Search

One of the approaches to tackle the problem of limited electrolyte electrochemical stability, which controls the development of novel electrochemical storage devices, is the use of solid electrolytes. Here, we focus on one of the most promising among oxide-based glass-ceramic materials, Li1+xAlxGe2−xP3O12, to investigate the physical and chemical mechanisms that govern the enhancement of Li-conductivity upon variation of its composition and glass crystallization conditions during a two-step heat treatment. Using X-ray and neutron diffraction, small-angle neutron scattering and Raman spectroscopy we found that the addition of 6–18 mol% yttria makes the polyphosphate chains in glass more thermally stable. This leads to sudden and uniform glass crystallization over the whole volume. This peculiar glass structure governs the further crystallization behavior and ensures the optimal organization of intergrain boundaries. The highest Li-conductivity is achieved for a sample with 12 mol% yttria annealed for 2 hours at 750 °C. In addition, nuclear magnetic resonance together with bond valence sum analysis provides further insight into atomistic mechanisms of ionic conductivity in NASICON-based lithium-conductive ceramics. [ABSTRACT FROM AUTHOR]

Two methods of post-synthetic modification (Suzuki coupling and CuAAC click-reaction) were applied to Ir(III) complexes [Ir(C^N)2N^N]+ to provide the second highly selective donor site. One family of functionalized complexes was used to demonstrate the potential of post-synthetic modification for controlled construction of d–d and d–f binuclear complexes. The complexes obtained were characterized by CHN elemental analysis, NMR spectroscopy, ESI mass-spectrometry, FTIR spectroscopy and single crystal X-ray diffraction analysis. By means of XPS and NEXAFS spectroscopy the coordination of diimine donor site to the Ln(III) centre has been definitely confirmed. The photophysical properties of mono- and binuclear complexes were carefully investigated, and the evolution of luminescent characteristics during the formation of a system of connected metallocenters is also discussed. TDDFT calculations were used to describe the luminescence mechanism and to confirm the conclusions made on the basis of experimental data. [ABSTRACT FROM AUTHOR]

Understanding strongly correlated rare-earth intermetallic compounds requires knowledge of the nature of the fermionic quasiparticles in states near the Fermi level EF. We report on a pump-probe experiment using femtosecond time- and angle-resolved photoemission spectroscopy to determine lifetimes of hot quasiparticles in the heavy-fermion compound YbRh2Si2. An unoccupied band with electronlike dispersion and a band bottom 0.2 eV above EF was identified at Γ, in agreement with band structure calculations for the subsurface region. Hot quasiparticle lifetimes from 30 to 80 fs were found for energies between 0.4 and 0.1 eV above EF. These lifetimes generally follow the typical monotonous increase towards EF, in agreement with earlier studies on Yb and Rh elemental metals. However, at normal emission the lifetimes at around 0.2 eV exceed this trend by about +20 fs. This difference decreases with increasing photoemission angle and can be assigned to the particular band that is probed in YbRh2Si2. Potential microscopic scenarios are discussed. [ABSTRACT FROM AUTHOR]

Typically, topological superconductivity is reachable via proximity effect by a direct deposition of superconductor (S) on top of a topological insulator (TI) surface. Here, the double critical current in the Josephson junctions based on the topological insulator is observed in the fabricated planar Superconducting Quantum Interference Devicea. By measuring critical currents as a function of temperature and magnetic field, it is shown that the second critical current stems from the intrinsic superconductivity of the S–TI interface, which is supported by the modified Resistively Shunted Junction model and Transmission Electron Microscopy studies. This complex structure of the interface should be taken into account when the technological process involves Ar‐plasma cleaning. [ABSTRACT FROM AUTHOR]

Following the game‐changing high‐pressure CO (HiPco) process that established the first facile route toward large‐scale production of single‐walled carbon nanotubes, CO synthesis of cm‐sized graphene crystals of ultra‐high purity grown during tens of minutes is proposed. The Boudouard reaction serves for the first time to produce individual monolayer structures on the surface of a metal catalyst, thereby providing a chemical vapor deposition technique free from molecular and atomic hydrogen as well as vacuum conditions. This approach facilitates inhibition of the graphene nucleation from the CO/CO2 mixture and maintains a high growth rate of graphene seeds reaching large‐scale monocrystals. Unique features of the Boudouard reaction coupled with CO‐driven catalyst engineering ensure not only suppression of the second layer growth but also provide a simple and reliable technique for surface cleaning. Aside from being a novel carbon source, carbon monoxide ensures peculiar modification of catalyst and in general opens avenues for breakthrough graphene‐catalyst composite production. [ABSTRACT FROM AUTHOR]

Graphene growth and doping are well studied on flat surfaces of various materials. To further advance the technological implementation of graphene-based systems, fundamental studies need more appropriate model templates, whose surfaces would mimic substrates with non-trivial topography. Here, using electron and photoelectron diffraction and photoemission spectroscopy as well, we demonstrate how a curved tungsten crystal covered by a thin nickel film can properly be used as such platform, allowing the fabrication and comprehensive characterization of nitrogen-doped graphene. We show the way in which nitrogen impurities prefer to embed into the graphene matrix at different areas of the curved metallic surface with variable density of atomic steps. In particular, at atomically flat regions with a strong graphene-metal interaction, pyridinic configuration is the most abundant form of dopants, while graphitic nitrogen strongly dominates in places with a weak coupling of graphene to the substrate, i.e. , in the vicinity of the surface irregularities. We recognize single crystals with curvilinear surfaces as versatile platforms for the studies of not only low-dimensional materials, but also molecular adsorption, chemical reactions and catalysis on surfaces with complex structure. [Display omitted] • Configurations of dopants in N-graphene atop a curved Ni substrate are explored. • To study the atomic environment of dopants, photoelectron diffraction is applied. • Pyridinic N is the most abundant form at atomically flat regions. • Graphitic N strongly dominates in the vicinity of the steps. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a crucial process that drives the operation of several energy storage devices. ORR can proceed on the neat carbon surface in the absence of a catalyst, and its electrochemical activity is determined by its microstructure and chemical composition. Oxygen functional groups unavoidably existing on the carbon surface can serve as adsorption sites for ORR intermediates; the presence of some oxygen functionalities gives rise to an increase in the density of electronic states (DOS) at the Fermi level (FL). Both factors should have a positive impact on the electron transfer rate that was demonstrated for ORR in aqueous media. To study the O-groups effect on the aprotic ORR, which is now of interest due to the extensive development of aprotic metal-air batteries, we use model oxidized carbon electrodes (HOPG and single-layer graphene). We demonstrate that oxygen functionalities (epoxy, carbonyl, and lactone) do not affect the rate of one-electron oxygen reduction in aprotic media in the absence of metal cations since their introduction practically does not increase DOS at FL. However, in Li+-containing electrolytes, oxygen groups enhance both the rate of second electron transfer and carbon degradation due to its oxidation by LiO 2 yielding carbonate species. [Display omitted] [ABSTRACT FROM AUTHOR]

In order to study the performance, cycling stability and safety of electrochemical storage devices, various characterisation methods are applied. Magic angle spinning (MAS) NMR enables ex situ studies of electrochemical reactions with high resolution. In the present work, we follow the changes that occur in the MAS NMR spectra of lithiated graphitic materials after storage. The measuring time has been significantly shortened by using fine-grained graphitic material with 65% 13C-isotope enrichment. Our results show that for 13C graphitic electrode material with a low lithiation degree, visible changes in the 13C NMR spectra are observed already in few hours, whereas the samples with a higher lithiation degree demonstrated greater stability even after several days. We analyzed the deintercalation behavior in these materials using 7Li MAS NMR and oxidation processes using in situ X-ray photoelectron spectroscopy. During storage Li ions migrate to the other interlayers (redistribution), large pores and to the surface, where interaction with air takes place. Effects of charge transfer from Li to graphite across four graphitic layers guarantees that 13C NMR spectra are less affected by these effects. The key finding is that special care has to be paid to the ex situ characterisation of electrochemically prepared graphitized materials. Image 1 [ABSTRACT FROM AUTHOR]

This paper presents an experimental and theoretical study of the electronic structure of the fluorinated fullerene C60F36. UV photoemission spectroscopy (UPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy have been used for probing the density of electronic states in the valence and conduction bands of the compound. An assignment of spectral features was carried out using the results of ab initio B3LYP ground-state calculations of the electronic structure of C60F36. The sample of C60F36 is a mixture of three isomers. The calculations of the density of occupied states of these isomers revealed only a small effect of the π-system organization on the UPS profile. It was demonstrated that the CK-edge NEXAFS spectrum of the fluorinated fullerene can be successfully modeled using the (Z+1) approach properly treating the core hole impact on the spectral profile. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract It was shown, that the treatment of graphite oxide (GO) at a temperature of 1000 °C and a static pressure of 500 bar recovers the graphene layers. Addition of triphenylphosphine to GO helps in removal of oxygen during the treatment and allows introducing ca. 0.7 at% of phosphorus in the product. Most phosphorus atoms are bonded with oxygen as the 31P nuclear magnetic resonance spectrum showed. An analysis of the X-ray photoelectron P 2 p spectrum additionally found the components corresponding to C P and P P bonding. Assembling of phosphorus atoms into nanometer clusters was confirmed by transmission electron microscopy. Raman spectroscopy and electrical conductivity measurements revealed the n -type doping of graphitic material through the incorporation of phosphorus. [ABSTRACT FROM AUTHOR]

Abstract Hot pressing is one of the promising routes for graphitization of carbon materials. In the present work, high-pressure high-temperature behaviour of 13C-enriched fine-grained graphitic material has been studied by using a set of experimental tools such as scanning electron microscopy, Raman scattering, X-ray diffraction, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopies, and solid-state nuclear magnetic resonance (NMR) spectroscopy. The material has been annealed at a temperature of 1200 or 1500 °C using a stabilizing pressure of 5 GPa. It shown, that addition of small amount of water during the annealing at 1200 °C results in a better local atomic ordering of carbon material and increases the hydrocarbon fraction. Well-ordered graphite crystals enriched with 13C isotope are formed on the surface of nickel ampule at 1500 °C. An increase in processing time from 2 to 15 h decreases the defect density and improves the graphitization level of the material. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Titanium carbide attracts growing interest as a substrate for graphene growth and as a component of the composite carbon materials for supercapacitors, an electrode material for metal-air batteries. For all these applications, the surface chemistry of titanium carbide is highly relevant and being, however, insufficiently explored especially at atomic level is a subject of our studies. Applying X-ray photoelectron spectroscopy (XPS) to clean (111) and (755) surfaces of TiC, we were able to obtain the detailed spectroscopic pattern containing information on the plasmon structure, shake up satellite, the peak asymmetry and, finally, surface core level shift (SCLS) in C 1 s spectra. The latter is essential for further precise studies of chemical reactions. Later on, we studied interface between TiC (111) and (755) and graphene and found the SCLS variation due to strong chemical interaction between graphene and substrate. This interaction is also reflected in the peculiar band structure of graphene probed by angle-resolved photoelectron spectroscopy (ARPES). Based on LEED data the structure is close to (7√3 × 7√3)R30°, with graphene being slightly corrugated. We found that similarly to the graphene on metals, the chemical interaction between graphene and TiC can be weakened by means of intercalation of oxygen atoms underneath graphene. [ABSTRACT FROM AUTHOR]

We demonstrate that the ionic conductivity of Li1+xAlxGe2−x(PO4)3 glass-ceramic electrolytes can be tailored by adding Y2O3 to Li2O–Al2O3–GeO2–P2O5 melts. We found that the addition of 5 vol% Y2O3 causes noticeable changes in further glass crystallization process as the key parameters (glass crystallization temperature, viscosity and others) are affected. Small-angle neutron scattering data suggest that Y-containing glasses are suddenly crystallized upon heat treatment producing uniform Li1+xAlxGe2−x(PO4)3 ceramics. Due to the lower resistance of intergrain interfaces, such samples demonstrate a specific ionic conductivity of 0.5 mS cm−1, which is nearly 5 times higher in comparison to Y-free ceramics, prepared under similar conditions. We speculate that such an effect is caused primarily by better intergrain contact in Y-containing ceramics, along with better ionic transport in the grain bulk as evidenced by 7Li NMR. [ABSTRACT FROM AUTHOR]

13 C-enriched fine-grained graphitic material has been studied towards its potential for chemical and electrochemical applications. The structural and morphological modification of the material as results of pressure-assisted thermal treatment and gaseous BrF 3 and/or Br 2 room-temperature treatments has been investigated using a combination of the characterization tools: electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy, solid state nuclear magnetic resonance (NMR) spectroscopy and magnetic susceptibility measurements. It has been found that the starting material represents graphitized carbon with oxygen containing defects. The evidence of distorted sp 2 hybridization of carbon was found in the Raman and the 13 C NMR spectra. Under high pressure and temperature, some initially open graphitic edges are coupled that causes decreasing specific surface area and mean in-plane size of crystallites, and, generally, a higher degree of disorder. The Br 2 treatment improves the material structure due to removal of tiny graphitic flakes and oxygenated carbon groups. The use of BrF 3 results, in addition, in partial fluorination of graphitic material. Electrochemical characteristics along with a high degree of 13 C isotope enrichment enable the application of these graphitic materials in operando studies using methods sensitive to 13 C isotope, such as NMR. [ABSTRACT FROM AUTHOR]

A new method for synthesis of graphene-protected iron silicides has been tested, which consists in formation of graphene on Ni(111) followed by two-step intercalation of the system with Fe and Si. Characterization of the samples was performed in situ by low-energy electron diffraction, angular-resolved photoelectron spectroscopy, core-level photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in photoemission of Fe 3 p electrons. It is shown, that at 400 °C the intercalation of graphene/Ni(111) with iron occurs in a range up to 14 ML. The graphene layer strongly interacts with the topmost Fe atoms and stabilizes the fcc structure of the film. The in-plane ferromagnetic ordering of the film has a threshold nature and arises after the intercalation of 5 ML Fe due to the thickness-driven spin reorientation transition. Subsequent intercalation of graphene/Fe/Ni(111) with Si leads to the formation of the inhomogeneous system consisted of intercalated and nonintercalated areas. The intercalated islands coalesce at 2 ML Si when a Fe-Si solid solution covered with the Fe 3 Si surface silicide is formed. The Fe 3 Si silicide is ferromagnetic and has an ordered (√3 × √3)R30° structure. The graphene layer is weakly electronically coupled to the silicide phase keeping its remarkable properties ready for use. [ABSTRACT FROM AUTHOR]

YbCo2 Si2 is considered to serve as a stable-valent, isoelectronic reference for the extensively studied heavyfermion system YbRh2Si2 which is situated very close to an antiferromagnetic quantum critical point (QCP). The investigation of the Fermi surface (FS) topology of YbCo2Si2 and its comparison to YbRh2Si2 could help to unravel the strongly disputed nature of this quantum phase transition, whether it originates from a "local" or "itinerant" QCP. Here we study the electronic structure and FS of YbCo2Si2 by means of angle-resolved photoelectron spectroscopy (ARPES) and compare it to ab initio band structure calculations and FS modeling. Our approach allows the electronic structure at the surface and in the bulk to be disentangled. Identifying the bulk contribution, we demonstrate that YbCo2 Si2 exhibits a "small" FS, confirming the formation of a "large" FS in YbRh2Si2. This favors an itinerant QCP, instead of the widely discussed local scenario. Our study demonstrates that ARPES is a reliable tool for the study of bulk electronic states in intermetallic Kondo lattice systems despite the complexity induced by their three-dimensional character and the presence of pronounced surface states. [ABSTRACT FROM AUTHOR]

Fermi-surface topology governs the relationship between magnetism and superconductivity in iron-based materials. Using low-temperature transport, angle-resolved photoemission, and x-ray diffraction, we show unambiguous evidence of large Fermi-surface reconstruction in CaFe2As2 at magnetic spin-density-wave and nonmagnetic collapsed-tetragonal (cT) transitions. For the cT transition, the change in the Fermi-surface topology has a different character with no contribution from the hole part of the Fermi surface. In addition, the results suggest that the pressure effect in CaFe2As2 is mainly leading to a rigid-band-like change of the valence electronic structure. We discuss these results and their implications for magnetism and superconductivity in this material. [ABSTRACT FROM AUTHOR]

Highlights: [•] Electronic structure of rods-in-belt complexes was described via PES and NEXAFS. [•] With increasing size the molecule becomes more sensitive to X-ray damage effects. [•] The HOMO consists of a combination of the d-Cu/Ag and π-C C states. [•] HOMOs are positioned at about 2.2eV for Au Cu and 2.5eV BE for Au Ag complexes. [•] LUMOs are located on the C-skeleton including π*-C C and π*-C Caromatic orbitals. [Copyright &y& Elsevier]

We report a comparative study of the synthesis and the structural and electronic properties of hexagonal boron nitride (h-BN) and graphene layers grown on the Ir( 111) surface. By performing photoernission (PE) experiments time-dependently and supplementing them by low-energy electron diffraction (LEED) data, we demonstrate the differences and similarities of their formation, and we show the temperature regimes which allow these materials to be created with high crystalline quality. It has been demonstrated that synthesis at low temperatures leads to the formation of disordered domains of h-BN as well as graphene flakes on the metallic surface. The LEED patterns of such samples reveal a complex structure which indeed can be easily interpreted by using the model presented here. The angle-resolved PE study of h-BN/Ir(111) demonstrates the presence of replicated electronic states, which are quite similar to those detected and widely discussed for the graphenelIr(111) system. On the basis of these results and the corresponding model calculations, we argue that the appearance of these replicated bands is mainly caused by the geometrical corrugation of the system. [ABSTRACT FROM AUTHOR]

We present a study of the evolution of magnetism from the quantum critical system YbRh2Si2 to the stable trivalent Yb system YbCo2Si2. Single crystals of Yb(Rh1-xCox)2Si2 were grown for 0 ⩽ x ⩽ 1 and studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements, as well as photoemission spectroscopy. The results evidence a complex magnetic phase diagram, with a nonmonotonic evolution of TN and two successive transitions for some compositions resulting in two tricritical points. The strong similarity with the phase diagram of YbRh2Si2 under pressure indicates that Co substitution basically corresponds to the application of positive chemical pressure. Analysis of the data proves a strong reduction of the Kondo temperature TK with increasing Co content, TK becoming smaller than TN for x≈0.5, implying a strong localization of the 4f electrons. Furthermore, low-temperature susceptibility data confirm a competition between ferromagnetic and antiferromagnetic exchange. The series Yb(Rh1-xCox)2Si2 provides an excellent experimental opportunity to gain a deeper understanding of the magnetism at the quantum critical point in the vicinity of YbRh2Si2 where the antiferromagnetic phase disappears (TN → 0). [ABSTRACT FROM AUTHOR]

Abstract: Photoemission spectra of solid fluorinated fullerenes C60F x (x =18, 36) were measured in comparison with parent C60 using synchrotron radiation (hν =120eV) providing the spectra in the density of states mode. Creation of the ion-like bonding of fluorine and disappearance of the π-states were observed to be a result of fluorination. Disappearance of the upper lying π-states was revealed to be a reason of the band gap widening upon fluorination. [Copyright &y& Elsevier]

Abstract: The effect of hole doping on the crystal and electronic structure of La1− x Sr x Co1− y Nb y O3 (y=0.0–0.25) at the x=0.0; 0.2; 0.5 has been studied by neutron diffraction and X-ray absorption spectroscopy at the Co K and L2,3-edges. The preliminary analysis of the Co K and L2,3-edges X-ray absorption near edge structure (XANES) in La1− x Sr x Co1− y Nb y O3 series suggests that upon niobium doping, an increase of the intermediate Co3+ spin state and a decrease of low spin Co4+ states contributions occur. The possible explanation of the observed changes of crystal and electronic structure in these cobaltites is discussed. [Copyright &y& Elsevier]

High resolution Fe L-, Cu L-, S L-edge and O K-edge X-ray absorption near-edge structure (XANES) spectra of synthetic bornite and the samples oxidized in air and leached in a ferric chloride solution have been recorded and compared with the spectra of chalcopyrite. The pre-edge shoulder in the Cu L-edge spectrum of bornite and the strong leading peak in the spectrum of chalcopyrite were attributed to the electron transitions to the minor density of unoccupied Cu 3d states, and the post-edge features were related to the states of s- and p-type. The Fe L-edge XANES showed the presence of predominant Fe2+ for chalcopyrite, and some quantity of Fe2+ for bornite cannot be excluded despite XPS and Mössbauer spectroscopy had previously detected only Cu+ and Fe3+ species in both minerals. The Cu L- and S L-edge spectra of bornite considerably modify and become similar to those of chalcopyrite after the oxidative leaching that produces the heavily metal-depleted surface layers, and the Fe L-edge XANES shows only a slightly increased contribution of Fe2+. The multiparticle configurations involving Fe2+ and Cu2+ or holes at S atoms may play a role in the L-spectra. [Copyright &y& Elsevier]

XPS, Fe Lα,β and Cu Lα,β X-ray emission and Fe L-, Cu L-, S L-edge and O K-edge absorption spectroscopies, Mo¨ssbauer spectroscopy and cyclic voltammetry were applied to study reacted surface layers of natural chalcopyrite, CuFeS2. The surfaces became metal-depleted after the anodic oxidation in 1 M HCl and the leaching in 1 M H2SO4+0.2 M Fe2(SO4)3 or 1 M HCl+0.4 M FeCl3 solutions, with the sulfur excess and iron/copper ratio been higher in the last instance, and were enriched in copper after the electrochemical reduction. The electronic structures of the metal-deficient layers up to several tenths of micrometer thick were similar to that of chalcopyrite, except that the density of the highest occupied states depended on sulfur anions formed (predominant S3-anions after the ferric sulfate treatment, S4-anions after the ferric chloride leaching or the potential sweep to 0.9 V, etc.). The layers created by the preliminary oxidation had only a small effect on the chalcopyrite voltammetry. We suggest a new reaction mechanism considering a role of the surface changes, including disordering and Anderson localization of the electronic states. [Copyright &y& Elsevier]

Efficient control over the grain boundaries (GBs) is a vital aspect in optimizing the graphene growth conditions. A number of methods for visualization of GBs were developed for graphene grown on weakly interacting surfaces. Here, we utilize oxygen intercalation to reveal GBs and study their morphology for graphene strongly bound to the cobalt surface. We demonstrate that upon the intercalation of oxygen, GBs in polycrystalline graphene become easily detectable due to graphene cracking and selective oxidation of the substrate, thus giving a direct insight into the graphene micro- and nanostructure by means of different electron microscopy methods, including scanning electron microscopy, photoemission microscopy and low-energy electron microscopy. [Display omitted] • Grain boundaries of graphene strongly bound to the Co(0001) surface are visualized. • Patterned distribution of domains is revealed in polycrystalline graphene/Co. • Graphene coverage prevents the Co(0001) surface from oxidation at low exposures. • Lateral growth of cobalt oxide areas is observed under polycrystalline graphene. • After deintercalation of oxygen a part of graphene remains quasi-freestanding. [ABSTRACT FROM AUTHOR]

Abstract: Photoemission spectra of valence electrons of solid C60F18 were measured in X-ray photon energy range being close to the excitation of fluorine F 1s core electron into the first unoccupied state. Enhancement of photoemission cross sections was revealed due to Auger decay of fluorine vacancy in which electron of neighboring carbon atom takes part. [Copyright &y& Elsevier]

Using resonant angle-resolved photoemission spectroscopy and electron band-structure calculations, we explore the electronic structure and properties of Sm atoms at the surface and in the bulk of the antiferromagnet SmRh2Si2. We show that the Sm atoms reveal weak mixed-valent behavior both in the bulk and at the surface. Although trivalent 4f emission strongly dominates, a small divalent 4f signal near the Fermi energy can be clearly resolved for surface and bulk Sm atoms. This behavior is quite different to most other Sm-based materials which typically experience a surface valence transition to a divalent state of Sm atoms at the surface. This phenomenon is explained in analogy to the isostructural Ce compound, where strong 4f hybridization stabilizes mixed-valent ground state both in the bulk and at the surface, and which were described in the light of the single-impurity Anderson model. Implications for other RERh2Si2 (RE = rare-earth elements) compounds are discussed. [ABSTRACT FROM AUTHOR]

The potential of resonant inelastic soft x-ray scattering to measure 4f crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For CeCu2Si2 we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce M4,5 edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic properties of the solid solutions have been studied by neutron diffraction and X-ray absorption near edge structure (XANES) measurements. Our data are in agreement with the following scenarios. The first scenario is about the magnetic phase separation into regions with different content of Co/Co ions in different spin states. The second one is about the gradual thermal excitation of the Co ions from low- to intermediate- or high-spin state in wide temperature range. [Copyright &y& Elsevier]

We investigated the insertion-extraction behaviors of Li and Na ions in graphitic materials using solid-state NMR. A unique advantage of high-degree 13 C-isotope enrichment of graphitic material allowed sensitive and metastable graphite intercalation compounds to be measured in a short time. Ex situ 13 C magic-angle spinning NMR spectra of 13 C fine-grained graphite are presented as a function of state-of-charge. The observations are discussed with respect to graphite intercalation phenomena, which include the effects of charge transfer and the demagnetizing field. Dramatic narrowing of the 13 C NMR signal in metal-intercalated graphite evidences quasi-complete charge transfer occurring between lithium and graphite host material and resulting in reducing the macroscopic field effects. Upon Na insertion, incomplete charge transfer is observed and explained by inaccessibility of graphitic interlayer space for Na ions in our study. In addition, critical issues of reversibility of Li- and Na-ion electrochemical cells and solid electrolyte interphase formation are considered on the atomic scale. The knowledge gained in the present work can be applied to advanced high-power-density electrode materials for safe and fast-charging metal-ion batteries or for novel spintronic concepts with controlled spin-polarized charge carrier injection and transport combined with the possibility to manipulate magnetic anisotropy.

High-resolution solid-state NMR based on combined rotation and multipulse spectroscopy (CRAMPS) has been applied to study chemical structures of dental tissues. The samples of human enamel, crown dentine and root dentin studied in this work were used without chemical pre-treatment. The quantitative ¹H NMR spectra permit an assignment to different structures and a quantification of the content of hydroxyl groups. While there is 40% hydroxyl content in the enamel, there is significantly less in the dentin, 14% in the crown and 9% in the root. Thus this study provides the direct evidence of OH⁻ ion deficiency in all dental tissues supporting earlier findings that bone and dental mineral apatite is poorly hydroxylated.