(Digital Presentation) Operando x-Ray Emission/Absorption Spectroscopy to Characterize Electronic Structure Changes of Transition Metals in Lithium-Ion Batteries

Effects of Heat Treatment on Microstructure, Hardness and Local Structure in a Compositionally Complex Alloy

Optimizing electronic structure and surface morphology are of great importance to achieve highly active and stable electrocatalyst for hydrogen evolution reaction (HER). In this paper, the vertically aligned Cu doped Ni/Ni3S2 nanosheet was successfully deposited on Ti mesh (NiCux/Ni3S2/TM, x = Cu/Ni atomic ratio in NiCux) by facile electrodeposition method. Phase composition, surface morphology and electronic structure information were characterized by XRD, SEM, TEM and XPS. The results unraveled that Cu doping induced the changes in both electronic structure and surface morphology of Ni/Ni3S2 sample, which were in favor of promoting the breakage of H-O bond in H2O and optimizing Ni-Hads adsorption energy, thus improving HER activity with decreased overpotential at −10 mA/cm2 by 202 mV. The influence of Cu(NO3)2 precursor content on HER activity of as-prepared NiCux/Ni3S2/ TM was investigated. NiCu0.57/Ni3S2/TM prepared with 1.2 mM Cu(NO3)2 exhibited the highest electrocatalytic activity toward HER with overpotential of 239 mV at −10 mA/cm2 and Tafel slope of 86 mV/dec. The enhanced activity and superior stability for NiCu0.57/Ni3S2/TM were ascribed to the change in electronic structure and surface morphology.

X-ray absorption, photoelectron and Raman spectroscopic techniques are used to investigate relationships between hierarchical organization of the skeleton and local electronic and atomic structure of femoral bone in knee compartments and to understand the osteoarthritic (OA) related changes in the structure. As samples the medial and lateral condyles of the femur resected during total knee arthroplasty in patients with medial compartmental knee osteoarthritis were used. Site-dependence of the O 1s-1 and P 2p-1 photoelectron line shapes, Ca 2p near edge X-ray absorption fine structure and Raman shifts is revealed. It indicates on essential OA-related changes in electronic and atomic structure and molecular architecture and dynamics in subchondral femoral bone. Differences between the spectroscopic characteristics of core and valence excited healthy and pathology damaged bone are examined within the 3DSL model. Perspectives for development of novel methods for medical imaging and diagnosis of subchondral bone at subcellular level are discussed.

Layered alkali transition metal oxides (i.e., LiMO2 and NaMO2, M=transition metal) are the premier class of cathode materials in lithium- and sodium-ion battery system. The safety characteristics of LiMO2 cathode based LIBs are one of the most critical barriers to be overcome for the large scale application such as EV. One of the main reasons that might cause safety hazards of the LIB is associated with the thermal instability of charged Li1-xMO2 cathode materials, which is related to the occurrence of exothermic reactions between flammable electrolyte and liberating oxygen from charged Li1-xMO2 at high temperature. Based on the structural homology between the layered LiMO2 and NaMO2, we expect that the investigation of thermal stability of charged Na1-xMO2cathode materials is also important for the practical use of SIBs. However, few attentions have been paid on safety issue of SIBs. In this study, the thermal stability of charged Na1-xMO2 cathode materials is investigated by using combined in situ time-resolved X-ray diffraction and mass spectroscopy (TR-XRD/MS), which allows simultaneous observation of the structural changes and gas species that are evolved during thermal decomposition of charged cathode materials, especially O2 gas in our interest. In addition, the ex situ/in situ X-ray absorption spectroscopy (XAS) has been also utilized to look at the local and electronic structural changes occurring during thermal decomposition in an elemental selective way. By utilizing combined X-ray techniques, we are able to get better understanding of structural and electronic structure changes in charged cathode materials during thermal decomposition. In this presentation, the thermal decomposition behavior of charged Na1-xMO2(M=Co, Cr) cathodes will be covered. Acknowledgement The work done at Brookhaven National Lab. was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. DOE under Contract No. DE-SC0012704.

The theory of the electronic structure of clean metal and semiconductor surfaces is reviewed, starting from an effective one-electron Schrodinger equation. Methods for solving the Schrodinger equation at surfaces are briefly described, and the effects of the surface on the electronic wavefunctions are discussed using simple models. The results of detailed calculations of the surface electronic structure of s-p bonded metals, transition metals and semiconductors are reviewed, with an emphasis on the effect of the local environment on the density of states. Properties like the work function and surface energy depend on the surface electronic structure, and their variation with material and surface is discussed; the surface energy contains an important contribution from the interaction between electrons, and this will be considered in some detail. The change in electronic structure compared with the bulk leads to changes in atomic structure, with surface reconstruction on semiconductor and some metal surfaces, and this is also discussed. The interplay between theory and experiment is very important in surface studies, and the theoretical surface energy bands reviewed compare well with experimental photoemission results; this comparison has proved particularly useful for understanding surface reconstructions.

The observation of ultrafast and coherent control of spins in magnetic materials at room temperature [1-2] has prompted the experimental and theoretical efforts to understand the underlying mechanisms driving such magnetic phenomena. In order to understand the driving mechanisms, in this non-equilibrium regime, it is necessary to disentangle the relevant interactions (exchange, spin-lattice, electron-phonon, coulomb etc.).Stoichiometric B2 ordered epitaxial (001) FeRh undergoes a first order magnetic phase transition from antiferromagnetic (AFM) to ferromagnetic (FM) at ≈ 380K. In the AFM phase of FeRh, only Fe has net magnetic moment, whereas in the FM phase both Fe and Rh carry net moments. The phase transition is also accompanied by a ≈ 1% isotropic lattice expansion in the bulk BCC structure, and changes in electronic structure, see [3-5] and refs. therein. Since magnetic and structural dynamics can occur at different timescales, it makes FeRh an ideal candidate for disentangling relevant interaction mechanisms at different timescales. The phase transition has been extensively studied theoretically and experimentally [6-10], in thermal equilibrium (static heating) and at ultrafast time scales (fs- optical excitation), but a precise knowledge of the roles of the electronic, phononic and spin sub-systems remains elusive.We have studied the laser-driven AFM to FM phase transition in FeRh with X-ray absorption spectroscopy (tr-XAS) around the Fe L3 edge. The experiments were performed at the SCS Instrument of the European XFEL. We also performed the density functional theory (DFT) calculations to simulate the XAS spectra at different time delays including magnetic, lattice and temperature changes. Temperature modelling was done using two temperature model (2TM).In this contribution, we will discuss the changes in the electronic band structure of FeRh in the femto- and picosecond timescales, derived from the X-ray absorption spectroscopy measurements at the Fe L3 absorption and compare them with the density functional theory simulations. **

The corrugated layer structure bismuth has been successfully tailored into negative thermal expansion along c axis by size effect. Pair distribution function and extended X-ray absorption fine structure are combined to reveal the local structural distortion for nanosized bismuth. The comprehensive method to identify the local structure of nanomaterials can benefit the regulating and controlling of thermal expansion in nanodivices.

INTRODUCTION Positive electrode material, Li(Ni,Co)O2 system, of Li-ion battery has been attractive because it has the advantage in low environmental load due to low Co content. There are many previous works about the Li(Ni,Co)O2 and the aluminum-substituted one because of high heat stability. However, detail structural changes during electrochemical processes are still ambiguous for site occupancy, local structures, and electronic structures even though these would play important roles on the battery characteristics. In this research, we used several quantum beam techniques to reveal the crystal structures, electronic and nuclear densities, and local structures of LiNi0.8Co0.2O2 during charge process. EXPERIMENTAL To synthesize the LiNi0.8Co0.2O2, the precursor was prepared by co-precipitation method. The co-precipitated material was annealed at 800 °C in air for 15 h. The product was identified by powder XRD and ICP-OES. To study change of crystal and electronic structure of this cathode material during electrochemical process, cathode materials were prepared by four charge depths, and were investigated using the synchrotron X-ray diffraction (BL02B2, SPring-8) and neutron diffraction (BL20, J-PARC). The data was analyzed with the Rietveld technique using Rietan-FP and Z-Rietveld, and by the MEM using the Dysnomia and Z-MEM programs. To examine the local structures, X-ray absorption spectroscopy (BL14B2, SPring-8) and X-ray total scattering (BL04B2, SPring-8) were measured. RESULTS AND DISCUSSION The neutron diffraction patterns were measured for the cathode after 2nd discharge process as well as the pristine electrode. It was demonstrated that the crystal structure analysis by ex-situ measurement could be successfully performed even for the electrode with an amount of about 10 mg. The values of 3b-6c bond length decreased and λ2, which expresses the distorted degree of the Li-O6 and M-O6 octahedra, were increased with increasing charge depth. Synchrotron-based experiments using high energy X-ray total scattering and pair distribution function (PDF) analysis (Fig. 1) indicated that the oxygens arranged to crystallographic a-b plane were disturbed in the charge state of 4.3 V after 2nd cycle (Fig. 2). ACKNOWLEDGMENTS This research was supported by the RISING-project of the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Observation of lateral band-bending in the edge vicinity of atomically-thin Bi insulating film formed on Si(111) surface

Adsorption of formaldehyde molecule on the pristine and transition metal doped graphene: First-principles study

The characteristics of the lattice on either side of the metal-semimetal transition in Ni1- delta S have been determined using a panoply of experimental methods-specific heat, Mossbauer absorption inelastic neutron scattering, ultrasonic and X-ray diffraction. These different methods provide a coherent picture of the changes in lattice dynamics and thermodynamic properties at the first-order phase transition. Most significant is the softening of the acoustic modes, and in particular the decrease in the shear constant C44 in the high-temperature metallic phase. The transition as a function of temperature is mainly driven by the associated lattice entropy and not directly by electronic or magnetic entropy resulting from the change in electronic structure. Nevertheless, the change in electronic structure is probably indirectly responsible for the change in C44 in the metallic phase through modification of the population regions of the Fermi surface under shear stress.

Measurements of the structure of hexagonal RMnO3 [R = rare earths (Ho) and Y] for temperatures significantly above the ferroelectric transition temperature (TFE) were conducted to determine the nature of the transition. The local and long range structural measurements were complemented by ab initio molecular dynamics simulations. With respect to the Mn sites in YMnO3 and HoMnO3, we find no large atomic (bond distances or thermal factors), electronic structure changes, or rehybridization on crossing TFE from local structural methods. The local symmetry about the Mn sites is preserved. With respect to the local structure about the Ho sites, a reduction of the average Ho–O bond with increased temperature is found. Ab initio molecular dynamics calculations on HoMnO3 reveal the detailed motions of all ions. Above ∼900 K there are large displacements of the Ho, O3, and O4 ions along the z axis which reduce the buckling of the MnO3/O4 planes. The changes result in O3/O4 ions moving to toward central points between pairs of Ho ions on the z axis. These structural changes make the coordination of Ho sites more symmetric thus extinguishing the electric polarization. At significantly higher temperatures, rotation of the MnO5 polyhedra occurs without a significant change in electric polarization. The Born effective charge tensor is found to be highly anisotropic at the O sites but does not change appreciably at high temperatures.

Electronic band structure of ZrNCl and HfNCl

The oxygen-evolving complex (OEC) in photosystem II (PS II) was studied in the S0 through S3 states using 1s2p resonant inelastic X-ray scattering spectroscopy. The spectral changes of the OEC during the S-state transitions are subtle, indicating that the electrons are strongly delocalized throughout the cluster. The result suggests that, in addition to the Mn ions, ligands are also playing an important role in the redox reactions. A series of Mn(IV) coordination complexes were compared, particularly with the PS II S3 state spectrum to understand its oxidation state. We find strong variations of the electronic structure within the series of Mn(IV) model systems. The spectrum of the S3 state best resembles those of the Mn(IV) complexes Mn3(IV)Ca2 and saplnMn2(IV)(OH)2. The current result emphasizes that the assignment of formal oxidation states alone is not sufficient for understanding the detailed electronic structural changes that govern the catalytic reaction in the OEC.

Depth-resolved X-ray absorption spectroscopy (DR-XAS) measurements were performed for the direct observation of the chemical state and local structure at the LiCoO2 electrode–solid electrolyte model interface, which can contribute towards the enhancement of the power density in all solid-state lithium batteries. The charge transfer resistance, measured by AC impedance spectroscopy, of the LiCoO2 electrode–solid electrolyte interface decreased with the introduction of a NbO2 interlayer at the interface, while the resistance increased with ZrO2 and MoO2 interlayers. Using DR-XAS with a depth resolution of about 7 nm, the changes in electronic structure and local structure of the LiCoO2 electrode were clarified. The extended X-ray absorption fine structure of DR-XAS revealed that the introduction of the NbO2 layer is effective for restricting the large Co–O bond change at the interface during delithiation. This interlayer relieved the stress at the interface due to the volume change of LiCoO2 during delithiation and then decreased the activation energy for the charge transfer process.