Fe 2p Research Articles

A novel activation for ilmenite using potassium permanganate and its effect on flotation response

This study proposed a novel activation method for ilmenite by using potassium permanganate as an oxidant and a surface modifier. The valence state of iron atoms on the ilmenite surface was transformed under weak-acid conditions; therefore, the interaction between Fe sites on the ilmenite surface and sodium oleate was enhanced. The flotation of ilmenite was improved with a high recovery close to 90 %. The activation mechanism was studied via batch flotation, zeta-potential measurements, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The results showed that under weak-acid conditions, potassium permanganate promoted the interaction between sodium oleate and ilmenite. The addition of potassium permanganate resulted in new characteristic absorption peaks in the infrared spectra of the ilmenite, and the chemical shifts at 1559.78 cm−1 and 1444.94 cm−1 were greater than those of the unactivated ilmenite. The positive shift of the binding energy of Fe 2p promoted the electron supply of Fe(II) to the permanganate ions. The Fe(III) content on the ilmenite surface greatly increased, making the interaction with sodium oleate easier. Thus, potassium permanganate promoted the valence transition of Fe(II) to Fe(III) and enhanced the adsorption between minerals and collectors, which ultimately improved the flotation recovery of ilmenite.

Synthesis and Characterization of SrFexMn1-x(O,F)3-δ Oxide (δ = 0 and 0.5) and Oxyfluoride Perovskite Films.

We report the synthesis and characterization of as-grown SrFexMn1-xO2.5 epitaxial films, which were also subjected to postgrowth oxidation and topotactic fluorination to obtain SrFexMn1-xO3 and SrFexMn1-xO2.5-δFγ films. We show how both the B-site cation and anion composition influence the structural, electronic, and optical properties of this family of perovskite materials. The Fe substitution of Mn in SrMnO2.5 gradually expands the c-axis parameter, as indicated by X-ray diffraction. With increasing x, the F content incorporated under identical fluorination conditions increases, reaching its maximum in SrFeO2.5-δFγ. In the compounds with mixed B-site occupation, the Fe 2p photoemission peaks are shifted upon fluorination, while the Mn 2p peaks are not, suggesting inductive effects lead to asymmetric responses in how F alters the Mn and Fe bonds. Electronic transport measurements reveal all compounds are insulators, with the exception of SrFeO3, and demonstrate that fluorination increases resistivity for all values of x. Optical absorption spectra in the SrFexMn1-xO2.5 and SrFexMn1-xO3 films evolve systematically as a function of x, consistent with a physical scenario in which optical changes with Fe substitution arise from a linear combination of Mn and Fe 3d bands within the electronic structure. In contrast, the F incorporation induces nonlinear changes to the optical response, suggesting a more complex impact on the electronic structure in materials with concurrent B-site and anion site substitution.

Insight into the degradation of Orange G by persulfate activated with biochar modified by iron and manganese oxides: Synergism between Fe and Mn

In this study, sludge-derived biochar (SDBC) loaded with metal oxides was successfully synthesized via a simple impregnation method, including monometallic-based SDBC (Fe, F-SDBC; Mn, M-SDBC) and bimetallic-based SDBC (Fe and Mn, FM-SDBC). Results demonstrated that FM-SDBC possessed higher activation capacity than F/M-SDBC. The degradation of Orange G (OG) under different pH were explored. Leaching of metal ions and cycling test showed that FM-SDBC possess extraordinary stability and reusability during repeated activation of persulfate (PS). It was evidenced by quenching studies that both SO4·－ and ·OH were generated in FM-SDBC/PS. The XPS spectra of Fe 2p and Mn 2p before and after reactions indicated that the activation of PS on FM-SDBC was in company with the redox cycling of Fe and Mn species. Through the kinetics study, the contribution of Mn occupied the dominant position at the beginning, and Fe did in subsequent activation process in FM-SDBC/PS system. Synergistic mechanism between Fe and Mn in FM-SDBC could be attributed to (1) mutual electron transfer between Fe and Mn; (2) the formation of Fe-Mn bonds, which facilitated electron transfer between Fe and Mn to some extent. Based on the synergistic mechanism aforementioned, bimetallic-based biochar, especially FM-SDBC prepared in this study, had the benefits of high efficiency, stability, reusability and waste control by waste, which provided new insights into sulfate radical (SO4·－)-based advanced oxidation processes in practical application.

Electronic structures and magnetization reversal in Li0.5FeCr1.5O4

By employing temperature (T)-dependent soft x-ray magnetic circular dichroism (XMCD) in the Fe and Cr 2p absorption edges, the electronic structures of Li0.5FeCr1.5O4 spinel ferrite, which exhibits magnetization compensation, have been investigated. This work provides evidence that (i) both Fe and Cr ions are trivalent, (ii) most of Fe3+ ions occupy the A (Td) sites, while Cr3+ ions occupy the B (Oh) sites, (iii) the magnetic moments of Fe and Cr ions are coupled antiferromagnetically, and (iv) they are reversed at ∼255 K. The sum-rule analysis of Fe and Cr 2p XMCD spectra reveals that the orbital magnetic moments of Fe and Cr ions in Li0.5FeCr1.5O4 are much larger than those of metallic Fe and Cr, implying the large spin–orbit coupling and the non-fully occupied t2g orbitals of Fe3+ and Cr3+ ions. Based on these findings, we have provided a comprehensive model for the electronic and spin configurations of Fe and Cr ions in (Fe)A[Li0.5Cr1.5]BO4.

Oil industry waste based non-magnetic and magnetic hydrochar to sequester potentially toxic post-transition metal ions from water

Solid waste conversion to value-added products is a stepping stone towards sustainable environment. Herein, sesame oil cake (SOC), an oil industry waste was utilized as a precursor to develop hydrochar (HC) samples by varying reaction temperature (150–250 °C) and time span (2–8 h), chemically treated with 10% H2O2 to optimize a sample with maximum yield and Pb(II) adsorption. Highest yield (29.2 %) and Pb(II) (24.57 mg/g at Co: 15 mg/L) adsorption was observed on SOCHC@200 °C/6 h, magnetized (mSOCHC@200 °C/6 h) for comparative study. XRD displayed highly crystalline SOCHC@200 °C/6 h and amorphous mSOCHC@200 °C/6 h, both having a characteristic cellulose peak at 14.9°. mSOCHC@200 °C/6 h displayed superparamagnetic behavior with 11.2 emu/g saturation magnetization. IR spectra confirmed the development of samples rich in oxygen containing functionalities; an additional peak for iron oxides appeared at 586 cm−1 in mSOCHC@200°C/6 h spectrum. Four major peaks at 531.9, 399.9, 348.2 and 284.7 eV, assigned to O 1s, N 1s, Ca 2p and C 1s, respectively were observed during XPS analyses. An additional peak at 710.3 eV, ascribed to Fe 2p was observed in mSOCHC@200C/6 h XPS spectrum, while a peak at 143.2 eV for Pb 4f appeared in spectra of both Pb(II) saturated samples. pH dependent (maximum at ∼6.7), exothermic Pb(II) adsorption was found. About 50–70% (at Co: 25 mg/L) adsorption on both SOCHC@200 °C/6 h and mSOCHC@200 °C/6 h was accomplished in a minute, attaining equilibrium in 180 and 240 min, respectively. Error functions and superimposed qe, exp. and qe, cal. values supported Langmuir isotherm model applicability, with respective qm values of 304.9 and 361.7 mg/g at 25 °C for SOCHC@200 °C/6 h and mSOCHC@200 °C/6 h. Kinetic data was fitted to PSO model. Highest (between 92.2 and 88.9 %) amount of Pb(II) from SOCHC@200 °C/6 h and mSOCHC@200 °C/6 h was eluted by 0.01 M HCl.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

Complex hybridization physics in CaFe2As2 - a high resolution hard x-ray photoemission study

Employing high resolution hard x-ray photoemission spectroscopy, we investigate the electronic structure of an exotic Fe-based superconductor, CaFe2As2, which exhibits rich temperature pressure phase diagram and dichotomy on achieving superconductivity on application of pressure. The experimental valence band spectra exhibit significant differences for experiments at different surface sensitivities. We discover that the change in angle between light polarization and surface normal leads to similar orbital selective spectral response suggesting requirement of different methodology to probe the surface-bulk differences. Thus, the final state effects of the core level spectroscopy has been exploited to reveal the depth-resolved information. Strong features related to plasmon excitations have been observed in various core level spectra. Ca 2p spectra exhibit evidence of significant hybridization with the conduction electrons, and distinct features corresponding to the surface and bulk electronic structures while As core levels remain unaffected. The depth-resolved Fe 2p spectra at different temperatures exhibit interesting features suggesting structural anomaly may be a bulk property. All these results reveal complexity in the hybridization physics between Fe, As and Ca states presumably leading to exoticity in this material.

A self‐consistent multiple‐peak structure of the photoemission spectra of metallic Fe 2p as a function of film thickness

The Fe 2p spectrum has a very complex peak structure and a very strong background. Based on the comparison of the spectra for iron film with varying thicknesses, an experimental multiple‐peak structure for the metallic Fe 2p spectrum is proposed. The analysis required the use of state‐of‐the‐art background modeling (including the active approach) and peak‐fitting methods (including the simultaneous fitting method). A key aspect that allowed for this analysis is that the peak components are the same for various Fe film thicknesses, but with varying relative intensities. The early stages of oxidation are analyzed. The angular dependence of the peak components is also discussed.

Structural characterization, dielectric, magnetic and optical properties of double perovskite Bi2FeMnO6 ceramics

Double perovskite Bi2FeMnO6 (BFMO) oxides are promising candidate for single-phase multiferroic system. However, up to date only a limited works are carried out to synthesize the BFMO ceramics, and most of them have the issues of impure phases. In this work, we report on the structural, dielectric, magnetic, and optical properties of single-phase BFMO ceramics synthesized by solid-state reaction method. The BFMO ceramics crystallized in a rhombohedral structure with R3c space group, and their grains exhibited polyhedron morphology with average size of 15.0 µm. X-ray energy dispersive spectroscopy revealed the ceramic grains with atomic ratio of Bi:Fe:Mn equal to 2.0:1.16:0.90. XPS spectra of Fe 2p and Mn 2p core levels confirm the mixed chemical valence states of Fe (Fe2+ and Fe3+) and Mn (Mn3+ and Mn4+) in the BFMO ceramics. O 1s XPS spectra reveal the oxygen existing in the forms of lattice oxygen and oxygen vacancies while bismuth is present as Bi3+. Dielectric measurements demonstrate that the BFMO ceramics have much high dielectric constant (in the order of 104) in the frequency below 102 Hz but decrease fast with increasing the frequency. The same phenomenon appeared for the dielectric loss. A dielectric relaxation behavior with activation energy of 0.34 eV was observed in the BFMO ceramics, which was due to the thermal motion of the oxygen vacancies. The BFMO ceramics exhibit antiferromagnetic nature but a weak ferromagnetic behavior at 2 K. Sharp cusp peaks were observed in the zero-field-cooling (ZFC) curves and bifurcations between the field-cooling (FC) and ZFC curves were observed. Both of them shifted to low temperature as increasing the external applied magnetic field, indicating a spin-glass like behavior in the system. UV–Vis absorption spectra demonstrated a broad absorption peak in the wavelength range of 300–800 nm and a direct optical band gap of ~1.23 eV for the BFMO ceramics. Such narrow optical band gap as well as the high dielectric constant at room temperature enable the BFMO ceramics to be promising candidate used for solar cells, sensors, bolometer and optoelectronic devices.

Magnetic properties of graphene oxide functionalized with “Au” and “Fe2O3” nanoparticles: A comparative study

Abstract Reduced graphene oxide (r-GO) nanocomposites are very useful for different applications such as magnetic storage media and bio-imaging/biomedical applications and recently have been found to be very useful in electronic and magnetic resonance imaging contrast agent where r-GO was functionalized with silica coated gold and iron oxide nanoparticles. The potential material for these different applications was established by experimental data where the microstructural, electronic, electrical and magnetic properties were studied. In the present study, we have compared the electronic and magnetic properties of these nanocomposites (r-GO: Au NPs & r-GO: Fe2O3 NPs) using different experimental data. The data is verified with density functional theory (DFT) calculations to elucidate the relationship between the density of state (DOS) and their magnetic properties. Coupled with the experimental data, the DFT studies revealed that the magnetization enhancement of rGO: Au-NPs is mainly due to the nano-sized clusters with addition of Au 3d and O 2p orbital states as contributors; whereas that of r-GO: Fe2O3 NPs is mainly due to Fe 2p, Fe 3d and O 2p orbital states as contributors.

Thermal Analysis of Photoelectron Emission (PE) and X-ray Photoelectron Spectroscopy (XPS) Data for Iron Surfaces Scratched in Air, Water, and Liquid Organics

Little is known about the temperature dependence of electron transfer occurring at real metal surfaces. For iron surfaces scratched in seven environments, we report Arrhenius activation energies obtained from the data of photoelectron emission (PE) and X-ray photoelectron spectroscopy (XPS). The environments were air, benzene, cyclohexane, water, methanol, ethanol, and acetone. PE was measured using a modified Geiger counter during repeated temperature scans in the 25–339 °C range under 210-nm-wavelength light irradiation and during light wavelength scans in the range 300 to 200 nm at 25, 200, and 339 °C. The standard XPS measurement of Fe 2p, Fe 3p, O 1s, and C 1s spectra was conducted after wavelength scan. The total number of electrons counted in the XPS measurement of the core spectra, which was called XPS intensity, strongly depended on the environments. The PE quantum yields during the temperature scan increased with temperature, and its activation energies (ΔEaUp1) strongly depended on the environment, being in the range of 0.212 to 0.035 eV. The electron photoemission probability (αA) obtained from the PE during the wavelength scan increased with temperature, and its activation energies (ΔEαA) were almost independent of the environments, being in the range of 0.113–0.074 eV. The environment dependence of the PE behavior obtained from temperature and wavelength scans was closely related to that of the XPS characteristics, in particular, the XPS intensities of O 1s and the O2− component of the O 1s spectrum, the acid–base interaction between the environment molecule and Fe–OH, and the growth of non-stoichiometric FexO. Furthermore, the origin of the αA was attributed to the escape depth of hot electrons across the overlayer.

Redox Control of Charge Transport in Vertical Ferrocene Molecular Tunnel Junctions

Summary Controlling charge transport through molecular tunnel junctions is of crucial importance for exploring basic physical and chemical mechanisms at the molecular level and realizing the applications of molecular devices. Here, through a combined experimental and theoretical investigation, we demonstrate redox control of cross-plane charge transport in a vertical gold/self-assembled monolayer (SAM)/graphene tunnel junction composed of a ferrocene-based SAM. When an oxidant/reductant or electrochemical control is applied to the outside surface of the neutral single-layer graphene top electrode, reversible redox reactions of ferrocene groups take place with charges crossing the graphene layer. This leads to counter anions on the outer surface of graphene, which balance the charges of ferrocene cations in the oxidized state. Correspondingly, the junctions switch between a high-conductance, neutral state with asymmetrical characteristics and a low-conductance, oxidized state with symmetrical characteristics, yielding a large on/off ratio (>100).

A Kinetic study of Tb3+ and Dy3+ co-substituted CoFe2O4 spinel ferrites using temperature dependent XRD, XPS and SQUID measurements

In this research work, we have investigated the structural development of Tb3+ and Dy3+ co-substituted CoFe2O4 ferrites using temperature and time dependent XRD measurements. Sol-gel auto combustion technique was used to synthesized Tb3+ and Dy3+ co-substituted spinel ferrites with composition CoFe2-x-y TbxDyyO4 (x + y = 0.0–0.25). Various characterization techniques such as High temperature XRD, XPS and SQUID were used to observe the Kinetics mechanism as well as the impact of co-substitution on the structural and magnetic properties. Room temperature XRD scans showed that the synthesized materials having single phase and were crystalline in nature. The crystallite size was lied in nano regime ranging from 26.07 to 21.92 nm and lattice parameters were found to be decreased with increasing rare earth metal ions contents. Temperature and time dependent XRD data suggested that structure of investigated samples not degrade even at temperature 900 °C which was maintained for 2 h. The ionic states of Co2+, Tb3+, Dy3+ and Fe3+ were confirmed by X-ray Photoelectron spectrometry measurements along with the binding energies of Co2p, Tb 2p, Dy 2p, Fe 2p which confirmed the tetrahedral and octahedral sites for substituted ions. Room temperature magnetic measurements of annealed nanoferrites were carried out by operating the SQUID magnetometer in VSM mode. The data demonstrated that increasing concentrations of substituent (Tb3+and Dy3+) resulted in the reduction of various magnetic parameters such as remanence, saturation magnetization and Coercivity. The calculated values of saturation magnetization and coercivities were found in the range of 78.1–45.15emu/g and 742–543Oe respectively. This study concluded that cation distribution and crystallite size is effective in controlling the structural, morphological and magnetic properties.

XPS characterization of transition metal oxalates

X-ray photoelectron spectroscopy (XPS) was employed to characterize the surface composition, atoms’ chemical state and electronic structure of oxalates MeC2O4·nH2O (Me = Mn, Fe, Co, Ni, Cu); their structure was characterized by XRD. Core-level Me 2p, Fe 3p, Fe 3s, C 1s, O 1s, X-ray induced Auger Me LMM, O KVV and valence band spectra are presented along with a number of parameters derived from the spectra analysis. A comparative analysis of FeC2O4 and Fe2(C2O4)3 oxalates is performed. The XPS parameters for the oxalates are compared to those for respective oxides. Variation of spin-orbit splitting, multiplet splitting, energy separation and intensity of satellites in the Me 2p spectra across the series of the compounds is considered in terms of changes in the electronic structure and strength of the Me–O bonding. The strong effect of covalency of the ligand (C2O42– vs. O2–) is demonstrated. Auger parameters α′(Me) and α′(O) are determined and used for estimating the initial state effects in photoemission. The surface charging of the oxalates is shown to be mainly dependent on the surface composition and stoichiometric atomic ratios. In the C 1s and O 1s spectra of the oxalates, intense satellites are revealed for the first time.

XPS characterization of surface layers of stainless steel nitrided in electron beam plasma at low temperature

The results of the influence of low-temperature plasma nitriding at 350 °C on the CrN and FeN bonds formation of Fe-Cr-Ni austenitic steel before and after nanostructure frictional treatment are presented. The measurements of high-energy resolved X-ray photoelectron Fe 2p, Cr 2p, Ni 2p and N 1s spectra and valence bands (VB) showed that chromium and iron form CrN and FeN bonds whereas the nickel is in metallic state. It is concluded that the expanded austenite formed directly on the surface of the steel after low temperature plasma nitriding can be classified as a nanocomposite medium consisting of CrN and FeN clusters dispersed in a Fe-Cr-Ni-N matrix.

Different Insights into Silicate Rectorite Modification and Its Role in Removal of Heavy Metal Ions from Wastewater

In the field of water management, the separation of metal contaminants from wastewater is very important and challenging. This study systematically investigated the effect and underlying mechanism of silicate rectorite (REC) on the removal of heavy metal ions (Cr(VI) and Pb(II)) from wastewater. The adsorption and removal capacity of REC was further improved by its novel modification with ferric chloride hexahydrate. Compared to natural REC, the modified rectorite (Fe-REC) showed comparatively superior adsorption efficiency for both Cr(VI) and Pb(II) due to the chemisorption of Fe3+ on the REC surface as its oxidation state (Fe–O, Fe–OH, Fe–OOH). Adsorption on Cr(VI) attributed to the reaction between iron hydroxy complexes (FeOH2+, Fe(OH)2+ and Fe(OH)3(aq)) and Cr(VI) species (HCrO4− and CrO42−) in the aqueous solution. This reaction was perfectly consistent with the binding energy shifts in O 1s and Fe 2p species, as reflected by XPS analysis. While, the existence of –Al–OH and –Si–OH in silicate REC slurry reacted with PbOH+ colloids produced from lead ions hydrolysis to promote Pb(II) adsorption. Zeta potential after modification and removal occurred to shift positively or negatively to testify the adsorption of Fe3+ and heavy metal ions. Freundlich and Langmuir isotherms conformed adsorption process for Cr(VI) and Pb(II), respectively.

Investigation of chemical bonding and supercapacitivity properties of Fe3O4-rGO nanocomposites for supercapacitor applications

Iron oxide decorated reduced graphene oxide (Fe3O4/rGO) nanocomposites were synthesized using a one-step chemical reduction method. The XRD results reveal the diffraction planes at 2θ = 36.53° and 43.04° corresponding to the planes (311) and (400) respectively for Fe nanoparticles and the broadened peak at 26.52° was observed corresponds to plane (002) for rGO which confirmed the formation of Fe3O4 in rGO sheets. FTIR results shows the chemical bonding at around 580.96 cm−1, 1191.61 cm−1, 1559.36 cm−1, 2358.27 cm−1, 2987.45 cm−1 and 3360 cm−1 attributes for the FeO, CO, CC, CO, C-H2 and OH bonds respectively whereas Raman shift for Fe3O4 was found in the range of 100–800 cm−1. The ID/IG ratios varied from 2.5 to 1.55 as Fe(NO3)3 concentration increases from 5 mM to 25 mM. The estimated bandgap for rGO and rGO/Fe3O4 are 2.60 eV, and from 2.52 to 2.34 eV respectively as the Fe(NO3)3 concentration increases from 5 mM to 25 mM. The atomic percentage of Fe(2p), C(1s), and O (1s) was varied as 0.75–7.11 at.%, 86.09–69.58 at.% and 13.16–23.31 at.% as the Fe(NO3)3 concentration increases from 5 mM to 25 mM. The maximum specific capacitance was achieved at 416 F/g for 25 mM of Fe3O4/rGO nanocomposite with cyclic stability of 88.57% at a current density of 5Ag−1 over 1000 cycles. Hence, Fe3O4/rGO nanocomposite can be considered as a good candidate for the supercapacitor electrode applications.

Site-Selective Orbital Interactions in an Ultrathin Iron-Carbene Photosensitizer Film.

We present the first experimental study of the frontier orbitals in an ultrathin film of the novel hexa-carbene photosensitizer [Fe(btz)3]3+, where btz is 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene). Resonant photoelectron spectroscopy (RPES) was used to probe the electronic structure of films where the molecular and oxidative integrities had been confirmed with optical and X-ray spectroscopies. In combination with density functional theory calculations, RPES measurements provided direct and site-selective information about localization and interactions of occupied and unoccupied molecular orbitals. Fe 2p, N 1s, and C 1s measurements selectively probed the metal, carbene, and side-group contributions revealing strong metal–ligand orbital mixing of the frontier orbitals. This helps explain the remarkable photophysical properties of iron-carbenes in terms of unconventional electronic structure properties and favorable metal–ligand bonding interactions—important for the continued development of these type of complexes toward light-harvesting and light-emitting applications.

Analysis of the Fe 2p XPS for hematite α Fe2O3: Consequences of covalent bonding and orbital splittings on multiplet splittings.

The origins of the complex Fe 2p X-Ray Photoelectron Spectra (XPS) of hematite (α-Fe2O3) are analyzed and related to the character of the bonding in this compound. This analysis provides a new and novel view of the reasons for XPS binding energies (BEs) and BE shifts, which deepens the current understanding and interpretation of the physical and chemical significance of the XPS. In particular, many-body effects are considered for the initial and the final, 2p-hole configuration wavefunctions. It is shown that a one-body or one-configuration analysis is not sufficient and that the many-body, many-determinantal, and many-configurational character of the wavefunctions must be taken into account to describe and understand why the XPS intensity is spread over an extremely large number of final 2p-hole multiplets. The focus is on the consequences of angular momentum coupling of the core and valence open shell electrons, the ligand field splittings of the valence shell orbitals, and the degree of covalent mixing of the Fe(3d) electrons with the O(2p) electrons. Novel theoretical methods are used to estimate the importance of these various terms. An important consequence of covalency is a reduction in the energy separation of the multiplets. Although shake satellites are not considered explicitly, the total losses of intensity from the angular momentum multiplets to shake satellites is determined and related to the covalent character of the Fe-O interaction. The losses are found to be the same for Fe 2p1/2 and 2p3/2 ionization.

Halamishite, Ni5P4, a new terrestrial phosphide in the Ni–P system

Halamishite, Ni5P4, is a new natural phosphide discovered in pyrometamorphic assemblages of the Hatrurim Formation (Mottled Zone), Southern Levant. The mineral occurs as minute grains up to 20 μm in size intimately intergrown with zuktamrurite, FeP2, and transjordanite, (Ni,Fe)2P, which are disseminated in fine-grained diopside microbreccia. Chemical composition of the holotype material (electron microprobe, wt%): Ni 69.23, Fe 1.80, P 29.59, total 100.62, was recalculated to (Ni4.90Fe0.13)5.03P3.97 on the basis of nine atoms per formula unit. The ideal formula of halamishite is Ni5P4. In reflected light, the mineral is white with beige tint, non-pleochroic. It is moderately anisotropic and bireflectant (ΔR589 = 7.2%). Reflectance values for the four wavelengths recommended by the IMA Commission on Ore Microscopy are [Rmax/Rmin (%), λ (nm)]: 44.3/36.6, 470; 49.2/42.1, 546; 51.3/44.1, 589; 53.3/46.1, 650. Crystal structure of halamishite was solved and refined to R1 = 0.031 based on 425 unique observed [I ≥ 2σ(I)] reflections. The mineral is hexagonal, space group P63mc, a 6.8184(4), c 11.0288(8) A, V 444.04(6) A3, Z = 4. Dx calculated for an empirical formula is 6.249(1) g cm−3. Halamishite is named for its type locality, the Halamish wadi in the Hatrurim basin, Negev Desert, Israel. It is a naturally occurring analogue of synthetic Ni5P4, the compound widely used in electro- and photocatalytic applications. Due to chemical proximity to the Ni5P4 end-member, halamishite can be used as a geothermometer indicating that formation of phosphide assemblages had occurred at a temperature below 870 °C.