Pressure-dependent magnetization and magnetoresistivity studies on tetragonal FeS (mackinawite): revealing its intrinsic metallic character

Highly efficient removal of aqueous Hg(II) by FeS micro-flakes

FeS (mackinawite) is known to be effective in the sorption of aqueous Hg(II). However, FeS nanoparticles are apt to aggregate and easy to be oxidized, which limits their wide applications. Here, we have synthesized FeS micro-flakes which can be uniformly dispersed in water without aggregation. Owing to the good stability and dispersibility, FeS micro-flakes exhibit high efficiency in the removal of Hg(II) from water. The sorption of Hg(II) on the FeS micro-flakes is more consistent with the pseudo-second-order kinetic model and Langmuir model, indicating that the sorption of Hg(II) is mainly monolayer sorption dominated by chemical sorption. The maximum sorption capacity is 2680 mg/g at pH 5.6 and 30 °C, significantly higher than those of FeS nanoparticles and other Hg(II) scavengers. The pH studies indicate that FeS (0.31 g/L) can effectively remove >97.6 % of 200 mg/L Hg(II) in the pH range of 2-12 at 30 °C. Powder X-ray diffraction, elemental and sorption analyses suggest that Hg(II) is removed via chemical precipitation and surface adsorption. This study demonstrates the potential and viability of FeS micro-flakes for efficient removal of aqueous Hg(II).

Facile synthesis and magnetic and electrical properties of layered chalcogenides K2CoCu3Q4 (Q for S and Se)

Layered transition-metal chalcogenides have attracted great interest due to their unique electronic and optical properties. Here, we represent two layered quaternary chalcogenides K2CoCu3S4 and K2CoCu3Se4 prepared by a convenient hydrothermal route. From powder XRD and TEM analyses, K2CoCu3Q4 possesses a tetragonal ThCr2Si2-type structure with a random arrangement of Co and Cu atoms. The phase purity of the samples was confirmed by ICP, SEM, and EDS analyses, and the oxidation states of Co and Cu atoms were determined to be +3 and +1 by XPS spectra. Both samples show a weak ferromagnetic behavior at low temperature induced by spin-canted antiferromagnetic ordering. The temperature dependent resistivity, ρ(T), reveals a metallic nature for stoichiometric K2CoCu3S4. The semiconducting behavior of K2CoCu3Se4 could be explained better by variable range hopping (VRH) rather than adiabatic small polaron hopping (SPH). This new series of layered chalcogenides may offer a promising candidate for potential electronic applications.

Selective orbital reconstruction in tetragonal FeS: A density functional dynamical mean-field theory study

Transport properties of tetragonal iron monosulfide, mackinawite, show a range of complex features. Semiconductive behavior and proximity to metallic states with nodal superconductivity mark this d-band system as unconventional quantum material. Here, we use the density functional dynamical mean-field theory (DFDMFT) scheme to comprehensively explain why tetragonal FeS shows both semiconducting and metallic responses in contrast to tetragonal FeSe which is a pseudogaped metal above the superconducting transition temperature. Within local-density-approximation plus dynamical mean-field theory (LDA+DMFT) we characterize its paramagnetic insulating and metallic phases, showing the proximity of mackinawite to selective Mott localization. We report the coexistence of pseudogaped and anisotropic Dirac-like electronic dispersion at the border of the Mott transition. These findings announce a new understanding of many-particle physics in quantum materials with coexisting Dirac-fermions and pseudogaped electronic states at low energies. Based on our results we propose that in electron-doped FeS substantial changes would be seen when the metallic regime was tuned towards an electronic state that hosts unconventional superconductivity.

Overcoming the Limiting Step of Fe2O3 Reduction via in Situ Sulfide Modification

Iron-based alkaline batteries are extremely attractive due to iron's environmental friendliness, and low cost. The parasitic reaction of H2 evolution and the poor electrical conductivity of the discharge products are among the major barriers for the commercialization of these batteries. In this paper, we first show that O(2-) diffusion inside the solid Fe2O3 particles is the rate-limiting step in the reduction reaction. In situ sulfide modified Fe2O3, which has a core-shell structure verified by SEM, XRD and XPS analysis, has excellent electrical and ionic conductivity. The functional mechanism of sulfide in the reaction was identified as in the potential region around -1.071 V (vs Hg/HgO), the outside layer of Fe2O3 was reduced to amorphous FeS, which has good electrical conductivity and enlarges the electrochemical reaction interface. O(2-) diffusion inside the Fe2O3 particle is still the rate-limiting step. In the potential region around -1.15 V (vs Hg/HgO), amorphous FeS ages to FeS (pyrrhotite), FeS2 (marcasite), and FeS0.9 (mackinawite), which have high electrical conductivity. FeS0.9 can also introduce vacancies into Fe2O3 particles, which can greatly enhance O(2-) diffusion and the ionic conductivity, and the surface reaction is the rate-limiting step. In summary, after in situ sulfide modification, the ohmic overpotential and ion diffusion overpotential for Fe2O3 reduction were significantly reduced. The reduction reaction rate increases 26 times and the discharge capacity of Fe2O3 electrode increases 78 times after sulfide modification.

Ammonia and iron cointercalated iron sulfide (NH3)Fe0.25Fe2S2: hydrothermal synthesis, crystal structure, weak ferromagnetism and crossover from a negative to positive magnetoresistance

(NH₃)Fe_0.25Fe₂S₂ is successfully synthesized, which behaves as a ferromagnetic semiconductor and exhibits a novel crossover from a negative to positive magnetoresistance.

Structural transition and superconductivity in hydrothermally synthesized FeX (X = S, Se)

Superconductivity in iron chalcogenides FeX (X = S, Se) depends on the synthesis route and is tied to different crystal structures.

Synthesis, crystal structure and physical properties of [Li0.85Fe0.15OH][FeS]

The layered compound [Li_0.85Fe_0.15OH][FeS], whose structure features alternately packed [Li_0.85Fe_0.15OH] and [FeS] layers, was synthesized via a hydrothermal method.