Home – Home – Jornals – Journal of Structural Chemistry 2016 number 7

We describe the development of activity at the Siberian Center for Synchrotron and Terahertz Radiation at Budker Institute of Nuclear Physics (BINP), SB RAS, since 1974, when the history of experiments with synchrotron radiation (SR) in the world was just beginning - there were no dedicated sources of radiation and works can be carried out at several nuclear centers in the world. BINP made a significant contribution to the development of synchrotron radiation sources, and SB RAS institutes did their part for development of SR application to problems of chemistry, catalysis, biology, geology and materials science. The experiments were made at VEPP-3/VEPP-4 installation.

The potent equipment of the shared-use center “Siberian Synchrotron and Terahertz Radiation Center” at Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (BINP SB RAS) enables conduction of time-resolved X-ray diffraction experiments using synchrotron radiation of the VEPP-3/VEPP-4 storage rings. These experiments are performed mostly for institutions of the Siberian Branch of the Russian Academy of Sciences (SB RAS). The experiments yielded novel techniques, which have been implemented for investigation into the dynamics of the nucleation and formation of nanoparticles under explosion and shock wave impact with a nanosecond-scale time resolution (the X-ray exposure time is 73 ps), dynamics of structural transformations in chemical reactions, and kinetics of chemical reactions during gasless combustion (SHS) with a millisecond-scale time resolution, obtaining structural information about the state of catalysts and so on.

Residual stresses in rolled tungsten after pulsed irradiation with a plasma and an electron beam at the GOL-3 facility were measured. The mechanical stresses were derived from the strain, which was measured by the change in the interplanar distance in different directions. The interplanar distance was gaged from the shift of the peak of diffraction scattering of X-rays. The measured tension turned out to be a tensile stress along the surface. The tension along the direction of rolling and grinding was approximately three times larger than that in the perpendicular direction. The work was carried out at the VEPP-3/VEPP-4 complex.

Modernization of the experimental station mounted on the beamline No.2 of VEPP-3 synchrotron radiation electron storage ring at Siberian Synchrotron and Terahertz Radiation Center and intended for X-ray diffraction studies of the structure and phase composition of functional materials with high angular resolution and the possibility of using the effect of resonance scattering has been done. In operating mode the diffractometer of the beamline is equipped with a perfect flat analyzer crystal Ge (111), located in front of the detector. XRD patterns can be obtained in the range of photon energies from 7 to 18 keV (or wavelength range ~0.18 ÷ 0.07 nm). The angular range of the X-ray registration is limited to 2θ = 140 °.

The brief review has been presented about the application of X-ray fluorescent analysis using synchrotron radiation (storage ring VEPP-3, BINP SB RAS) for determination of elemental composition of the samples of different nature - biological and geological samples, objects of environment, archeological objects, and new materials. The feature of the presented research is the employment of the unique properties of synchrotron radiation, which allow analyzing samples of small mass (of the order of several milligrams), and also scanning core of bottom sediments with high resolution (less than 1 mm) that is not practical to realize by traditional analysis methods.

The study of the electronic structure of H₂Pc was carried out to examine the structure of the lowest unoccupied molecular orbitals (LUMO) of molecule phthalocyanine by X-ray absorption spectroscopy using quantum-chemical calculations. The theoretical calculations were performed on the stationary theory (frozen orbital approximation, Z +1 model) and time-dependent density functional theory (TDDFT). A consideration of K -edges absorption spectra of carbon and nitrogen in the common scale of binding energies allows estimating the contributions of AO of all phthalocyanine atoms to the LUMO, defining the sequence of levels, the binding energies of the corresponding levels, and also the character of electronic interactions between individual atoms. It was shown that the best agreement between the experimental and theoretical pre-edge structures of the absorption spectra of nitrogen and carbon for H₂Pc is observed in the case of the application of stationary density functional theory in Z +1 model to account for an X-ray hole. In this case the 2 p _p AO of the Na_(1,2) and Сa atoms make a predominant contribution to the LUMO. The 2 p _p AO of the Na _(1,2) atoms mainly contribute to the boundary LUMO with the energy ~ -2.3 eV.

Cu(II) acetate-bipyridine complex has been synthesized. A series of experimental and theoretical spectroscopic studies was carried out for the freshly prepared sample. The local atomic and electronic structure was theoretically analyzed based on functional density theory and the structural models of the complex was obtained for various solvents. IR and XANES spectra were experimentally measured and modelled in the framework of functional density theory in a generalized gradient approximation to provide information on the chemical bond and local surroundings of copper. The powder X-ray pattern of the Cu(II) complex was obtained. The measured ESR spectra of the acetate-bipyridine complex at room temperature for the solid sample and solution in DMF confirms the formation of the mononuclear square planar complex.

In the work X-ray K-edges of chromium dichalcogenides (M = V, Fe; x = 0-0.40) and MCrX₂ (M = Cu, Ag, Na; X = O, S, Se) were studied experimentally and theoretically. Comparison of fine structures of experimental XANES spectra obtained using a synchrotron radiation source and theoretical absorption spectra modelled using FDMNES software package allows one to study the influence of types of intercalate M, chalcogene X and also the effect of the cation substitution of chromium atoms by vanadium and iron on XANES structure of K-edges in and MCrX₂.

Changes of the structure and phase composition occurring during the interaction of copper and its alloys in the solid-state phase with the liquid melts of indium, gallium and tin are considered. It is shown that the phase and morphological composition of interaction products depends on the relations between the rates of diffusion and the rates of reagent dissolution. Structural transformations that take place during contact melting and eutectic crystallization in the zones of indium - tin and indium - bismuth contacts are also considered. A hypothesis concerning the nature and microstructure of eutectics is proposed.

A local atomic structure around titanium positions in Ti-bearing hibonite (CaAl₁₂O₁₉) has been studied. The structural models of substitution of different substitution defects Ti-Al in hibonite by titanium atoms have been considered. Optimization of structural models of hibonite has been done by means of density functional theory calculations using pseudopotential approximation as implemented in VASP 5.3 code. Gibbs free energies analysis has shown that models of substitution of M2 and M4 aluminum positions by titanium atoms are the most probable. For the most probable structural models of Ti-bearing hibonite theoretical X-ray absorption near-edge structure (XANES) spectra near the titanium K -edge have been calculated. Significant differences in theoretical XANES spectra calculated for different structural models with non-optimized and optimized atomic structure have been demonstrated. Changes in the intensity of pre-edge structure of Ti K -XANES spectra for different substitution models of aluminum by titanium have been observed which relate to different titanium coordination in structural models. Energy shift of spectral features towards lower energy for optimized models implies increase of interatomic distances in local surroundings of Ti absorbing atoms.

The behavior of Li-exchanged natrolite Li_1.92Na_0.10[Al_2.02Si_2.98O₁₀]x2H₂O at compression in penetrating (water-containing) medium was studied by in situ synchrotron powder diffraction in diamond anvil cell up to 2.5 GPa. Within 0-1.3 GPa the compression is almost isotropic, and upon the further pressure increase the sample undergoes additional hydration, leading to abrupt volume expansion by 22%, a record value for natrolite. In the proposed model for the high-pressure phase Li₂[Al₂Si₃O₁₀]x6H₂O the Li⁺ cations have no contact with the framework O-atoms and are surrounded by "water-jacket" in the form of semi-octahedron (tetragonal pyramid) composed of five H₂O molecules. Such polyhedra, lining up along the channel axis, are joined through their edges and create a "water" column expanding the structure.

The behavior of K-exchanged gonnardite K_2,18Na_0,04Ca_0,02(H₂O)_2,2 [Al_2,26Si_2,74O₁₀] at compression in penetrating water-containing medium was studied by synchrotron powder diffraction in diamond anvil cell. In contrast to the initial gonnardite, which exhibits the transition to high-hydrated paranatrolite at elevated humidity, its K-exchanged form is not capable of over-hydration even at high pressure. Within the whole studied pressure range (up to 4.8 GPa) the sample experiences the compression. At 3.5-4 GPa the compression anomaly is observed, which is interpreted as a phase transition accompanied by the symmetry lowering from tetragonal to monoclinic. The high-pressure structure evolution of K-exchanged forms of gonnardite and natrolite is compared; the difference in their behavior is explained by distinct configuration of the framework water-cation subsystem.

The formation of the high-pressure hydrous phase Mg₃Si₄O₁₀(OH)₂xxH₂O (10 Å phase) through the reaction ‘talc+water’ at 450°C and 4 GPa was studied using diamond anvil cell. The powder diffraction measurements in situ , performed at the Siberian Center of Synchrotron and Terahertz Radiation (SSTRC), were applied to refine the lattice parameters, atomic coordinates and the occupancy of interlayer H₂O site in the structure of 10 Å phase at 450°C and 4 GPa. The lattice parameters are a = 5.234(1), b = 9.053(2), c = 10.87(1) Å, β = 99.2(1)^о, and V = 508.5(6) ų (space group C2/m). The results of Rietveld refinement show the best fit for the trioctahedral mica structure with split position Ow of the interlayer H₂O molecule. The half occupancy of the Ow site corresponds to one H₂O molecule per formula unit.

Nanocomposites based on PtPd-nanoparticles with chemical ordering like disordered solid solution on surface of multilayer graphene have been prepared through thermal shock of mechanically obtained mixture of double complex salt [Pd(NH₃)₄][PtCl₆] and different carbon materials - exfoliated graphite, graphite oxide and graphite fluoride. An effect of original carbon precursors on formation of PtPd bimetallic nanoparticles was studied using X-ray absorption spectroscopy (XAFS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was shown that the distribution of bimetallic nanoparticles over the multilayer graphene surface as well as the particles size distribution is controlled by the graphene precursors. For all nanocomposites, the surface of the nanoparticles was found to be Pd-enriched. In case when the thermal exfoliated graphite and graphite oxide were used as the graphene precursors a thin graphitized layer covered the nanoparticles surface. Such a graphitized layer was not observed in the nanocomposite, which used the fluorinated graphite as the precursor.

Ge K-edge EXAFS (Extended X-Ray Absorption Fine Structure) spectra have been measured for multilayer semiconducting heterosystems containing interacted groups of quantum dots ("molecules from quantum dots") ordered in rings on different stages of their growth depending on topologic parameters and growth conditions. In accordance with our results obtained previously for the quantum dots of SiGe, for the molecules of quantum dots it was found that deformation at the interface leads to decrease in the interatomic distance of Ge-Ge by ~0.03 Å. Effect of heterosystem topology and temperature at different stages of their growth on interlayer diffusion was investigated. It was found that at the first growth stage (growth of "seeded islands" serving as a basis for obtaining the molecules) at 700°C a concentration of Ge atoms in the system is ~38%. With further growth of the vertically-matched quantum dots groups the concentration of Ge increases up to ~43-47% depending on the growth conditions. Comparable analysis of different modes of EXAFS measurements was performed to determine precisely structural parameters of heterosystem SiGe with different thickness grown on Si(100) surface.

In the work the results of structural studies of nanocomposite systems based on ZnS:Cu (5 at.% and 10 at.%) deposited by explosive evaporation on porous anodic aluminum oxide matrices fulfilled by EXAFS and X-ray phase analysis techniques have been presented. The composites under study are promising for applications in electroluminescent light sources. The results of the studies of emission intensity of light sources depending on frequency and amplitude of exciting field have also been presented.

The microwave synthesis of quantum dots based on CdS has been performed, the temperature ( T 180°C and 150°C) and synthesis duration (10 min and 5 min) have been varied. The analysis of the peak broadening in X-ray diffraction has shown that the average particle size in the synthesized samples is 10.02 nm for the CdS _{T = 180°C} sample and 5.22 nm for the CdS _{T = 150°C} sample. For both synthesis temperatures particles of sphalerite phase are formed but the sample CdS _{T = 180°C} contained some impurity of wurtzite phase too. Cd K -XANES spectra in the standard samples and quantum dots have been recorded using a Rigaku R-XAS X-ray absorption laboratory spectrometer. The theoretical analysis of the Cd K -XANES spectra of bulk samples of CdS and CdS nanoparticles has been performed. It has been shown that the theoretical difference spectra between bulk CdS and CdS with decreased lattice parameters demonstrate the same tendency as the experimental difference spectra between bulk CdS and the quantum dot samples under study. It has been shown that the theoretical Cd K -edge HERFD-XANES spectrum in CdS demonstrates considerably more detailed structure pointed to the need of the analysis of experimental Cd K -edge HERFD-XANES spectra to pick out more precise information on local atomic structure parameters of small semiconducting quantum dots.

Colloidal quantum dots of the CdSe family have been studied by X-ray absorption near edge structure (XANES) spectroscopy and computer modelling. Cd K -edge XANES spectra in colloidal quantum dots based on varisized CdSe nanoparticles have been recorded. Atomic structure of CdSe particles and also CdSe particles doped by transition metal atoms Mn and Co has been modelled based on the density functional theory. The embedding of the doping atoms is shown to result in considerable changes in the local atomic structure of CdSe particles. XANES spectra have been calculated above the Cd K -edge in CdSe particles, above the Mn K -edge in CdSe:Mn particles, above the Co K -edge in CdSe:Co particles. The sensitivity of XANES spectroscopy to small changes in structural parameters of the nanoparticles of CdSe family has been demonstrated that furnishes an opportunity to apply it for the verification of atomic structure parameters around positions of cadmium and doping atoms of transition metals in quantum dots based on CdSe.

The synthesis conditions of multi-walled carbon nanotubes (MWCNTs) indirectly determine their application potential through the decisive role in the characteristics of individual tubes: diameter distribution, structure and defectiveness of graphene walls, the amount of metal impurities and amorphous carbon. In the present work, we have studied the influence of the catalyst composition and synthesis conditions on the diameter distribution and the structure of nanotube walls. We have observed the influence of the particle size for MWCNT synthesis ( i.e. size effect) on catalytic activity by ex situ and in situ techniques: in situ X-ray diffraction on synchrotron radiation (SRXRD), gas chromatography, and ex situ transmission electron microscopy. The data obtained by in situ SRXRD are in agreement with the results collected using laboratory tubular fix-bed catalytic reactor allowing thereby extending the applicability of the approach. For the first time we have shown the increase of the fraction of graphene walls in the total MWCNT diameter with time.

Magnetic nanoparticles and those doped with rare-earth metal ions having spinel structure were synthesized, possessing the average particles size of 11.3-13.4 nm. According to Mossbauer spectroscopy data it can be concluded that prepared iron oxide nanoparticles are γ-Fe₂O₃. For materials containing rare-earth elements the decrease of octahedral component surface was observed in comparison to non-doped material, what can be explained by Eu³⁺, Sm³⁺ и Gd³⁺ ions occupying the octahedral position.

The crystal, local and electronic structure of complex oxides Ln₂Hf₂O₇ (Ln = Gd, Tb, Dy) formed as result of annealing of amorphous mixed hydroxides LnHf(OH)₇x n H₂O (precursors) have been studied using a set of modern local-sensitive techniques of structural analysis based on the interaction of synchrotron radiation with condensed matter (XAFS spectroscopy, PDF analysis, anomalous X-ray diffraction). It was shown that the thermal treatment of precursors in the temperature range 600-700°C/3 h induces the formation of nanocrystallites with the fluorite structure characterized by the considerable inequivalence of local surrounding of Ln³⁺ and Hf⁴⁺ cations. It was found that the cation ordering of the pyrochlore type takes place in nanocrystals of gadolinium hafnate Gd₂Hf₂O₇ and terbium hafnate Tb₂Hf₂O₇. The phase transition fluorite - pyrochlore goes through the formation of the pyrochlore nanodomains in the matrix of well-crystallized fluorite. In the case of Gd₂Hf₂O₇ the formation of the pyrochlore local structure is completed at annealing temperature ~1000-1200°C/3 h and at > 1300°C/3 h the pyrochlore phase is detected by the diffraction techniques. In Tb₂Hf₂O₇ the process of the pyrochlore phase formation exhibits the more complex behavior. Nanocrystals of dysprosium hafnate Dy₂Hf₂O₇ retain the structure of defect fluorite in the whole temperature range of the heat treatment (up to 1600°C).

In this paper, a study of pure and doped samarium magnetite nanoparticles synthesized using a microwave synthesis in aqueous solution was performed. The shape, size and structure of the pure and samarium doped magnetite nanoparticles were determined by X-ray diffraction, transmission electron microscopy, X-ray absorption spectroscopy and Mössbauer spectroscopy. The magnetic properties of the nanoparticles were investigated using a vibrating sample magnetometer. It was found that the samarium doped magnetite nanoparticles were superparamagnetic with high saturation magnetization. The doping with a small amount of samarium allowed to reduce the size of nanoparticles, their size distribution, increase resistance to oxidation and improve their magnetic characteristics.

The use of the modern installations with the synchrotron radiation allowed obtaining the information about the dynamics of rapid transformation of adamantane into diamond within 2 ms under shock-wave action with nanosecond time resolution. The yield of diamond was 30%. An explanation of adamantane-diamond transformation is proposed. Hydrogen evolved during adamantane decomposition easily diffuses over diamond lattice. However, during synthesis time (~1 μs) hydrogen does not have enough time to go out of diamond particles. Experiment was made at accelerate complex VEPP-3/VEPP-4.

The present study deals with the electronic structure of the bioactive anticancer drugs based on platinum (II) complexes: cisplatin PtCl₂(NH₃)₂, carboplatin PtC₆H₁₂N₂O₄ and oxaliplatin PtC₈H₁₄N₂O_4, which are being used in cancer treatment. The purpose of the work wasto examine the molecular and electronic structure of platinum (II) coordination complexes when they undergo hydrolysis, which is crucialin order to better understand their antitumor properties. The density functional theory (DFT) was used to investigate the electronic structureof the platinum (II) complexes under study. The process of hydrolysis was simulated, and the structure and geometry of hydrolyzed platinum complexes were determined. The electronic structure, energy levels of occupied and unoccupied MOs and the distribution of the total and partial electron density of states (DOS) were shown and the UV-Vis and oscillation spectra of the hydrolyzed platinum(II) complexes were calculated. The theoretical calculations were verified by the experimentally obtained data by applying the method of X-ray absorption at PtL₃-edge as well as UV-Vis and IR spectroscopic techniques.

The compressibility of γ-K₂CO₃ within the pressure range of 0.001-23.3 kbar and room temperature was determined by in situ synchrotron powder diffraction measurements in diamond anvil cell. The modification of the diffraction pattern was fixed at P > 23.3 kbar. This modification can be explained by a reconstructive phase transition. The amorphization of the high pressure phase was fixed on decompression.

The work is devoted to the experimental study of coronene C₂₄H₁₂ at high pressure and room temperature using in situ X-ray diffraction in a diamond anvil cell. The high-pressure phase P 2/ m of coronene was found at 0.9 GPa, the PV -equation of state for P2/m coronene phase was defined to 4 GPa: K₀ = 10.8(3) GPa, K₀'= 7. At 5.9 GPa partial amorphization of coronene was observed. After the decompression to ambient pressure the high-pressure phase P2/m was preserved, that can be related with partial amorphization.