X-ray Absorption Spectroscopy Study Research Articles

First results of in-situ X-ray Absorption Spectroscopy study on charging-discharging cycles of lithium ion battery at Indus-2 SRS

An electrochemical cell with Kapton X-ray windows has been in-house developed and related facilities have been set-up for in-situ X-ray Absorption Spectroscopy (XAS) measurements on electrode materials of Li-ion batteries at the Energy Scanning EXAFS beamlines (BL-09) at Indus-2 Synchrotron Source at Indore, India. The set-up has been tested by carrying out in-situ XAS measurements at Mn K-edge on a Li-ion battery with LiMn2O4 as cathode material during charging and discharging when Li ions are de-intercalated and intercalated respectively. The in-situ XAS measurements, (which comprise of both XANES and EXAFS measurements) reveal electronic and structural changes at the Mn sites of the cathode material during the charging/discharging processes which are not fully reversible. Such in-situ studies are very important since cyclic instability of batteries during the charging/discharging processes depend on the variation in the local structure around the active atoms of the electrode materials and thus the above facility would open up a new avenue to the users of Indus-2 synchrotron facility at India in elucidating such phenomena in new generation batteries with novel electrode materials.

Yttrium complexation and hydration in chloride-rich hydrothermal fluids: A combined ab initio molecular dynamics and in situ X-ray absorption spectroscopy study

Accurate knowledge of rare earth elements (REE) speciation in high pressure – high temperature fluids is required to model REE transport and precipitation in subduction zones and magmatic-hydrothermal environments, and the formation of rare metal deposits. Recent experiments (lanthanum, ytterbium, erbium) have demonstrated that REE chloride complexes are the main REE form in many hydrothermal fluids (Migdisov et al., 2016). However, the speciation of yttrium (Y(III)), a cation with an ionic radius similar to that of Ho(III), remains poorly constrained in chloride-rich hydrothermal solutions.We used ab initio molecular dynamics (MD) simulations to calculate the nature of Y(III)-Cl complexes and the thermodynamic properties of these species at temperatures up to 500 °C and pressures of 800 bar and 1000 bar. The MD results were complemented by in situ X-ray absorption spectroscopy (XAS) measurements. Our results indicate that at temperatures below 200 °C, chloro-complexes do not form readily, even in highly concentrated brines. At ambient condition, the Y(III) aqua ion binds to eight water molecules in a square antiprism geometry, which is consistent with previous ab initio studies (Ikeda et al., 2005a). The thermodynamic integration method was employed to calculate the formation constants (logKΘ) of Y(III)-Cl− complexes in two simulation boxes containing different Y:Cl ratios; we obtained very consistent results of the standard logKΘ of the individual complexes from the two independent calculations, which confirms that the thermodynamic integration method is reliable and not significantly affected by technical limitations in box size, box composition, or simulation time.Based on the derived formation constants, we fit modified Ryzhenko–Bryzgalin (MRB) equation of state parameters, which enable extrapolation of the formation constants at elevated temperature and pressure. The results are consistent with the XAS data, and show that the stability of Y(III)-Cl complexes increases with increasing temperature, Y(III) forming high order Cl− complexes (up to YCl4−) in high salinity solutions at high temperature and pH = 3. We also compare the extrapolated logKΘ with the available data for other REE at 150 °C, 200 °C and 250 °C. At 200 °C, yttrium behaves more like a heavy REE, but from 200 °C to 250 °C, the formation constants of Y(III)-Cl complexes increase dramatically and behave more like the light REE. The difference of Cl− dominant species between Ho(III) (HoCl2+) and Y(III) (YCl2+) may account for the formation of anomalous Y/Ho ratios in some hydrothermal environments.

The coordination core and charge of chromium in Metakaolin-geopolymers as revealed by X-Ray absorption spectroscopy

Geopolymers obtained by mixing metakaolin powder with tannery wastewater and NaOH pellets are proposed as 3D aluminosilicate network to chemically entrap Cr(III) species. X-ray Absorption Spectroscopy studies show the absence of toxic Cr(VI). The analysis of EXAFS also reveals a Cr(III) first coordination shell formed by 6 oxygens and a second shell of 7/8 Al or Si atoms, indicating strong bonding with the aluminosilicate network.

X-ray absorption spectroscopic studies on solid oxide fuel cells and proton-conducting ceramic fuel cells

Abstract X-ray absorption spectroscopy (XAS) is one of the best techniques to obtain the information on the electronic and local structures of materials. In the last few decades, XAS becomes a common analytical technique for the investigation of solid oxide fuel cells and proton-conducting ceramic fuel cells. In particular, operando and/or advanced XAS measurements can be recently available with the increased accessibility of synchrotron radiation. In this article, recent trends of solid oxide fuel cell and proton-conducting ceramic fuel cell researches using XAS are overviewed.

Unravelling the Role of Fe-Mn Binary Active Sites Electrocatalyst for Efficient Oxygen Reduction Reaction and Rechargeable Zn-Air Batteries.

Transition-metal atoms and/or heteroatom-doped carbon nanostructures is a crucial alternative to find a nonprecious metal catalyst for electrocatalytic oxygen reduction reaction (ORR). Herein, for the first time, we demonstrated the formation of binary (Fe-Mn) active sites in hierarchically porous nanostructure composed of Fe, Mn, and N-doped fish gill derived carbon (Fe,Mn,N-FGC). The Fe,Mn,N-FGC catalyst shows remarkable ORR performance with onset potential (Eonset) of 1.03 V and half-wave potential (E1/2) of 0.89 V, slightly better than commercial Pt/C (Eonset = 1.01 V, E1/2 = 0.88 V) in alkaline medium (pH > 13), which is attributed to the synergistic effect of Fe-Mn dual metal center as evidenced from X-ray absorption spectroscopic study. We proposed that the presence of Fe-Mn binary sites is actually beneficial for the O2 binding and boosting the ORR by weakening the O═O bonds. The homemade rechargeable Zn-air battery performance reveals the open-circuit voltage of 1.41 V and a large power density of 220 mW cm-2 at 260 mA cm-2 current density outperforming Pt/C (1.40 V, 158 mW cm-2) with almost stable charge-discharge voltage plateaus at high current density. The present strategy enriches a route to synthesize low-cost bioinspired electrocatalyst that is comparable to/better than any nonprecious-metal catalysts as well as commercial Pt/C.

X-ray absorption spectroscopy study of Ga-doping in reactively sputtered ZnO films

Ga-doped ZnO (GZO) films were grown by reactive co-sputtering of a Zn-GaAs target (3% area coverage of Zn by GaAs) at 375 °C with different partial pressures of oxygen. The resistivity of GZO films increases drastically from ≲10−3 Ω-cm to ~ 0.2 Ω-cm as the O2 in the sputtering atmosphere is changed from 5 % to 6 %. The films grown at 5% or lower O2 have the Ga/Zn ratio of ~ 0.1 and display low resistivity with carrier concentration ~ 1021 cm−3, while the films grown at 6% or higher O2 have lower Ga/Zn ratio of ~ 0.01 and display high resistivity with carrier concentration ~ 1019 cm−3. Extended X-ray absorption fine structure (EXAFS) measurements at Zn and Ga K-edges reveal substitutional incorporation of Ga in low resistivity films. X ray photoelectron spectroscopy (XPS) studies reveal a substantial decrease in oxygen vacancies together with increase in oxygen interstitials, in high resistivity GZO films. EXAFS measurements of the high resistivity films show a substantial increase in Ga-O and Ga-Zn bond distances and Ga-O coordination, indicating incorporation of oxygen interstitials in the vicinity of Ga. The comparison of measured and simulated X–ray absorption near edge spectra at O K-edge, together with XPS and EXAFS results, provides adequate experimental evidence of the presence of acceptor type (GaZn+Oi) defect complex, which cause carrier compensation in high resistivity films.

Absence of Y-pocket in 1-Fe Brillouin zone and reversed orbital occupation imbalance in FeSe

The FeSe nematic phase has been the focus of recent research on iron-based superconductors (IBSs) due to its unusual properties, which are distinct from those of the pnictides. A series of theoretical/experimental studies were performed to determine the origin of the nematic phase. However, they yielded conflicting results and caused additional controversies. Here, we report the results of angle-resolved photoemission and X-ray absorption spectroscopy studies on FeSe detwinned by a piezo stack. We fully resolved band dispersions with orbital characters near the Brillouin zone (BZ) corner, and revealed an absence of any Fermi pocket at the Y point in the 1-Fe BZ. In addition, the occupation imbalance between {d}_{{xz}} and {d}_{{yz}} orbitals was the opposite of that of iron pnictides, consistent with the identified band characters. These results resolve issues associated with the FeSe nematic phase and shed light on the origin of the nematic phase in IBSs.

In Situ X-ray Diffraction and X-ray Absorption Spectroscopic Studies of a Lithium-Rich Layered Positive Electrode Material: Comparison of Composite and Core-Shell Structures.

Lithium- and manganese-rich transition-metal oxide (LMR-NMC) electrodes have been designed either as heterostructures of the primary components ("composite") or as core-shell structures with improved electrochemistry reported for both configurations when compared with their primary components. A detailed electrochemical and structural investigation of the 0.5Li2MnO3-0.5LiNi0.5Mn0.3Co0.2O2 composite and core-shell structured positive electrode materials is reported. The core-shell material shows better overall electrochemical performance compared to its corresponding composite material. While both configurations gave the same initial charge capacity of ∼300 mAh/g when cycled at a rate of 10 mA/g at 25 °C, the core-shell sample gives a discharge capacity of 232 mAh/g compared to 208 mAh/g delivered by the composite sample. Also, the core-shell sample gave better rate capability and a smaller first-cycle irreversible capacity loss than the composite sample. The improved performance of the core-shell material is attributed to its lower surface reactivity and limited structural change since the more stable Li2MnO3 shell screens the more reactive Ni-rich core material from interacting with either air or electrolyte at high potentials, thereby preventing electrode surface modification. In situ X-ray diffraction correlated with electrochemical data revealed that the composite sample shows stronger volumetric changes in the lattice parameters during charging to 4.8 V. In addition, X-ray absorption spectroscopy showed an incomplete Ni reduction process after the first discharge for the composite sample. From these results, it was shown that this leads to a more severe degradation in the composite material that affects Li+ intercalation in the subsequent discharge, thereby resulting in its poorer performance. Furthermore, to confirm these results, another LMR-NMC material with a different composition (having a Ni-poor core)-0.5Li2MnO3-0.5LiNi0.33Mn0.33Co0.33O2-was investigated. The core-shell structured positive electrode material also gave an improved electrochemical performance compared to the corresponding composite positive electrode material. These results show that the core-shell configuration could effectively be used to improve the performance of the LMR-NMC materials to enable future high-energy applications.

Ru doping effect on the structural, electronic, transport, optical and dye degradation properties of layered Li2MnO3

Ru doped Li2MnO3 compositions show the presence of redox couples Mn+3–Mn+4 and Ru+4–Ru+5. Due to the presence of these redox couples in Li2Mn1−xRuxO3 (x = 0.05, 0.1), Ru doped compositions show (i) change in structure (ii) large decrease in impedance(~ 107 to ~ 105 Ohm) (iii) degrade methyl orange and methylene blue solution (pH-6) in quick time in presence of tungsten (W) bulb and sun light. Synchrotron X-ray powder diffraction studies show the change in lattice parameters with Ru doping at Mn site in Li2Mn1−xRuxO3 (x = 0.05, 0.1). Raman and Infrared spectroscopic studies show the shift in Mn–O stretching mode of Li2MnO3 towards lower wave number with Ru doping. Soft X-ray absorption spectroscopic studies show the presence of mixed valences of Mn+3, Mn+4, Ru+4 and Ru+5 in Li2Mn1−xRuxO3 (x = 0.05, 0.1) using L2,3 and M4 edge. UV–Vis diffuse reflectance spectroscopic studies show the optical band gap in visible light range in Ru doped Li2Mn1−xRuxO3 (x = 0.05, 0.1) compositions. The presence of 5 mg of Li2Mn0.9Ru0.1O3 degrades 5 ml of methyl orange solution (10 mg/L) of pH 6 in 5 min and methylene blue solution (10 mg/L) of pH 6 in 3 min of exposure in W bulb light.

Sequestration of Selenite and Selenate in Gypsum (CaSO4·2H2O): Insights from the Single-Crystal Electron Paramagnetic Resonance Spectroscopy and Synchrotron X-ray Absorption Spectroscopy Study.

Gypsum is the most common sulfate mineral on Earth's surface and is the dominant solid byproduct in a wide variety of mining and industrial processes, thus representing a major source for heavy metal(loid) contamination, including selenium. Gypsum crystals grown from the gel diffusion technique in 0.02 M Na2SeO4 solution at pH 7.5 and 0.02 M Na2SeO3 solutions at pH 7.5 and 9.0 contain 828, 5198, and 5955 ppm Se, respectively. Synchrotron Se K-edge X-ray absorption spectroscopic analyses show that selenite and selenate are the dominant species in Se4+- and Se6+-doped gypsum, respectively. The single-crystal EPR spectra of Se4+- and Se6+-doped gypsum after gamma-ray irradiation reveal five selenium-centered oxyradicals: SeO2-(I), SeO2-(II), SeO2-(III), SeO3-, and HSeO42-. The former three radicals provide unequivocal evidence for the substitution of their paramagnetic precursor SeO32- for SO42- in the gypsum structure, while the latter two confirm the replacement of SeO42- for SO42-. These results demonstrate that gypsum has a significant capacity for sequestrating both selenite and selenate in the structure but has a marked preference for the former, thus confirming important controls on the mobility and bioavailability of selenium oxyanions and pointing to optimal applications of gypsum for remediating selenium contamination under neutral to alkaline conditions.

Cationic disorder: A pathway for demonstrating inverse exchange bias in Gd2CoRuO6

We report here the observation of the inverse exchange bias phenomenon in the ferrimagnetic double-perovskite ${\mathrm{Gd}}_{2}{\mathrm{CoRuO}}_{6}$. The compound crystallizes in a monoclinic structure (space group $P{2}_{1}/n$), and it undergoes long-range magnetic ordering below ${T}_{C}=60$ K. The ferrimagnetic state of the sample is manifested through magnetization reversal at low temperature. In order to corroborate the role of local structure on the magnetic properties of ${\mathrm{Gd}}_{2}{\mathrm{CoRuO}}_{6}$, we have performed a combined magnetization and x-ray absorption spectroscopy study on two different samples prepared through different cooling protocols (slow cooling and furnace cooling). Extended x-ray absorption fine-structure analysis indicates the presence of strong antisite disorder between Co and Ru in both samples. However, the slow-cooled sample shows completely random antisite disorder, whereas, small Co- and Ru-rich patches appear in the furnace-cooled sample. In both samples, a significant amount of mixed valency in Co and Ru ions is evident from our x-ray absorption near-edge structure. The antiparallel ordering along with different temperature dependence of the three magnetic sublattices, Gd, Co, and Ru, can be responsible for negative magnetization, whereas the inverse exchange bias effect can be attributed to the mixed interfacial coupling between adjacent magnetic nanoclusters. The difference in local structure can nicely be accounted for by the observed variations of the magnetic properties between two samples of ${\mathrm{Gd}}_{2}{\mathrm{CoRuO}}_{6}$.

Oscillatory Behavior in Oxidation of Propane Over Nickel Foil and Films

The oxidation of propane was studied over Ni foil, a thick Ni/Si film, and a thin Ni/Si film in a flow reactor under oxygen-deficient conditions at a total pressure near 1 mbar. The thickness of the foil was 125 µm, while the thickness of the films was 20 and 1.5 µm, respectively. It was shown that regular self-sustained reaction-rate oscillations arise only over the Ni foil and the thick Ni/Si film. The relaxation-type oscillations appear at 700 °C after an induction period of approximately 50 min, which is accompanied by the formation of a rough and porous structure over their surfaces. According to krypton adsorption measurements, the effective surface area of the treated catalysts increases significantly. CO, CO2, H2, and H2O were detected as products in the gas phase. The results of operando X-ray absorption spectroscopy study indicate that the oscillations originate due to periodical oxidation and reduction of nickel. The highly active state is Ni in the metallic state, while the transition to the poorly active state is accompanied by the growth of NiO layer on the catalyst surface. The upper layer of the catalysts with a thickness of at least 15 nm is involved in the oxidation/reduction process. In contrast, no oscillations appeared in the oxidation of propane over the thin Ni/Si film. In this case, the thickness of the Ni layer is not sufficient for the formation of a porous structure over the thin Ni film. As a result, the thin Ni film cannot provide high activity in the catalytic oxidation of propane that is sufficient for the self-sustained oscillations to occur. The reasons that lead to oscillatory behavior in the oxidation of propane over nickel are discussed.

Synergetic effect on catalytic activity and charge transfer in Pt-Pd bimetallic model catalysts prepared by atomic layer deposition.

Pt-Pd bimetallic nanoparticles were synthesized on TiO2 support on the planar substrate as well as on high surface area SiO2 gel by atomic layer deposition to identify the catalytic performance improvement after the formation of Pt-Pd bimetallic nanoparticles by surface analysis techniques. From X-ray absorption near edge spectra of Pt-Pd bimetallic nanoparticles, d-orbital hybridization between Pt 5d and Pd 4d was observed, which is responsible for charge transfer from Pt to Pd. Moreover, it was found from the in situ grazing incidence X-ray absorption spectroscopy study that Pt-Pd nanoparticles have a Pd shell/Pt core structure with CO adsorption. Resonant photoemission spectroscopy on Pt-Pd bimetallic nanoparticles showed that Pd resonant intensity is enhanced compared to that of Pd monometallic nanoparticles because of d-orbital hybridization and electronic states broadening of Pt and Pd compared monometallic catalysts, which results in catalytic performance improvement.

Recent progress in high pressure X-ray absorption spectroscopy studies at the ODE beamline

ABSTRACTHigh pressure energy-dispersive X-ray absorption spectroscopy is a valuable structural technique, especially, when combined with a nano-polycrystalline diamond anvil cell. Here we present recent results obtained using the dispersive setup of the ODE beamline at SOLEIL synchrotron. The effect of pressure and temperature on the X-ray induced photoreduction is discussed on the example of nanocrystalline CuO. The possibility to follow local environment changes during pressure-induced phase transitions is demonstrated for α-MoO based on the reverse Monte Carlo simulations.

On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation

CoFe2O4 nanoparticles (NPs) were synthesized by using a colloidal one-pot synthesis method based on the decomposition of metal acetylacetonates in the presence of oleyl amine. The characterization by X-ray diffraction, transmission electron microscopy and N2physisorption revealed non-porous spinel phase CoFe2O4 NPs with an average particle size of 4 nm. The unsupported metal oxide NPs were applied in the selective oxidation of 2-propanol in a continuously operated fixed-bed reactor under quasi steady-state conditions using a heating rate of 0.5 k min−1. 2-Propanol was found to be oxidatively dehydrogenated over CoFe2O4 yielding acetone and H2O with high selectivity. Only to a minor extent dehydration to propene and total oxidation to CO2 was observed at higher temperatures. The detected low-temperature reaction pathway with maxima at 430 and 510 K was inhibited after the initial 2-propanol oxidation up to 573 K, but an oxidative treatment in O2 or N2O atmosphere led to full regeneration. No correlation between the desorbing amount or the surface oxygen species investigated by O2 temperature-programmed desorption experiments and the low-temperature activity was observed. The amounts of evolving CO2 during the TPO experiments indicate deactivation due to formation of carbonaceous species. Inhibition experiments with pre-adsorbed reaction intermediates and infrared spectroscopy identified acetate species as reversible poison, whereas carbonates are rather spectators. In addition, carbon deposition was detected by X-ray photoelectron spectroscopy, which also revealed a minor influence of cobalt reduction during the deactivation process as confirmed by X-ray absorption spectroscopy studies.

Low temperature, solution processed spinel NiCo2O4 nanoparticles as efficient hole transporting material for mesoscopic n-i-p perovskite solar cells

Spinel Nickel cobaltite oxide (NiCo2O4) have received great interest due to its usage in several industrial applications. The motivation of the present study is to explore the usefulness of spinel Nickel cobaltite oxide as inorganic charge transporting layer for standard perovskite solar cells (PSCs). This is the first demonstration of successful use of NiCo2O4 nanoparticles as hole transporting layer (HTL) in standard PSCs with the triple cation perovskite material. The synthesis of nanoparticles was done using a facile chemical precipitation method without the use of surfactant. The synthesized nanoparticles were characterized by the various techniques like X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), Field emission scanning electron microscopy (FE-SEM), and UV–vis spectroscopy (UV–vis). The co-ordination of Ni in Co3O4 matrix, as well as M+nO bond lengths, were confirmed by the XAS studies. The standard mesoporous PSCs were fabricated by spin-coating a thin layer of NiCo2O4 (120 nm), and fabricated PSCs show an esteemed power conversion efficiency (PCE) of >14% (under standard illumination conditions) and long-term stability (under ambient condition RH = 30–40%) as compared to the spiro-based PSCs. To improve the device performance further we also fabricated the PSCs using the interfacial hole transporting layer, presenting a PCE of >16% with almost negligible hysteresis that is comparable to the normal standard PSCs based on spiro-OMeTAD as HTL. The performance of PSCs was further analysed by Electrochemical Impedance Spectroscopy (EIS), Photoluminescence (PL), Time-resolved Photoluminescence (TrPL) studies. The results showed the reduced recombination resistance in the PSCs using NiCo2O4 as well as interfacial layer. These outcomes indicate the effectiveness of NiCo2O4 interlayer for stable and highly efficient perovskite solar cells.

Structural, electronic, transport and magnetic studies of LaCo1 − xNixO3 (x = 0, 0.3) thin films

We present here a study on structural, electronic, transport, and magnetic properties of single-phase (001) oriented compressively strained thin films of LaCoO3 (LCO) and LaCo0.7Ni0.3O3 (LCNO). The films were deposited on the LaAlO3 (001) single crystal substrate using pulsed laser deposition. Electronic structure investigations by x-ray absorption spectroscopy (XAS) measurements at various edges (Co-L3,2, Ni-L3,2, and La-M5,4) confirm +3 charge states for Co, Ni, and La ions in all samples. The XAS study also reveals a transition in the spin state of Co+3 (low spin to intermediate/high spin), which is attributed to induced strain and Ni substitution. Electrical transport measurements suggest the semiconducting behavior for LCO and LCNO thin films in the measured temperature range. We found a drastic change in resistivity (ρ) and magnitude with Ni substitution. An in-depth analysis of the conduction mechanism governing the transport behavior in thin films has been done using various theoretical models. Different conduction mechanisms (Arrhenius law and Effros-Shklovski-type variable range hopping) have been observed to govern conduction in different temperature ranges, suggesting disorder controlled transport in these films. The magnetization measurements show a magnificent increase in saturation magnetization for LCNO and ferromagnetic ordered states, which persists even up to room temperature.

Nano-polycrystalline diamond anvils: key devices for XAS at extreme conditions: their use, scientific impact, present status and future needs

ABSTRACTNano-polycrystalline diamonds (NPDs) have become fundamental tools for cutting-edge X-ray absorption spectroscopy (XAS) studies at high P/T conditions that opened up new research directions by overcoming previous limitations. Indeed, NPDs yield a continuous and weak X-ray background signal which enables the collection of high-quality XAS data of materials compressed in diamond anvil cells. This is a critical advantage over the classically used single-crystal diamonds that generate strong parasitic signals (glitches) which render the analysis of XAS data in many cases impossible. In this contribution we give an overview of the impact and the scientific opportunities that NPDs opened up for extreme condition XAS spectroscopy at the European Synchrotron Radiation Facility and discuss future needs.

X-ray absorption spectroscopy study of cobalt mononitride thin films

We present a comprehensive study to resolve the debate about the structure of cobalt mononitride (CoN). In contradiction with theoretical predictions, experimentally CoN has been claimed to synthesize in a rock-salt (RS) and in a zinc-blende (ZB)-type structure under ambient pressure and temperature. Utilizing X-ray absorption near-edge spectroscopy (XANES) at Co and N K-edges and extended X-ray absorption fine structure (EXAFS) at Co K-edge, we investigated the structure of CoN in detail. The presence of a strong pre-edge feature at the Co K-edge and the absence of t $$_2$$ feature at the N K-edge indicate towards the tetrahedral coordination that is expected in the ZB-type structure of CoN. Theoretical simulations of XANES spectra unambiguously confirm the ZB-type structure in CoN. Also from EXAFS data, we found that Co–N and Co–Co bond distances match well with ZB-CoN. Magnetic properties of CoN were examined using polarized neutron reflectivity and bulk magnetization measurements. It was found that CoN sample exhibits a paramagnetic behaviour as expected in ZB-CoN. Obtained results clearly demonstrate that CoN indeed crystalizes in the ZB-type structure, and the possibility of the RS-type CoN can be ruled out under ambient pressure and temperature. It is anticipated that the information about the structure of CoN can be utilized for its usage in emerging areas such as low-cost catalyst in oxygen and hydrogen evaluation reactions, high capacity anode in ion batteries and in photovoltaic applications.

Effects of Nonstoichiometry and Plastic Deformation on Charge and Spin States of Cobalt Ions in LnBaCo2BaO5.5 – δ (Ln = Tb, Eu): Soft X-ray Absorption Spectroscopy Studies

We present results of soft X-ray absorption spectroscopy studies of nonstoichiometric Tb1 ‒ yBa1 +yCo2 –xO5.5 – δ cobaltites and EuBaCo2O5.5 cobaltite powders subjected to mechanical impact (milling in a ball mill). It was established that in octahedra of Tb1 – yBa1 + yCo2 – xO5.5 – δ cobaltates Co3+ ions are in the high spin state. In EuBaCo2O5.5 powder after milling in a ball mill, a surface area (5–10 nm) of particles was found to be decomposed into Co3O4, BaCO3, and EuCoO3 phase components. A knowledge of the low-spin state of Co3+ ions in EuCoO3 and Co3O4 and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo2O5.5 sample (subjected to ball milling) near its surface, which is inaccessible to standard X-ray phase analysis.