Function Of Sulfur Concentration Research Articles

Bandgap engineering of BaTi(O$$_{1-\text{x}}$$S$$_\text{x}$$)$$_{3}$$ as a function of sulfur concentration

Bandgap engineering of BaTi(O$$_{1-\text{x}}$$S$$_\text{x}$$)$$_{3}$$ as a function of sulfur concentration

Evolution of lattice, spin, and charge properties across the phase diagram of FeSe1−xSx

A Raman scattering study covering the entire substitution range of the FeSe$_{1-x}$S$_x$ solid solution is presented. Data were taken as a function of sulfur concentration $x$ for $0\le x \le 1$, of temperature and of scattering symmetry. All type of excitations including phonons, spins and charges are analyzed in detail. It is observed that the energy and width of iron-related B$_{1g}$ phonon mode vary continuously across the entire range of sulfur substitution. The A$_{1g}$ chalcogenide mode disappears above $x=0.23$ and reappears at a much higher energy for $x=0.69$. In a similar way the spectral features appearing at finite doping in A$_{1g}$ symmetry vary discontinuously. The magnetic excitation centered at approximately 500 cm$^{-1}$ disappears above $x=0.23$ where the A$_{1g}$ lattice excitations exhibit a discontinuous change in energy. The low-energy mode associated with fluctuations displays maximal intensity at the nemato-structural transition and thus tracks the phase boundary.

Kinetics of Lithium-Polysulfide Flow Batteries

We recently demonstrated that the high solubility of polysulfides in nonaqueous electrolytes can be exploited to make a high energy density lithium-sulfur flow battery with low storage cost1–3. Here we used a new approach, whereby percolating networks of nanoscale conductor particles (in this case carbon black) are incorporated within the electrode forming an embedded current collector which distributes electrochemical activity throughout the volume of the flow electrode, rather than being confined to the surfaces of stationary current collectors. Compared to the traditional approach, this architecture enables significantly higher capacity (~1200 mAh / g S) and reversibility by allowing cycling of polysulfide solutions (2.0-2.5V) into the precipitation regime (~2V), where discharge proceeds via precipitation of insoluble Li2S, as shown in Figure 1.The majority of the available capacity of this battery lies in this precipitation regime. Therefore, understanding the kinetics of the precipitation process is essential to improving the reversibility and rate capability of lithium-sulfur flow batteries. Here, we will discuss the nucleation and growth kinetics of the precipitates on various conductive substrates, including various carbon surfaces and conducting oxides. Moreover, we will discuss the effects of cycling conditions and substrate on the morphology of the precipitates, examples of which are shown in Figure 2. The precipitation of lithium sulfide has long been a challenge for lithium-sulfur batteries due to its low electronic conductivity4,5, so controlling the morphology of precipitates can reduce losses due to Ohmic polarization.For a given depth of discharge, higher electrode level energy densities (Wh/L) may be obtained by increasing the sulfur concentration in the polysulfide solution. However, as sulfur concentration—and therefore electrode capacity—increase, the current needed to cycle at a fixed C-Rate increases as well. Therefore, it is important to understand the concentration-dependent transport and kinetic properties of lithium polysulfide solutions so that the rate-limiting mechanisms may be appropriately addressed. We have undertaken a systematic effort to characterize the ionic conductivity and exchange current density of lithium polysulfide solutions in various solvents as a function of sulfur concentration and solution composition (i.e. n in Li2Sn). Figure 3 shows the concentration-dependent ionic conductivity of Li2S8 solutions in selected non-aqueous solvents. Acknowledgements:This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.Figure captions:Figure 1. Fivefold higher reversible capacity for the nanoscale conductor suspension (1.5 vol% carbon black) compared to a traditional carbon fiber current collector when galvanostatically cycling in a non-flowing cell with a lithium anode.Figure 2. Scanning electron microscope image of lithium sulfide precipitates on a network of multi-walled carbon nanotubes after first discharge of a stationary lithium polysulfide cell at C/4 rate. On the circled nanotube, lithium sulfide particles merge together to form a conformal coating.Figure 3. Ionic conductivity of lithium polysulfide solutions (Li2S8) in selected nonaqueous solvents at varying sulfur concentrations from 1-8M.1. Fan, F. Y. et al. Polysulfide Flow Batteries Enabled by Percolating Nanoscale Conductor Networks. Nano Lett. (2014). doi:10.1021/nl500740t2. Demir-Cakan, R. et al. Li--S batteries: simple approaches for superior performance. Energy {&} Environ. Sci. 6, 176 (2012).3. Yang, Y., Zheng, G. & Cui, Y. A membrane-free lithium/polysulfide semi-liquid battery for large-scale energy storage. Energy {&} Environ. Sci. 6, 1552 (2013).4. Bruce, P. G., Freunberger, S. A., Hardwick, L. J. & Tarascon, J.-M. Li – O 2 and Li – S batteries with high energy storage. Nat. Mater. 11, 19–30 (2012).5. Manthiram, A., Fu, Y. & Su, Y.-S. Challenges and prospects of lithium--sulfur batteries. Acc. Chem. Res. 46, 1125–1134 (2013).

Zinc complexation in aqueous sulfide solutions: Determination of the stoichiometry and stability of complexes via ZnS (cr) solubility measurements at 100 °C and 150 bars

The solubility of ZnS (cr) was measured at 100 °C, 150 bars in sulfide solutions as a function of sulfur concentration ( m(S total) = 0.02–0.15) and acidity (pH t = 2–11). The experiments were conducted using a Ti flow-through hydrothermal reactor enabling the sampling of large volumes of solutions at experimental conditions, with the subsequent concentration and determination of trace quantities of Zn. Prior to the experiments, a long-term in situ conditioning of the solid phase was performed in order to attain the reproducible Zn concentrations (i.e. solubilities). The ZnS (cr) solubility product was monitored in the course of the experiment. The following species were found to account for Zn speciation in solution: Zn 2+ (pH t < 3), Zn (HS) 2 0 (pH t 3–4.5), Zn (HS) 3 - (pH t 5–8), and ZnS(HS) − (pH t > 8) (pH t predominance regions are given for m(S total) = 0.1). Solubility data collected in this study at pH t > 3 were combined with the ZnS (cr) solubility product determined at lower pH to yield the following equilibrium constants ( t = 100 °C, P = 150 bars): Zn 2 + + 2 HS - = Zn(HS) 2 0 ( aq ) log β 2 = 9.52 ± 0.06 , Zn 2 + + 3 HS - = Zn(HS) 3 - log β 3 = 12.39 ± 0.06 , Zn 2 + + 2 HS - = ZnS(HS) - + H + log β 11 = 2.92 ± 0.06 . The solubilities of ZnS (cr), determined beyond the Zn 2+ predominance region (at pH t > 2.5), are lower than the sphalerite solubilities previously reported in the literature, resulting in lower values of the formation constants for the Zn–S–HS complexes. The results of this study indicate that in natural sulfide-rich fluids the maximum Zn concentrations are attained at pH = p K 1(H 2S), where Zn (HS) 3 - predominates.

Effect of cross‐linking on the free volume properties of natural rubber

AbstractWe used Positron Annihilation Lifetime Spectroscopy (PALS) to investigate the effect of cross‐linking on the free volume properties of Natural Rubber (NR) composites. In order to form any meaningful product for industrial purposes, NR is mixed with different compounds, then cured in a process called vulcanization. One of the most important compounds used in the mixing process is sulfur. Sulfur forms cross‐links with NR restricting the mobility of the polymer chains. Addition of sulfur and vulcanization reduce the o‐Ps lifetime and intensity. By compating un‐vulcanized and vulcanized samples we show that sulfur inhibits Ps formation and that with cross‐link formation during vulcanization the o‐Ps lifetime and intensity both decrease with increasing sulfur concentration. Swelling measurements were also done using toluene absorption to measure cross–link density as a function of sulfur concentration. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Review of positron annihilation spectroscopy studies of rubber with carbon black filler

Positron annihilation lifetime spectra have been measured for rubber polymers with carbon black (CB) fillers as a function of temperature, sulfur concentration, type of CB fillers and type of polymer. The purpose of the study is to understand how the CB fillers and other components of the vulcanized composite affect the positron lifetime in polymer materials. The polymer samples to be studied include natural rubber (NR) with different sulfur concentration, Sn-SSBR either unloaded or loaded with CB N115 or N762, both vulcanized and unvulcanized Duradene 706 samples. The results show that CB fillers have no effect on the ortho-positronium lifetime but decrease the intensity of ortho-positronium; and the decrease in intensity depends on the type of CB. On the other hand both ortho-positronium lifetime and intensity decrease as a function of sulfur concentration.

Room-temperature electrical conductivity studies of sulfur-modified microcrystalline diamond thin films

The room-temperature electrical conductivity of sulfur-incorporated microcrystalline diamond (μc-D:S) thin films synthesized by hot-filament chemical vapor deposition was investigated as a function of sulfur concentration. The films were prepared using a 0.3% CH4/H2 gas mixture and hydrogen sulfide (H2S) as dopant source on intrinsic Si(001) substrates. The μc-D:S films exhibited an increase in n-type conductivity with increase in H2S concentration from 0 to 200 ppm, followed by a decrease in conductivity and sign reversal for the films grown with 500 ppm of H2S. These films were also characterized using scanning electron microscopy, atomic force microscopy, and Raman spectroscopy techniques. The findings are discussed in terms of the role of sulfur in the films. The films grown at the highest [H2S] possess the highest carrier concentration (∼1.07×1017/cm3) and the lowest carrier Hall mobility (0.01 cm2 V−1 s−1). Since the conductivity is affected by carrier concentration and crystallinity, the relatively low experimental conductivity values are connected to low mobilities arising from crystal defects and grain boundaries induced by sulfur addition, and to low carrier concentrations due to incomplete ionization of S atoms.

Effects of Sulfur Concentration on the Electron Field Emission Properties of Nanocrystalline Carbon Thin Films

ABSTRACTThe electron field emission properties of sulfur-assisted nanocrystalline carbon (n-C: S) thin films grown on molybdenum substrates by hot-filament CVD technique using methane-hydrogen (CH4/H2) and hydrogen sulfide-hydrogen (H2S/H2) gas mixtures were investigated. The field emission properties of the S-assisted films are reported as a function of sulfur concentration. The incorporation of S caused structural and microstructural changes that were characterized with SEM, AFM and Raman spectroscopy (RS). The S-assisted films show smoother surfaces and smaller grains than those grown without. The lowest turn-on field measured was around 4.5 – 5.0 V/μm films grown with 500 ppm of hydrogen sulfide and at 900 °C. The electron field emission properties of S-assisted films were also compared to those grown without sulfur (i.e., intrinsic). An inverse correlation between the threshold field (Ec) and sulfur concentration was found. These finding are attributed to defect induced states within the electronic band structure.

Structural and optical parameters of films deposited on quartz substrates by laser ablation

laser ablated films deposited on quartz substrates have been studied in order to obtain information on their structural and optical properties as a function of sulphur concentration (x). Transmittance and reflectance spectra at room temperature were carried out to obtain the energy gap modulation, the absorption coefficient and refractive index. By using the Newton-Raphson algorithm, the values of the real part of the refractive index in the transparent region were deduced including the effect of non-uniformity of the film thickness. The wavelength dependence of n was extrapolated for the weak and medium absorption range by means of two different models: the classical Cauchy formula and the single effective oscillator model proposed by Wemple and Di Domenico. From the latter theory, two physical parameters known as oscillator energy and oscillator strength, respectively, were obtained. These parameters have been related to the optical gap and structural properties of the deposited alloys. In the strong absorption region, the absorption coefficient and the optical gaps were calculated for each x-value. A quadratic trend was found for the x-dependence of the band gap, in agreement with the corresponding bulk alloy.

Effect of surface impurities segregation and ion sputtering on ion driven deuterium permeation through copper

The deuterium permeation through a polycrystalline copper membrane driven by an ion beam (3 keV D 2 +) was measured as a function of temperature (573–873 K) and surface impurity concentration. For copper a single-impurity layer can be prepared by combining thermal annealing and argon ion bombardment. The surface recombination coefficient was evaluated from the measured permeation flux. Under assumption that the segregation of sulphur on the surface results in modification of the activation energy for chemisorption, E C, the value of E C was calculated as a function of sulphur concentration.

Photoelectrical properties of Au/GaAs (1−x)S x/Mo structures as a function of sulfur concentration

In this paper we present results of a study of the influence of sulfur on the photoelectrical properties of experimental Au/GaAs (1− x) S x /Mo structures. The GaAs (1− x) S x polycrystalline layer was deposited by radio frequency sputtering in a mixed argon and hydrogen sulfide gas. The open-circuit voltage ( V oc ), the short-circuit current ( I sc ) under a given illumination have been measured as a function of the molar fraction x from 0 to 0.26. For the Au/GaAs (1− x) S x /Mo structure the diminution in interface state activity with the increase of x corresponds to an improvement of the open-circuit voltage and is limited by the increase of bulk and ohmic contact resistance. A variation of sulfur concentration at the back contact shows the good interface properties of the GaAs (1− x) S x compound.

The Photovulcanization of Butyl and SKB (Polybutadiene) Rubbers

Abstract It is known that the mechanical properties of raw and vulcanized rubbers change markedly under the action of light in which not only oxidation processes but also photovulcanization processes in which sulfur is involved play an essential part. In view of the wide interest shown lately in questions of radiation vulcanization of polymers, as well as the possibility of reducing the photodegradation effect upon the mechanical properties of some polymers, we made studies of the photovulcanization of butyl rubber (degradation by irradiation) and SKB (polybutadiene) rubber (structure formation by irradiation). The study was made on films 200µ thick of purified butyl rubber with a molecular weight of about 42,000 and an unsaturation of about 1%. Both ordinary (twice crystallized) sulfur and radioactive S35 were used. The films obtained from a solution of rubber plus sulfur on cellophane were irradiated with a PRK-7 lamp through a Pyrex glass light filter and distilled water at a distance of 25 cm. Then determinations were made of the absorption spectrum and the static modulus 30 minutes and 24 hours after applying the load. The amount of free sulfur remaining in samples extracted previously was determined from the intensity of the S35 radiation. SKB not containing PBNA was reprecipitated from a benzene solution. When films of SKB (200µ thick) were irradiated, the light filters UFS-1, ZhS-4 and OS-5 were used. After the irradiation of the SKB films their static modulus was determined 30 minutes after the application of the load. When we irradiated butyl rubber containing 0.25 to 2.5% sulfur, we observed a distinct photovulcanization optimum (see Figure 1) in the modulus as a function of irradiation time like that which occurs in thermal vulcanization, and an optimum of the photovulcanization rate as a function of sulfur concentration.