Orthorhombic Marcasite Research Articles

Rationally designed urchin-like structured cobalt diselenide (o-CoSe2) for the sensitive voltammetric detection of carbendazim fungicide in vegetables and water samples

In this article, we report the electrochemical sensor based on the urchin-like structured orthorhombic marcasite cobalt diselenide (o-CoSe2) prepared by a simple hydrothermal method for the sensitive detection of carbendazim (CBZ) in food and water samples. The as-prepared hierarchical structured o-CoSe2 has generous active sites/edges, and high surface area, which significantly improves the electrochemical activity towards the detection of CBZ. Moreover, differential pulse voltammetry (DPV) was used to investigate the analytical performance of the prepared sensor. Under the optimized condition, o-CoSe2 modified glassy carbon electrode (o-CoSe2/GCE) shows a rapid anodic current response to CBZ with the minimized potential of + 0.93 V vs Ag/AgCl in pH-7. The proposed sensor possessed the linear range of 0.01–2.43 µM and 2.43–382.43 µM accompanying detection limit of 1.69 nM. Furthermore, the designed sensor existing excellent long-term stability, anti-interference, and reproducibility. Finally, the practical applicability of the prepared sensor for the detection of CBZ was tested in the tomatoes and river water samples, resulting in satisfactory recoveries of 97.2–98.6% and 97.8–99.2%.

Phase Evolution, Polymorphism, and Catalytic Activity of Nickel Dichalcogenide Nanocrystals

The nickel chalcogenide family contains multiple phases, each with varying properties that can be applied to an expansive range of industrially relevant processes. Specifically, pyrite-type NiS2 and NiSe2 have been used as electrocatalysts for oxygen or hydrogen evolution reactions. These pyrites have also been used in batteries and solar cells due to their optoelectronic and transport properties. The phase evolution of pyrite NiS2 and polymorphism of NiSe2 have briefly been studied in the literature, but there has been limited work focusing on the phase transformations within each of these two systems. Using experiments and calculations, we detail how pyrite NiS2 nanocrystals decompose into hexagonal α-NiS, and how the synthesis of pyrite NiSe2 nanocrystals is affected by the presence of two polymorphs, a metastable orthorhombic marcasite phase and a more stable cubic pyrite phase. Each reaction can be controlled by fine-tuning the reaction parameters, including temperature, time, and the precursor identity and concentration. Interestingly, both NiS2 and NiSe2 nanopyrites are active catalysts in the selective reduction of nitrobenzene to aniline, in agreement with other catalysts containing an fcc (sub) lattice. Our results demonstrate a feasible, logical process for synthesizing nanocrystalline pyrites without common byproducts or impurities. This work can help in solving a major problem suspected in preventing pyrite FeS2 and similar materials from large-scale use: the presence of small amounts of secondary phases and impurities.

Electrochemical deposition of p-type FeS2 thin films absorber layer for photovoltaic cell

Electrochemical deposition (ECD) of FeS2 thin films from aqueous solution contains FeSO4, Na2S2O3.5H2O and H2SO4. ECDs were performed at different bath temperatures (30, 40, 50, 60 and 70°C) with constant pH (~2). FESEM images shows that the grains are as deposited films with stoichiometric iron pyrite thin films were successfully formed at 50, 60 and 70°C and S/Fe ratio in as-deposited films were ~2. GAXRD studies of as-deposited at 30 and 40°C FeS2 thin films shows a minor phase of orthorhombic marcasite and major cubic pyrite phase observed. As-deposited thin films at 50, 60 and 70°C brings about the formation of FeS2 with single crystalline cubic phases with a strong (111) preferred orientation and without any contribution of marcasite phase. When the bath temperature was increased, as-deposited thin films of crystalline size, thickness and roughness value increased due to rate of formation FeS2 increased. Raman spectra of the FeS2 thin films presented characteristic peaks of S-S active mode at 377 cm-1. The optical spectra of the as-deposited FeS2 thin films with different bath temperatures showed a clear absorption edge band gap of these films from 0.86 to 0.96 eV. As-deposited FeS2 thin films at different bath temperatures show p-type conductivity. Copyright © 2017 VBRI Press.

Synthesis and Characterization of Ultrathin FeTe2 Nanocrystals.

Ultrathin crystals including monolayers have been reported for various transition-metal dichalcogenides (TMDCs) with van der Waals bonds in the crystal structure. Herein, we report a detailed synthesis procedure and characterization of ultrathin iron ditelluride crystals. This material crystallizes in an orthorhombic marcasite Pnnm crystal structure whose bonding is dominantly covalent and without loosely connected van der Waals (vdW) bonds, making monolayer FeTe2 synthesis less straightforward than other TMDC monolayer syntheses. The chemical vapor deposition synthesis process described is simple, effective, and results in a range of crystal thicknesses from approximately 400 nm down to the FeTe2 monolayer.

Formation of metastable phases of ferrous sulfide via pulsed Nd:YAG laser deposition: Experimental and theoretical study

Highly polymorphic ferrous sulfide exhibits attractive optical, semiconducting, magnetic and biocatalytic properties related to its phase modification. Nd:YAG laser ablation of ferrous sulfide (FeS) in vaccum results in noncongruent deposition of nanostructured FeS1-x thin films. Deposits have been carried out on Ta, Al and Cu substrates and achieved thin films were analyzed using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and electron diffraction in order to characterize morphology, chemical composition and phase transformation induced by ablative process. Round-shaped and ring-like particles, shapeless agglomerates as well as flat discontinuous areas have been observed for all the coats deposited on various substrates. However, using HRTEM, in agreement with electron diffraction, different phase compositions on various substrates have been detected. Cubic pyrite phase (FeS2) has been detected on Ta substrate. Metastable rhombohedral smythite Fe9S11 and cubic pyrite FeS2 have been found on Al substrate. And cubic pyrite FeS2, metastable rhombohedral smythite Fe9S11 and metastable orthorhombic marcasite FeS2m have been revealed on Cu substrate. The detected crystalline nanograins in all deposits were surrounded by amorphous phase. Furthermore, to gain deep insight into the electronic structure of obtained stable (cubic pyrite) and less known unstable phases (orthorhombic marcasite and rhombohedral smythite) the density functional theory is employed and important characteristics such as band gap values have been calculated.

Pulsed Nd:YAG deposition of nanostructured FeS1-x containing meta-stable phases

Pulsed near-IR laser irradiation of ferrous sulfide (FeS) in a vacuum allows a non-congruent ablation and deposition of nanostructured FeS1-x thin films. Deposition has been performed on Al, Ta and Cu unheated substrate and analyzed by scanning (SEM) and high resolution transmission electron microscopy (HRTEM) and electron diffraction. Morphologically, the similar homogeneous, dark, metallic and adhesive appearanceshave been revealed for all the coats deposited on various substrates (by SEM). However, using HRTEM in agreement with electron diffraction, different phase composition on various substrates has been detected. Cubic pyrite phase (FeS2) has been detected on Ta substrate. Cubic pyrite (FeS2) and metastable rhomboedric smythite Fe9S11 have been found in case of Al substrate. Cubic pyrite (FeS2), metastable rhomboedric smythite Fe9S11 and metastable orthorhombic marcasite (FeS2m) revealed HRTEM analysis of the film on Cu substrate. In case of all deposits the detected crystalline nanograins were surrounded by amorphous matrix.

Single Step Electrochemical Deposition of p-Type Undoped and Co2+ Doped FeS2 Thin Films and Performance in Heterojunction Solid Solar Cells

Undoped and Co2+ doped FeS2 thin films (Co compositions are 1 to 5 mole%) were deposited on indium tin oxide glass substrate by a single step electrochemical deposition (ECD) method at low temperature (70 °C). Glancing angle X-ray diffraction (GAXRD) and Raman spectra showed that as-deposited undoped and Co2+ doped FeS2 thin films have a cubic pyrite structure without any trace of orthorhombic marcasite phase. Co2+ doping does not affect the cubic structure of FeS2 thin films with a strong (111) plane preferred orientation in all the doped thin films. The height profiling of 3 mole% of Co2+ doped FeS2 thin film by atomic force microscopy revealed a smooth surface with uniform distribution of particles and low roughness values. Co2+ (3, 4 and 5 mole%) doped thin films show a strong absorption peak in the higher wavelength region. Magnetic measurement reveals that Co2+ doping into the FeS2 lattice induces ferromagnetism. The Co2+ in FeS2 thin films acts as the acceptor and the original p-type conductivity is retained. Solar light irradiation with the intensity of 100 mW/cm2 on Co2+ (3 mole%) doped FeS2 thin film cell resulted in a power conversion efficiency of 5.42%.

Synchrotron charge density studies of chemical bonding in the polymorphs of FeS2

The experimental charge density (CD) distributions in both polymorphs of the photovoltaic compound iron-disulphide (FeS2; cubic pyrite and orthorhombic marcasite) will be described.[1] The CDs are determined by multipole modelling using synchrotron X-ray diffraction data collected at 10 K on extremely small single crystals (<10 mu) thus minimizing the influence of systematic errors such as absorption, extinction and TDS, and exploiting experiences gained from our recent synchrotron studies of CoSb3.[2] The analysis of the charge density in both polymorphs of FeS2 provides an opportunity to see how the different geometries affect local atomic properties, such as 2-center chemical bonding, atomic charges and d-orbital populations. In particular, the data and the resulting multipole models enable us to link the atomic-centered view that emerges from the multipole analysis with the band structure approach. This is carried out by combination with results from periodic calculations on the compounds in the experimental geometries using WIEN2k, thereby providing unambiguous answers to a number of unsolved issues regarding the nature of the bonding in FeS2. The chemical bonding will be characterized by topological analyses showing that the Fe-S bonds are polar covalent bonds, with only minor charge accumulation but significantly negative energy densities at the bond critical points. Using the IAM as reference, density is found to accumulate in-between the atoms, supporting a partial covalent bonding description. The homopolar covalent S-S interaction is seemingly stronger in pyrite than in marcasite, determined not only from the shorter distance but also from all topological indicators. Integrated atomic (Bader) charges show significantly smaller values than those estimation based on crystal-field theory of Fe2+, S-1. In connection with this, the experimentally derived d-orbital populations on Fe are found to deviate from the commonly assumed full t2g set, empty eg set, and they fit very well with the theoretical individual atomic orbitals projected density of states showing a higher dxy participation in the valence band in marcasite compared with pyrite. Thus, the differences between the two polymorphic compounds are directly reflected in their valence density distributions and d-orbital populations.

Effect of Temperature on H<sub>2</sub>S/CO<sub>2</sub> Corrosion Behaviors of P110-3Cr Steel

Flowing solution environment containing H2S/CO2 was simulated by high temperature and high pressure autoclave. Corrosion behaviors of P110-3Cr pipeline steels were investigated by Weight loss, Scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Energy dispersive spectrometer (EDS). Effect of temperature on corrosion rate and corrosion product was discussed. The results showed that corrosion rate of P110-3Cr steel decrease at the beginning and then increased with rising temperature. The corrosion types are general corrosion. P110-3Cr has resistance to local corrosion. Mackinawite (FeS0.9) is formed as corrosion product in low-temperature condition. With temperature increasing the corrosion products are dominated by mackinawite (FeS0.9) and Cubic iron sulfide (Fe3S4). When temperature increased to 150 ¡æ, the corrosion products are made up of Hexagonal iron sulfide (Fe0.96S) and Orthorhombic Marcasite (FeS2). No siderite (FeCO3) is detected, the corrosion is controlled by H2S; Cr is rich in the corrosion scale.

First-Principles Study of X-ray Absorption Spectra of FeS2

It is well known for a long time that FeS2 has two stable crystal phases, cubic pyrite (space group Pa 3) and orthorhombic marcasite (Pnnm) structures. Surprisingly, local coordinations around Fe and S atoms are quite similar between the two phases. For example, Fe is almost octahedrally coordinated by six S atoms at a distance of 2.26 A in pyrite and at 2.23–2.25 A in marcasite (see Table I). Dumbbell structure of the nearest neighbor S atoms with a bond distance of about 2.2 A is commonly seen in the both phases. X-ray absorption spectroscopy (XAS) is a useful tool to investigate the element-specific electronic structure of condensed matter systems. In particular, local geometry and symmetry around a given site are also analyzed by combining electronic structure calculations with experiments. XAS spectra at S and Fe K-edges have been measured for NiAs-type FeS and pyrite FeS2 and the observed first peak at the S K-edge and the pre-edge structure at the Fe K-edge are attributed to a transition to the empty anti-bonding states formed by hybridization of Fe 3d and S 3p orbitals. Although several first-principles density-functional-theory (DFT) calculations have been reported for Fe sulfides including pyrite and marcasite FeS2 since then, no theoretical analysis on XAS spectra has been performed for Fe–S systems. Discharge and charge reactions in Li/FeS2 and Na/FeS2 were experimentally studied for ion-battery applications. Among them, Kitajou et al. have measured XAS spectra at Fe K-edge for pyrite FeS2 and Na discharged FeS2 and found some variations in the main peak region while the pre-edge structure retains its shape by discharge. In this note, we present some theoretical results of XAS spectra of FeS2 in the pyrite and marcasite phases by performing firstprinciples DFT calculations. Electronic-structure calculations are carried out within the generalized gradient approximation (GGA) by Perdew, Burke, and Ernzerhof (PBE). One-electron Kohn–Sham equations are self-consistently solved by the all-electron full-potential linearized augmented plane wave method (FLAPW) in a scalar relativistic scheme. Experimental crystal structure including lattice constants and internal parameters is assumed throughout the calculation. XAS spectrum can be computed by using Fermi’s golden rule for the transition probability from an initial state jii to a final state j f i by x-ray with the photon energy h ! as Ið!Þ 1⁄4 2 h X

As—Cu—Fe—S (Arsenic—Copper—Iron—Sulfur)

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structural and Electrical Properties of Cr1‐xRuxSb2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

As-Cu-Fe-S (Arsenic-Copper-Iron-Sulfur)

The As-Cu phase diagram [1988Sub] depicts three intermediate phases: Cu6As (mineral name: algodonite, alg), Cu3As (domeykite, dom), and Cu5As2 (koutekite, kt). Cu6As, with a homogeneity range that includes the composition Cu8As, is a low-temperature phase, forming peritectoidally from (Cu) and Cu3As at 325 °C. Both Cu3As and Cu5As2 have highand low-temperature modifications [1988Sub]. The As-Fe phase diagram [Massalski2] depicts three stoichiometric compounds: Fe2As (Cu2Sb type tetragonal), FeAs (MnP type orthorhombic), and FeAs2 (FeS2marcasite type orthorhombic; mineral name: loellingite, lo). The As-S system [Massalski2] has three intermediate phases: As4S3 (dimorphite, dm), AsS (realgar, rl), and As2S3 (orpiment, orp). There are no intermediate phases in the Cu-Fe system. A metastable liquid miscibility gap is known [Massalski2]. The Cu-S system [1983Cha] is characterized by the presence of two liquid miscibility gaps. The gap at Cu-rich compositions has a monotectic temperature of 1105 °C. Cu1.76-1.79S [CaF2 type face-centered cubic (fcc); mineral name: digenite, dg] forms congruently at 1130 °C. Cu2S (chalcosite, cc) is monoclinic at low temperatures and has the B82 type hexagonal structure between 103 and 435 °C. Above 435 °C, it has the CaF2 type cubic structure and is continuous with digenite. CuS (B18 type hexagonal; mineral name: covellite, cv) forms peritectoidally at 507 °C. There are two intermediate phases in the Fe-S system: the metal-deficient monosulfide Fe1−xS (NiAs type hexagonal; mineral name: pyrrhotite, po) and FeS2 (cubic pyrite, py or orthorhombic marcasite).

Structural and electrical properties of Cr1−xRuxSb2

Electrical resistivity, Hall coefficient, thermoelectric power, and crystal structure were studied for the pseudo-binary system Cr1−xRuxSb2. The results of powder X-ray diffraction measurements showed that all the prepared samples of Cr1−xRuxSb2 (0≤x≤1) were in a single phase of the orthorhombic marcasite structure. The electrical measurements show that Cr1−xRuxSb2 (0≤x≤1) are all semiconductive in spite of the gradual change of valence electron number by substituting Ru for Cr. It was found that logρ of the samples for x<0.7 exhibits T−1/2 temperature dependence in certain temperature range. These temperature changes of ρ are the same as those of the variable range hopping (VRH) conduction with Coulomb gap in the impurity conduction range of usual semiconductors.

Surface states and reactivity of pyrite and marcasite

The sulphur surface sites of pristine marcasite surfaces and their reactivity during initial air oxidation were investigated for the first time using synchrotron radiation excited photoelectron spectroscopy (SRXPS). Both S 2p and Fe 2p spectra were collected and compared to those of the polymorph pyrite. A new sulphur surface component is found additionally to the two known pyrite surface signals. Due to the non-isotropic character of the orthorhombic marcasite structure, its peak intensity depends strongly on the surface orientation. Its binding energy is close to the region of short-chained polysulphides. The signal is assigned to sulphur trimers produced by electron transfer between surface near sulphur dimers and S − formed after ruptures of SS bonds which results in S 2− and S 3 2−. In the cubic crystal arrangement of pyrite the stabilisation of S − to S 2− is realised by an electron transfer from iron to sulphur only. A confirmation of this assumption is found in the Fe 2p spectra. The contribution of Fe 3+ species — a result of the electron transfer process — is considerably less pronounced for marcasite. The mechanism of initial oxidation is different for marcasite and pyrite. The sulphur species responsible for the new spectroscopic component are the most reactive sites at the marcasite surface, while S 2− is oxidised first in case of pyrite. The signals indicating the products of marcasite oxidation in the S 2p spectrum are less intense as expected from the intensity decreasing of the trimer peak. Therefore, an oxidation of sulphur trimers to elemental sulphur is assumed which could not be detected because of its volatility in the vacuum of the air lock system.

Structural and electrical properties of Co 1− xRu xSb 2

Electrical resistivity, Hall coefficient, thermoelectric power and crystal structure were measured for the pseudo-binary system Co 1− x Ru x Sb 2. By the results of X-ray analysis, the monoclinic distortion from the orthorhombic marcasite structure decreases gradually and disappears at about x=0.14. The electrical measurements show that Co 1− x Ru x Sb 2 (0≤ x≤1) are all semiconductive, in spite of the gradual change of valence electron number, by substituting Ru atom for Co. It was found that log ρ of the samples for 0.1≤ x≤0.9 exhibit T −1/4 and T −1/2 temperature dependence in the lower temperature range. These temperature changes of ρ are the same as those of the variable range hopping (VRH) conduction in the impurity conduction range of the usual semiconductors.

Electronic Structure, Pressure Dependence and Optical Properties of FeS2

ABSTRACTA revisited electronic structure study of iron pyrite, FeS2, has been performed using a new Tight-Binding Linear Muffin-Tin Orbital (TB-LMTO) technique in which the radii of overlapping MT spheres are determined from a full potential construction. The interstitial spheres were chosen to provide an efficient packing of space while ensuring that the overlap between the spheres remain small. We have found that this treatment of interstitial spheres results in a dramatic improvement in the description of the electronic structure and the binding energy curves for FeS2 in comparison with a previous LMTO calculation. In particular, the energy band gap, the equilibrium lattice constant and the bulk modulus are all in much better agreement with experimental observations. Moreover, the calculated equation of state is in excellent accord with recent measured P- V data up to pressures of 15GPa with overall deviations of less than 10%. The predicted reflectivity spectrum of FeS2 as a function of pressure gives the observed behaviour of the optical edge. The bonding behaviour the orthorhombic marcasite phase of FeS2 is also discussed within this new TB-LMTO formalism.

Pressure induced phase transition in MnTe 2

Energy dispersive high-pressure powder X-ray experiments have been performed for MnTe 2 up to a pressure of 20 GPa. MnTe 2 undergoes a discontinuous transformation from the cubic pyrite type structure to the orthorhombic marcasite type structure at 7.0±0.5 GPa upon increasing pressure. The transformation is accompanied by a large reduction in the specific volume ( ΔV/ V=0.18) which probably reflects different magnetic properties of the two modifications of MnTe 2.