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Proceedings of the 13th International Conference on Synchrotron Radiation Instrumentation, SRI2018, Taipei, Taiwan, 10 Jun 2018 - 15 Jun 2018; AIP conference proceedings 2054, 060031 (2019). doi:10.1063/1.5084662, Beamline P64 at PETRA III is dedicated to x-ray absorption spectroscopy experiments which require high flux, like quick extended x-ray absorption fine structure spectroscopy on the sub-second time scale, high-resolution resonant emission spectroscopy, and x-ray absorption fine-structure spectroscopy of highly diluted systems. The beamline is installed at the high-energy storage ring PETRA III. The source is a 2 m-long undulator. The beamline covers an energy-range from 4 keV to 44 keV, which was required by the user community. Mirrors can be used to reduce the intensity of higher harmonics, and to focus the beam. A conventional photo-diode and a 100-pixel high-purity Ge-detector are used in fluorescence extended x-ray absorption fine-structure spectroscopy for diluted samples., Published by AIP Publ., Melville, NY

Polycrystalline CuMo 1 − x W x O 4 solid solutions were studied by resonant X-ray emission spectroscopy (RXES) at the W L 3 -edge to follow a variation of the tungsten local atomic and electronic structures across thermochromic phase transition as a function of sample composition and temperature. The experimental results were interpreted using ab initio calculations. The crystal-field splitting parameter Δ for the 5d(W)-states was obtained from the analysis of the RXES plane and was used to evaluate the coordination of tungsten atoms. Temperature-dependent RXES measurements were successfully employed to determine the hysteretic behaviour of the structural phase transition between the α and γ phases in CuMo 1 − x W x O 4 solid solutions on cooling and heating, even at low ( x 0.10 ) tungsten content. It was found that tungsten ions have octahedral coordination for x > 0.15 in the whole studied temperature range (90-420 K), whereas their coordination changes from tetrahedral to octahedral upon cooling for smaller ( x ≤ 0.15 ) tungsten content. Nevertheless, some amount of tungsten ions was found to co-exists in the octahedral environment at room temperature for x 0.15 . The obtained results correlate well with the color change in these solid solutions.

X-ray diffraction and x-ray absorption spectroscopy at the Cu K-edge were used to study the atomic structure in copper nitride (Cu3N) thin films. Textured nanocrystalline films are obtained upon dc magnetron sputtering on substrates heated at about 190 °C, whereas amorphous films having strongly disordered structure already in the second coordination shell of copper are deposited in the absence of heating.

Microcrystalline and nanocrystalline (6 nm) CuO were studied in situ by the Cu K-edge X-ray absorption spectroscopy as a function of pressure (0-20 GPa) and temperature (10-300 K). Pressure dependence of X-ray absorption near edge structure (XANES) was interpreted within the full-multiple-scattering formalism based on the relaxed atomic structure determined by ab initio linear combination of atomic orbital (LCAO) calculations. Temperature dependence of the mean-square relative displacement (MSRD) for the four shortest Cu–O distances was obtained from the analysis of extended X-ray absorption fine structure (EXAFS) and described by the correlated Einstein model with the characteristic temperature θ E =589 K. It was found that the thermal motion of copper and four oxygen atoms forming square-planar coordination is strongly correlated.

The experiment at HASYLAB/DESY was performed within the project I-20180036 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Filipe Correia is grateful to the Fundação para a Ciência e Tecnologia (FCT, Portugal) for the Ph.D. Grant SFRH/BD/111720/2015 . Joana Ribeiro is grateful to the Project WinPSC - POCI-01-0247-FEDER-017796, for the research grant, co-funded by the European Regional Development Fund (ERDF) , through the Operational Programme for Competitiveness and Internationalisation (COMPETE 2020), under the PORTUGAL 2020 Partnership Agreement. The authors acknowledge the funding from the following institution Fundação para a Ciência e Tecnologia (FCT, Portugal) /PIDDAC through the Strategic Funds project reference UID/FIS/04650/2013. The Spanish Ministry of Economy, Industry, and Competitiveness through the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV-2015-0496), projects No. MAT2017-90024-P (TANGENTS)-EI/FEDER and MAT2015-70850-P (HIBRI2), and the Generalitat de Catalunya through grant 2017-SGR-00488 . M. K. acknowledges the Ph.D. programme in Materials Science from Universitat Autonoma de Barcelona in which she is enrolled., Transparent n-type niobium-doped titanium dioxide thin films (TiO2:1.5 at.%Nb) with pronounced thermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering. The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques. The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Ti and Nb K-edges. A set of radial distribution functions were extracted from the simultaneous analysis of EXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopant atoms modify the local environment of the films, but their average structure remains close to that of the anatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very high absolute Seebeck coefficient (S = 155 μV/K) for n-type TiO2 was achieved with Nb doping, yielding a maximum power factor and thermoelectric figure of merit of 0.5 mW m−1 K−2 and 0.18 at a temperature of 300 K, respectively, for a 150 nm thick film. From frequency-domain thermoreflectance experiments, a thermal conductivity value of 1.3 W m−1 K−1 was obtained for the optimized TiO2:Nb film., Fundo Regional para a Ciência e Tecnologia POCI-01-0247-FEDER-017796; Generalitat de Catalunya 2017-SGR-00488; MAT2015-70850-P,HIBRI2; SEV-2015-0496,MAT2017-90024-P; UID/FIS/04650/2013; European Regional Development Fund; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

We studied powder samples of europium titanates Eu1−x2+Eux3+TiO3+x/2 prepared by sol-gel and coprecipitation methods with subsequent thermal treatment of precursors at different conditions (reducing or oxidizing atmosphere, temperature, exposure time). We have revealed a radical rearrangement in the local, electronic and crystal structure of europium titanates depending on synthesis conditions. The combination of synchrotron X-ray diffraction (s-XRD), X-ray absorption (XANES and EXAFS), infrared and Raman spectroscopies supplemented by photoluminescence and simultaneous thermal analysis was used in our study. It is shown that the combined XANES and thermogravimetric analysis gives clear evidence of a change in the oxidation state of europium cations from Eu2+ to Eu3+. The comparison of s-XRD, XANES, and EXAFS data allowed us to explain the local structure rearrangement during the phase transition from cubic perovskite Eu2+TiO3 (space group P m 3 ¯ m ) to pyrochlore phase Eu23+Ti2O7 (space group F d 3 ¯ m ) through intermediate layered perovskite Eu23+Ti2O7 with monoclinic structure (space group P 2 1 ) under annealing in oxidizing atmosphere. The Raman spectroscopy study pointed to significant changes in the local structure of the anionic sublattice upon the observed phase transitions. The analysis of luminescence spectra has shown that Eu3+ cations occupy positions with low local site symmetry in all synthesized compounds regardless of the type of the crystal structure.

The journal of chemical physics 152(21), 214301 (2020). doi:10.1063/1.5138641 special issue: "ltrafast molecular sciences by femtosecond photons and electrons", Oligonuclear complexes of d4–d7 transition metal ion centers that undergo spin-switching have long been developed for their practical role in molecular electronics. Recently, they also have appeared as promising photochemical reactants demonstrating improved stability. However, the lack of knowledge about their photophysical properties in the solution phase compared to mononuclear complexes is currently hampering their inclusion into advanced light-driven reactions. In the present study, the ultrafast photoinduced dynamics in a solvated [2 × 2] iron(II) metallogrid complex are characterized by combining measurements with transient optical-infrared absorption and x-ray emission spectroscopy on the femtosecond time scale. The analysis is supported by density functional theory calculations. The photocycle can be described in terms of intra-site transitions, where the FeII centers in the low-spin state are independently photoexcited. The Franck–Condon state decays via the formation of a vibrationally hot high-spin (HS) state that displays coherent behavior within a few picoseconds and thermalizes within tens of picoseconds to yield a metastable HS state living for several hundreds of nanoseconds. Systematic comparison with the closely related mononuclear complex [Fe(terpy)2]2+ reveals that nuclearity has a profound impact on the photoinduced dynamics. More generally, this work provides guidelines for expanding the integration of oligonuclear complexes into new photoconversion schemes that may be triggered by ultrafast spin-switching., Published by American Institute of Physics, Melville, NY

The authors thank T. Chauveau (LSPM) for help with Rietveld analysis, A. Jamali (LRCS) for assistance with SEM measurements, and Drs. Y. Tange (SPring-8) and N. Guignot (SOLEIL) for help in synchrotron experiments that were carried out during beamtimes allocated to proposals 2017A1047 & 2018A1121 at SPring-8 and proposal 20170092 at SOLEIL. Ab initio calculations have been performed using Rurik and Arkuda supercomputers. This work was financially supported by the European Union’s Horizon 2020 Research and Innovation Programme under Flintstone2020 project (grant agreement No. 689279). Z.W. thanks the National Science Foundation of China (grant No. 11604159). A.R.O. thanks the Russian Ministry of Science and Higher Education (grant 2711.2020.2 to leading scientific schools)., New boron-rich sulfde B6S and selenide B6Se have been discovered by combination of high pressure – high temperature synthesis and ab initio evolutionary crystal structure prediction, and studied by synchrotron X-ray difraction and Raman spectroscopy at ambient conditions. As it follows from Rietveld refnement of powder X-ray difraction data, both chalcogenides have orthorhombic symmetry and belong to Pmna space group. All experimentally observed Raman bands have been attributed to the theoretically calculated phonon modes, and the mode assignment has been performed. Prediction of mechanical properties (hardness and elastic moduli) of new boron-rich chalcogenides has been made using ab initio calculations, and both compounds were found to be members of a family of hard phases., Horizon 2020 Framework Programme 689279 Ministry of Science and Higher Education of the Russian Federation 2711.2020.2 National Natural Science Foundation of China 11604159 Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Thermochromic phase transition was studied in CuMoO₄ using the Cu and Mo K-edge x-ray absorption spectroscopy in the temperature range of 10–300 K. The hysteretic behavior has been evidenced from the temperature dependence of the pre-edge shoulder intensity at the Mo K-edge, indicating that the transition from brownish-red γ-CuMoO₄ to green α-CuMoO₄ occurs in the temperature range of 230–280 K upon heating, whereas the α-to-γ transition occurs between 200 and 120 K upon cooling. Such behavior of the pre-edge shoulder at the Mo K-edge correlates with the change of molybdenum coordination between distorted tetrahedral in α-CuMoO₄ and distorted octahedral in γ-CuMoO₄. This result has been supported by ab initio full-multiple-scattering x-ray absorption near edge structure (XANES) calculations.

The work was supported by philanthropist MikroTik and administrated by the University of Latvia Foundation. The experiment at HASYLAB/DESY was performed within the project I-20160149 EC., Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Mo K-edge is used to follow the thermochromic γ-to-α phase transition in copper molybdate (CuMoO4). The temperature dependence (10–300 K) of the radial distribution function (RDF) for the Mo–O atom pairs in the first coordination shell of molybdenum atoms is reconstructed by the regularization-like method from the experimental EXAFS spectra. The analysis of the RDFs suggests that the transition occurs gradually within the two-phase coexistence range of 225–275 K. The local environment of molybdenum atoms transforms upon the γ-to-α phase transition from strongly distorted octahedral to less distorted tetrahedral coordination., MikroTik; University of Latvia Foundation; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Physica status solidi / B 255, 1800074 (2018). doi:10.1002/pssb.201800074, Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Mo K-edge is used to follow the thermochromic γ-to-α phase transition in copper molybdate (CuMoO4). The temperature dependence (10–300 K) of the radial distribution function (RDF) for the Mo–O atom pairs in the first coordination shell of molybdenum atoms is reconstructed by the regularization-like method from the experimental EXAFS spectra. The analysis of the RDFs suggests that the transition occurs gradually within the two-phase coexistence range of 225–275 K. The local environment of molybdenum atoms transforms upon the γ-to-α phase transition from strongly distorted octahedral to less distorted tetrahedral coordination., Published by Wiley-VCH, Weinheim

The authors are grateful to Professor Alain Polian for providing the NDAC cell., High-pressure (0–26.7 GPa) Cu K-edge X-ray absorption spectroscopy is used to study possible structural modifications of anti-perovskite-type copper nitride (Cu3N) crystal lattice. The analysis of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), based on theoretical full-multiple-scattering and single-scattering approaches, respectively, suggests that at all pressures the local atomic structure of Cu3N remains close to that in cubic (Formula presented.) phase. Therefore, the transition to metal state above 5 GPa, observed previously using pressure-dependent electrical resistance and optical absorption measurements, is explained by the band gap collapse due to a decrease of the unit cell volume. We found that the lattice parameter of Cu3N is reduced by ≈2% upon increasing pressure up to 26.7 GPa, and the structure is restored upon pressure release., This study was supported by Latvian National Research program IMIS2. The experiment at the SOLEIL synchrotron radiation facility received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) CALIPSO under Grant agreement no. 312284; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

EXAFS spectroscopy is an element-specific method that can provide perhaps the most extensive information on the local atomic structure and lattice dynamics for a broad class of materials. Conventional methods of EXAFS data treatment are often limited to the nearest coordination shells of the absorbing atom due to the difficulties in accurate accounting for the large number of correlated structural parameters that have to be included in the analysis. In this study we overcome this problem by applying novel simulation-based method: reverse Monte Carlo simulations, coupled with the evolutionary algorithm and with a powerful signal processing technique – wavelet transform. This complex approach was applied to the analysis of the W L3-edge and Co K-edge EXAFS spectra of crystalline CoWO4, which exists in antiferromagnetic state below 55 K. Temperature dependence of the local environment up to 4.3 Å around both metal ions was reconstructed in the range from 10 K to 300 K, and the rigidity of the tungstate structure due to zigzag chains of WO6 and CoO6 octahedra was analyzed.

Extended X-ray absorption fine structure (EXAFS) spectroscopy and molecular dynamics (MD) simulations are two complementary techniques widely used to study the atomic structure of materials. Their combined use, known as the MD-EXAFS approach, allows one to access the structural information, encoded in EXAFS, far beyond the nearest coordination shells and to validate the accuracy of the interaction potential models. In this study we demonstrate the use of the MD-EXAFS method for a validation of several force-field models on an example of the cubic-perovskite SrTiO3 and hexagonal wurtzite-type ZnO crystals.

A novel reverse Monte Carlo/evolutionary algorithm scheme was applied to the analysis of the W L3-edge and Mn(Co) K-edges EXAFS spectra from multiferroic MnWO4 and Mn0.7Co0.3WO4. A 3D structural model, consistent with the experimental data, was obtained, and the influence of composition and temperature on the local structure of tungstates is discussed.

Nanostructured tungstates, such as CoWO4 and CuWO4, are very promising catalytic materials, particularly for photocatalytic oxidation of water. The high catalytic activity of tungstate nanoparticles partially is a result of their extremely small sizes, and, consequently, high surface-to-volume ratio. Therefore their properties depend strongly on the atomic structure, which differ significantly from that of the bulk material. X-ray absorption spectroscopy is a powerful technique to address the challenging problem of the local structure determination in nanomaterials. In order to fully exploit the structural information contained in X-ray absorption spectra, in this study we employ a novel evolutionary algorithm (EA) for the interpretation of the Co and Cu K-edges as well as the W L3-edge extended X-ray absorption fine structure (EXAFS) of nanosized CoWO4 and CuWO4. The combined EA-EXAFS approach and simultaneous analysis of the W L3 and Co(Cu) K-edge EXAFS spectra allowed us for the first time to obtain a 3D structure model of the tungstate nanoparticles and to explore in details the effect of size, temperature and transition metal type.

This work has been supported by the Latvian National Research Program IMIS2. The EXAFS experiment has been financed from the European Community's Seventh Framework Programme under grant agreement No. 226716 (Project I-20100098 EC). J.T. also gratefully acknowledges support from the National Science Foundation under the DMREF program Grant No. CHE-1534184., Reverse Monte Carlo simulations coupled with evolutionary algorithm were employed for the analysis of the temperature dependent (10–300 K) Cu K-edge extended X-ray absorption fine structure (EXAFS) spectra of polycrystalline copper nitride (Cu3N) with the goal to extract information on the thermal disorder and interatomic correlations in anti-perovskite-type crystal lattice. The obtained results are discussed in comparison with metallic copper and perovskite-type rhenium trioxide. The analysis of EXAFS spectra suggests that the anisotropy of copper atom vibrations is significantly enhanced upon increasing temperature, leading to pronounced tilting motion of NCu6 octahedra. Strong correlation in the motion of atoms was found along –N–Cu–N– atomic chains but it reduces rapidly with an increase of interatomic distance. Finally, anticorrelated motion of neighboring Cu atoms occurs along Cu–Cu bonds and is consistent with breathing-type motion of NCu6 octahedra., National Science Foundation CHE-1534184; Seventh Framework Programme 226716; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Conventional methods of EXAFS data analysis are often limited to the nearest coordination shells of the absorbing atom due to the difficulties in accurate accounting for the so-called multiple-scattering effects. Besides, it is often difficult to resolve the non-equivalent groups of atoms in a single coordination shell due to strong correlation between structural parameters. In this study we overcome these problems by applying two different simulation-based methods, i.e., classical molecular dynamics (MD) and reverse Monte with evolutionary algorithm (EA), to the analysis of the Zn K-edge EXAFS data for wurtzite-type bulk ZnO. The RMC/EA-EXAFS method allowed us to separate the contributions of thermal disorder and the effect of noncentrosymmetric zinc oxide structure, being responsible for its piezoelectrical and pyroelectrical properties. The MD-EXAFS method allowed us to test the accuracy of several available force-field models, which are commonly used in the MD simulations of ZnO nanostructures.

Non-stoichiometric nickel oxide (Ni 1 − x O) thin films were prepared by DC magnetron sputtering technique in mixed Ar/O 2 atmosphere and studied by synchrotron radiation Ni K-edge x-ray absorption spectroscopy, x-ray diffraction and scanning electron microscopy. The use of advanced modelling technique, combining classical molecular dynamics with ab initio multiple-scattering extended x-ray absorption fine structure calculations, allowed us to describe the structure relaxation and dynamics in nanocrystallites and to estimate their size and the concentration of nickel vacancies.

The electronic, structural and phonon properties of antiferromagnetic triclinic CuWO 4 have been studied using the first-principles spin-polarized linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange–correlation density functional (DFT)/Hartree–Fock (HF) scheme. In addition, the local atomic structure around both Cu and W atoms has been probed using extended X-ray absorption fine structure (EXAFS) spectroscopy. We show that, by using the hybrid DFT–HF functional, one can accurately and simultaneously describe the atomic structure (the unit cell parameters and the atomic fractional coordinates), the band gap and the phonon frequencies. In agreement with our EXAFS results, the LCAO calculations reproduce a strong distortion of both the CuO 6 and the WO 6 octahedra, which occur due to the first-order and second-order Jahn–Teller effects, respectively. We found that the HF admixture of 13–16%, which is implemented in the PBE0–13% and WCGGA–PBE-16% functionals, produces the best result for CuWO 4 . The calculated properties agree well with the available experimental data provided by diffraction, optical, X-ray photoelectron and Raman spectroscopies.

High-pressure phase of boron oxide, orthorhombic \b{eta}-B2O3, has been studied in situ by synchrotron X-ray diffraction to 22 GPa and Raman scattering to 46 GPa at room temperature. The bulk modulus of \b{eta}-B2O3 has been found to be 169(3) GPa that is in good agreement with our ab initio calculations. Raman and IR spectra of \b{eta}-B2O3 have been measured at ambient pressure, all experimentally observed bands have been attributed to the theoretically calculated ones, and the mode assignment has been performed. Based on the data on Raman shift as a function of pressure, combined with equation-of-state data, the Gr\"uneisen parameters of all experimentally observed Raman bands have been calculated. \b{eta}-B2O3 enriched by 10B isotope has been synthesized, and the effect of boron isotopic substitution on Raman spectra has been studied.

Optical measurements were carried out by infrared spectroscopy on AA′3B4O12 A-site ordered quadruple perovskite EuCu3Fe4O12 (microscopic sample) as function of temperature. At 240 K (=TMI), EuCu3Fe4O12 undergoes a very abrupt metal to insulator transition, a paramagnetic to antiferromagnetic transition and an isostructural transformation with an abrupt large volume expansion. Above TMI, optical conductivity reveals a bad metal behavior and below TMI, an insulating phase with an optical gap of 125 meV is observed. As temperature is decreased, a large and abrupt spectral weight transfer toward an energy scale larger than 1 eV is detected. Concurrently, electronic structure calculations for both high and low temperature phases were compared to the optical conductivity results giving a precise pattern of the transition. Density of states and computed optical conductivity analysis identified Cu3dxy, Fe3d and O2p orbitals as principal actors of the spectral weight transfer. The present work constitutes a first step to shed light on EuCu3Fe4O12 electronic properties with optical measurements and ab-initio calculations.

Scandium fluoride (${\mathrm{ScF}}_{3}$), having cubic ${\mathrm{ReO}}_{3}$-type structure, has attracted much scientific attention due to its rather strong negative thermal expansion (NTE) in the broad temperature range from 10 to 1100 K. Here we use the results of diffraction and extended x-ray absorption fine-structure (EXAFS) spectroscopy to interpret the influence of NTE on the temperature dependence of infrared absorption spectra of ${\mathrm{ScF}}_{3}$. Original infrared absorption and EXAFS experiments in a large temperature range are presented and interpreted using ab initio lattice dynamics simulations within and beyond quasiharmonic approximations. We demonstrate that ab initio electronic structure calculations, based on the linear combination of atomic orbitals method with hybrid functionals, are able to reproduce well the experimental values of lattice parameter ${a}_{0}$, band gap ${E}_{g}$, and lattice dynamics in ${\mathrm{ScF}}_{3}$. However, the simulations performed within quasiharmonic approximation fail to reproduce the temperature dependence of two infrared active bands due to the F--Sc--F bending (at 220 ${\mathrm{cm}}^{\ensuremath{-}1}$) and Sc--F stretching (at 520 ${\mathrm{cm}}^{\ensuremath{-}1}$) modes present in the infrared absorption spectra. To overcome this problem, an approach beyond the quasiharmonic approximation is proposed: It accounts for the negative thermal expansion of the lattice and for fluorine atom displacements due to strong F vibrational motion perpendicular to the cubic axes and allows us to explain qualitatively the temperature behavior of infrared spectra of ${\mathrm{ScF}}_{3}$.

Photoluminescence and excitation spectra of microcrystalline and nanocrystalline nickel tungstate (NiWO₄) were measured using UV-VUV synchrotron radiation source. The origin of the bands is interpreted using comparative analysis with isostructural ZnWO₄ tungstate and based on the results of recent first-principles band structure calculations. The influence of the local atomic structure relaxation and of Ni²⁺ intra-ion d–d transitions on the photoluminescence band intensity are discussed.

Physica scripta 91(5), 054003 (2016). doi:10.1088/0031-8949/91/5/054003, Extended x-ray absorption fine structure (EXAFS) spectroscopy combined with reverse Monte Carlo (RMC) and evolutionary algorithm (EA) modelling is used to advance the understanding of the local structure and lattice dynamics of copper nitride (Cu$_3$N). The RMC/EA-EXAFS method provides a possibility to probe correlations in the motion of neighboring atoms and allows us to analyze the influence of anisotropic motion of copper atoms in Cu$_3$N., Published by The Royal Swedish Academy of Sciences, Stockholm

The photoluminescence spectra and luminescence excitation spectra of pure microcrystalline and nano-sized ZnWO4 as well as the Zn x Ni1−x WO4 solid solutions were studied using vacuum ultraviolet (VUV) synchrotron radiation. The samples were also characterized by x-ray powder diffraction. We found that: (i) the shape of the photoluminescence band at 2.5 eV, being due to radiative electron transitions within the [WO6]6− anions, becomes modulated by the optical absorption of Ni2+ ions in the Zn x Ni1−x WO4 solid solutions; and (ii) no significant change in the excitation spectra of Zn0.9Ni0.1WO4 is observed compared to pure ZnWO4. At the same time, a shift of the excitonic bands to smaller energies and a set of peaks, attributed to the one-electron transitions from the top of the valence band to quasi-localized states, were observed in the excitation spectrum of nano-sized ZnWO4.

The electronic, structural and phonon properties of antiferromagnetic wolframite-type NiWO4 have been studied using first-principles spin-polarized LCAO calculations based on the hybrid Hartree-Fock (HF)/density functional (DFT) scheme. The influence of different percentages of HF contribution, i.e. different correlation strength, on the structure and phonon frequencies has been investigated and compared with the available experimental data.

The structure relaxation in nanocrystalline NiO (nano-NiO, 13 nm crystallite size) has been studied by X-ray absorption spectroscopy at the Ni K-edge at 300 K. Conventional single-scattering analysis of the EXAFS signals from the first two coordination shells showed a lattice volume expansion by about 1% and a contraction of the Ni–O bonds by about 0.5% in nano-NiO compared to microcrystalline NiO. A more sophisticated approach, based on a combination of classical molecular dynamics and ab initio multiple-scattering EXAFS theory, allowed us to interpret both static relaxation and lattice dynamics in nano-NiO.

First-principles quantum chemistry calculations within the periodic linear combination of atomic orbitals (LCAO) formalism have been used to probe electronic and phonon properties of crystalline 5d transition metal oxides ReO3, ZnWO4 and CaWO4. The obtained equilibrium crystal structure is in good agreement with known crystallographic data. Rhenium trioxide is correctly predicted to be a metal, whereas both tungstates—a wide gap insulating compounds. The phonon frequencies, calculated by the frozen phonon method, agree rather well with those obtained by infrared and Raman spectroscopies.

ZnWO4 powders, synthesized using co-precipitation technique and annealed in air at different temperatures in the range of 80-800 � C, were studied by Raman and photoluminescence spectroscopy. ZnWO4 single crystal was used for comparison. The interpretation of the observed variations of the Raman spectra and intrinsic photoluminescence band upon annealing is suggested.

Ab initio quantum chemistry calculations of the structural and electronic properties of monoclinic wolframite-type ZnWO 4 crystal have been performed within the periodic linear combination of atomic orbitals (LCAO) method using six different Hamiltonians, based on density functional theory (DFT) and hybrid Hartree-Fock-DFT theory. The obtained results for optimized structural parameters, band gap and partial density of states are compared with available experimental data, and the best agreement is observed for hybrid Hamiltonians. The calculations show that zinc tungstate is a wide band gap material, with the direct gap about 4.6 eV, whose valence band has largely O 2p character, whereas the bottom of conduction band is dominated by W 5d states.

The nanostructured oxide materials such as ZnO, ZrO2, and Y3Al5O12 (YAG) are perspective materials for transparent scintillating and/or laser ceramics. The luminescence properties of single crystals, nanopowders and ceramic were compared. Nominally pure and rare-earth doped nanopowders and ceramics have been studied by means of time-resolved luminescence spectroscopy. The fast blue luminescence band was studied in ZnO ceramics sintering from different raw materials. The luminescence centres of ZrO2:Y were compared in a single crystal, ceramic and nanopowder. It is shown that ceramic sintering parameters have a strong influence on time-resolved luminescence characteristics in cerium-doped YAG. © 2008 Elsevier Ltd. All rights reserved.

The luminescence excitation spectra, luminescence spectra and the nanosecond-scale decay kinetics were studied. The ZnO and ZnO:Al nanopowders were prepared by vaporization-condensation in a solar furnace using different raw powders: commercial, hydrothermal and those obtained by plasma synthesis. Exciton-phonon as well as exciton-exciton interaction processes in nanopowders, a bulk crystal and ZnO ceramics were studied and compared. The fast decay and low afterglow intensity of ZnO nanopowders and ceramics support these materials for scintillators.

International audience; Raman spectra of rhombohedral boron monosulfide (r-BS) were measured under pressures up to34 GPa at room temperature. No pressure-induced structural phase transition was observed, whilestrong pressure shift of Raman bands towards higher wavenumbers has been revealed. IR spectroscopyas a complementary technique has been used in order to completely describe the phononmodes of r-BS. All experimentally observed bands have been compared with theoretically calculatedones and modes assignment has been performed. r-BS enriched by 10B isotope was synthesized,and the effect of boron isotopic substitution on Raman spectra was observed and analyzed.

Ferroelectrics 483(1), 68 - 74(2015). doi:10.1080/00150193.2015.1058687, A novel reverse Monte Carlo/evolutionary algorithm scheme was applied to the analysis of the W L3-edge and Mn(Co) K-edges EXAFS spectra from multiferroic MnWO4 and Mn0.7Co0.3WO4. A 3D structural model, consistent with the experimental data, was obtained, and the influence of composition and temperature on the local structure of tungstates is discussed., Published by Taylor & Francis, London [u.a.]

Nanostructured tungstates, such as CoWO$_{4}$ and CuWO$_{4}$, are very promising catalytic materials, particularly for photocatalytic oxidation of water. The high catalytic activity of tungstate nanoparticles partially is a result of their extremely small sizes, and, consequently, high surface-to-volume ratio. Therefore their properties depend strongly on the atomic structure, which differ significantly from that of the bulk material. X-ray absorption spectroscopy is a powerful technique to address the challenging problem of the local structure determination in nanomaterials. In order to fully exploit the structural information contained in X-ray absorption spectra, in this study we employ a novel evolutionary algorithm (EA) for the interpretation of the Co and Cu K-edges as well as the W L$_{3}$-edge extended X-ray absorption fine structure (EXAFS) of nanosized CoWO$_{4}$ and CuWO$_{4}$. The combined EA-EXAFS approach and simultaneous analysis of the W L$_{3}$ and Co(Cu) K-edge EXAFS spectra allowed us for the first time to obtain a 3D structure model of the tungstate nanoparticles and to explore in details the effect of size, temperature and transition metal type.

A novel reverse Monte Carlo/evolutionary algorithm scheme was applied to the analysis of the W L3-edge and Mn(Co) K-edges EXAFS spectra from multiferroic MnWO4 and Mn0.7Co0.3WO4. A 3D structural model, consistent with the experimental data, was obtained, and the influence of composition and temperature on the local structure of tungstates is discussed.

The atomic and electronic structure of tin tungstates, α-SnWO4, α-Sn1.03W0.99O4 and β-SnWO4 ,w as studied by the W L3-edge X-ray absorption spectroscopy and first-principles linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange-correlation density functional (DFT)/ Hartree–Fock (HF) scheme. It was found that the crystal structure of both α-phases is built up of strongly distorted WO6 octahedra, whereas that of β-SnWO4 is composed of nearly regular WO4 tetrahedra. In addition, there are distorted SnO6 octahedra in both α- and β-phases. The metal–oxygen octahedra distortion is explained by the second-order Jahn–Teller effect. The influence of pressure on the structure of α-SnWO4 and β-SnWO4 was studied in detail based on the calculated equations of state. The compressibility of β-SnWO4 was found to be larger than that of α-SnWO4. The existence of the insulatorto-metal transition was theoretically predicted in α-SnWO4 at about 16 GPa and was explained by a symmetrization of metal–oxygen octahedra leading to a strong interaction of Sn 5s ,W5 d and O 2p states and closing of band gap.