Sulfur Crystals Research Articles

Photoinduced discharge in sulfur single crystals using strongly and weakly absorbed light

We report on the photoinduced discharge of sulfur single crystals using light in the range 400–580 nm, i.e., from strongly to weakly absorbed light. The results are interpreted in terms of a phenomenological model consistent in an equivalent RC circuit.

Kras a geneza złóż siarki w Polsce

KARST AND THE ORIGIN OFSULPHURDEPOSITS INPOLAND Summary Recent studies by the present author on the geological structure and the origin of sulphur deposits inPolandas well as on karst in gypsum and in sulphur-bearing deposits have led to the following conclusions: 1. Karst development in gypsum occurred in two phases. The first phase took place just after the deposition of gypsum, i.e. during the formation of the Chodenice Beds, in the deeper parts of the basin; the second phase took place after the deposition of the lower series of the Pecten clays with Neobulimina longa , i.e. during the deposition of clays with Hanzawaia crassiseptata in the deeper part of the basin. The second phase continued till the Sarmatian. 2. Karst processes in gypsum were confined only to the emerging areas of anticlinal structures. The emergence of these structures occurred in two phases corresponding to the two phases of karst processes in gypsum. 3. Only those gypsum deposits which were subjected to both phases of karst processes could have been affected by biochemical and physico-chemical processes which led to the transformation of gypsum deposits into limestones sulphur. It was namely the karst processes in gypsum which facilitated the circulation of waters, as well as the formation of an aqueous basin in gypsum deposits, and opened the ways for the migration of bitumens. 4. An indispensable factor in the transformation of gypsum deposits into limestones with sulphur – till the very end of this process – is a continuous flow or movement of water so that karst caverns can be filled with water all the time. On the other hand, when sulphur deposits have already been formed they must be completely covered with water if sulphur is to be preserved; thus the lack of the flow or movement of water – a basin which is not rejuvenated – is necessary here. In the case of the deposit in Tarnobrzeg, water was supplied by the River Vistula as a result of deep erosion, which extended as far as the Baranow Beds. Such basic changes in the character of the water basin as those described above can be explained in the following way. Caverns which measure a few metres in diameter have been encountered frequently in gypsum deposits (borehole Posądza 40s). No caverns of that size can be found in the already exploited sulphur deposits in Piaseczno and Machow. This fact can be explained as due to differences in the resistance of rocks to compression. The resistance is large in gypsum, particularly in laminated gypsum; it is small in limestones with sulphur. The mass occurrence of brecciated sulphur ores shows that the top of the deposits collapsed and, that this happened at the time when the transformation of gypsum deposits into limestones with sulphur was quite advanced. In the final stage of the formation of sulphur deposits they were becoming compact; the caverns were compressed and dense sulphur was formed. The compactness of the sulphur deposit and the compression of caverns was undoubtedly caused first of all by the pressure of the ovelying mass of Sarmatian clays, which measured a few dozen metres in thickness. As a result of this, the collector, i.e. gypsum affected by karst processes, showed reduced permeablity. When the transformation of gypsum deposits into limestones with sulphur had been completed, the flow of waters from the surface was stopped; the deposit waters (not rejuvenated) preserved the deposit. Karst processes ceased gradually, and the role of karst as a deposit-forming factor ended. Since the deposit became compact the evidence of the activity of two phases in the development of karst processes was almost completely destroyed. Yet some unobliterated traces of different karst processes are frequently encountered in the exposed and exploited deposits in Piaseczno and Machow. These are small caverns in sulphur-bearing limestones, lined with dusty sulphur or sulphur crystals, limestone stalactites, limestone stalactites covered with sulphur crystals, concretion sinters, dome-like, fine, stalagmites with barite crystals or barite stalactites. The youngest karst forms described here are the result of mining activity, which began when pumps for the purpose of draining the deposit were switched on. Huge amounts of mineral substances were pumped together with water: calcium sulphates, strontium sulphates, barium sulphates, calcium carbonates, and hydrogen sulphide. Thus the balance between the sulphur deposit and the solution of the above-mentioned saturating compounds was upset. The removal of mineral substances from the deposit led to the formation of small caverns, filled with fine sinters. The time when the presently observed karst phenomena originated is definitely determined by the fact that sinter forms – stalactites and stalagmites of calcium carbonates, strontium sulphates and barium sulphates – could not have been formed when the deposit was completely covered with water.

Carrier recombination in orthorhombic sulphur

The paper deals with the recombination of photogenerated excess carriers in orthorhombic sulphur crystals. Unlike other low mobility materials, such as anthracene, the electron and hole mobilities in sulphur are widely different (μ e ⪡ μ h ). This property forms the basis of the double injection technique used in the volume recombination experiments. Two Xenon flash tubes on opposite sides of the platelet specimen generate the interacting carriers. During the electron transit an essentially uniform distribution of holes is produced for a short time. From the observed reduction in the electron current pulse the volume recombination coefficient is deduced. It is in close agreement with the value predicted by the Langevin theory, implying that volume recombination in sulphur is diffusion controlled. Approximate agreement with this theory has also been found in recombination experiments within the surface region, employing a delayed field technique. In addition transient experiments have been carried out on the intensity and field dependence of the number of photogenerated carriers extracted from the surface region. A Poole-Frenkel model can account for the field dependence even at E≅800 Vcm −1, so that the photogeneration in orthorhombic sulphur appears to be predominantly controlled by the field lowering of the potential barrier.

Photoluminescence in chalcogenide crystals showing small polaron conduction; orthorhombic sulphur and As4S4

Photoluminescence and excitation spectra have been observed in single crystals of orthorhombic sulphur and As4S4 at temperatures between 10 and 350K. Broad luminescence bands are observed, well below the fundamental absorption edge. These are discussed in terms of a radiative transition in which one of the carriers is self-trapped by phonon interactions.

Physico-chemical Properties of Selenium-Tellurium-Sulfur Crystals

Abstract The temperature dependence of electric conductivity and Vickers hardness of Selenium–Tellurium–Sulfur (Se–Te–S) crystals were studied. The conductivity decreased with an increase in sulfur content, remaining almost constant when the sulfur content was 40–80 atomic % at 20 and 30 atomic % of tellurium content. When tellurium content was 10%, both conductivity and hardness decreased abruptly when sulfur content exceeded 10%. It was found by means of X-ray diffraction that a hexagonal crystal structure with size twice the lattice constant of Se–Te crystals is formed when the sulfur content is 20% at 10% of tellurium content. When sulfur content exceeds 80%, the crystal structure becomes similar to that of pure sulfur (orthorhombic) at 20 and 30% of tellurium.

Self-diffusion in α-sulphur crystals

Abstract Self-diffusion of 35S labelled molecules in highly perfect single crystals of orthorhombic sulphur has been studied by the serial sectioning technique. Measured lattice self-diffusion coefficients are considerably lower than those previously published for this solid. This difference is believed to be a consequence of a significant contribution from diffusion along dislocations in the crystals used in the previous study. Self-diffusion perpendicular to the [001] direction can be represented by an equation of the form D=2 × 1013exp[-(215±11 kJmol−1)/RT]m2s−1. Self-diffusion coefficients in the [001] direction are 2–4 times lower. This distinct anisotropy is probably a consequence of the marked structural anisotropy of this phase of sulphur.

Dislocations in α-sulphur

Abstract A study has been made of the solvent etching of naturally-occurring (001), (011), {111} and {113} faces and prepared (110) faces of orthorhombic sulphur crystals grown from solution in carbon disulphide. No pitting was observed on the (011) and {113} faces. Etching of the remaining faces revealed crystallographically-shaped pits, the shapes and distributions of which were consistent with their formation at the emergent ends of dislocations in the lattice. The probable geometry of the dislocations is discussed. Deformation by point indentation indicated that slip occurs predominantly on {111} glide planes. An X-ray topographic study is also reported, which complements the above results. Direct evidence is presented on the geometry of the active slip systems and on the mobility of individual dislocations. Of the observed slip systems it is shown that only (11) [110], (11) [110], (111) [110], (11) [10] are facile; {111} 〈10〉 or 〈01〉 and (001) [100] or 〈10〉 are much more difficult to activate. The ex...

The growth and perfection of orthorhombic (α) sulphur single crystals

A study has been made of the influence of growth parameters on the rates of growth, the perfection and morphology of orthorhombic sulphur crystals grown from solution in carbon disulphide. The rates of growth of crystals grown from good seeds show the variation with supersaturation expected for growth by a screw dislocation mechanism. Topographic studies support this conclusion. Both solvent incorporation and dislocation content depend on the rate of growth, being greatest in the more rapidly grown crystals. The latter is very low in carefully prepared crystals and is virtually zero in crystals grown at low rates from carefully prepared seeds. Dislocation free specimens of up to 120g in weight have been prepared.

Oxidation of elemental sulfur by Sulfolobus acidocaldarius.

Oxidation of elemental sulfur by Sulfolobus acidocaldarius, an autotroph which grows at high temperatures and low pH, was examined by use of (35)S-labeled elemental sulfur. When cultured at pH 3.2 and 70 C, S. acidocaldarius oxidized elemental sulfur essentially quantitatively to sulfuric acid. Oxidation rate paralleled growth rate and decrease in pH of the culture medium. Elemental sulfur was not oxidized under these conditions if the culture was poisoned with formaldehyde. During the growth phase, the proportion of cells attached to the sulfur crystals increased progressively, and in the later phases of growth over 10 times more cells were attached to sulfur than were free. Doubling times for eight strains growing on elemental sulfur varied from 37 to 55 h. The organism grows much more rapidly on yeast extract than on sulfur. In a medium containing both sulfur and yeast extract, sulfur oxidation was partially inhibited, although growth was excellent.

Étude de la répartition des dislocations dans un monocristal de soufre alpha par topographies aux rayons x

Large single crystals of orthorhombic sulphur have been grown from a CS2 solution. Most of the dislocations form bundles originating at the seed and lie roughly normal to the major growth faces. The remaining parts of the crystal are practically dislocation-free. Most common Burgers vectors are 12[110] and 12[1ovbar|10] which can be easily interpreted from the atomic structure.

Anisotropy of Electron and Hole Mobilities in Orthorhombic Sulphur Crystals

AbstractThe anisotropy of the electron and hole mobility in orthorhombic sulphur has been investigated measuring the transit times of optically generated carriers. The sulphur crystals have been grown from a temperature controlled CS2 solution. The hole mobilities at room temperature along the main directions μp[100] = (7.4 ± 0.4) cm2 V−1 s−1, μp[001] = (4.6 ± 0.3) cm2 V−1 s−1, and μp[010] = (2.3 ± 0.2) cm2 V−1 s−1 decrease with increasing temperature like μp[100], [001] ∼ T−3/2 and μp[010] ∼ T−1. Below room temperature the hole mobilities are trap controlled. The electron transport is an activated process governed by the activation energies ϵn[001] = (0.166 ± 0.003) eV, ϵn[100] = (0.157 ± 0.003) eV, and ϵn[010] = (0.153 ± 0.003) eV. The electron mobilities are interpreted in terms of the small polaron theory.

On the structure of fibrous sulfur

In a recent paper Tuinstra (1966) has described the results of his interpretation of the diffraction pattern of fibrous sulfur. This pattern is notable for a very intense equatorial reflection at d= 4.04/~. This reflection has been described as 'broad' (Prins & Tuinstra, 1963); its position is accordingly difficult to measure precisely. Tuinstra's description of the structure includes structural details of the infinite helical chains of sulfur atoms together with the way in which they pack together. Evidence for the correctness of this structure is presented in the form of a table which includes observed and calculated values of the intensities and of 4 sinE 0fi~2. The agreement between the observed intensities and the corresponding calculated values is apparently quite good. For example, the second most intense reflection on the equator, at d=460/~, is, in the text, stated to have about one-tenth the intensity of the strongest equatorial reflection (referred to above); the respective calculated intensity values for the proposed structure are 120 and 1000. We have prepared samples of fibrous sulfur, following the procedure of Prins, Schenk & Hospel (1956). Fiber diagrams of these preparations, taken with Cu radiation, are presented in Fig. 1. These photographs, which were deliberately underexposed, were taken with (a) no Ni filter, (b) one Ni filter (thickness 0.00035 in), and (c) two Ni filters, and were timed so that intensity of the strongest reflection would be very nearly the same on all three. The general appearance of the three photographs resembles closely those of fibrous sulfur which have been published previously (Prins, Schenk & Hospel, 1956; Prins, Schenk & Wachters, 1957) and are as well in agreement with tabulated diffraction data (Prins & Tuinstra, 1963; Tuinstra, 1966), with, however, one crucial exception: the reflection at d= 460/~ is obviously largely the/~ of the reflection at 404 A. A structure for fibrous sulfur which requires a strong reflection to be observed at 4.60 A. cannot, therefore, be accepted. This conclusion is supported by the recent work of Geller & Lind (1969) and Lind & Geller (1969) who examined single crystals of pressure-induced sulfur, and concluded that this material is the same as fibrous sulfur prepared at atmospheric pressure by the method of Prins et al. The details of the structure deduced by Lind & Geller are not the same as those presented by Tuinstra. The reflection at d= 4.60/~ is indexed by Geller & Lind as 002, with an observed F of 284, and the reflection at d= 4.04/~ is a combination of 080 and 042, both with observed F values of 858. The ratio of the intensities* to be expected on a fiber diagram is thus 1:27, a value which is in serious disagreement with the ratio 1:8 calculated for Tuinstra's structure, but is in satisfactory agreement with the ratio 1 : 25 calculated for the structure of Geller & Lind. It is difficult to estimate this ratio from Fig.l(c), but it appears possible from this and other photographs that it may be as small as 1:50 or less, a result which suggests that fibrous and pressure-induced sulfur might have slightly different structures. As pointed out by Geller & Lind, the correspondence between the two diffraction patterns is very close, so this difference, if it exists, cannot be very large.

Raman spectrum and force constants of S 42−

Raman spectroscopy using a He-Ne laser as excitation source has been used to identify a new species of molecular sulfur in concentrated aqueous solutions of sulfur in sodium sulfide. A normal coordinate vibrational analysis has been performed based on a non-linear four-atom model having SS bond lengths = 2.04 A ̊ , SSS bond angles = 105°, and the SSSS dihedral angle = 90°. The potential function used was the internal-rotation-excluded version of the Mizushima-Morino potential (1) and the force constants were the generalized valence forces derived by Venkateswarlu and Thirugnanasambandam (2) from a normal coordinate analysis of the S 8 molecule. Excellent agreement between observed and predicted Raman shifts and polarization characteristics was obtained. The four-atom species is presumably present in aqueous solution as the S 4 2− dianion. The mechanism of crystallization of rhombic sulfur and trigonal selenium from solutions in sodium sulfide is discussed in terms of this tetra-atomic species.

Carrier Transport and Generation in Orthorhombic Sulphur Crystals by Pulsed X-Rays

A study of the dependence of the carrier mobilities on temperature and crystal thickness in orthorhombic sulphur crystals was performed using 0.4 µsec X-ray pulses in order to avoid surface effect. The saturation of the collected charge at applied fields exceeding 40 kV/cm was found to be due to the so-called “schubweg effect.” At 290°K the values of schubweg per unit field for electrons and holes are estimated at 6×10 -7 and (1-5)×10 -6 cm 2 V -1 , respectively. With the mobility data, the results lead to the lifetimes of 800 µsec for electrons and 66 µsec for holes. The number of carrier pairs generated by X-rays is relatively insensitive to temperature. The energy necessary to create an electron-hole pair lies between 16 and 30 eV. The effect of excitons on carrier generation may be important in uniform excitation by X-rays.

Hole and electron traps in orthorombic sulphur

In this paper a new assignment of electron and hole traps solution grown orthorombic sulphur crystals has been made. A new level at 1.0 eV, only indirectly observed by other authors, has been identified with an electron peak in the thermally stimulated conductivity data and it has been shown that the filled traps are confined to the penetration volume of the exciting light rather than being in the bulk of the specimen. For the light intensities used bias fields of up to 5kV/cm did not alter this situation.

Transport properties of vapor grown orthorhombic sulfur crystals

Crystals of orthorhombic sulfur have been grown from the vapor phase and their electrical transport properties are compared with those of CS 2 solution grown and natural sulfur crystals. The temperature dependence of the hole drift mobilities shows that the transport mechanism is trap controlled. The trap depth in the vapor grown crystals is 0.22 eV which is the same as that for the solution grown crystals. However, the trap density (10 17 cm −3) in the vapor grown crystals is 1–4 orders of magnitude higher than found in the solution grown crystals. The trap is attributed to a structural defect in both types of crystal. The electron transport is by an intermolecular hopping process 3 which becomes trap controlled at lower temperatures. The trap depth and density are 0.4±0.1 eV and 10 14 cm −3 respectively. Thermally stimulated conductivity measurements have been made on vapor grown, solution grown and natural crystals. Peaks at 0.17 eV and 0.2 eV are correlated with electron and hole mobility activation energies respectively.

Aus elektrochemischen kontakten injizierte raumladungsbeschränkte ströme von defektelektronen in orthorhombischen schwefel-einkristallen

Dark injection of positive space charge limited (SCL) currents into single crystals of orthorhombic sulfur from oleum contacts leads to a power law dependence of the current on the applied voltage. This behaviour is interpreted as being due to an exponential trap distribution. This assumption was verified by determining the dependence of the current on the thickness of the crystals which agrees with that predicted for this case by SCL current theory. The total density of traps was determined to N t 0 = 1.10 15 cm −3, the distribution function is characterized by kT c = 0.13 eV.

Anomalous photovoltaic effect in orthorhombic sulfur

Larger than band gap photovoltages have been observed in single crystals of orthorhombic sulfur grown from CS 2 solution or the vapor phase.

Dark injection of holes into crystals of orthorhombic sulfur and of gallium sulfide

Oleum forms an injecting contact for holes with sulfur and gallium sulfide single crystals. Charge injection is preceded by the formation of sulfur radical ions in the surface of these crystals.

Gas hydrates in aqueous-organic systems: III. Hydrate formation in polyacrylamide gel

Summary The formation of gas hydrates in polyacrylamide gels was attempted using hydrate formers with different solubilities in water. Hydrate crystals of highly water-insoluble trichlorofluoromethane formed only at the gel-hydrate former interface. Hydrate crystals of highly water-soluble ethylene oxide formed abundantly within the gel, and the depth of penetration depended on the equilibration time prior to initiation of crystallization. Equilibration for 166 hrs resulted in the formation of ethylene oxide hydrate throughout a 5-cm column of gel. All ethylene oxide samples were observed to recrystallize following the initial crystallization process. Hydrate crystals of highly watersoluble sulfur dioxide and slightly soluble dichlorofluoromethane also formed within the gel. The sulfur dioxide hydrate crystals were present in quantities similar to those obtained with ethylene oxide, whereas the dichlorofluoromethane hydrate crystals were far less abundant. Several of the experiments were successfully repeated using an agar substrate. In the case of dichlorofluoromethane, the quantity of hydrate crystals in the gel was influenced by the method of formation. This was not true of ethylene oxide hydrate.