Mean Valence Research Articles

X-Ray Absorption Spectroscopic Studies on Electronic Structure in La0.6Sr0.4Co0.8Fe0.2O3-δ Perovskite-Type Oxides

In order to investigate the variation of the electronic structure of La0.6Sr0.4Co0.8Fe0.2O3-δ depending on its oxygen nonstoichiometry, X-ray absorption spectroscopy of the material annealed under various oxygen partial pressures was performed. Co/Fe L-edge XANES spectra indicated that the mean valence of Co ion decreased with decreasing oxygen partial pressure, while that of Fe ion was almost independent of oxygen partial pressure. This suggested that Co ion rather than Fe ion preferentially compensated the charges caused by the formation of oxygen vacancies.

Studies on Defect Structures of (La,Sr)2NiO4 by Using X-ray Absorption Spectroscopy

Ni <I>K-edge</I> X-ray absorption spectroscopy was applied to investigate the electronic and defect structures of La2-<I>x</I>Sr<I>x</I>NiO4{plus minus}δ (<I>x</I> = 0 - 1.0) annealed under various oxygen partial pressures. X-ray absorption near edge structure (XANES) indicated that the mean valence of Ni ions increased by increasing Sr contents and oxygen partial pressure, accompanied by variation of oxygen nonstoichiometry, in the composition range having excess oxygens and oxygen vacancies. Ni <I>L-edge</I> XANES spectra of La2-<I>x</I>Sr<I>x</I>NiO4{plus minus}δ were used to decide the valence state and the spin state of Ni ions. By increasing Sr contents and oxygen partial pressure, it was found that Ni(II) ions decreased and the low spin state of Ni(III) ions increased.

Combining photoemission and optical spectroscopies for reliable valence determination in YbS and Yb metal

Hard x-ray photoemission and optical spectroscopies have been performed on YbS and Yb metal to determine the precise $f$-electron occupation. A comparison of the photoemission spectra with the energy-loss functions in bulk and surface, obtained from optical reflectivity, enables us to distinguish between the energy-loss satellite of ${\text{Yb}}^{2+}$ peak and the ${\text{Yb}}^{3+}$ multiplet. The results clearly indicate a purely divalent Yb state except for the surface of YbS which is altered by oxidation. We demonstrate that the present method is highly reliable in identifying the electronic structure and the mean valence in $f$-electron systems.

Influence of Sc 3+ on LiMn 2O 4 cathode materials at elevated temperature

Sc 3+ -doped lithium manganese oxides were synthesized by solid-state reaction. The influences of doping element on structure, mean valence of manganese, and electrochemical performances were studied by X-ray diffraction (XRD), galvanostatic charge-discharge and cyclic voltammetric tests, and also electrochemical impedance spectroscopy (EIS). XRD tests showed that doped lithium manganese oxides were pure spinel structure without other phases. Redox titration and visible spectrophotometry tests indicated that the mean valence of manganese in doped lithium manganese oxides was higher than that of pure one. LiSc 0.02Mn 1.98O 4 remained 92.9% of the initial specific discharge capacity after 50th cycle at a constant current of 50 m/g, and the reversibility of LiSc 0.02Mn 1.98O 4 was improved in comparison with pure LiMn 2O 4 at 50 °C. EIS indicated that film deposition on spinel particles was suppressed because of Sc 3+ doping, and the charge transfer between the surface film and spinel particles with increasing temperature for Sc 3+ -doped materials became easier as compared with undoped one.

Reduction of the Yb valence inYbAl3nanoparticles

Measurements of specific heat, dc magnetic susceptibility, and Yb ${L}_{\text{II}}$ and ${L}_{\text{III}}$ x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) on ${\text{YbAl}}_{3}$ milled alloys are reported. X-ray diffraction patterns are consistent with a reduction in particle size down to 10 nm and an increase in the lattice strain up to 0.4% for 120 h of milling time. A decrease in the mean valence from 2.86 for the unmilled alloy to 2.70 for 120 h milled ${\text{YbAl}}_{3}$ is obtained from the analysis of XANES spectra. From the analysis of spectra in the EXAFS region, an increase in the mean-square disorder of neighbor distance with milling time is detected in good agreement with the results of x-ray diffraction. Size effects strongly influence the magnetic and thermal properties. The value for the maximum of the magnetic susceptibility decreases around 30% for 120 h milled alloy and an excess specific heat, with a peak around 40 K in the milled samples, is derived. These changes in the physical properties along the milled ${\text{YbAl}}_{3}$ alloys are associated with the reduction in particle size. Such a reduction leads to the existence of a large number of ${\text{Yb}}^{2+}$ atoms at the surface with respect to the bulk affecting the overall electronic state.

Intermediate-Valence Behavior of YbCu5-xAlxaround Quantum Critical Point Measured by Resonant Inelastic X-ray Scattering at YbL3Absorption Edge

An x-ray spectroscopy study was performed for YbCu 5- x Al x ( x = 0.0–2.0) using high-resolution partial-fluorescence yield (PFY) and resonant inelastic x-ray scattering (RIXS) at the Yb L 3 absorption edge. From a careful analysis of the PFY and RIXS spectra, the mean-valence of Yb was estimated and is found to increase quite rapidly for compositions between 0 ≤ x ≤1.0, indicating strong intermediate-valence behavior. The mean valence continues to increase gradually with x and becomes nearly trivalent for x = 2.0. Our results, however, reveal that valence fluctuation occurs even at x =1.5, for which non-Fermi liquid quantum critical behavior is known. The valence evolution cannot be explained solely in terms of chemical pressure effects. The study suggests the role of valence-coupled spin fluctuations for the quantum critical behavior.

Dramatic effects of excess oxygen on physical properties and crystal structure of La 0.95Sr 0.05MnO y single crystal

We have examined the effects of excess oxygen on the magnetization, electrical transport properties and crystal structure of La 0.95Sr 0.05MnO y . An antiferromagnetic insulator phase confirmed in the as-grown crystal at low temperatures changed to a ferromagnetic insulator phase after the introduction of excess oxygen. The ferromagnetic transition temperature, T C , systematically increased with increasing oxygen content, y , due to an increase in the mean valence of manganese. However, the T C of crystals with excess oxygen was lower than that of the La 1− x Sr x MnO 3.00 having identical manganese valence. This is considered to be a result of the competition among the mean valence of manganese, the concentration of cation vacancies, and the mean ionic radius of cations at the A-site.

Observation of bulk electronic states of Kondo semiconductor YbB 12 by high-resolution soft X-ray photoemission spectroscopy

Bulk valence band photoemission spectra of the Kondo semiconductor YbB 12 were measured with use of soft X-ray ( h ν = 700 eV) at 20 and 200 K and the Kondo resonance behavior was confirmed. Sharp bulk Yb 2+ 4f peaks are observed in the vicinity of Fermi level on fractured single crystals. From the spectra is estimated the Yb mean valence as 2.86 ± 0.01 at 20 K and 2.91 ± 0.01 at 200 K. The whole peaks of the Yb 3+ 4f multiplets are found to shift by ∼ 30 meV toward higher binding energies with decreasing the temperature from 200 to 20 K. On the other hand, the shift of the peak energy position of the Yb 2+ 4f spectra toward lower binding energies with decreasing the temperature is found to be less than 10 meV. The temperature dependence of the Yb 4f photoemission spectra is well explained by the non-crossing approximation (NCA) calculation based on the single impurity Anderson model (SIAM).

The valence state of Yb ion in YbInAu2 compound at high pressure determined by x-ray diffraction and x-ray absorption near edge structure measurements

X-ray diffraction patterns and LIII-edge x-ray absorption near edge structure (XANES) spectra of YbInAu2 and LuInAu2 compounds have been measured at high pressure and room temperature using a diamond anvil cell and a synchrotron radiation at SPring-8. YbInAu2 is more compressible at pressures lower than 4GPa than above it; the evaluated bulk modulus by Birch-type equation of state is 54.7GPa which is one-half of that of the LuInAu2 (112.5GPa). The mean valence v¯ of Yb ion in YbInAu2 determined by the XANES measurement is an increasing function of pressure: 2.71(2) at normal pressure and 2.94(2) at 10GPa. The rate of increase in v¯ with pressure is two times larger at pressures below 4GPa than that above 4GPa. However, the v¯ is described by a linear increasing function of the lattice compression: v¯=v¯0+2.9∣ΔV∕V0∣ where v¯0 is 2.71. The extrapolation to the trivalent state gives the critical pressure of 13GPa.

Oxygen potential of (Pu 0.91Am 0.09)O 2− x

Oxygen potentials of (Pu 0.91Am 0.09)O 2− x were measured by thermogravimetric analysis with H 2O/H 2 gas equilibrium and dilute O 2 gas at 1123 K, 1273 K and 1423 K. The oxygen potentials were extremely high from stoichiometry to O/M = 1.99 and were somewhat lower than those of AmO 2− x near stoichiometry. On the other hand, those below O/M = 1.96 were much lower than those of AmO 2− x . Valence state changes of Am and Pu in the oxide were assumed, and experimentally determined data were examined using the slope of the plot of oxygen partial pressure versus deviation from stoichiometry, the oxygen potential as a function of mean valence state of metal, activity coefficient of AmO 2− x and the partial molar enthalpy and entropy of oxygen. It was concluded through these examinations that aspects of the oxygen potential of (Pu 0.91Am 0.09)O 2− x could be interpreted by the present assumption and that several interactions between Am and Pu could exist.

A rapid method for labelling CD4 + T cells with ultrasmall paramagnetic iron oxide nanoparticles for magnetic resonance imaging that preserves proliferative, regulatory and migratory behaviour in vitro

A number of techniques have been developed to track the migration of T cells in vivo, but they all suffer significant shortcomings, including the examination of selected organs rather than the organism as a whole — thus precluding longitudinal studies — or limitations imposed by poor spatial resolution and the application of ionizing radiation. By conjugating the HIV tat peptide to ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles in a reaction yielding a mean valence of 45, a magnetic resonance (MR) contrast agent was synthesised that allowed T cells to be efficiently labelled within just 5 min. The USPIO nanoparticles were incorporated into both the cytoplasm and nucleus of labelled cells, which retained normal in vitro proliferative responses to a polyclonal stimulus; suppressive responses mediated by labelled CD4 + CD25 + regulatory T cells; chemotactic responses to the chemokine CXCL-12; and transmigration of an activated endothelial monolayer. We believe that this rapid, efficient and essentially non-toxic approach to labelling both murine and human T cells for MRI holds considerable promise, paving the way for the wider immunological application of this exciting technology.

Valence ratings of emotional and non-emotional words in children

Words of varying emotional content are widely used as stimuli in studies that examine the cognitive responses to threat in childhood anxiety disorders. To date, there are limited data on word stimuli that elicit emotional responses in children. The purpose of this study was to collect children’s valence ratings of different types of emotional words. Typically developing children ( n = 174; ages: 9–11 years) rated a pre-selected list of 81 words from three emotional categories: threat, positive, and neutral. Children’s valence ratings differentiated the three word categories with strong internal consistency in each category. Furthermore, females provided more extreme valence ratings than males. Mean valence ratings and word characteristics for each word are provided. These words can potentially be used to develop experimental paradigms that examine reactions to emotional words in children with and without anxiety disorders.

Temperature dependent X-ray absorption spectroscopy of the valence transition in EuNi 2(Si 0.20Ge 0.80) 2

We investigate the temperature induced mixed valence transition in EuNi 2(Si 0.2Ge 0.8) 2 using Eu 3d–4f X-ray absorption spectroscopy (XAS). The unoccupied 4f states are studied as a function of temperature (27–120 K), across the critical valence temperature, T v = 80 K . The Eu 3d–4f X-ray absorption spectra show systematic changes of the mixed valency with temperature. The Eu 2 + and Eu 3 + spectral features match very well with atomic multiplet calculations. The observed non-integral mean valence changes systematically from ∼ 2.70 ± 0.03 (27 K) to ∼ 2.35 ± 0.03 (120 K), consistent with bulk-sensitive measurements.

Physical Properties of Oxygen Composition Controlled La1-xSrxMnOy Single Crystals

AbstractWe have investigated the effect of high-temperature post-annealing and control of excess oxygen for La1-xSrxMnOy (0.05 ≤ x ≤ 0.2) single crystals. Thin plate-like single crystals prepared by careful cutting and polishing enabled the control of excess oxygen for the single crystals by post-annealing for relatively short times at various temperatures. Post-annealed crystals with y ∼ 3.00 exhibited higher TC than that of as-grown crystals due to homogenization of cation and oxygen compositions and reduction of local lattice strains. With an increase of y, TC systematically increased for all Sr compositions. Competition between an increase of mean valence of manganese and generation of cation vacancy determines the TC of La1-xSrxMnOy crystals.

Processus émotionnel dans la schizophrénie : étude de la composante d’évaluation

Resume Le premier objectif de cette etude etait de tester l’hypothese de polarite, c’est-a-dire l’hypothese selon laquelle l’evaluation des evenements positifs vs negatifs implique des mecanismes emotionnels differents. Le second objectif etait d’eclaircir un paradoxe apparent dans la litterature sur la schizophrenie : la tendance des patients schizophrenes a sous-evaluer le niveau de desagrement des stimuli negatifs suggere un trouble dans l’evaluation des evenements negatifs, alors que le fait que l’anhedonie constitue un trait clinique essentiel de la schizophrenie suggere au contraire la presence d’un trouble touchant principalement l’evaluation des evenements positifs. Les stimuli utilises dans notre etude etaient des photographies emotionnellement positives ou negatives, a caractere social ou non. Sur chaque photographie, deux bordures, pouvant etre soit identiques soit differentes, ont ete ajoutees. Dans une premiere experience, dite « implicite », il etait demande a des patients schizophrenes et a leurs temoins de decider si les bordures superieure et inferieure des photographies etaient identiques ou differentes. Dans une seconde experience, dite « explicite », il leur etait demande de juger si les photographies etaient agreables ou desagreables. Deux resultats obtenus sont en faveur de l’hypothese de polarite : 1) dans la condition d’evaluation implicite, l’effet du facteur polarite differait entre les patients et leurs temoins ; 2) dans la condition d’evaluation explicite, les patterns de reponse des patients et de leurs temoins differaient selon la polarite des stimuli non sociaux. De plus, les resultats ont mis en evidence un deficit dans le jugement hedonique de photographies negatives sociales et de photographies positives non sociales chez les patients schizophrenes, suggerant ainsi que le paradoxe apparent decrit ci-dessus s’eclaircit des lors que la composante sociale des stimuli est consideree. Les resultats obtenus suggerent que la polarite et la composante sociale des evenements evalues par les patients schizophrenes sont des parametres a considerer dans les prochaines etudes concernant les troubles affectifs dans la schizophrenie.

Temperature-induced valence transition in EuNi 2(Si 0.20Ge 0.80) 2 studied by hard X-ray photoemission spectroscopy

The temperature-induced mixed valence transition in EuNi 2(Si 0.20Ge 0.80) 2 has been investigated by hard X-ray (5940 eV) photoemission spectroscopy (HX-PES) for fractured surfaces, with a probing depth larger than 5 nm. The Eu 3d core-level states are studied below and above the critical valence transition temperature, T v = 80 K. The HX-PES spectra at 40 and 120 K show the mixed valence transition, with clear changes in the divalent and trivalent Eu 3d chemically shifted features. The Eu 3d HX-PES spectra indicate a mean valence of 2.70 ± 0.03 at 40 K which changes to 2.40 ± 0.03 at 120 K, in good accordance with the results of bulk Eu III-edge X-ray absorption spectroscopy measurements.

Selective numbing and hyperarousal in male and female Bosnian refugees with PTSD

Emotional numbing is an important symptom of PTSD, but it is not clear whether it affects both positive and negative affect equally or not. To address this question we administered Lang’s Looking at Pictures test, in which a series of pictures are rated for valence (pleasant–unpleasant) and arousal (high–low), to 10 male and 11 female Bosnian refugees suffering from PTSD (DSM-IV criteria) and to control groups of 11 male and 10 female Bosnian refugees with similar trauma exposure but without PTSD or any other major mental illness. The mean valence ratings for unpleasant, neutral, and pleasant pictures of both PTSD and control males and females were similar to normal ratings. Likewise, the mean arousal ratings for unpleasant, neutral, and pleasant pictures of both male and female controls were similar to normals, with both unpleasant and pleasant pictures rated more arousing than neutral pictures. In contrast, in both males and females with PTSD pleasant pictures were rated as almost completely non-arousing. Thus, in Bosnian refugees affective numbing is seen primarily with pleasant or positive stimuli.

Bulk-sensitive high-resolution photoemission study of a temperature-induced valence transition system EuPd 2Si 2

Eu 4f electronic structures of a temperature-induced valence transition system EuPd 2Si 2 have been investigated by bulk-sensitive high-resolution photoemission spectroscopy at temperatures from 20 to 300 K. The bulk Eu 2+ 4f component is definitely distinguished from two surface Eu 2+ 4f components. The changes in the spectral intensity of the bulk Eu 2+ and Eu 3+ 4f configurations and in the energy separation between these states are observed in the temperature dependent photoemission spectra. These temperature dependences are related to the valence transition of EuPd 2Si 2. The Eu mean valence is evaluated to be 2.75±0.03 at 20 K and 2.30±0.05 at 300 K. These values are in good agreement with those evaluated from Mössbauer and Eu L III-edge X-ray absorption measurements.

The valence state of Yb metal under high pressure determined by XANES measurement up to 34.6 GPa

The purpose of this study was to accurately determine the valency of Yb at high pressure and room temperature and to clarify the relation between the valence state and the crystal structure of Yb metal. L III-edge X-ray absorption near-edge structure (XANES) spectra were measured to determine the valence state of Yb metal in the pressure range from 0 to 34.6 GPa at room temperature, using a diamond anvil cell (DAC) and synchrotron radiation at SPring-8. In the fcc phase, Yb metal exhibits mixed valence (the mean valence v ̄ >2.1 ). At the fcc-to-bcc phase transition, a 0.1 jump is found in v ̄ . In the bcc phase, v ̄ ( P) is an increasing function of pressure with downward curvature, reaching only 2.55 at 26 GPa. The v ̄ is only 2.65 in the hcp phase at 34.6 GPa. A tendency for saturation in v ̄ ( P) to values smaller than 3.0 is found.

High-temperature fcc phase of Pr: Negative thermal expansion and intermediate valence state

A high-temperature angle-dispersive synchrotron radiation diffraction study has revealed the double hexagonal-close-packed-to-face-centered-cubic (dhcp-to-fcc) transformation in the Pr metal occurring martensitically between 575 and 1035 K. The high-temperature fcc phase shows a negative thermal expansion in the range 600--800 K, attributed to the $4f$-electron delocalization. A phenomenological theory is developed, which explains consistently the observed effect in terms of the mean valence variation of the metal as a function of temperature; it also predicts the existence of an isostructural phase transition and of a critical end point of a gas-liquid type in compressed Pr. The analysis of published data on $P\ensuremath{-}T$ variation of conductivity of Pr supports this prediction.