Investigation Of Local Structure Research Articles

Formation of Ag clusters in zeolite X studied by in situ EXAFS and infrared spectroscopy

The in situ investigation of local structures by means of Ag K-edge EXAFS and infrared spectra for fully and partially Ag+ exchanged zeolite X (Agx–X; x=86, 66 and 12, where x is number of Ag atoms in unit cell) were carried out from room temperature to 300°C under vacuum. By evacuation at room temperature the coordination number of oxygen around Ag, NAg–O, decreases due to the removal of water molecules. By heating samples under vacuum, Ag clusters grew up via step that Ag–Ag interaction was weakened for Ag86–X and Ag66–X. On the other hand, for Ag12–X, the process with weak Ag–Ag interaction did not exist but Ag cluster was formed just by heating in a vacuum. These differences may have depended on the amount of residual Na+ ions in the zeolite cavity. From the infrared and EXAFS results it was suggested that the mobile Na+ ions in the cavity accelerated to produce Ag clusters for Ag12–X and Ag66–X in low temperature. On the other hand, Ag+ ions were only thermally excited in Ag86–X because there was no Na+ ion in the zeolite cavity. EXAFS result indicated the two types of Ag clusters which were characterized by the Ag coordination number, NAg–Ag=3.0±0.4 (cluster I) and 4.7±0.4 (cluster II). The Ag cluster formation proceeded step by step as these two types of clusters. It was contrasted to Ag zeolite 4A that only the middle size Ag clusters that NAg–Ag=3.8±0.4 exist.

Local structure investigation of clean energy materials through pair distribution function analysis

Local structure investigation of clean energy materials through pair distribution function analysis

Imaging techniques for elements and element species in plant science

Revealing the uptake, transport, localization and speciation of both essential and toxic elements in plants is important for understanding plant homeostasis and metabolism, subsequently, providing information for food and nutrient studies, agriculture activities, as well as environmental research. In the last decade, emerging techniques for elemental imaging and speciation analysis allowed us to obtain increasing knowledge of elemental distribution and availabilities in plants. Chemical imaging techniques include mass spectrometric methods such as secondary ionization mass spectrometry (SIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and synchrotron-based techniques such as X-ray fluorescence spectroscopy (SRXRF), and so forth. On the other hand, X-ray absorption spectroscopy (XAS) based on synchrotron radiation is capable of in situ investigation of local atomic structure around the central element of interest. This technique can also be operated in tandem with SRXRF to image each element species of interest within plant tissue. In this review, the principles and state-of-the-art of these techniques regarding sample preparation, advantages and limitations, and improvement of sensitivity and spatial resolution are discussed. New results with respect to elemental distribution and speciation in plants revealed by these techniques are presented.

Investigation of Local Electronic Structures of Materials Using Scanning Tunneling Microscope

Investigation of Local Electronic Structures of Materials Using Scanning Tunneling Microscope

Theoretical investigation of ESR spectra and local structure for VO 2+ in Ba 2Zn(HCOO) 6(H 2O)

The electron spin resonance spectra (characterized by g factors g , g ⊥ and hyperfine structure constants A  and A ⊥) of Ba 2Zn(HCOO) 6(H 2O) (BZFA): VO 2+ crystal are calculated from high order perturbation formulas. The calculated results are in good agreement with the observed values. The local structure parameters of [VO(H 2O) 5] 2+ clusters are also obtained from the calculation. The magnitudes of the metal–ligand distances parallel and perpendicular to the C 4-axis are, respectively, R ≈0.163 nm and R ⊥≈0.210 nm. It is shown that the local structure around the V 4+ ion possesses a compressed tetragonal distortion along C 4-axis.

シュウ酸エタノール共沈法により合成したLiイオン電池正極材料LiNi0.5Mn0.5O2の局所構造の検討

シュウ酸エタノール共沈法により合成したLiイオン電池正極材料LiNi0.5Mn0.5O2の局所構造の検討

Importance of Neutron Scattering for Materials Science: Expectations on Magnetic Holography

The neutron scattering technique is an indispensable probe for structural investigations of materials, particularly, for observations of light atoms and magnetic moments. Using the IMR neutron powder diffractometer HERMES, which can observe scattering patterns in wide Q rage at once, we have succeeded in performing neutron holography experiments in a Pd-H compound. Holography will become a quite important technique for local structure investigations of materials. Moreover, as the next stage, magnetic holography with polarized neutrons must be promising. [DOI: 10.1380/ejssnt.2011.422]

Local structure investigation of oxide ion and proton defects in Ge-apatites by pair distribution function analysis

In this communication we provide a direct insight into the local structure and defects of oxygen excess Ge-apatites, in both dry and deuterated states, by means of pair distribution function analysis.

Analysis of deformation structures in Pliocene and Quaternary deposits of the Hyblean Plateaux (south-eastern Sicily)

A singular association of deformation structures that have disturbed terrains up to Quaternary age, has been detected along the rocky coast of Vendicari (south-eastern Sicily). These structures are soft sediment deformations consisting of autoclastic breccias, diapyr-like injections and thixotropic wedges, as well as fractures, generally opened and filled by sediments. Both soft and brittle deformations can be due either to trigger mechanisms internal to the sedimentary environment or to external causes. In order to define the deformation mechanisms affecting the deposits, the local paleo-environmental reconstruction and detailed deformation structure investigations have been performed. Moreover, fractures have been analysed by a mesostructural study and the examination of the microscopic features of the filling materials, to highlight possible relationships with the stress field induced by regional tectonics. The multi-theme analysis allowed us to discard internal trigger mechanisms as responsible of the deformations and to reasonably infer these deformation structures as being seismically induced. This interpretation is also supported by similarities with structures studied in other areas worldwide and commonly interpreted as seismites. The link between these records of seismic activity and the eastern Sicily seismicity is set into evidence by the analysis of the historical accounts which report the occurrence of structures similar to those detected at Vendicari, in several sites close to the study area. A major result of the present study is to improve the catalogue of deformation features, recorded in sedimentary units, attributed to earthquakes.

Influence of Zn on Structure and Magnetic Properties of Rapid Quenched (Fe-Zn)-Cu-Nb-Si-B Alloys

The aim of this work was to study the influence of Zn on the formation of nanostructure in Fe73.5−xZnxCu1Nb3Si13.5B9 (x = 1, 3, 5) ribbons prepared by the melt-spinning technique. X-ray diffraction measurements proved amorphous state of the sample with x = 1. The sample with x = 3 contains a small fraction of Fe3Si phase and the sample with x = 5 is in nanocrystalline state with the average grain size of about 25 nm. The reduced radial distribution function G(r) was calculated for local structure investigation. Increasing Zn content enhances crystallization during solidification which leads to increase of magnetocrystalline anisotropy and consequently to increase of coercivity.

Ab initio investigation of local magnetic structures around substitutional 3 d transition metal impurities at cation sites in III–V and II–VI semiconductors

The local magnetic structures around substitutional 3 d transition metal impurities at cation sites in zinc blende structures of III–V (GaN, GaAs) and II–VI (ZnTe) semiconductors are investigated by using a spin-polarized density functional theory. We find that Cr-, Co-, Cu-doped GaN, Cr-, Mn-doped GaAs and Cr-, Fe-, Ni-doped ZnTe are half metallic with 100% spin polarization. The magnetic moments due to these 3 d transition metal (TM) ions are delocalized quite significantly on the surrounding ions of host semiconductors. These doped TM ions have long range interactions mediated through the induced magnetic moments in anions and cations of host semiconductors. For low impurity concentrations Mn in GaAs also has zero magnetic moment state due to Jahn–Teller structural distortions. Based upon half metallic character and delocalization of magnetic moments in the anions and cations of host semiconductors these above mentioned 3 d TM-doped GaN, GaAs and ZnTe seem to be good candidates for spintronic applications.

X-ray micro- fluorescence, diffraction and absorption spectroscopy for local structure investigation of a radioactive zinc ferrite deposit

X-ray micro- fluorescence (μXRF), diffraction (μXRD) and absorption spectroscopy (μXAS) techniques have been used to investigate the micro-crystalline and chemical structure of a radioactive zinc ferrite corrosion deposit phase formed on a zirconium dioxide substrate. Micro- fluorescence provides structural information based on the elemental distribution analysis, μXRD allows the determination of lattice parameters of crystalline compounds while μXAS yields data related to the atomic environment, such as coordination number and the distances to the nearest neighbours. The μXAS and the μXRD results are compared including a discussion of precision and accuracy of both techniques.

EPR investigation of local structure for [Mn(H 2O) 6] 2+ cluster in [M(H 2O) 6]XCl 6:Mn 2+ (M = Zn, Mg, Cd, Ca; X = Pt, Sn) systems at different temperatures

A theoretical method for studying the inter-relation between the local structure and EPR spectra is established by diagonalizing the complete energy matrices. For [M(H 2O) 6]XCl 6:Mn 2+ (M = Zn, Mg, Cd, Ca; X = Pt, Sn) systems, the calculated results demonstrate that the local structures around the octahedral Mn 2+ centers in the doped systems are very similar despite of the host crystals being different. Furthermore, it is shown that the EPR zero-field parameter D depends simultaneously on the local structure parameters R and θ while ( a − F) depends mainly on R, whether the doped systems are at liquid-nitrogen temperature or room temperature.

Molecular dynamics investigation of dynamical heterogeneity and local structure in the supercooled liquid and glass states of Al

Molecular dynamics simulations are performed to study the structure and dynamical heterogeneity in the liquid and glass states of Al using a frequently employed embedded atom potential. While the pair correlation function of the glass and liquid states displays only minor differences, the icosahedral short-range order (ISRO) and the dynamics of the two states are very different. The ISRO is much stronger in the glass than in the liquid. It is also found that both the most mobile and the most immobile atoms in the glass state tend to form clusters, and the clusters formed by the immobile atoms are more compact. In order to investigate the local environment of each atom in the liquid and glass states, a local density is defined to characterize the local atomic packing. There is a strong correlation between the local packing density and the mobility of the atoms. These results indicate that dynamical heterogeneity in glasses is directly correlated to the local structure. We also analyze the diffusion mechanisms of atoms in the liquid and glass states. It is found that for the mobile atoms in the glass state, initially they are confined in the cages formed by their nearest neighbors and vibrating. On the time scale of $\ensuremath{\beta}$ relaxation, the mobile atoms try to break up the cage confinement and hop into new cages. In the supercooled liquid states, however, atoms continuously diffuse. Furthermore, it is found that on the time scale of $\ensuremath{\beta}$ relaxation, some of the mobile atoms in the glass state cooperatively hop, which is facilitated by the stringlike cluster structures. On the longer time scale, it is found that a certain fraction of atoms can simultaneously hop, although they are not nearest neighbors. Further analysis shows that these hopping atoms form big and more compact clusters than the characterized most mobile atoms. The cooperative rearrangement of these big compact clusters might facilitate the simultaneous hopping of atoms in the glass states on the long time scale.

Investigation of local flame structures and statistics in partially premixed turbulent jet flames using simultaneous single-shot CH and OH planar laser-induced fluorescence imaging

We report on the application of simultaneous single-shot imaging of CH and OH radicals using planar laser-induced fluorescence (PLIF) to investigate partially premixed turbulent jet flames. Various flames have been stabilized on a coaxial jet flame burner consisting of an outer and an inner tube of diameter 22 and 2.2 mm, respectively. From the outer tube a rich methane/air mixture was supplied at a relatively low flow velocity, while a jet of pure air was introduced from the inner one, resulting in a turbulent jet flame on top of a laminar pilot flame. The turbulence intensity was controlled by varying the inner jet flow speed from 0 up to 120 m/s, corresponding to a maximal Reynolds number of the inner jet airflow of 13,200. The CH/OH PLIF imaging clearly revealed the local structure of the studied flames. In the proximity of the burner, a two-layer reaction zone structure was identified where an inner zone characterized by strong CH signals has a typical structure of rich premixed flames. An outer reaction zone characterized by strong OH signals has a typical structure of a diffusion flame that oxidizes the intermediate fuels formed in the inner rich premixed flame. In the moderate-turbulence flow, the CH layers were very thin closed surfaces in the entire flame, whereas the OH layers were much thicker. In the high-intensity-turbulence flame, the CH layer remained thin until it vanished in the upper part of the flame, showing local extinction and reignition behavior of the flame. The single-shot PLIF images have been utilized to determine the flame surface density (FSD). In low and moderate turbulence intensity cases the FSDs determined from CH and OH agreed with each other, while in the highly turbulent case a locally broken CH layer was observed, leading to a significant difference in the FSD results determined via the OH and CH radicals. Furthermore, the means and the standard deviations of CH and OH radicals were obtained to provide statistical information about the flames that may be used for validation of numerical calculations.

Investigation of optical spectra and local structure for (CrF6)3− cluster in Cs2NaAlF6:Cr3+ and Cs2NaGaF6:Cr3+ systems

To investigate the local structure of the (CrF6)3− cluster for Cr3+ in Cs2NaAlF6 and Cs2NaGaF6, the unified calculations of the whole EPR, optical spectra are made based on the 120×120 complete energy matrices which are constructed on the basis of the complete set of the basis ∣J, MJ〉. The results demonstrate that Cr3+ substitute for the two inequivalent M3+ sites rather than the Na+ or Cs+, which accord with the conclusion of several experiments. Simultaneously, the local structure parameters are determined and the relationship between the structure and the temperature has been discussed.

Investigation of local lattice structure around Cr3+ ions at the trigonal and tetragonal sites in RbCdF3: Cr3+ crystal

The local lattice structure and EPR, optical spectra for Cr3+ doped in RbCdF3 crystal have been studied by diagonalizing the complete energy matrices. The results show that the local structure of the Cr3+ ions in RbCdF3 exhibits a compressed distortion at the trigonal and tetragonal sites. The compressed distortion can be ascribed to the fact that the radius of Cr3+ ion is smaller than that of Cd2+ ion, and therefore Cr3+ ion will draw the fluorin ligands inwards. The variational ranges of the local structural parameters for Cr3+ doped in RbCdF3 crystal R = 1.9491 Å ∼ 1.9814 Å, θ = 55.234° ∼ 55.286° at the trigonal site and R 1 = 1.8617 Å ∼ 1.8928 Å, R 2 = 1.9527 Å ∼ 1.9851 Å at tetragonal site are obtained respectively, and the EPR and optical spectra agree well with the experimental results.

In silico local structure approach: A case study on Outer Membrane Proteins

The detection of Outer Membrane Proteins (OMP) in whole genomes is an actual question, their sequence characteristics have thus been intensively studied. This class of protein displays a common beta-barrel architecture, formed by adjacent antiparallel strands. However, due to the lack of available structures, few structural studies have been made on this class of proteins. Here we propose a novel OMP local structure investigation, based on a structural alphabet approach, i.e., the decomposition of 3D structures using a library of four-residue protein fragments. The optimal decomposition of structures using hidden Markov model results in a specific structural alphabet of 20 fragments, six of them dedicated to the decomposition of beta-strands. This optimal alphabet, called SA20-OMP, is analyzed in details, in terms of local structures and transitions between fragments. It highlights a particular and strong organization of beta-strands as series of regular canonical structural fragments. The comparison with alphabets learned on globular structures indicates that the internal organization of OMP structures is more constrained than in globular structures. The analysis of OMP structures using SA20-OMP reveals some recurrent structural patterns. The preferred location of fragments in the distinct regions of the membrane is investigated. The study of pairwise specificity of fragments reveals that some contacts between structural fragments in beta-sheets are clearly favored whereas others are avoided. This contact specificity is stronger in OMP than in globular structures. Moreover, SA20-OMP also captured sequential information. This can be integrated in a scoring function for structural model ranking with very promising results.

Investigation of Local Structure and Dynamics in Li3xLa2/3-XTiO3 Perovskite by High Field 7Li MAS NMR

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Insight into Doping Effects in Apatite Silicate Ionic Conductors

AbstractNovel apatite‐type silicates are attracting considerable interest as a new family of oxide‐ion conductors with potential use in fuel cells and ceramic membranes. Combined computer modeling and X‐ray absorption (EXAFS) techniques have been used to gain fresh insight, at the atomic level, into the site selectivity and local structures of a wide range of dopants in these apatite materials. The results indicate that an unusually broad range of dopant ions (in terms of size and charge state) can substitute for La in the La9.33Si6O26 apatite, in accord with current experimental data. The range is much wider than that observed for doping on a single cation site in most other oxide‐ion conductors, such as the perovskite LaGaO3. In addition, our local structural investigation demonstrates that this dopant behavior is related to the flexibility of the silicate substructure, which allows relatively large local distortion and alteration of the site volumes. This could be a key factor in the high oxide‐ion conductivity exhibited by these apatite silicates. Indeed, the breadth of possible doping regimes in these novel materials provides new opportunities to design and optimize the conduction properties for fuel cell electrolytes.