Synchrotron Radiation X-ray Absorption Spectroscopy Research Articles

High-Temperature Structural and Electrical Properties of BaLnCo2O6 Positrodes.

The application of double perovskite cobaltites BaLnCo2O6−δ (Ln = lanthanide element) in electrochemical devices for energy conversion requires control of their properties at operating conditions. This work presents a study of a series of BaLnCo2O6−δ (Ln = La, Pr, Nd) with a focus on the evolution of structural and electrical properties with temperature. Symmetry, oxygen non-stoichiometry, and cobalt valence state have been examined by means of Synchrotron Radiation Powder X-ray Diffraction (SR-PXD), thermogravimetry (TG), and X-ray Absorption Spectroscopy (XAS). The results indicate that all three compositions maintain mainly orthorhombic structure from RT to 1000 °C. Chemical expansion from Co reduction and formation of oxygen vacancies is observed and characterized above 350 °C. Following XAS experiments, the high spin of Co was ascertained in the whole range of temperatures for BLC, BPC, and BNC.

Interdiffusion behaviors observation in TiN/ZrOxNy bilayer by XAS and ToF-SIMS

Interface behavior plays an important role in multilayer structure. The deep understanding of interface diffusion and reaction is necessary to improve the performance of device with multilayer structure. In the present work, we perform a detailed systematic study on interdiffusion and interaction between the TiN and ZrOxNy layers in the TiN/ZrOxNy bilayer system. A series of TiN/ZrOxNy bilayers with reverse deposition orders or with varied composition have been prepared by radio-frequency reactive magnetron sputtering. Synchrotron radiation x-ray absorption spectroscopy (XAS) and time of flight secondary ion mass spectrometry (ToF-SIMS) are both used to understand well interface diffusion behavior. The XAS results indicate that interaction and interdiffusion extent between TiN and ZrO2 (ZrOxNy) layers depend on deposition order of both layer. Herein the O atoms enter easily into the TiN layer by substituting the N atoms when the ZrO2 or ZrOxNy layer is deposited onto the TiN layer. No significant interaction between TiN and ZrN layers takes place in the TiN/ZrN sample. Both XAS results and ToF-SIMS depth profiles reveal that the interaction between TiN and ZrOxNy layers depends on the deposition order of the layers.

Dynamic oxygen adsorption on single-atomic Ruthenium catalyst with high performance for acidic oxygen evolution reaction

Achieving active and stable oxygen evolution reaction (OER) in acid media based on single-atom catalysts is highly promising for cost-effective and sustainable energy supply in proton electrolyte membrane electrolyzers. Here, we report an atomically dispersed Ru1-N4 site anchored on nitrogen-carbon support (Ru-N-C) as an efficient and durable electrocatalyst for acidic OER. The single-atom Ru-N-C catalyst delivers an exceptionally intrinsic activity, reaching a mass activity as high as 3571 A gmetal−1 and turnover frequency of 3348 O2 h−1 with a low overpotential of 267 mV at a current density of 10 mA cm−2. The catalyst shows no evident deactivation or decomposition after 30-hour operation in acidic environment. Operando synchrotron radiation X-ray absorption spectroscopy and infrared spectroscopy identify the dynamic adsorption of single oxygen atom on Ru site under working potentials, and theoretical calculations demonstrate that the O-Ru1-N4 site is responsible for the high OER activity and stability.

Tuning the interfaces in the ruthenium-nickel/carbon nanocatalysts for enhancing catalytic hydrogenation performance

The ruthenium-nickel bimetallic nanoparticles supported on carbon black (Ru-Ni/C) with various Ru and Ni loadings, while keeping a constant Ru/Ni atomic ratio (51/49), were synthesized at ambient temperature by liquid reduction with hydrazine hydrate as reducing agent and galvanic replacement reaction approaches. Different Ru-Ni interfaces (Ru-Ni-NiO with 1.250 wt% or 0.630 wt% Ru, and RuO2-NiO with 0.160 wt% Ru) were formed after being annealed in N2 at 380 °C for 3 h. Several techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and synchrotron radiation X-ray absorption spectroscopy (XAS) and in-situ XAS (in hydrogen) have been employed for structural characterization. It was found that most Ru atoms and a small amount of Ni atoms at the Ru-Ni-NiO interface were reduced, leading to the occurrence of hydrogen spillover and hence synergy effect of Ru, Ni and NiO active sites. However, such a synergy was not observed at the RuO2-NiO interface. The catalytic properties of the Ru-Ni/C nanocatalysts in the hydrogenation of benzene reaction were significantly improved due to the presence of particular Ru-Ni-NiO interface.

Co-doped carbon layer to lower the onset potential of hematite for solar water oxidation

Hematite is a promising photocatalyst for water oxidation while the practical performance of hematite has been hindered by poor conductivity and strong charge recombination. Here we report a Co-doped carbon layer on hematite to significantly enhance the solar water oxidation performance, which shows a large cathodic onset potential shift of 300 mV representing one of the largest values ever reported for hematite photoanodes. The final photocurrent at 1.23 V vs. RHE can also achieve a high value of 2.24 mA/cm2. Based on synchrotron radiation X-ray absorption spectroscopy, the thin Co-doped carbon layer consists of both sp2 carbon structure with good conductivity and embedded CoCO3 (or CoO) with good OER kinetics. A thin layer itself can also block the surface defects to suppress the recombination. Thus the Co-doped carbon layer can act as a triple functional material to simultaneously improve the surface conductivity, block the surface defects, and accelerate the OER process, which can finally result in a large onset potential shift. The facile method to decorate hematite with an effective carbon layer may help for the rational design of hematite with high efficiency.

Synchrotron Radiation Research and Analysis of the Particulate Matter in Deep Ice Cores: An Overview of the Technical Challenges

Airborne dust extracted from deep ice core perforations can provide chemical and mineralogical insight into the history of the climate and atmospheric conditions, with unrivalled temporal resolution, time span and richness of information. The availability of material for research and the natural complexity of the particulate, however, pose significant challenges to analytical methods. We present the developments undertaken to optimize the experimental techniques, materials and protocols for synchrotron radiation-based analysis, in particular for the acquisition of combined Synchrotron Radiation X-Ray Fluorescence and X-ray Absorption Spectroscopy data.

Surface modification using Sm-oxide of Fe- and Ni-substituted Li2MnO3 cathodes

We investigated the effect of coating Fe- and Ni-substituted Li2MnO3 cathodes (Li1.23Mn0.46Fe0.15Ni0.15O2, LMFN) with Sm oxide (Sm2O3). The cells with LMFN and Sm2O3-coated LMFN cathodes respectively showed 85% and 90% capacity retention and generated 4.3 and 1.6 mlg−1 of gas during 50 cycles, which verified that the Sm2O3 coating was effective. Observations with a scanning transmission electron microscope equipped with an energy dispersive X-ray spectroscopy analyzer showed that the Sm2O3 uniformly coated the LMFN. Synchrotron radiation X-ray absorption spectroscopy indicated that the Sm2O3 coating had little effect on the valence and/or electronic state of the Mn, Fe, and Ni during cycles. However, hard X-ray photoemission spectroscopy indicated that the Sm2O3 coating disturbed solid electrolyte interphase growth originating from the chemical reaction with the electrolyte solution and cathode electrode. The irreversible redox reactions of oxygen ions were also considerably suppressed. We believe that the improvements in cell properties had by using the Sm2O3-coated LMFN cathode will contribute to the development of next-generation storage devices.

Atomically dispersed nickel\u2013nitrogen\u2013sulfur species anchored on porous carbon nanosheets for efficient water oxidation

Developing low-cost electrocatalysts to replace precious Ir-based materials is key for oxygen evolution reaction (OER). Here, we report atomically dispersed nickel coordinated with nitrogen and sulfur species in porous carbon nanosheets as an electrocatalyst exhibiting excellent activity and durability for OER with a low overpotential of 1.51 V at 10 mA cm−2 and a small Tafel slope of 45 mV dec−1 in alkaline media. Such electrocatalyst represents the best among all reported transition metal- and/or heteroatom-doped carbon electrocatalysts and is even superior to benchmark Ir/C. Theoretical and experimental results demonstrate that the well-dispersed molecular S|NiNx species act as active sites for catalyzing OER. The atomic structure of S|NiNx centers in the carbon matrix is clearly disclosed by aberration-corrected scanning transmission electron microscopy and synchrotron radiation X-ray absorption spectroscopy together with computational simulations. An integrated photoanode of nanocarbon on a Fe2O3 nanosheet array enables highly active solar-driven oxygen production.

Coexistence of magnetization reversal and exchange bias in Mn-substituted CuCrO2

We systematically studied the magnetization reversal (MR) and exchange bias (EB) properties of Mn-doped CuCrO2 compounds. Single-phase ceramic samples of CuCr1−xMnxO2 (x = 0–0.2) were synthesized with the sol-gel method. Synchrotron radiation X-ray absorption spectroscopy of the Mn 2p, Cr 2p core levels showed that the Cr ion is trivalent and the Mn ion is in a mixed valence state of Mn3+/4+. All the Mn-doped samples, due to the double-exchange interaction between Cr3+–O–Mn3+ and Mn3+–O–Mn4+, showed a ferromagnetic transition in field-cooling magnetization. Interestingly, zero-field-cooling magnetization reversed from positive to negative as temperature decreased below the compensation temperature. The x = 0.05 sample also showed exchange bias. The coexistence of MR and EB in the system can be explained by the competition between ferromagnetic and antiferromagnetic order.

Silver binding in argentiferous manganese oxide minerals investigated by synchrotron radiation X-ray absorption spectroscopy

The knowledge of the nature of silver occurrence and sites in argentiferous manganese oxides is significant for developing better process to extract silver from manganese-silver ores. Synchrotron radiation has been used to collect Ag K-edge X-ray absorption spectroscopy of three natural and five synthetic samples of silver-containing manganese oxide, basically in the phases of tunnel-type cryptomelane or todorokite and layer-type birnessite or chalcophanite. Data were also gathered on five standards including Ag foil, Ag2O, Ag2SO4, Ag2CO3, and AgNO3 to compare the local environments of Ag atoms with the samples. Ag K-edge XANES studies show that Ag is present in most of the samples in Ag+ oxidation state, except in the Ag-Tod sample through annealing step in the form of Ag0 nanoparticles which are also identified by TEM. The natural samples from Xiangguang manganese-silver ores exhibit similar coordination distances as the corresponding tunnel or layer structured synthetic samples. In the argentiferous cryptomelanes, silver cations do not occupy the tunnel centers like K+, but rather place on the common face sites of the cubic cage formed by MnO6 octahedra, coordinated with about four oxygen anions at ~ 2.4 A bond distances proved by the EXAFS results. In the silver-exchanged birnessites or natural argentiferous chalcophanite, silver cations probably occupy a tetrahedral coordination to interlayer O atoms and a position located above or below the vacant cavities in the Mn octahedra layers.

Nickel and platinum in high-temperature H2O + HCl fluids: Implications for hydrothermal mobilization

The dissolution of NiS and NiAs (nickeline) in 0.1 and 1 molal HCl at 400 °C, 80 MPa, and of PtAs2 (sperrylite) and Pt metal in 1 and 6.86 molal HCl at 500 °C, 80 MPa was studied in-situ using synchrotron radiation X-ray fluorescence and absorption spectroscopy. The Pt concentration in the fluid averaged 8 · 10−5 molal (12.8 ppm) during dissolution of Pt metal in 6.86 molal HCl, and was below the minimum detection limit (mdl; 2.6 · 10−5 molal) in all other experiments. Dissolution of NiS was congruent or nearly congruent. Equilibrium was attained rapidly in about 250 min at an initial HCl concentration of 1 molal HCl, and in about 500 min at 0.1 molal HCl. Addition of HCl resulted in a large increase in the Ni solubility from 7.2 · 10−3 molal Ni (423 ppm) at 0.1 molal HCl to 8.72 · 10−2 molal Ni (4959 ppm) at 1 molal HCl. Dissolution of NiAs in 0.1 and 1 molal HCl was incongruent. A steady state was not reached even at a run duration of more than 16 h, and the maximum recorded Ni concentrations in the fluid were much lower than the Ni solubility in the corresponding experiments with NiS at the same HCl molality. Measured K-edge XANES spectra in comparison with literature data indicated that arsenic in the fluid was present as As(V) and that nickel complexed with Cl and H2O as tetrahedral [NiCl2(H2O)2]0 and [NiCl3(H2O)]− and octahedral [NiCl2(H2O)4]0 species. In addition, Raman spectra of H2O + NiCl2 and H2O + NiCl2 + HCl solutions and of H2O + HCl fluids reacted with NiS crystals were acquired at temperatures (T) up to 600 °C and pressures (P) up to 1.15 GPa. All spectra at T ≥ 300 °C and P < 600 MPa showed a previously not reported Raman peak at ∼280 cm−1 together with a weaker peak at ∼230 cm−1. These peaks can be assigned to Ni–Cl vibrations. The band at 280 cm−1 was not detected at the other P-T conditions. Based on calculated vibrational frequencies available in the literature, it may stem from the species [NiCl4]2– or [NiCl2(H2O)4]0, although particularly the first assignment is in conflict with the information from published XAS data.The results of this study demonstrate that nickel is readily mobilized by acidic chloridic hydrothermal fluids, but platinum remains practically immobile in such fluids at any HCl concentration that is conceivable to occur in nature. Therefore, the enrichment of Pt relative to Ni in footwall-type deposits in the Sudbury District and the growth of large sperrylite crystals are likely related to magmatic processes. Furthermore, the experiments point to the importance of redox reactions for the mobilization and precipitation of arsenides and suggest that arsenate species are more stable in hydrothermal fluids than previously thought.

The evolution of magnetization switching of LuCrO3 by the effect of Mn doping

The crystal structure, magnetic properties and electronic structures of LuCr1-xMnxO3 (x = 0, 0.1, 0.2, and 0.3) series samples were systematically investigated. The crystal structure of the Mn-doped LuCrO3 samples is orthorhombic structure with Pbnm, consistent with the pristine LuCrO3. Synchrotron radiation x-ray absorption spectroscopy of Mn 2p, Cr 2p and O 1s core levels show that Cr ion is trivalent and its valence state does not change with doping. However, the valence state of Mn ions for samples with x = 0.1 and 0.3 is mainly in Mn2+ while it is dominated by Mn3+ for the sample x = 0.2. This leads to the diversely unoccupied 3d states of transitional metal ions, which hybridized with O 2p levels. The energy diagram of each transitional metal ions in our samples were provided. More interesting, magnetic data shows the negative magnetization in zero-field-cooling MZFC(T) curve below TN. And the evolution of MFC(T) and MZFC(T) curves coming to converge and intersect with each other are caused by Mn doping. Also, multiple magnetic phases with a new magnetic phase transition at 30 K were induced by the effect of Mn doping. Our results demonstrate that the antiferromagnetic coupling of Mn2+ being antiparallel with spin moment of Cr3+ is favor of the magnetization switching while the ferromagnetic coupling of Mn3+ overcomes the Cr3+ ions ordering and destroys the magnetization switching.

Low Voltage Charge/Discharge Behavior of Manganese Hexacyanoferrate

Recently, Prussian blue analogues (PBAs) have been reported to exhibit a low voltage charge/discharge behavior with high capacity (300–545 mAh/g) in lithium-ion secondary batteries (LIBs) [...]

Size-Induced Structural Phase Transition at ∼6.0 nm from Mixed fcc–hcp to Purely fcc Structure in Monodispersed Nickel Nanoparticles

We have investigated the core issue of atomic lattices in monodispersed Ni nanoparticles (NPs) of sizes 3.8 nm to 10.1 nm using detailed analysis of X-ray diffraction, synchrotron radiation X-ray absorption spectroscopy (XAS) and magnetization data. This has revealed the very remarkable coexistence of atomic face-centered cubic (fcc) and hexagonal closed-packed (hcp) lattices in samples with particle size less than or equal to 6.0 nm with the prevalence of only fcc phase beyond this. They are also associated with reduced coordination number, modified electronic structure, and surface atom coordination with ligands. Magnetization data furthermore reveal coexistence of ferromagnetism and superparamagnetism at 300 K. Considered to be due to dominant roles of ligands, they are likely to open up far-reaching implications to their future applications.

Observation of selective surface element substitution in FeTe0.5Se0.5 superconductor thin film exposed to ambient air by synchrotron radiation spectroscopy**Project supported by the Chinese Academy of Sciences (Grant No. 1G2009312311750101) and the National Natural Science Foundation of China (Grant Nos. 11375228, 11204303, and U1332105).

A systematic investigation of oxidation on a superconductive FeTe0.5Se0.5 thin film, which was grown on Nb-doped SrTiO3 (001) by pulsed laser deposition, has been carried out. The sample was exposed to ambient air for one month for oxidation. Macroscopically, the exposed specimen lost its superconductivity due to oxidation. The specimen was subjected to in situ synchrotron radiation photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS) measurements following cycles of annealing and argon ion etching treatments to unravel what happened in the electronic structure and composition after exposure to air. By the spectroscopic measurements, we found that the as-grown FeTe0.5Se0.5 superconductive thin film experienced an element selective substitution reaction. The oxidation preferentially proceeds through pumping out the Te and forming Fe–O bonds by O substitution of Te. In addition, our results certify that in situ vacuum annealing and low-energy argon ion etching methods combined with spectroscopy are suitable for depth element and valence analysis of layered structure superconductor materials.

A Mixed-Valent Uranium Phosphonate Framework Containing U(IV) , U(V) , and U(VI).

It is shown that U(V) O2 (+) ions can reside at U(VI) O2 (2+) lattice sites during mild reduction and crystallization process under solvothermal conditions, yielding a complicated and rare mixed-valent uranium phosphonate compound that simultaneously contains U(IV) , U(V) , and U(VI) . The presence of uranium with three oxidation states was confirmed by various characterization techniques, including X-ray crystallography, X-ray photoelectron, electron paramagnetic resonance, FTIR, UV/Vis-NIR absorption, and synchrotron radiation X-ray absorption spectroscopy, and magnetism measurements.

Incorporation of Mn inAlxGa1−xNprobed by x-ray absorption and emission spectroscopy, high-resolution microscopy, x-ray diffraction, and first-principles calculations

Synchrotron radiation x-ray absorption and emission spectroscopy techniques, complemented by high-resolution transmission electron microscopy methods and density functional theory calculations are employed to investigate the effect of Mn in Al$_{x}$Ga$_{1-x}$N:Mn samples with an Al content up to 100%. The atomic and electronic structure of Mn is established together with its local environment and valence state. A dilute alloy without precipitation is obtained for Al$_{x}$Ga$_{1-x}$N:Mn with Al concentrations up to 82%, and the surfactant role of Mn in the epitaxial process is confirmed.

Antiferromagnetic long-range spin ordering in Fe- andNiFe2-dopedBaTiO3multiferroic layers

We report on the Fe doping and on the comparative Ni-Fe codoping with composition close to $\mathrm{NiF}{\mathrm{e}}_{2}$ of fully oxidized $\mathrm{BaTi}{\mathrm{O}}_{3}$ layers (\ensuremath{\sim}20 nm) elaborated by atomic oxygen plasma assisted molecular beam epitaxy; specifically any role of oxygen vacancies can be excluded in our films. Additionally to the classical in situ laboratory tools, the films were thoroughly characterized by synchrotron radiation x-ray diffraction and x-ray absorption spectroscopy. For purely Fe-doped layers, the native tetragonal perovskite structure evolves rapidly toward cubiclike up to 5% doping level above which the crystalline order disappears. On the contrary, low codoping levels $(\ensuremath{\sim}5%\mathrm{NiF}{\mathrm{e}}_{2})$ fairly improve the thin film crystalline structure and surface smoothness; high levels (\ensuremath{\sim}27%) lead to more crystallographically disordered films, although the tetragonal structure is preserved. Synchrotron radiation magnetic dichroic measurements reveal that metal clustering does not occur, that the Fe valence evolves from ${\mathrm{Fe}}^{2+}$ for low Fe doping levels to ${\mathrm{Fe}}^{3+}$ for high doping levels, and that the introduction of Ni favors the occurrence of the ${\mathrm{Fe}}^{2+}$ valence in the films. For the lower codoping levels it seems that ${\mathrm{Fe}}^{2+}$ substitutes ${\mathrm{Ba}}^{2+}$, whereas ${\mathrm{Ni}}^{2+}$ always substitutes ${\mathrm{Ti}}^{4+}$. Ferromagnetic long-range ordering can be excluded with great sensitivity in all samples as deduced from our x-ray magnetic absorption circular dichroic measurements. On the contrary, our linear dichroic x-ray absorption results support antiferromagnetic long-range ordering while piezoforce microscopy gives evidence of a robust ferroelectric long-range ordering showing that our films are excellent candidates for magnetic exchange coupled multiferroic applications.

In situ chemical transformations of silver nanoparticles along the water-sediment continuum.

In order to accurately assess the potential environmental risk posed by silver nanoparticles (Ag-NPs), their transformation and fate must be investigated in natural systems. This has proven to be very challenging due to the difficulties encountered in retrieving/analyzing NPs dispersed in complex and heterogeneous environmental matrices at relevant (i.e., low) concentrations. In this study, we overcame this challenge by immobilizing functionalized Ag-NPs onto plasma polymerized solid substrates to form "nano in situ deployment devices" (nIDDs). This method allowed us to retrieve and analyze the Ag-NPs after 48 h of direct exposure in freshwater-sediment and saltwater-sediment environments. The type and extent of Ag-NPs transformation was expected to vary along the water-sediment continuum as sediments typically contain steep gradients in solute concentrations and redox potential. To trace the distribution of redox sensitive elements (e.g., Fe, Mn), Diffusive Equilibration in Thin-films (DET) devices were inserted into the sediments alongside the nIDDs. Chemical transformation of the immobilized Ag-NPs across the water-sediment continuum was investigated after retrieval by synchrotron radiation X-ray Absorption Spectroscopy. Linear combination fitting of Ag K-edge X-ray absorption spectra indicated that the chemical transformations of Ag-NPs in both freshwater and saltwater sediments were strongly affected by the redox conditions over the investigated range. Silver bound to reduced sulfur was the principal product of Ag-NP transformations but different extents of transformation were observed for Ag-NPs exposed to different depths in the sediment. These field results add important insights about the transformation of Ag-NPs in heterogeneous environments.

Characterization of thick conducting molybdenum films: Enhanced conductivity via thermal annealing

Electrical resistivity measurements vs. frequency were performed on two molybdenum coatings grown by RF magnetron sputtering technique on a sapphire substrate at room temperature and annealed at different temperatures. Data show that the surface resistivity changes with the annealing while the conductivity of these Mo coatings can be almost doubled. In agreement with other researches, the results confirm that Mo coatings with an electrical conductivity comparable to that of copper can be obtained optimizing the thickness and the post-deposition annealing process. Morphological and structural investigations on Mo coatings were performed before and after annealing by synchrotron radiation X-ray diffraction and X-ray absorption spectroscopy to identify the chemical status of Mo, to probe the presence of different oxides and to control the multiphase nature of these metallic films.