Japan Synchrotron Radiation Research Institute Research Articles

Investigation of Stable Structures and Electronic States of Spinel MgCo2−ZNi0.5MnAlzO4 (z = 0, 0.3) during Discharge Process As Cathode Materials for Magnesium Rechargeable Batteries Using First-Principles Calculations

Introduction Recently, it is focused on storage batteries materials for reduce of greenhouse gases. In particular, the development of large equipment like as electric vehicles is driving demand for storage battery materials. Although lithium-ion batteries are currently used as storage battery devices, Li metal is a rare metal and expensive, and the development of higher capacity battery materials is needed. Our research group is focusing on magnesium secondary battery cathode materials. In previous report, spinel MgCo2-xMnxO4 (x=0~0.5) (space group Fd-3m) has synthesized and evaluated its battery characteristics, showing an initial discharge capacity of more than 200mAh/g when the Mn substitution amount is x=0.5.1) Since the inclusion of substituted species improves battery properties, we synthesized Al substituted spinel MgCo2-zNi0.5MnAlzO4. In this study, we reported that Mg/Co cation mixing, which was particularly problematic at z=0.3 was reduced compared to MgCo2-xMnxO4 resulting in improved cycle properties.2) The purpose of this study is to clarify the stable local structure of pristine and discharge process of spinel type MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) and to determine the contribution of Al substitution to the electronic structure by performing electron density calculation. Calculation The structural relaxation calculation was performed by generalized gradient approximation (GGA) exchange-correlation potential used with a plane-wave cutoff energy of 550 eV, and 1×2×2 k-point mesh was applied, corresponding to the inverses of the lattice constants on Vienna Ab-initio Simulation Package (VASP) code. The convergence criterion for structural optimization was that the energy difference per iteration be less than or equal to 0.02 eV/Å. 2×1×1 supercell was created and structural relaxation calculation was performed on various initial structural models to determine the energetically optimal structure. Initial structure models were constructed to ensure reproduction of the occupancies determined by an average structure analysis from Rietveld analysis using synchrotron X-ray diffraction. Result and discussion In this study, we performed structural relaxation calculations for spinel-type MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) to obtain the stable structure before and during charge-discharge. The initial model before charging and discharging was created based on the occupancy of each site obtained by crystal structure analysis using neutron diffraction measurements.2) The initial model at discharge was obtained by inserting Mg into the 16c vacancy site in the stable structure before charging and discharging. Figure 1 shows the stable structure after structural relaxation calculations before for a-1) z=0 and b-1) z=0.3 and after discharge (y=0.375) for a-2) z=0 and b-2) z=0.3, respectively. The solid circled Mg is the inserted one, and the dotted circle is the 8a site that became vacant after the structural relaxation calculation in Fig. 1. The crystal structure in pristine was spinel structure, however, it is found that the 4-coordinated 8a site became a vacancy and Mg occupied the 16c site, changing the crystal structure to a rocksalt structure after discharge. Since the 8a and 16c site are close to each other, the insertion of Mg into the 16c site causes a structural change due to the repulsion between atoms and cations on the 8a site, which leads to a chain transfer to other vacancy 16c sites. In particular, models with large structural changes tended to have stable structures. It is also found that Mg remained at the 8a site in z=0.3 shown in b-2) than in z=0 shown in a-2), and that Co at the 8a site could not move to the vacancy in z=0, and that the amount of change in the entire structure is less than that in z=0.3. As a result of partial density of states (PDOS) calculation, it is confirmed that Co and Mn had 2.6 ~ 2 valence and Mn is considerably close to 3 valence during discharge. It is also found that the PDOS of Ni did not almost change before and after discharging, and that no valence change occurred. These results are consistent with those of previously reported XANES measurements.2) Therefore, the model in Fig. 1 determined in this study is considered to be valid. Acknowledgement This research was financially supported by JST, ALCA-SPRING Grant Number JPMJAC1301, Japan. This work was also supported in part by JSPS KAKENHI Grant Number 20K15382, Japan. Dr. Koji Ohara of JASRI (Japan Synchrotron Radiation Research Institute for assistance with synchrotron X-ray total scattering measurements (BL04B2, SPring-8, Proposal Nos. 2019B1249).1) Y. Idemoto, M. Ichiyama et al., J. Power Sources, 482 , 228920 1-9 (2021)2) Y. Hirata, Y. Idemoto et al., ECS Meeting s, MA2020-02 , 3451 (2020) Figure 1

In-Situ Observation of Adsorption Species on Platinum Catalyst in Oxygen Reduction Reaction Using High Energy Resolution XAFS

The oxygen reduction reaction (ORR) on Pt surfaces, for examples, Pt single crystals, polycrystalline Pt electrodes, Pt nanoparticles (NPs), Pt-based alloys, and core–shell Pt nanostructures, has been discussed in the last few decades.In polymer electrolyte fuel cells (PEFCs), hydrogen peroxide and its radicals are known to be fatal attacking species not only for electrode catalysts but also for carbon materials and polymer membranes.A thorough understanding of ORR schemes has led to the development of seamless four-electron reduction cathodes, contributing to improved endurance reliability of both anion-exchange membrane (AEM) and proton-exchange membrane (PEM) fuel cells.In this study, the reaction pathway, and intermediate species such as molecular oxygen, in the ORR were investigated in alkaline and acidic environments, respectively.In this work, High Energy Resolution Fluorescence Detection X-ray Absorption Spectroscopy (HERFD-XAS) at the Pt L III-edge, which enhances resolution by partially collecting fluorescent X-ray was employed.X-ray absorption fine structure (XAFS) can detect the electronic structure of Pt, and its high energy resolution makes it possible to distinguish between different adsorption species on the surface of Pt nanoparticles.In addition, photon-in photon-out experiments using hard X-ray with high penetrating ability make it relatively easy to perform in-situ/operando measurements in potential controlled solutions.Carbon-supported Pt nanoparticles as powder catalysts were used for measurement as more realistic conditions, and the species adsorbed on the Pt nanoparticles were analyzed while controlling under the potentials both in acidic and basic electrolyte solutions with N2 or O2 gas bubbling.In N2-saturated solutions, the XANES spectra of the Pt LIII-edge reflected the presence of the adsorption species such as Pt-O (*O), Pt-OH (*OH), Pt-H (*H), as well as PtO2 oxide and Pt metallic states without any adsorption, during the ORR with the potential change.In O2-saturated solutions, one additional adsorption species of molecular oxygen was observed in both acidic and basic electrolyte solutions. It was analyzed that the intermediate species adsorbed to platinum in a side-on configuration as a superoxide anion in an alkaline environment.This intermediate species is identified as hydrogen superoxide, also known as hydroperoxyl radical, with the chemical formula HO2 by being protonated in an acidic environment.The results of research on adsorption species using HERFD-XAS have provided important knowledge for designing catalysts that enable seamless four-electron reduction.The preferred cathode catalyst design will be discussed in detail in an oral presentation at the 244th ECS Meeting. Acknowledgments: The synchrotron radiation experiments were performed at the BL11XU in the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Numbers of 2012B3506, 2013A3506, 2014A3506, 2014B3506, 2015B3506, 2016A3556 2019A3508, 2019B3508, 2020A3508, 2021A3508, 2021B3508, 2022A3508 and 2022B3597 at BL11XU). This work was supported by JSPS KAKENHI Grant Number JP22H02188). Figure 1

高圧スライド法を用いたTi同素変態のその場放射光X線解析

In this study, severe plastic deformation through high-pressure sliding (HPS) was applied for in situ high-energy X-ray diffraction analysis at SPring-8 in JASRI (Japan Synchrotron Radiation Research Institute). Allotropic transformation of pure Ti was examined in terms of temperatures, pressures and imposed strain using a miniaturized HPS facility. The true pressure applied on the sample was estimated from the peak shift. Peak broadening due to local variation of pressure was reduced using white X-ray. The phase transformation from α phase to ω phase occurred at a pressure of ∼4.5 GPa. Straining by the HPS processing was effective to promote the transformation to the ω phase and to maintain the ω phase even at ambient pressure. The reverse transformation from ω phase to α phase occurred at a temperature of ∼110℃ under ambient pressure, while under higher pressure as ∼4 GPa, the ω phase remained stable even at ∼170℃ covered in this study. It was suggested that the reverse transformation from the ω phase to the α phase is controlled by thermal energy.

Damage-Free Femtosecond X-Ray Laser Snapshot Imaging of Catalyst Layer Nano-Structures of Polymer Electrolyte Fuel Cells

The realization of the hydrogen society, where hydrogen is used as clean and renewable energy, is desired to reduce carbon dioxide emissions and achieve sustainable development. The polymer electrolyte fuel cell (PEFC) is a key technology for automobiles in the hydrogen society as an alternative to conventional internal combustion engines. However, further improvements in PEFC performances are required for the full-scale spread of fuel cell vehicles. This study aims to image the nanostructures of the catalyst layer, which is particularly important in determining the performance of PEFCs, and correlate the observed structures with mass transfer in the catalyst layer. The catalyst layer contains catalyst-loaded carbon supports thinly covered with an ionomer responsible for proton conduction. We are especially interested in observing the support structure and ionomer coverage.We performed coherent X-ray imaging studies on the catalyst particles of PEFCs using an X-ray free-electron laser (XFEL) facility: SACLA (SPring-8 Angstrom Compact free electron LAser). Femtosecond XFEL allows us to capture radiation-damage-free snapshot images by outrunning major radiation damage processes. Damage-free imaging is of great value because radiation damage often causes a problem in high-resolution electron microscopy observation of ionomers. We used the coherent diffractive imaging (CDI) technique to observe catalyst particles of PEFCs. In CDI, sample images are reconstructed from measured coherent diffraction patterns using phase-retrieval calculation instead of objective lenses. CDI enables quantitative phase imaging and allows high-contrast imaging of the catalyst particles, which are almost transparent to X-rays.The measurement was carried out for catalyst particles in the dried condition and in solution. Our study showed that the image contrast can be adjusted by changing the electron density of the volume surrounding the sample1). The dried sample was prepared by dropping catalyst ink onto a silicon nitride membrane and air-dried. The solution sample was enclosed in micro-liquid enclosure arrays2,3) developed at Hokkaido University. The coherent diffraction patterns were measured by irradiating the sample catalyst particles with the 100-nm-focused XFEL beam with a photon energy of 4 keV using MAXIC-S (Multiple Application X-ray Imaging Chamber-S)4). The phase-retrieval calculation reconstructed the sample images. Fig. 1 shows a reconstructed image of a catalyst particle in water. The reconstructed image shows many white spots, which can be interpreted as platinum-cobalt catalysts. The pixel size of the reconstructed image is 1.3 nm, demonstrating among the highest spatial resolution in X-ray imaging. We will continue our study to observe the support structures and their ionomer coverage to understand the mass transfer in the catalyst layer.This work was supported by the FC-Platform of NEDO (New Energy and Industrial Technology Development Organization). The XFEL experiments were performed at SACLA with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Nos. 2020A8106, 2021A8010, and 2021B8019).

Β-Feooh Nanorods As a Highly Active Self-Repairing Anode Catalyst for Alkaline Water Electrolysis Powered By Renewable Energy

The use of renewable energy as a primary energy source is urged because of the rapid progress of global warming. Because the renewable energy is unevenly distributed in terms of place and time, the production of hydrogen from renewable energy is crucial. Alkaline water electrolysis is a cost-effective technology for this purpose, though the degradation of electrodes under fluctuating power of renewable energy is recently regarded as a crucial problem. We have recently reported that a in-situ repair of anode catalyst (self-repairing catalyst), supplying fresh catalyst from electrolyte is quite useful to improve the lifetime under unsteady operation [1]. A hybrid cobalt hydroxide nanosheet (Co-ns) was used as the self-repairing catalyst, whereas its electrocatalytic activity is moderate. In this study, we demonstrate the use of β-FeOOH nanorods (β-FeOOH-nr) as a highly active and durable self-repairing catalyst. Because β-FeOOH-nr consists of iron as a metallic element, it is promising for its low cost and resource abundance. β-FeOOH-nr was synthesized by the coprecipitation of Fe3+ with tris(hydroxymethyl)aminomethane, followed by heating at 80 °C. The width and length of β-FeOOH-nr were 3–6 nm and 4–200 nm, respectively. The Fe K-edge XANES analysis showed that β-FeOOH-nr consists of Fe3+ species. Electrochemical tests were performed in a three-electrode PFA cell, using a nickel wire, a nickel coil, and a reversible hydrogen electrode, as working, counter, and reference electrodes, respectively. The β-FeOOH-nr was dispersed in 1 M KOH as an electrolyte. β-FeOOH-nr was first deposited on the nickel wire electrode by constant current electrolysis at 1 A·cm–2 for 240 min (30 min × 8 cycles). β-FeOOH-nr formed a thin layer of bundled nanorods and exhibited the oxygen evolution reaction (OER) overpotential of 320 mV at 100 mA cm–2, while previously reported Co-ns exhibited 342 mV. In addition, the activation of β-FeOOH-nr-coated electrode is almost finished at the first 30 min of the electrolysis, whereas Co-ns required 240 min for the activation. Because β-FeOOH-nr-coated electrode exhibited high OER activity with a small amount of β-FeOOH-nr deposited on the electrode, β-FeOOH-nr could activate electrode with shorted electrolysis time. The β-FeOOH-nr-coated electrode indicated the redox peak due to Ni2+/Ni3+ at 1.44 V vs. RHE which is at higher potential than that of a bare nickel electrode, implying that β-FeOOH-nr formed composite with active nickel species, such as Ni(OH)2 as highly active materials. The durability of the catalyst-coated electrode was examined in the presence of β-FeOOH-nr in the electrolyte by the newly reported shutdown-based accelerated durability test (SD-ADT) [2]. SD-ADT consists of multiple cycles of constant current electrolysis at 600 mA·cm–2 for 1 min and potential retainment at low potential of 0.5 V vs. RHE for 1 min. A bare nickel electrode is degraded only within 50 cycles by the SD-ADT (OER overpotential reached 640 mV at the 200th cycle), whereas β-FeOOH-nr-coated nickel electrode retained its low OER overpotential of 285 mV in at least 4000 cycles. Comparing with the SD-ADT in the absence of β-FeOOH-nr in the electrolyte, it was shown that β-FeOOH-nr was deposited during the SD-ADT to repair degraded electrode. In conclusion, β-FeOOH-nr was shown to be a useful anode catalyst for alkaline water electrolysis powered by fluctuating renewable energy. By dispersing β-FeOOH-nr in an electrolyte, the alkaline water electrolyzer can establish self-repairing system with very long lifetime under frequent potential change. The synchrotron radiation experiments were performed at the BL16B2 of SPring-8 with approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2021A5310). This work was supported by the JSPS KAKENHI (grant number 20H02821) from Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan. Part of this study uses outcomes of the development of fundamental technology for the advancement of water electrolysis hydrogen production in the advancement of hydrogen technologies and utilization projects (grant number JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) in Japan.

High Resolution Observation of Liquid Water in Polymer Electrolyte Fuel Cell Using X-Ray Nano Computed Tomography

Polymer electrolyte fuel cells (PEFCs) are attracting attention as energy device of low environmental impact because of their high generation efficiency and their emitting only water. The gas supplied to the PEFC is humidified, and water is produced at the cathode catalytic layer by the electrochemical reaction between oxygen and protons. The gas diffusion layer (GDL) and micro porous layer (MPL) in PEFC plays an important role in the transport of oxygen and water. When liquid water accumulates in the GDL, the supply of oxygen to the cathode is inhibited, resulting in poor generation performance. In order to maintain the performance of PEFCs, it is important to manage the water in the cell.Attempts have been made to visualize the liquid water in GDLs and MPLs for better GDL and MPL design; X-ray micro computed tomography (micro-CT) is one powerful tool for this. Visualization of liquid water in GDLs and MPLs using micro-CT has so far revealed the behavior of the produced water[1,2]. However, in previous studies, it has been difficult to visualize liquid water in the catalyst layer, which is the reaction field where the water is produced. This is because the spatial resolution of micro-CT is larger than a µm, which is insufficient for analyzing liquid water in the catalytic layer. X-ray CT measurements with a resolution of at least 150 nm are needed to measure the distribution of liquid water in the cross section of the catalyst layer. In this study, a measurement system to reveal the distribution of liquid water in the catalyst layer was developed using a 150 nm-spatial-resolution X-ray CT with a synchrotron radiation x-ray microscope called X-ray nano-CT.A GDL specimen prepared cut to a disk shape with 1 mm diameter. The GDL specimen mounted on a copper stage with high thermal conductivity connected Peltier element module. The micro-CT and nano-CT measurements were carried out in BL20XU beamline at SPring-8, Japan. An X-ray beam energy was 30 keV with a double crystal monochromator. The nano-CT measurements were performed using Zernike phase contrast with voxel size of 38.4 nm. We measured the micro-CT and nano-CT of the dry condition of the GDL specimen. Then, the GDL specimen injected liquid water was scanned. Injection of liquid water into the GDL specimen is not easy because of water-repellent of GDLs. Helium gas saturated water vapor at 40 °C was sprayed to the GDL at 30 ml/min, then the GDL cooled to 10 °C using a Peltier element module and the vapor was condensed inside of the GDL. The measurement setup is shown in Figure 1. This water injection in GDL method was based on the method reported by Kato et al [2].Figure 2 shows the optical system of the nano-CT used in this study. The optical system of this nano-CT provides a condenser zone plate for sample illumination, a Fresnel zone plate for enlarged image, and phase ring for Zernike phase contrast. These optics allow CT with a high spatial resolution of 150 nm to be measured even for materials with low X-ray absorption.A three-dimensional structure of GDL was revealed by CT measurements in each scale order. The distribution of liquid water in GDL were visualized with nanoscale spatial resolution (Figure 3). We have successfully visualized the three-dimension distribution of liquid water in the GDL with nm order scale using nano-CT. The newly established nano-CT with a spatial resolution of 150 nm order is extremely useful for elucidating liquid-water behavior in PEFCs containing catalyst layers, which was not clear before. Acknowledgements This work is based on results obtained from a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). This study was partially supported by the Synchrotron radiation experiments performed at BL20XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal numbers 2021A2009, 2021B1015).

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Crystal orientation and residual stress in TiN film by synchrotron radiation

Abstract The residual stress in a TiN film, the thickness of which is less than 1 µm, deposited by arc ion plating was measured using the SPring-8 synchrotron radiation facility installed at Japan Synchrotron Radiation Research Institute (JASRI). Films thicker than 300 nm have a {111} texture, whereas those with a thickness of 100 nm have a relatively random orientation. Instead of the conventional laboratory X-ray equipment, ultrabright synchrotron radiation can be used to precisely measure the residual stress in thin films with a thickness of 100 to 800 nm. The residual stress in thicker TiN films is about 7 GPa in compression and it is not affected by the film thickness. The slightly small compressive stress in a film of 100 nm in thickness may be due to the different crystal orientations in the film.

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

Structure tracking of nuclear wave packet oscillations by femtosecond time-resolved X-ray absorption spectroscopy

Progress in technology in recent decades has brought not only huge leaps in our knowledge across many fields, but has also led to the development of new tools that help and support the pursuit of such knowledge. Spectroscopy, the study of the interaction between matter and electromagnetic radiation, is used in chemistry, physics, astronomy and other fields, and allows scientists to investigate the physical and electronic structure as well as composition of materials. A number of techniques, including X-ray spectroscopy, have been developed to detect and measure materials in this way. Dr Tetsuo Katayama, from the Japan Synchrotron Radiation Research Institute (JASRI), is part of a team furthering research in this field.

Negative thermal expansion of Ca2RuO4 with oxygen vacancies**Project supported by the National Natural Science Foundation of China (Grant Nos. 11874328 and 11574276). The SXRD experiments were performed at the BL02B2 and BL04B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI; proposal Nos. 2019A1167, 2019A1095, and 2019A1340). We also acknowledge the help of Beamline Scientists Dr.

Oxygen vacancies have a profound effect on the magnetic, electronic, and transport properties of transition metal oxides but little is known about their effect on thermal expansion. Herein we report the effect of oxygen defects on the structure formation and thermal expansion properties of the layered perovskite Ca2RuO4 (CRO). It is shown that the CRO containing excess oxygen crystallizes in a metallic L-CRO phase without structure transition from 100 K to 500 K and displays a normal thermal expansion behavior, whereas those with oxygen vacancies adopt at room temperature an insulating S-CRO phase and exhibit an enormous negative thermal expansion (NTE) from 100 K to about 360 K, from where they undergo a structure transition to a high temperature metallic L-CRO phase. Compared to the L-CRO containing excess oxygen, the S-CRO structure has increasingly large orthorhombic strain and distinctive in-plane distortion upon cooling. The in-plane distortion of the RuO6 octahedra reaches a maximum across 260 K and then relaxes monotonically, providing a structure evidence for the appearance of an antiferromagnetic orbital ordering in the paramagnetic phase and the Ag phonon mode suppression and phase flip across the same temperature found recently. Both the L- and S-CRO display an antiferromagnetic ordering at about 150–110 K, with ferromagnetic ordering components at lower temperature. The NTE in S-CRO is a result of a complex interplay among the spin, orbital, and lattice.

Doping Induces Structural Phase Transitions in All-Inorganic Lead Halide Perovskite Nanocrystals

This work was supported by the National Natural Science Foundation of China (Grant Nos. 11874275 and 11574225), and one project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). The SPring-8 experiment was performed with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2019B1056). Computational work was supported by Supercomputing Laboratory at King Abdullah University of Science and Technology (KAUST).

Evaluation of Anisotropic Three-Dimensional Strain Relaxation in Stripe-Shaped Ge1-xSnx Mesa Structure

Background and purpose Ge1-xSnx has a higher electron and hole mobility than Si, which attract much attention as a next-generation channel material [1]. Moreover, it is expected further mobility enhancement by applying appropriate strain. However, the strain field in the nano-fabricated channel region changes complicatedly depending on the channel shape, therefore accurate strain evaluation is strongly desired. In this study, we evaluate the anisotropic three-dimensional strain relaxation in the Ge1-xSnx stripe-shaped mesa structures by oil-immersion Raman spectroscopy and X-ray diffraction (XRD) measurement using synchrotron radiation. Experiment The Ge1-xSnx layers were epitaxially grown on Ge (001) substrate for 34, 55 and 45 nm with Sn concentrations of 3.2, 2.1, and 1.3%, respectively by home-made metal organic chemical vapor deposition (MOCVD) using t-C4H9GeH3 (tertiary-butyl-germane) and (C2H5)4Sn (tetra-ethyl-tin) as precursors[2]. After the epitaxial film formation, stripe-shaped mesa structures were fabricated by electron beam lithography and dry etching. Figure1 shows the schematic diagram of sample. The length (L) in the major axis directions along the stripe was fixed at 10 μm and the width (W) in the minor axis directions perpendicular to the stripe were varied as 0.1, 0.2, 0.5 and 1.0 μm. In-plane biaxial strain was measured by oil-immersion Raman spectroscopy, and the strain of the in-plane direction and the direction perpendicular to the substrate surface were measured by XRD using synchrotron radiation. In the oil-immersion Raman spectroscopy, the wavelength of the excitation light source was 532 nm, the focal length of the spectrometer was 2000 mm, the objective lens was immersion lens with the numerical aperture NA = 1.4, and the oil in the medium had the refractive index of n = 1.5. In the XRD measurement, the wavelength of the incident X-ray was 1.23968 Å. Figure2 shows an SEM image of a stripe-shaped Ge1-xSnx mesa structure with L = 10μm. As shown in Fig. 2, the X-ray diffraction intensity was sufficiently obtained by covering many stripes with the same shape in the X-ray irradiation area. Results and Discussion Figure3 and 4 show the stress along of the in-plane major axis and the minor axis directions determined by oil-immersion Raman spectroscopy, where L was fixed and W were varied as 0.1, 0.2, 0.5, 1.0 μm. As shown in Fig. 3, the stress increases with increasing Sn concentration. The stress of the major axis direction is not relaxed by W reduction regardless of Sn concentration. On the other hand, as shown in Fig. 4, the stress of the minor axis direction perpendicular to the stripe is relaxed at W = 0.2 μm or less regardless of Sn concentration. Since oil-immersion Raman spectroscopy cannot evaluate the strain perpendicular to the substrate surface, XRD measurement was performed. Observed XRD profiles for W = 0.1 and 0.2 μm indicated lattice shrinkage in the direction perpendicular to the surface. From the above, we have comfilmed the relaxation due to the nano-fabrication of the stripe Ge1-xSnx mesa structure occurs in the in-plane minor axis direction and the direction perpendicular to the substrate surface while preserving the strain of the in-plane major axis direction, for the sample W = 0.2 μm or less. Acknowledgements The synchrotron radiation experiments were performed at the BL19B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2016A1529, 2017A1702, 2017B1843 and 2017B1930).

Slow Magnetic Relaxation in a Palladium–Gadolinium Complex Induced by Electron Density Donation from the Palladium Ion

AbstractInvited for the cover of this issue are David C. Izuogu and Takefumi Yoshida with the group of Masahiro Yamashita and co‐workers at Tohoku University, Karlsruhe Institute of Technology, Aoyama Gakuin University, Japan Synchrotron Radiation Research Institute, Tohoku University Institute for Materials Research, University of Cambridge, University of Nigeria, Nsukka and National Institute for Materials Science. Read the full text of the article at 10.1002/chem.201800699.

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) [...]

In-Plane Biaxial Strain Evaluation Induced in Ge1-X Sn x Films Using Oil-Immersion Raman Spectroscopy

Introduction Germanium Tin (GeSn) has a potential to supersede Si as channel material for next generation LSI. The hole mobility of GeSn with 3% Sn concentration is higher than that of pure Ge [1]. Strain or strain relaxation is certainly induced in the channel region through the device process. In addition, it is well known that carrier mobility is varied by the strain. Therefore, we believe that it is important to evaluate the precise strain states. In our previous reports, we have evaluated the anisotropic strain in Si and Si1-x Ge x using oil-immersion Raman spectroscopy, which can excite both longitudinal optical (LO) mode and transverse optical (TO) mode. In this study, we evaluated the in-plane biaxial strain induced in Ge1-x Sn x films using oil-immersion Raman spectroscopy. Experiment We evaluated the strain induced in the Ge1-x Sn x films which were epitaxially grown on (001) Ge substrate by the metal-organic chemical vapor deposition (MOCVD) [2]. Sn concentrations in Ge1-x Sn x films were 1.8, 2.2, and 3.2%, respectively, which were defined by Rutherford backscattering spectrometry. From transmission electron microscopy measurements, thicknesses of Ge1-x Sn x films were 104, 17, and 34 nm, respectively. In the oil-immersion Raman spectroscopy, the excitation light with wavelength of 532 nm irradiated the Ge1-x Sn x films under the conventional (001) backscattering configuration. The light path was immersed by the high refractive index oil. The numerical aperture (NA) of the immersion lens and refractive index of the oil were 1.4 and 1.5, respectively. In the XRD measurements, synchrotron radiation was used for the X-ray source with the energy of 10 or 12 keV. Out-of-plane strain εL in the Ge1-x Sn x films was measured from 004 diffraction. Results and discussion Fig. 1 shows the LO and TO mode Raman spectra from the GeSn0.018 film. These spectra were calibrated by the strain free bulk Ge peak at 300 cm-1. From Raman spectroscopy and XRD results, we derived phonon deformation potentials (PDPs) of the strained Ge1-x Sn x , which is indispensable to evaluate stress. The PDPs (p and q) can be derived by solving equation 1, where Δω, ω0, εL, and ε|| are Raman wavenumber shift, strain-free Raman shift, in-plane strain, and out-of-plane strain, respectively. The derived p and q were plotted in figure 2. In this figure, p and q for pure Ge (x=0) are reported by S. C. Jain et al. [3]. As shown in this figure, the p and q suggest almost constant for the Ge1-x Sn x (x < 0.032). Using the derived PDPs, we calculated the anisotropic stresses (σ xx and σ yy ) induced in Ge1-x Sn x films. As a result, we obtained σ xx = -0.40 and σ yy = -0.40 GPa for the strained GeSn0.018, σ xx = -0.47 and σ yy = -0.47 GPa for the strained GeSn0.022, and σ xx = -0.68 and σ yy = -0.68 GPa for the strained GeSn0.032. From these results, we can confirm that the stresses induced in Ge1-x Sn x films were almost isotropic states. In this work, the PDPs for Ge1-x Sn x were derived for the first time. Acknowledgements This study was partially supported by the Japan Society for the Promotion of Science through a Grant-in-Aid for Science Research B (No. 24360125). XRD measurements were performed at BL19B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Nos. 2014B1613, 2014B1892, 2015A1971, 2015B1925, and 2016A1529).

X-Ray Spectroscopic Studies on the Electronic Structures of LiNiO2-Based Cathode Materials for Lithium-Ion Batteries

Introduction For development and popularization of electric vehicles, it is indispensable to improve the safety and the capacity of secondary batteries not only in a usual operating condition but also in harsh operating environments (e.g., at high temperature and in an overcharge condition). Basic knowledge regarding the electronic and bonding states of functional 3d transition metal (TM) elements is necessary to design and develop cathode materials of lithium-ion batteries in this direction. Core-level X-ray spectroscopies provide the element-selected information about electronic states of constituent elements. In this study, we applied X-ray spectroscopies to LiNiO2-based cathode materials to investigate the electronic and bonding states of Ni in different states of charge. Experimental All the samples for X-ray spectroscopies were prepared by using a two-electrode cell comprised of LiNi0.80Co0.15Al0.05O2 as an active material of a working electrode, Li metal as a counter electrode, and mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate containing 1.0 mol dm− 3 LiPF6. The cell was charged at a current density of 1 mA cm−2 (ca. 1 C rate) at room temperature. X-ray absorption spectroscopy (XAS) was performed at the Ni and Co K-edges at the BL33XU (the Toyota beamline) and at the Ni and Co L 2,3-edges and at the O K-edge at the BL27SU of SPring-8, Japan. X-ray emission spectroscopy was also carried out at the Ni K-edge at the BL39XU and the BL33XU of SPring-8. Local structural analysis based on extended X-ray absorption fine structure (EXAFS) was done by using ATHENA and ARTEMIS with the scattering phase shift and the effective scattering amplitudes calculated by FEFF9.05. Results The oxidation state of Ni is often estimated by using an empirical index of absorption energy, at which normalized absorbance is 0.5. This empirical method was applied to the present system, and revealed that the absorption energy at the Ni K-edge monotonically increased as the state of charge approached from 0 to 100 and slightly decreased as the cell was more overcharged. In general, the change in the electronic state of Ni involves that in local structure around Ni, which suggests that structural parameters such as coordination numbers and bond length for the first coordination Ni–O should be alternate indicators of the oxidation state of Ni. Actually, it was found that these structural parameters could be good indicators of average Ni valence. The structural parameters monotonically increased even in the overcharge region as the cell was charged, differently from the above-mentioned empirical absorption energy. The difference in the changing trend of the oxidation-state indicator and the electronic structure of Ni was further investigated by using 3d TM L 2,3-edge and O K-edge XAS and X-ray emission spectroscopy, which will be discussed in the conference. Acknowledgement X-ray spectroscopic studies were performed at the BL27SU, the BL33XU, and BL39XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) with the proposal numbers of 2014B1582, 2014B7008, and 2014B1574.

An Operando Fluorescence XAS Study of a Ni/YSZ Anode in a Solid Oxide Fuel Cell

Introduction Solid oxide fuel cells (SOFC) have high energy conversion efficiencies because of their ability to directly convert the chemical energy stored in fuels into electrical energy. Ni/YSZ (yttria-stabilized zirconia) cermet is commonly used for SOFC anodes, because Ni provides excellent catalytic activity and current collectability and YSZ provides good ionic conductivity and structural support. However, Ni/YSZ facies several problems such as instability upon redox cycling, nickel coarsening, carbon deposition and so on. Therefore, designing anode materials with high durability is a key objective in the development of SOFC technology. Especially, it is essential to understand the redox behavior of the Ni electrocatalysts at work. Operando X-ray absorption spectroscopy (XAS) is a powerful tool to investigate the relationship between the oxidation state of active site and cell performance under an operating condition. Hence in this work, we developed an operando fluorescence XAS measurement system for SOFC to study the oxidation state of the working Ni electrocatalyst at temperatures ranging from 973 to 1073 K. Experimental Figure 1a depicts a two-chamber SOFC for operando fluorescence XAS measurement developed in the present work. An anode-supported cell having a groove for the investigation of the interfacial region between the Ni/YSZ anode and the YSZ electrolyte was installed to the operando XAS measurement system. The lidded XAS instrument was heated up to 1073 K in the air to melt the seal material (Pyrex glass), and subsequently NiO in the anode was reduced in a gas flow consisting of 4% H2, 3% H2O, and N2 balance. After completing gas seal and NiO reduction, the reactor temperature was lowered to 973 K for operation. The Ni K-edge XAS measurement was implemented at the BL33XU (the Toyota beamline) of SPring-8 in fluorescence mode by irradiating the bottom center of the groove at the anode and detecting the emitted X-ray with a four-element silicon drift detector. The anode potential was measured or adjusted with reference to the potential of lanthanum strontium cobalt ferrite cathode. Results The operando XAS technique was applied to the reduction of NiO at the Ni/YSZ anode at 1073 K. Figure 1b shows a chronopotentiogram of the Ni/YSZ anode and corresponding change in average Ni valence estimated by the height of the main peak at the Ni K-edge. The average Ni valence and the anode potential exhibited different changing trends in the reduction process. There seemed to exist four regions for anode potential (i.e., two potential transition and two plateau regions) and two regions for average Ni valence. In situ observation with a CCD camera clarified that the reduction of NiO around the anode–electrolyte interface started in region 2 and continued until region 4. Operando XAS measurement was also conducted to examine the oxidation state of Ni in a high-power operation at 973 K. As a time-averaged oxidation state, Ni at the Ni/YSZ anode kept its metallic state even though the anode potential was so high as −0.4 V. The oxidation behavior of Ni at the anode as mentioned above and its relationship with degradation in the high-power operation will be further discussed in the conference. Acknowledgements The authors are grateful to Prof. Koji Amezawa of Tohoku University for his fruitful advices and discussion on the development of the operando fluorescence XAS measurement system for SOFC. All the XAFS measurements were performed at the BL33XU (the Toyota beamline) of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) with the proposal numbers of 2014B7024, 2015A7024, and 2015B7024. Figure 1

Operando soft X-Ray Absorption and Raman Spectroscopic Study on Magnesium Deposition By Using Ether-Based Electrolyte

Magnesium rechargeable battery, which uses magnesium metal anode, is one of the candidates for the next generation batteries. The magnesium metal anode has a high theoretical volumetric capacity (3832 mAh/cm3), and relative low reduction potential (-2.356 V vs. standard hydrogen potential). However, conventional electrolytes consisting of inorganic salts and ester solvents, as widely used in lithium ion batteries, do not occur reversible deposition/dissolution of magnesium metal. This is because a passivation layer is formed at the magnesium metal anode surface that blocks both magnesium ions and electron transport. The limitation of available electrolytes prevents the magnesium battery from being used in a practical application.Recently, it has been reported that reversible magnesium deposition/dissolution reactions can occur in inorganic magnesium salts dissolved in glyme-based solvents electrolytes 2, 3. However, the reaction mechanism of magnesium metal anode has not been clearly understood. To clarify the reaction mechanism, it is necessary to investigate the interfacial structure of magnesium ion at anode/electrolyte interface. In this study, we investigated the bulk structure of the glyme-based electrolyte using Raman spectroscopy, X-ray absorption spectroscopy (XAS) and the theoretical calculation. Furthermore, we observed the electronic and local structure of the electrolyte at the interface during magnesium deposition using operando soft x-ray absorption spectroscopy.0.5 M Mg(TFSA)2/triglyme and 0.5 M Mg(TFSA)2/2-MeTHF electrolytes were prepared by stirring Mg(TFSA)2 with triglyme or 2-MeTHF in an Ar-filled glove box. Raman spectroscopic measurements were carried out using LabRAM HR-800 equipped with He-Ne laser (633 nm) at room temperature. operando XAS measurements at Mg K-edge were conducted at the beam line BL27SU at SPring-8 (Japan). XAS spectra were obtained at different potential during magnesium deposition. Magnesium deposition/dissolution occurred in Mg(TFSA)2/triglyme as observed in previous report3. In contrast to Mg(TFSA)2/triglyme, magnesium metal deposition did not observe in Mg(TFSA)2/2-MeTHF. Raman spectroscopy showed that TFSA anion exists as uncoordinated state with magnesium ion in the Mg(TFSA)2/triglyme, while TFSA anion strongly coordinates with magnesium ion in the 2-MeTHF-based electrolyte. operando Mg K-edge XAS observed that the local structure attributed to first coordination shell changed more smaller with decreasing potential in the Mg(TFSA)2/triglyme than in the Mg(TFSA)2/2-MeTHF at anode/electrolyte interface. In the Mg(TFSA)2/triglyme, the solvation structure of magnesium ion without coordination of TFSA anion, may suppress its local structure change during approaching the anode/electrolyte interface, resulting in the reversible magnesium deposition/dissolution. ACKNOWLEDGMENTS This study was partially supported by Synchrotron radiation experiment was performed at BL27SU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI). REFERENCES [1] Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich M.; Levi, E., Nature, 2000, 407, 724-727.[2] Ha, S.-Y.; Lee, Y.-W.; Woo, S. W.; Koo, B.; Kim, J.-S.; Cho, J.; Lee, K. T.; Choi, N.-S., ACS Appl. Mater. Interfaces, 2014, 6, 4063-4073.[3] Orikasa, Y.; Masese, T.; Koyama, Y.; Mori, T.; Hattori, M.; Yamamoto, K.; Okado, T.; Huang, Z. -D.; Minato, T.; Tassel, C.; Kim, J.; Kobayashi, Y.; Abe, T.; Kageyama, H.; Uchimoto, Y., Sci. Rep., 2014, 4, 5622.

Study on Reaction Magnesium Deposition Mechanism By Operando Soft X-Ray Absorption Spectroscopy

Magnesium rechargeable batteries have much attention for next generation batteries because of the high theoretical volumetric capacity, safety, and abundance of magnesium metal anode. In order to improve the efficiency of magnesium metal anode, it is required to develop the electrolyte that enables magnesium deposition and dissolution reversibly. Although Grignard reagents have been widely known as the electrolyte for magnesium deposition/dissolution[1], the stability of the electrolytes in high potential and their corrosive nature are major problems. In recent years, magnesium deposition/dissolution in magnesium inorganic salts with triglyme solvents have been reported[2,3]. For the further development of electrolyte for magnesium batteries, the reaction mechanism at electrolyte/magnesium metal interface should be elucidated. In this study, we have developed operando soft X-ray measurement system and apply to the analysis of electronic and local structure of electrolyte during magnesium deposition. Furthermore, bulk structure of electrolyte is investigated by Raman spectroscopy, X-ray absorption spectroscopy (XAS) and the theoretical calculation. 0.5 M Mg(TFSA)2/triglyme and 0.5 M Mg(TFSA)2/2-MeTHF electrolytes were prepared by mixing Mg(TFSA)2 (KISHIDA CHEMICAL Co., Ltd., 99.9%>) with triglyme (KISHIDA CHEMICAL Co., Ltd. 99%>) or 2-MeTHF (Merck, 98%>) in an Ar-filled glove box. Electrochemical properties of the electrolyte were investigated by cyclic voltammetry (CV) with the three-electrode cell. Platinum plate and magnesium rod were used as working electrode and counter electrode, respectively. Operando XAS measurements at Mg K-edge were carried out at the beam line BL27SU at SPring-8 (Japan). XAS spectra were obtained at different potential during magnesium deposition. Raman spectroscopic measurements were carried out using LabRAM HR-800 (HORIBA, Ltd.) equipped with He-Ne laser (633 nm) at room temperature. While magnesium deposition/dissolution is observed in Mg(TFSA)2/triglyme and Grignard system, magnesium is not deposited in Mg(TFSA)2/2-MeTHF. From the results of Raman spectroscopy, TFSA anion exists as uncoordinated state with magnesium ion in the triglyme system, while TFSA anion coordinates with magnesium ion in the 2-MeTHF system. Fourier transform from Mg K-edge EXAFS oscillation measured at different potentials in 0.5 M Mg(TFSA)2/triglyme and 0.5 M Mg(TFSA)2/2-MeTHF indicate that peak intensity of Mg-O bond decreases with decreasing potential.The decreases of peak intensity reflect the desolvation process of triglyme and 2-MeTHF from magnesium ion. These results suggested that reason of high overpotential in 0.5 M Mg(TFSA)2/2-MeTHF is specific adsorption of TFSA anion. The specific adsorped TFSA anion may inhibits charge transfer raction of magnesium ion. ACKNOWLEDGMENTS This study was partially supported by the Research and Development Initiative for Scientific Innovation of New Generation Battery (RISING) Project under the auspices of New Energy and Industrial Technology Development Organization (NEDO), Japan. Synchrotron radiation experiment was performed at BL27SU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI). REFERENCES [1] Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich M.; Levi, E., Nature, 407, 724 (2000). [2] Ha, S.-Y.; Lee, Y.-W.; Woo, S.W.; Koo, B.; Kim, J.-S.; Cho, J.; Lee, K.T.; Choi, N.-S., ACS Appl. Mater. Interfaces 6, 4063 (2014). [3] Orikasa, Y.; Masese, T.; Koyama, Y.; Mori, T.; Hattori, M.; Yamamoto, K.; Okado, T.; Huang, Z. -D.; Minato, T.; Tassel, C.; Kim, J.; Kobayashi, Y.; Abe, T.; Kageyama, H.; Uchimoto, Y., Sci. Rep., 4, 5622 (2014).