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International audience; Cyclic dinuclear molybdenum(vi) complexes [MoO2(L1–3)]2 (1, 2-α, 2-β and 3) were synthesized through the use of coordination-driven self-assembly of a MoO22+ core and 4-aminobenzoylhydrazone ligands (salicylaldehyde (H2L1), 3-methoxysalicylaldehyde (H2L2) or 4-methoxysalicylaldehyde 4-aminobenzoylhydrazone (H2L3)). Their X-ray diffraction (XRD) analysis revealed that these types of ligands could serve as organic linkers for cis-octahedral complexes containing a MoO22+ core. Mononuclear complexes [MoO2(L1–3)(MeOH)] (1a–3a) and [MoO2(L1–3)(EtOH)] (1b, 2b-α, 2b-β and 3b) were also obtained. In the presence of strong donors, such as dmf, ligand substitution occurred and the structures of 1–3 changed into [MoO2(L1)(dmf)] (1c), [MoO2(L2)(dmf)] (2c) and [MoO2(L3)(H2O)]·dmf (3c·dmf), respectively. The dioxidomolybdenum(vi) complexes were tested for catalytic epoxidation of cyclooctene under eco-friendly reaction conditions by using aqueous tert-butyl hydroperoxide (TBHP) as an oxidant without the addition of an organic solvent. The present study showed much better activity of the dinuclear catalysts than the mononuclear ones due to the weak donor properties of the amino group and high geometric constraints occurring in such small sized self-assembled systems as confirmed by density functional theory calculations.

International audience; The focus of this work was on the synthesis, characterization and catalytic activity of Mo(vi) complexes with hemilabile polydentate ligands that show a high tendency to form discrete small-sized self-assembled structures. A series of mononuclear, [MoO2(L1 or 3)(MeOH)] (1a and 3a) and [MoO2(L1)(EtOH)] (1b), and dinuclear, [MoO2(L1–3)]2 (1–3), complexes was synthesised by using 2-aminobenzoylhydrazone ligands derived from salicylaldehyde (H2L1), 3-methoxy-2-hydroxybenzaldehyde (H2L2) and 4-methoxy-2-hydroxybenzaldehyde (H2L3). Different reaction conditions led to the formation of several crystalline forms of the dinuclear cyclic species [MoO2(L1 or 3)]2 (1-α, 1-β, 1-γ, 1·CH3CN, 3-α, 3-β and 3·2CH3CN), a feature which is observed for the first time in the case of the metallosupramolecular compounds incorporating cis-MoO22+ subunits. These complexes were tested as catalysts for cyclooctene epoxidation under eco-friendly reaction conditions by using aqueous tert-butyl hydroperoxide as an oxidant without the addition of an organic solvent. The use of the hemilabile ligands provided the opportunity to employ relatively stable coordinatively saturated dinuclear Mo(vi) complexes, which in turn offered access to highly reactive pentacoordinated species in the presence of olefins. Lastly, the hemilabile ligand induced catalytic enhancement was addressed by using density functional theory calculations.

The present chapter gives an overview of the application of Attenuated total reflection - Infrared spectroscopy (ATR-IR) to the environmentally important mineral - aqueous electrolyte interface. At these interfaces the important adsorption processes occur that limit the availability of potentially toxic solutes. These retention processes may retard for example the migration of solutes in aquifer systems or even immobilize them on the aquifer material, which is usually a natural mineral. We give an introduction to the approach and an overview of its possible applicability (and in this context its use in contributing to the understanding of the acid-base chemistry of (oxy)(hydr)oxide mineral surfaces, the adsorption of anions and cations like the uranyl-ion, and the formation of ternary surface complexes can be mentioned in general). Our contribution focuses on a review on the interaction of small organic molecules with oxidic surfaces and we highlight previous studies and point to some controversary issues in selected studies that continue to exist despite extensive research. Obviously such studies relate to other vibrational spectroscopies like Raman or sum frequency generation vibrational spectroscopies. Finally we discuss results from an experimental study on the mineral gibbsite (Al(OH)3) in the presence of 5-sulfosalicylic acid (5-SSA).

International audience; Ceria (CeO$_2$) nanoparticles are known to be very often used in various applications from biomedicine to fuel cells. To optimize the applications, detailed information about the physicochemical properties such as size, shape, and charge of nanoparticles should be available. Therefore, in our study we performed a systematic study of ceria nanoparticles ranging from synthesis to comprehensive experimental and theoretical characterization. We synthesized ceria nanoparticles using two synthesis paths which led to the formation of two types of ceria nanoparticles. The structure and charging properties of both types of ceria nanoparticles were studied by using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), particle charge detector (PCD) for surface charge density, and a ZetaPlus instrument for electrophoretic mobility measurements. The results suggested that in the case where hydrolysis of Ce(NO$_3$)$_3$ at room temperature was applied nanoparticles with morphology close to a spherical, more exactly truncated octahedron were synthesized. On the other hand, nanoparticles obtained by hydrothermal synthesis had characteristic cube-like morphology. Finally, for more complete understanding and interpretation of the studied system, we prepared a theoretical model based on the classical density functional theory for electrolyte solutions coupled with the surface charge regulation via the law of mass action. Even without using fitting parameters, the theory adequately describes the experimental data. All the results obtained in our study could serve as a basis for obtaining tuned and engineered ceria nanoparticles with optimized physicochemical properties which could lead to the improved applications of the nanotechnology in the biomedical research.

Higher symmetries frequently amaze human beings because of the illusions and incredible landscapes such symmetries can produce. For example, imagine the unearthly pictures of the Dutch graphic artist M.C. Escher. He made use of glide symmetry and reflection to produce unbelievable transitions and transformations of objects and beings, as illustrated in Figure 1(a). However, the history of higher symmetries started much earlier. Escher was partially inspired by the Moorish tessellations in the Alhambra in Granada, Spain, such as the ones pictured in Figure 1(b). The authors would like to thank Oskar Zetterström for providing the photo in Figure 5(a). This work was partly funded by the Spanish Government, under grant TEC2016-79700-C2-2-R; the French Government, under National Research Agency (ANR) Modeling and De - sign of Holey Metasurfaces project grant ANR JCJC 2016, ANR-16-CE24-0030; the Vinnova project High-5 (grant 2018-01522), under the Strategic Program on Smart Electronic Systems; the Stiftelsen Åforsk project Higher-Symmetric Materials for 5G Communications (grant 18-302); and COST Action SyMat CA18223, supported by COST (European Cooperation in Science and Technology), www.cost.eu.

The atomic structure, electronic structure and physical properties of $(TiZrNbCu)_{(1-x)}Ni_x$ (x $\leq$ 0.5) metallic glasses (MG) were studied in both the high-entropy (0, Comment: 40 pages, 8 figures

The synthesis and properties of a novel hetero-tetranuclear compound [Cr2(bpy)4(μ-O)4Nb2(C2O4)4]·3H2O (1 ; bpy = 2, 2′-bipyridine), investigated by single-crystal X-ray diffraction, magnetization measurements, IR, UV/visible spectroscopy, electron paramagnetic resonance (EPR ; X- and Q-bands and high-field), and density functional theory (DFT) calculations, are reported. Crystal structure of 1 (orthorhombic Pcab space group) consists of a square-shaped macrocyclic {; ; ; ; ; Cr2(μ-O)4Nb2}; ; ; ; ; core in which CrIII and NbV ions are alternately bridged by oxo ions and three uncoordinated water molecules. The intramolecular CrIII···CrIII distances through the −O–NbV–O– bridges are 7.410(2) and 7.419(2) Å, while diagonal separation is 5.406(2) Å. The temperature dependence of magnetization M(T) evidences an anti-ferromagnetic ground state, which originates from a magnetic interaction between two CrIII ions of spin 3/2 through two triatomic −O–NbV–O– diamagnetic bridges. A spin Hamiltonian appropriate for polynuclear isolated magnetic units was used. The best-fitting curve for this model is obtained with the parameters gCr = 1.992(3), J = −12.77(5) cm–1, and |D| = 0.17(4) cm–1. The CrIII···CrIII dimer model is confirmed by EPR spectra, which exhibit a pronounced change of their shape around the temperature corresponding to the intradimer coupling J. The EPR spectra simulations and DFT calculations reveal the presence of a single-ion anisotropy that is close to being uniaxial, D = −0.31 cm–1 and E = 0.024 cm–1.

We report $^{105}$Pd NMR and NQR measurements on a single crystal of Ce$_3$Pd$_{20}$Si$_6$, where antiferroquadrupolar and antiferromagnetic orders develop at low temperature. From the analysis of NQR and NMR spectra, we have determined the electric field gradient (EFG) tensors and the anisotropic Knight shift ($K$) components for both inequivalent Pd sites - Pd($32f$) and Pd($48h$). The observed EFG values are in excellent agreement with our state-of-the-art DFT calculations. The principal values of the quadrupolar coupling are $(20.37 \pm 0.02)$ MHz and $(5.45 \pm 0.02)$ MHz, for the Pd($32f$) and Pd($48h$) site, respectively, which is large compared to the Larmor frequency defined by the gyromagnetic constant $\gamma = 1.94838$ MHz/T for $^{105}$Pd. Therefore, the complete knowledge of $K$ and the EFG tensors is crucial to establish the correspondence between NMR spectra and crystallographic sites, which is needed for a complete analysis of the magnetic structure, static spin susceptibility, and the spin-lattice relaxation rate data and a better understanding of the groundstate of Ce$_3$Pd$_{20}$Si$_6$., Comment: 7 pages; 6 figures, 2 tables; accepted for publication in Journal of Physics: Condensed Matter

International audience; X-ray computed tomography (CT) is a non-destructive technique that offers a 3D insight into the microstructure of thick (opaque) samples with virtually no preliminary sample preparation. Since its first medical application in 1973, the technique has improved dramatically in terms of acquisition times and resolution. The best resolution achievable for both parallel-and cone-beam setups is presently sub-micron. The macroscopic properties (stiffness, resistance, permeability, durability,. . .) of cementitious materials are known to be significantly affected by their multiscale microstructure. This calls for x-ray CT investigations of cementitious materials down to the smallest length-scales. The present review first provides background information on the technique (including image-processing). It then covers various applications of x-ray CT to cementitious materials: imaging of the porous network, durability experiments, damage experiments,… , cutting-edge nanotomography experiments. Current challenges such as time-and chemically-resolved experiments are also discussed.

International audience; The aim of this work is to estimate the parameters of elastoplastic and damage laws for nodular graphite cast iron from a cyclic uniaxial test on a dog-bone sample. The paper focuses on the identification of material parameters coupling finite element models and full-field measurements. The gap between the measured and simulated data is used to estimate the quality of the proposed constitutive postulates. Last, a cyclic uniaxial experiment is carried out in a lab tomograph to reveal the damage micro-mechanism. Digital volume correlation is used to measure displacement fields in the bulk of the sample. The correlation residuals are used to detect the damage mechanism occurring in the heterogeneous microstructure of the material.

Recent studies (J. Alloys Compd. 695 (2017) 2661) of the electronic structure and properties of (TiZrNbCu)1-xNix (x ≤ 0.25) amorphous high entropy alloys (a-HEA) have been extended to x = 0.5 in order to compare behaviours of a-HEA and conventional Ni-base metallic glasses (MG). The amorphous state of all samples was verified by thermal analysis and X-ray diffraction (XRD). XRD indicated a probable change in local atomic arrangements, i.e. short-range-order (SRO) for x ≥ 0.35. Simultaneously, thermal parameters, such as the first crystallization temperature Tx and the liquidus temperature showed a tendency to saturate for x ≥ 0.35. The same tendency also appeared in the magnetic susceptibility χexp and the linear term in the low temperature specific heat γ. The Debye temperatures and Young's moduli also tend to saturate for x ≥ 0.35. These unusual changes in SRO and all properties within the amorphous phase seem correlated with the change of valence electron number (VEC) on increasing x.

The lubrication theory is mostly concerned with the behavior of a lubricant flowing through a narrow gap. Motivated by the experimental findings from the tribology literature, we take the lubricant to be micropolar fluid and study its behavior in a thin domain with rough boundary. Instead of considering (commonly used) simple zero boundary condition, we impose physically relevant (nonzero) boundary condition for microrotation and perform asymptotic analysis of the corresponding 3D boundary value problem. We formally derive a simplified mathematical model acknowledging the roughness-induced effects and the effects of the nonzero boundary conditions on the macroscopic flow. Using the obtained asymptotic model, we study numerically the influence of the specific rugosity profile on the performance of a linear slider bearing. The numerical results clearly indicate that the use of the rough surfaces may contribute to enhance the mechanical performance of such device. Croatian Science Foundation University of Zagreb Ministerio de Economía y Competitividad Junta de Andalucía

Comprehensive study of selected properties of four (TiZrNbCu)1-xNix (x ≤ 0.25) amorphous high entropy alloys (a-HEA) has been performed. These alloys, depending on the cooling rate, form either amorphous or crystalline (mostly two phase [1]) structure. This offers unique opportunity to study the impact of amorphisation on properties of HEA. The samples were ribbons about 20 µm thick and their fully amorphous state was verified by X-ray diffraction. The surface morphology, the actual composition and the distribution of components were studied with SEM equipped with EDX. The properties selected were the low temperature specific heat (LTSH), the magnetic susceptibility χexp and the Youngs modulus (E). Whereas LTSH and χexp were measured at the as-cast samples, E was measured both at as-cast and relaxed (short anneal [2] close to glass transition temperature [1]) samples. LTSH revealed that the electronic density of states at the Fermi level, N(EF), decreases with increasing x, whereas the Debye temperature (ΘD) increases with x. This is similar to what observed in binary and ternary amorphous alloys of early transition metals (TE) with late transition metals [2] and indicates that N(EF) is dominated with d-electrons of TE. Accordingly, the free- electron like paramagnetic contribution to χexp also decreases with x, whereas E increases with x indicating stronger interatomic bonding. The applicability of the rule of mixture to these and other HEA is briefly discussed. . References: [1] A. Cunliffe, J. Plummer, I. Figueroa and I. Todd, Intermetallics 23, 204 (2012). [2] R. Ristić, J. R. Cooper, K. Zadro, D. Pajić, J. Ivkov and E. Babić, J. Alloys Compd. 621, 136 (2015) and references therein.

International audience; In this paper the nonlinear behavior of nodular graphite cast iron is investigated under in-plane biaxial loading regimes. Multiaxial experiments enable a wide variety of loading paths to be investigated. In the presented study two loading histories are proposed, namely, equibiaxial and " snail " loading paths corresponding to proportional and nonproportional regimes. The center gauge zone of the testing cruciform specimen is observed. Mean strain fluctuations are measured and presented in order to determine the material response for the prescribed biaxial loading paths. For the equibiaxial and snail loading histories finite element model updating will couple 2D-DIC measurements with 3D-FE analyses to calibrate material parameters describing elasticity, isotropic or kinematic hardening.

We derive a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological repository for radioactive waste. This model includes capillary effects and the gas high diffusivity. Moreover, it is written in variables (total hydrogen mass density and liquid pressure) chosen in order to be consistent with gas appearance or disappearance. We discuss the well possedness of this model and give some computational evidences of its adequacy to simulate gas generation in a water-saturated repository.

At the interface between complex insulating oxides, novel phases with interesting properties may occur, such as the metallic state reported in the LaAlO3/SrTiO3 system. While this state has been predicted and reported to be confined at the interface, some works indicate a much broader spatial extension, thereby questioning its origin. Here we provide for the first time a direct determination of the carrier density profile of this system through resistance profile mappings collected in cross-section LaAlO3/SrTiO3 samples with a conducting-tip atomic force microscope (CT-AFM). We find that, depending upon specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of microns into SrTiO3 to a few nanometers next to the LaAlO3/SrTiO3 interface. Our results emphasize the potential of CT-AFM as a novel tool to characterize complex oxide interfaces and provide us with a definitive and conclusive way to reconcile the body of experimental data in this system., Comment: This updated version contains new experimental data

International audience; SrTiO3 becomes a high-mobility metallic conductor when doped with oxygen vacancies at low concentrations (≥1016 cm−3). We show that the vacancy concentration in the SrTiO3 single crystal substrates could be controllably tuned by changing the thickness of oxide films (deposited by pulsed laser deposition at high temperature and low oxygen pressure). The obtained variation in the carrier density strongly influences the transport properties. The quantitative analysis of the experimental results leads toward new and accurate strategies for the design of multifunctional oxide heterostructures for electronics and spintronics.