ${\mathrm{MoS}}_{2}$ with trigonal prism and octahedral coordination indicates that ${\mathrm{MoS}}_{2}$ single layers adopt a structure in which the Mo atoms are octahedrally coordinated, as opposed to bulk ${\mathrm{MoS}}_{2}$ where the trigonal prism coordination is usually found. Besides the zone-center modes, strong Raman peaks have been observed at 156, 226, and 333 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The presence of these peaks is attributed to a zone-folding mechanism resulting from the formation of a 2${\mathit{a}}_{0}$\ifmmode\times\else\texttimes\fi{}${\mathit{a}}_{0}$ superlattice in the single layers of ${\mathrm{MoS}}_{2}$. The superlattice is, in turn, believed to correspond to the basal-plane atomic arrangement of a distorted octahedral structure. Lattice-dynamics calculations based on an octahedrally coordinated structure with a significant metal-metal interaction yield good agreement with the observed frequencies. When the single molecular layers restack and the sulfur-sulfur interaction between the layers is recovered, the layers convert back to the trigonal prismatic configuration of crystalline ${\mathrm{MoS}}_{2}$.

Problems of supersonic flow over bodies of prismatic configuration

Problems of supersonic flow over bodies of prismatic configuration

The Li/TiS2 cell with LiSCN electrolyte

An ambient temperature, rechargeable lithium/titanium disulphide cell with a lithium thiocyanate-1,3dioxolane (DOL)-1,2-dimethoxyethane (DME) organic electrolyte was investigated. Electrolyte compositions of 2.5–3.5 molal LiSCN in solvent compositions from 100% DOL to 0.80∶0.20::DOL∶DME were tested. NMR, infrared spectroscopy and linear-sweep voltammetric studies indicated that the electrolyte was thermally and electrochemically stable, except for the slow formation of dioxolane oligomers. Test cells contained 10–30 mAh cm−2 of TiS2 with two- to sixfold excess of Li in parallel-plate, prismatic configuration. Performance delivered 80–90% of theoretical charge on first discharge and showed not only a rate-dependent cycle life, but also sensitivities to the (anode loading)/(cathode loading) ratio and cathode charge density. Cells with 10–15 mAh cm−2 of TiS2 and four to sixfold excess Li operated 35–50 cycles atC/5 toC/15 rates, while 30 mAh cm−2 cathodes with 3∶1 ∶∶anode: cathode ratio cycled 10–20 cycles atC/10. Results of half-cell studies, performance variation with temperature and overcharge and overdischarge behaviour of the cells are presented. Possible causes of the loss of efficiency during cycling are discussed.

Analytical determination of heat flow shape factors for composite, prismatic bars of doubly-connected cross section

Cylindrical or prismatic configurations are used in many engineering situations (nuclear, mechanical, etc.). Oddly-shaped, doubly-connected geometries are required in some applications, and generated in general computer-oriented solutions by the research engineer. The title problem is solved in the present paper using an approximate conformal mapping approach. It is shown that the calculated shape factors are in good agreement with those obtained using a finite element code.

Hochdruckmodifikationen der Lanthaniden(III)sulfide Ln2S3 (Ln = Lu-Ho, Y) mit U2S3-Struktur / High Pressure Modifications of the Rare Earth Sulfides Ln2S3 (Ln = Lu-Ho, Y) with U2S3-Structure

New modifications of the rare-earth sesquisulfides Ln2S3 (Ln = Lu-Ho, Y) were found after high pressure, high temperature treatment and quenching to ambient conditions. The crystal structure of the prototype Tm2S3-III was determined from singlecrystal data. Tm2S3-III and the other members of the isotypic series Ln2S3-III are isostructural with U2S3. Some relations between the U2S3 structure and other structures with trigonal prismatic anion configurations are discussed.

Refraction of Thermal Neutrons by Shaped Magnetic Fields

The refractive bending of thermal neutrons by shaped magnetic fields has been studied experimentally and compared with that calculated from the field distribution. The small deflections, a few seconds arc, were measured on a double-crystal spectrometer utilizing matched perfect silicon crystals. Deflections were measured for a beam of polarized neutrons upon its polarization reversal for field regions of both prismatic and cylindrical configuration. The focusing and polarizing character of a magnetic lens have been observed.