Volume 57, Nº 7 (2016)

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.

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 keV 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 work was performed using a complex VEPP-3/VEPP-4.

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 2p_π AO of the Nα_(1,2) and Сα atoms make a predominant contribution to the LUMO. The 2p_π AO of the Nα_(1,2) atoms mainly contribute to the boundary LUMO with the energy ~–2.3 eV.

In the work X-ray K edges of chromium dichalcogenides CuCr_1-xM_x^′S₂ (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 CuCr_1-xM_x^′S₂ and MCrX₂.

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 TiK 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 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.

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.

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.

Colloidal quantum dots of the CdSe family have been studied by X-ray absorption near edge structure (XANES) spectroscopy and computer modelling. CdK 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 CdK edge in CdSe particles, above the MnK edge in CdSe:Mn particles, above the CoK 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.

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 Mössbauer 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.

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 present study deals with the electronic structure of the bioactive anticancer drugs based on platinum(II) complexes: cisplatin PtC_l2(NH₃)₂, carboplatin PtC₆H₁₂N₂O₄ and oxaliplatin PtC₈H₁₄N₂O₄, which are being used in cancer treatment. The purpose of the work was to examine the molecular and electronic structure of platinum(II) coordination complexes when they undergo hydrolysis, which is crucial in order to better understand their antitumor properties. The density functional theory (DFT) was used to investigate the electronic structure of 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 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 P2/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.