Search

A superconductor is a material that can conduct electricity without resistance below a superconducting transition temperature, [T.sub.c]. The highest [T.sub.c] that has been achieved to date is in the copper oxide system (1): 133 kelvin at ambient pressure (2) and 164 kelvin at high pressures (3). As the nature of superconductivity in these materials is still not fully understood (they are not conventional superconductors), the prospects for achieving still higher transition temperatures by this route are not clear. In contrast, the Bardeen-Cooper-Schrieffer theory of conventional superconductivity gives a guide for achieving high [T.sub.c] with no theoretical upper bound--all that is needed is a favourable combination of high-frequency phonons, strong electron-phonon coupling, and a high density of states (4). These conditions can in principle be fulfilled for metallic hydrogen and covalent compounds dominated by hydrogen (5,6), as hydrogen atoms provide the necessary high-frequency phonon modes as well as the strong electron-phonon coupling. Numerous calculations support this idea and have predicted transition temperatures in the range 50-235 kelvin for many hydrides (7), but only a moderate [T.sub.c] of 17 kelvin has been observed experimentally (8). Here we investigate sulfur hydride (9), where a [T.sub.c] of 80 kelvin has been predicted (10). We find that this system transforms to a metal at a pressure of approximately 90 gigapascals. On cooling, we see signatures of superconductivity: a sharp drop of the resistivity to zero and a decrease of the transition temperature with magnetic field, with magnetic susceptibility measurements confirming a [T.sub.c] of 203 kelvin. Moreover, a pronounced isotope shift of [T.sub.c] in sulfur deuteride is suggestive of an electron-phonon mechanism of superconductivity that is consistent with the Bardeen-Cooper-Schrieffer scenario. We argue that the phase responsible for high-[T.sub.c] superconductivity in this system is likely to be [H.sub.3]S, formed from [H.sub.2]S by decomposition under pressure. These findings raise hope for the prospects for achieving room-temperature superconductivity in other hydrogen-based materials., A search for high- (room)-temperature conventional superconductivity is likely to be fruitful, as the Bardeen-Cooper-Schrieffer (BCS) theory in the Eliashberg formulation puts no apparent limits on [T.sub.c]. Materials with light [...]

The anode materials that have been developed for solid oxide fuel ceils (SOFCs) are vulnerable to deactivation by carbon buildup (coking) from hydrocarbon fuels or by sulfur contamination (poisoning). We report on a mixed ion conductor, Ba[Zr.sub.0.1][Ce.sub.0.7][Y.sub.0.2-x][Yb.sub.x][O.sub.3-[delta]] , that allows rapid transport of both protons and oxide ion vacancies. It exhibits high ionic conductivity at relatively Low temperatures (500[degrees] to 700[degrees]C). Its ability to resist deactivation by sulfur and coking appears linked to the mixed conductor's enhanced catalytic activity for sulfur oxidation and hydrocarbon cracking and reforming, as well as enhanced water adsorption capability.

An X-ray spectroscopy and theoretical study of the chemical state of several sulfur bearing minerals and a synthetic sodium sulfite sample was performed. X-ray absorption and high-resolution K[alpha] X-ray emission spectra were recorded and compared to ab initio quantum chemical calculations. A consistent interpretation of the chemical shift in the K[alpha] emission spectra is obtained based on three different theoretical approaches (density functional theory, multiple scattering theory, and atomic multiplet theory). An analysis of the theoretical sulfur orbital population and valence bond is in agreement with the fluorescence energy position of the K[alpha] lines even within the sulfide ([S.sup.2-]) series. It is shown that the K[alpha] energy shifts can be used for a quantitative determination of the proportion of different sulfur species in heterogeneous samples.

The research presents the synthesis, structure, electrical and physical properties of the polar oxysulfide CaZnOS. The compound is found to exhibit a non-phase-matchable second harmonic generation, as it is ferroelectric and contains very small pyroelectric coefficient between the room temperature and the boiling point of water.

The synthesis of some compounds belonging to the [Cu.sub.2]Sn[S.sub.3]-[Cu.sub.2]Si[S.sub.3] system and the crystal structure determination are described. The compounds were found to crystallize in a monoclinic structure like the pure phases and there was a smooth decrease in the crystallographic parameters with x despite the large difference between the radii of Sn and Si.

Abstract -- Results of an X-ray fluorescence determination of sulfur and other elements in oils and liquid oil products are presented, obtained using a Spectro-Xepos energy-dispersive spectrometer with the excitation [...]

The compounds [Ce.sub.53][Fe.sub.12][S.sub.90][X.sub.3] (X=Cl, Br, I) consiered as the first examples of rare-earth transition-metal sulfide halides, are prepared using the reactive-flux method, through reaction of [Ce.sub.2][S.sub.3], FeS, or Fe and S in a Ce[X.sub.3] flux at 1320 K. Their structures are determined by single-crystal X-ray diffraction. The compounds are isostructural, crystallizing in the trigonal space group.

A hydrothermal reaction route using dithiol glycol as the sulfur source is used to synthesize wurtzite-type CdS nanostructures, also enabling generation of nanostructures with controllable geometric shapes and structures and thus, optical properties. Their photoluminescence peaks change due of the change in their shape, and these samples facilitate the study of evolution of crystal growth and optical properties, with the shape of the nanocrystals varying from nearly spherical particles to wires.

Two red and yellow-brown oxo-sulfido niobium aqua ions are isolated by treatment of Zn-reduced ethanolic solutions of Nb[Cl.sub.5] with HCl in the presence of sulfide followed by cation-exchange chromatography. The red aqua ion, [[Nb.sub.4]{[mu.sub.4]-S}{[mu.sub.2]-O}[.sub.5]{[H.sub.2]O}[.sub.10]][.sup.4+] is characterized and investigated and the yellow-brown aqua ion [[Nb.sub.5]{[mu.sub.3]-S}[.sub.2]{[mu.sub.3]-O}[.sub.2]{[mu.sub.2]-O}[.sub.2]{[H.sub.2]O}[.sub.14]][.sup.8+] is characterized.

The nitrosation reaction of [Ry(NO)[(py).sup.si][S.sub.4])]Br.THF with hydrazine in different nonaqueous solvents to form nitrous oxide and [Ru(N[H.sub.3])-([py.sup.si][S.sub.4])] is reported. The reaction of [Ry(NO)[(py).sup.si][S.sub.4])]Br.THF with N[H.sub.3] or [N.sub.3.sup.-] does not lead to a nucleophilic attack at the N[O.sup.+] ligand but to a deprotonation that yields neutral nitrosyl complex [Ru(NO){[py.sup.si][S.sub.4][(H.sup.+])}].

A strategy to locate spectroscopic probes in micelles is presented that involves establishing a 'benchmark' probe and 5-doxylstearic acid methyl ester (5DSE) is described by the zero-order-model (ZOM) for S[N.sub.c]S, [N.sub.c] as well as for ammonium dodecyl sulfate (Am12S) micelles. The displacements are well correlated with the volume fraction of the polar shell occupied by water and departures from the ZOM as small as 0.2 Angstrom might also be detected.

The effect of adding a static axial magnetic field, which is used to increase the confinement and the plasma heating via helicon wave propagation, is investigated. The results have shown that the unstable double layers, and therefore the axial electrostatic confinement, are suppressed in a large part of the parameter space and the magnetic confinement has led to a radially stratified plasma, the center being a low-electronegativity, high-density plasma and the edges being essentially an ion-ion plasma.

Explorations of the reactivity of Fe/Mo/S clusters of some relevance to the FeMoco nitrogenase has led to new double-fused cubane clusters with the Mo2Fe6S8 core as derivatives of the known (Cl4-cat)2Mo2Fe6S8(PPr3)6 (l) fused double cubane. New clusters are obtained by substitution reactions of the PPr3 ligands with Cl(super -), BH4(super -) and N3(super -).

The ferroelastic domain switching that occurs in the three single crystals due to external mechanical stress is studied. The critical stress values for switching from the ferroelastic twin domain to the paraelastic single domain are obtained.

The spectroscopic properties of poly(3,4-ethylenedithiathiophene) (PEDTT) which is a sulfur analogue of poly(3,4-ethylenedioxythiophene) (PEDOT) are studies by in situ techniques like IR, Vis and electron spin resonance (ESR) spectroelectrochemistry. Despite the topological equivalence of PEDTT and PEDOT, their IRAV signatures are found to be different and the results suggest very different conformations for the two materials.

A resorcarene derivative designed with pendant arms having sulfur donor atoms namely 5,11,17, -23-ethylthiomethylated calix[4] resorcarene is described. Electrical conductance provided key information regarding the composition of metal-ion complexes and their decomposition.

A study is conducted on the effect of particle size on the different process of hydration of tricalcium silicate, the nucleation, the growth and the thickness of the layer limiting the hydration rate. The thickness of the C-S-H layer when the reaction becomes limited by diffusion is estimated.

The interplay between Auger effects and ionization processes are studied in the limit of strong electronic confinement in core/shell CdSe/ZnS semiconductor nanocrystal quantum dots. The results suggest that Auger recombination accelerates ionization processes that lead to the occupation of dark, nonemissive nanocrystal states.

Abstract -- A new highly sensitive, stable, and accurate fluorometric method for the determination of indium(III) has been established in cetyltrimethylammonium bromide(CTMAB) microemulsion media. The excellent color-forming reagent 2,6,7-trihydroxy-9-(3,5-dibromo-4-hydroxyphenyl) fluorone [...]

Large-amplitude pH oscillations are measured during the oxidation of sulfur (IV) species by the bromate ion in aqueous solution in a continuous-flow stirred tank reactor (CSTR) in the absence of any additional oxidizing or reducing reagent. Agreement between calculated and measured dynamical behavior is found to be good and it is also found that increasing temperature decreases both the period length of oscillations in a CSTR and the Landolt time measured in a closed reactor.

The mechanisms that are responsible for the rapid deactivation of the (super 1)n(pi)* and (super 1)n(pi)(pi)* excited single states of the 9H isomer of adenine are investigated with multireference ab initio methods. Two novel photochemical pathways, leading to conical intersections of the S(sub 1) excited potential-energy surface with the electronic ground-state surface, are identified.

The photophysical properties of the newly synthesized starlike CdS are investigated, which was prepared from the lyotropic triblock copolymer solution. It is concluded that the starlike CdS shows the photogenerated charge carriers' diffusion from the tip edge of the conical nanolobes to the thicker inner part including the core, likely as the light-harvesting system of the organic dendrimer.

The direct spectroscopic observation of the dianisylcarbenium ion during the trifluoroethanolysis of dianisylmethyl chloride, a solvolysis reaction that proceed with fast ionization followed by slow trapping of the carbocation by the solvent is discussed. By using less stabilized benzhydrylium ions it may be possible to describe the change from S(sub N)1 to S(sub N)2 reactions on the basis of absolute rate constants.

It is shown that the electronic effects of sulfur in gamma-sulfenyl enones are not passed on to the carbonyl carbon through the pi bond. These effects arise from the substituents on the sulfur atom and the gamma-carbon and from the bulk of the nucleophile.

The claimed diradical character N2S2, a four-membered-ring system with 6(pi) electrons is reexamined. The characteristics as well as the electronic structure of N2S2 are composed with those for an isoelectronic pi system, Li2C4H4, motivated by theoretical and recent experimental investigations that confirmed its aromaticity.

CS2(super -) and S2(super -) anions are used as model systems to outline the methodology of negative-ion photoelectron imaging and general aspects of interpretation of the results. Photoelectron images recorded at a series of wavelengths are used to examine the electronic structure and the electron ejection dynamics for both the anions.

A simple and convenient one step route is described for preparing a series of chalcospinels [Fe.sub.1-x][Cu.sub.x][Cr.sub.2][S.sub.4] by using high frequency sound waves. The results have provided an effective method for synthesizing doped ternary chalcospinels displaying magnetoresistive properties.

An ab initio study of two series of carbon-to-carbon proton transfer reactions is conducted to examine the degree of aromaticity of [C.sub.4][H.sub.4]X (X = CH(-), NH, S, O, PH) and the antiaromaticity of [C.sub.4][H.sub.4]X (X = AlH, BH) is expressed at the transition state of the proton transfer and its effect on the respective intrinsic barriers. The results revealed a disproportionately large degree of aromaticity at the transition state for the aromatic systems and a disproportionately small degree of transition state antiaromaticity for the antiaromatic systems.

The enantioselective fluorination of readily available cyclic allylic chlorides with AgF was performed in presence of a Pd(0) catalyst and Trost bisphosphine ligand. The results supported a mechanism in which C-F bond formation occurs by an [S.sub.N]2-type attack of fluoride on a Pd(II)-allyl intermediate

The bisdithiazolyl radical is dimorphic, which is present in two distinct molecular and crystal modifications. The changes in conductivity of [beta]-bisdithiazolyl radical are interpreted in terms of a pressure-induced dimer-to-radical phase change and the response of the S...S-S...S [sigma]-bond in [beta]-bisdithiazolyl radical to heat and pressure is compared to that of related dimers possessing S...Se-Se...S [sigma] bonds.

The enantioselective intermolecular [2+2+2] cycloaddition reaction of two molecules of isocyanate and one molecule of allene is catalyzed by a nickel(0)/(S,S)-i-Pr-FOXAP complex, which has provided access to enantiomerically enriched dihydropyrimidine-2,4-diones.

Several time resolved photoluminescence measurements are conducted to explain the nonradiative energy transfer taking place from the CdSeS quantum dots to the gold nanofilm. The observed energy transfer is shown to lead to a significant reduction in the excitonic state lifetime of the quantum dots.

The article analyzes the synthesis and the properties of the various CdS/CdSe cosensitized oriented single-crystalline Ti[O.sub.2] nanowire arrays. The formation of various core-shell structure films via these arrays, which are also employed in solar cell applications, is also discussed.