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International audience; The mobility of 79Se, a fission product of 235U and long-lived radioisotope, is an important parameter in the safety assessment of radioactive nuclear waste disposal systems. Nonradioactive selenium is also an important contaminant of drainage waters from black shale mountains and coal mines. Highly mobile and soluble in its high oxidation states, selenate (Se(VI)O42–) and selenite (Se(IV)O32–) oxyanions can interact with magnetite, a mineral present in anoxic natural environments and in steel corrosion products, thereby being reduced and consequently immobilized by forming low-solubility solids. Here, we investigated the sorption and reduction capacity of synthetic nanomagnetite toward Se(VI) at neutral and acidic pH, under reducing, oxygen-free conditions. The additional presence of Fe(II)aq, released during magnetite dissolution at pH 5, has an effect on the reduction kinetics. X-ray absorption spectroscopy analyses revealed that, at pH 5, trigonal gray Se(0) formed and that sorbed Se(IV) complexes remained on the nanoparticle surface during longer reaction times. The Se(0) nanowires grew during the reaction, which points to a complex transport mechanism of reduced species or to active reduction sites at the tip of the Se(0) nanowires. The concomitant uptake of aqueous Fe(II) and Se(VI) ions is interpreted as a consequence of small pH oscillations that result from the Se(VI) reduction, leading to a re-adsorption of aqueous Fe(II) onto the magnetite, renewing its reducing capacity. This effect is not observed at pH 7, where we observed only the formation of Se(0) with slow kinetics due to the formation of an oxidized maghemite layer. This indicates that the presence of aqueous Fe(II) may be an important factor to be considered when examining the environmental reactivity of magnetite.

Physical chemistry, chemical physics 23(2), 1371 - 1380 (2021). doi:10.1039/D0CP05606E, Efficient hydrogen release from liquid organic hydrogen carriers (LOHCs) requires a high level of control over the catalytic properties of supported noble metal nanoparticles. Here, the formation of carbon-containing phases under operation conditions has a direct influence on the activity and selectivity of the catalyst. We studied the formation and stability of carbide phases using well-defined Pd/α-Al$_2$O$_3$(0001) model catalysts during dehydrogenation of a model LOHC, methylcyclohexane, in a flow reactor by in situ high-energy grazing incidence X-ray diffraction. The phase composition of supported Pd nanoparticles was investigated as a function of particle size and reaction conditions. Under operating conditions, we detected the formation of a Pd$_x$C phase followed by its conversion to Pd$_6$C. The dynamic stability of the Pd$_6$C phase results from the balance between uptake and release of carbon by the supported Pd nanoparticles in combination with the thermodynamically favorable growth of carbon deposits in the form of graphene. For small Pd nanoparticles (6 nm), the Pd$_6$C phase is dynamically stable under low flow rate of reactants. At the high reactant flow, the Pd$_6$C phase decomposes shortly after its formation due to the growth of graphene. Structural analysis of larger Pd nanoparticles (15 nm) reveals the formation and simultaneous presence of two types of carbides, Pd$_x$C and Pd$_6$C. Formation and decomposition of Pd$_6$C proceeds via a Pd$_x$C phase. After an incubation period, growth of graphene triggers the decomposition of carbides. The process is accompanied by segregation of carbon from the bulk of the nanoparticles to the graphene phase. Notably, nucleation of graphene is more favorable on bigger Pd nanoparticles. Our studies demonstrate that metastability of palladium carbides associated with dynamic formation and decomposition of the Pd$_6$C and Pd$_x$C phases is an intrinsic phenomenon in LOHC dehydrogenation on Pd-based catalysts and strongly depends on particle size and reaction conditions., Published by RSC Publ., Cambridge

A combination of wide-angle X-ray scattering (WAXS) and pair distribution function analysis was used to investigate the structural changes occurring in beech wood and apricot tree pruning samples during slow and fast pyrolysis up to 1400°C (1673 K). WAXS curve modeling with the program CarbX provides unique information about the arrangement of graphene layers described by intralayer, interlayer, disorder and dispersion structural parameters. Pair distribution function modeling in PDFgui revealed imperfections in single graphene sheets, such as bond shortening and curvature, when refinement is performed in different r ranges. The concentration of inorganic species, along with heating rate, influences the final structure of pyrolysis products. The heating rate was more important than sample composition for an increase in extent of the single graphene layer and average chord length, while the average graphene coherent stack height depended on both composition and heating rate. Higher fractions of inorganic material increased the average interlayer spacing and the number of graphene layers per stack.

Powder samples of Ag3LiIr2O6 and Ag3LiRu2O6 were synthesized from alpha-Li2IrO3 and Li2RuO3 respectively by ion exchange in an AgNO3 melt. The crystal structures of the title compounds were solved from high resolution laboratory X-ray powder diffraction (XRPD) patterns and from pair distribution function (PDF) analysis using synchrotron X-ray powder diffraction data. In both crystal structures edge sharing LiO6/3- and (Ir/Ru)O-6/3-octahedra form honeycomb like layers that are stacked in a staggered fashion. Silver cations, situated in-between the layers mediate the interlayer interactions by linear O-Ag-O bonds. Anisotropic peak broadening in the XRPD patterns and diffuse scattering occurring as streaks in the precession electron diffraction (PED) patterns indicate the presence of stacking faults, which could be also visualized by high resolution transmission electron microscopy (HRTEM). Possible alternative stacking sequences were derived from the ideal crystal and incorporated into a microstructure model. By applying a supercell approach that randomly generates and averages stacking sequences based on transition probabilities and combining it with a grid search algorithm, the microstructures, i.e. the degrees of faulting in the structures of the title compounds were refined to the measured XRPD data. In result the crystal structures of Ag3LiIr2O6 and Ag3LiRu2O6 were found to be vastly faulted with almost no coherence of the stacked layers.

Basaluminite is a poorly crystalline aluminium sulphate oxyhydroxide that precipitates in acid mine drainage waters and acid sulphate soils when pH increases above 4.5 approximately. The pH increase can be due to mixing with natural waters or by the addition of an alkaline reagent, a method commonly used in remediation treatments. Basaluminite is a scavenger of elements such as Se, As, Sb, Mo, P and rare earth elements (REEs) and acts as a vector for their transport in the environment. The retention of these elements has important environmental and economic impact due to their toxicity and to the potential extraction of REEs for technological applications. Despite the long history of basaluminite, initially described as a mineral in the late 40s, little is known about its stability and its eventual transformation in other less metastable phases. Here, the stability of synthetic basaluminite in aqueous solutions with different pH values and sulphate concentrations was studied for 81 days. Chemical analyses of the aqueous phase combined with High-Energy X-ray Diffraction and Pair Distribution Function (PDF) analyses of the solids were used to characterize the ageing process. In contact with water, basaluminite incongruently dissolves, precipitating amorphous Al-hydroxide and releasing sulphate to the solution. This process and the recrystallization of amorphous Al-hydroxide into nanoboehmite were enhanced with increasing pH. However, for high SO4 concentrations, such as those found in acid mine waters, the transformation to nanoboehmite was partially inhibited. The ageing processes highlighted here point to a potential pathway for the desorption of trace elements upon neutralization of acid mine drainage. Furthermore, PDF analyses of basaluminite show a high similarity with the local structure of a synthetic amorphous Al-hydroxide.

An La–Sr/CaO catalyst has been chemically imaged during activation and under operando conditions during the oxidative coupling of methane reaction (OCM) at high temperature using X-ray diffraction computed tomography (XRD-CT) in combination with full pattern Rietveld refinement. At room temperature the main components of the catalyst were present as carbonates and hydroxides. During the activation stage (temperature ramp) they decomposed, forming La2O3, SrO, and mixed CaO–SrO oxides. Under the OCM reaction conditions, the predominant phases present were (∼20% wt) La2O3 and CaO-SrO (∼45% wt), and these remained stable throughout the entire reaction, whereas SrO, formed during activation, reacted with produced CO2 leading to formation of SrCO3 (∼35% wt). Two polymorphs of SrCO3, orthorhombic and rhombohedral, were found to be stable under reaction conditions although the extent to which these phases were observed varied spatially and temporally with reactant gas composition. The presence of the high temperature rhombohedral polymorph can be associated with higher combustion activity, and since the Rietveld analysis is performed on a pixel-by-pixel basis, it is possible to observe, for the first time, domains of differing activity within the reactor.

International audience; Basaluminite is a poorly crystalline aluminum hydroxysulfate that precipitates in waters affected by acid mine drainage (AMD) and in acid sulfate soils (ASS). Its ability to sequester potentially toxic elements, such as Cu and As, makes it an important component of these systems, with strong environmental implications. Although it was initially described as a mineral, basaluminite is now considered a nanoscale variety of felsöbányaite, a rare mineral. In the present study, chemical analyses of natural and synthetic basaluminites are combined with data from advanced nanoscale characterization techniques such as high-energy X-ray diffraction (HEXD) and their corresponding pair distribution function (PDF) analyses, extended X-ray absorption fine structure (EXAFS), and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. X-ray scattering data are analyzed with reverse Monte Carlo (RMC) modeling to obtain an atomistic representation of the disorder presents in this nanomineral. Sulfur K-edge EXAFS results show that sulfate is coordinated to the aluminum-octahedral framework of basaluminite mainly through outer-sphere ligands, though the existence of inner-sphere ligands seems to be significant in synthetic samples. PDF analyses show that both synthetic and natural basaluminites have identical short-range order, with ~1.2 nm coherent domain size, and share structural characteristics with felsöbányaite. Interestingly, 27Al ssNMR reveals the presence of, respectively, ~1 and 5% of tetrahedral and pentahedral coordinations. RMC models of basaluminite highlight the presence of structural point defects. The understanding of this nanocrystalline character has important implications in terms of the reactivity of this nanomineral in AMD and ASS. The lack of correlation between the spatial and temporal occurrence of basaluminite and felsöbányaite suggests that the similarities between both mineral structures could be fortuitous, and highlights the need for a re-evaluation of the status of basaluminite as a nanomineral.

Mechanochemistry is flourishing in materials science, but a characterization of the related processes is difficult to achieve. Recently, the use of plastic jars in shaker mills has enabledin situX-ray powder diffraction studies at high-energy beamlines. This paper describes an easy way to design and manufacture these jars by three-dimensional (3D) printing. A modified wall thickness and the use of a thin-walled sampling groove and a two-chamber design, where the milling and diffraction take place in two communicating volumes, allow for a reduced background/absorption and higher angular resolution, with the prospect for use at lower-energy beamlines. 3D-printed polylactic acid jars show good mechanical strength and they are also more resistant to solvents than jars made of polymethyl methacrylate. The source files for printing the jars are available as supporting information.

International audience; Yttrium belongs to the rare earth elements (REEs) together with lanthanides and scandium. REEs are commonly used in modern technologies, and their limited supply has made it necessary to look for new alternative resources. Acid mine drainage (AMD) is a potential resource since it is moderately enriched in REEs. In fact, in passive remediation systems, which are implemented to minimize the environmental impacts of AMD, REEs are mainly retained in basaluminite, an aluminum hydroxysulfate precipitate. In this study, the solid and liquid speciation and the local structure of yttrium are studied in high-sulfate aqueous solutions, basaluminite standards, and samples from remediation columns using synchrotron-based techniques and molecular modeling. Pair distribution function (PDF) analyses and ab initio molecular dynamics density functional theory models of the yttrium sulfate solution show that the YSO4+ ion pair forms a monodentate inner-sphere complex. Extended X-ray absorption fine structure (EXAFS) and PDF analyses show that Y is retained by basaluminite, forming a monodentate inner-sphere surface complex on the aluminum hydroxide surface. EXAFS of the column samples shows that more than 72% of their signal is represented by the signal of basaluminite with which YSO4+ forms an inner-sphere complex. The atomic view of the REE configuration in AMD environments could facilitate a deeper research of REE recovery from waste generated in AMD remediation systems.

Powder samples of Ag3LiIr2O6 and Ag3LiRu2O6 were synthesized from α-Li2IrO3 and Li2RuO3 respectively by ion exchange in an AgNO3 melt. The crystal structures of the title compounds were solved from high resolution laboratory X-ray powder diffraction (XRPD) patterns and from pair distribution function (PDF) analysis using synchrotron X-ray powder diffraction data. In both crystal structures edge sharing LiO6/3- and (Ir/Ru)O6/3-octahedra form honeycomb like layers that are stacked in a staggered fashion. Silver cations, situated in-between the layers mediate the interlayer interactions by linear O-Ag-O bonds. Anisotropic peak broadening in the XRPD patterns and diffuse scattering occurring as streaks in the precession electron diffraction (PED) patterns indicate the presence of stacking faults, which could be also visualized by high resolution transmission electron microscopy (HRTEM). Possible alternative stacking sequences were derived from the ideal crystal and incorporated into a microstructure model. By applying a supercell approach that randomly generates and averages stacking sequences based on transition probabilities and combining it with a grid search algorithm, the microstructures, i.e. the degrees of faulting in the structures of the title compounds were refined to the measured XRPD data. In result the crystal structures of Ag3LiIr2O6 and Ag3LiRu2O6 were found to be vastly faulted with almost no coherence of the stacked layers.

Neutron and high-energy X-ray diffraction methods have been used to investigate deformation mechanisms (slip and twinning activities) during uniaxial tensile tests of Grade 1 commercially pure titanium (Ti-α). These two diffraction techniques have provided valuable and complementary information. The predictions made by an Elasto-Plastic Self-Consistent (EPSC) model, taking into account grain reorientation and stress relaxation induced by twinning activity, have been compared with the experimental data. Results clearly demonstrate that there is a good agreement between simulations and diffraction measurements. The EPSC model enables accurate predictions of: (i) the lattice strains developed in variously oriented {hk.l} grain families within the bulk material, (ii) the grain reorientation induced by twinning activity and (iii) the macroscopic stress-strain response. Two different textured products were studied in order to evaluate the influence of texture on the mesoscopic and macroscopic responses of Ti-α alloy.

Any poorly crystalline serpentine-type mineral with a lack of recognizable textural or diffraction features for typical serpentine varieties (i.e., chryotile, lizardite, and antigorite) is usually referred to as proto-serpentine. The formation of the so-called proto-serpentine seems ubiquitous in serpentinization reactions. It is related to dissolution-precipitation of strongly reactive particles prior to true serpentine formation (e.g., in veins where both chrysotile and proto-serpentine are described). However, the structural characteristics of proto-serpentine and its relation with serpentine crystalline varieties remain unclear. In this study a model describing the transformation from proto-serpentine to chrysotile is presented based on experimental chrysotile synthesis using thermogravimetric analyses, transmission electron microscopy, and high-energy X-ray diffraction with pair distribution function analyses. The combination of the high-resolution TEM and high-energy X-ray diffraction enables to resolve the local order of neo-formed particles and their structuration processes occurring during pure chrysotile formation (i.e., during the first three hours of reaction). The formation of individual nanotubes is preceded by the formation of small nanocrystals that already show a chrysotile short-range order, forming porous anastomosing features of hydrophilic crystallites mixed with brucite. This is followed by a hierarchical aggregation of particles into a fiber-like structure. These flake-like particles subsequently stack forming concentric layers with the chrysotile structure. Finally, the individualization of chrysotile nanotubes with a homogeneous distribution of diameter and lengths (several hundreds of nanometer in length) is observed. The competitive precipitation of brucite and transient serpentine during incipient serpentinization reaction indicates that both dissolution-precipitation and serpentine-particle aggregation processes operate to form individual chrysotile. This study sheds light into mineralization processes and sets a first milestone toward the identification of the factors controlling polymorph selection mechanisms in this fascinating system.

Mesostructural cellular foam (MCF) materials that were modified by Zr, Nb, and Mo incorporation, followed by APTMS (3-aminopropyl-trimethoxysilane) grafting and gold loading were studied using the pair distribution function (PDF) technique. Measurements were focused on changes in gold crystallite sizes and on local geometry changes in the supports. Initially, ex situ prepared samples were investigated at different stages of synthesis and after catalytic oxidation of carbon monoxide. The crystallization and agglomeration of gold species as well as carbon monoxide oxidation were then tracked by in situ high energy diffraction measurements. The influence of metal type (Nb or Mo) and incorporation method in the MCF material on the agglomeration of metallic gold particles during increasing calcination temperature was determined. The structure of MCF materials was preserved during calcination and oxidation of CO and local symmetry of gold particles is not changed under CO oxidation conditions. In samples oxidiz...

Amorphous transition metal oxides are recognized as leading candidates for electrochromic window coatings that can dynamically modulate solar irradiation and improve building energy efficiency. However, their thin films are normally prepared by energy-intensive sputtering techniques or high-temperature solution methods, which increase manufacturing cost and complexity. Here, we report on a room-temperature solution process to fabricate electrochromic films of niobium oxide glass (NbOx) and 'nanocrystal-in-glass' composites (that is, tin-doped indium oxide (ITO) nanocrystals embedded in NbOx glass) via acid-catalysed condensation of polyniobate clusters. A combination of X-ray scattering and spectroscopic characterization with complementary simulations reveals that this strategy leads to a unique one-dimensional chain-like NbOx structure, which significantly enhances the electrochromic performance, compared to a typical three-dimensional NbOx network obtained from conventional high-temperature thermal processing. In addition, we show how self-assembled ITO-in-NbOx composite films can be successfully integrated into high-performance flexible electrochromic devices.

A detailed study of the near-surface structure and composition of Nb, the material of choice for superconducting radio-frequency accelerator (SRF) cavities, is of great importance in order to understand the effects of different treatments applied during cavity production. By means of surface-sensitive techniques such as grazing incidence diffuse x-ray scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy, single-crystalline Nb(100) samples were investigated in and ex situ during annealing in an ultrahigh vacuum as well as in nitrogen atmospheres with temperatures and pressures similar to the ones employed in real Nb cavity treatments. Annealing of Nb specimens up to $800\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in a vacuum promotes a partial reduction of the natural surface oxides (${\mathrm{Nb}}_{2}{\mathrm{O}}_{5}$, ${\mathrm{NbO}}_{2}$, and NbO) into NbO. Upon cooling to $120\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, no evidence of nitrogen-rich layers was detected after nitrogen exposure times of up to 48 h. An oxygen enrichment below the Nb-oxide interface and posterior diffusion of oxygen species towards the Nb matrix, along with a partial reduction of the natural surface oxides, was observed upon a stepwise annealing up to $250\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Nitrogen introduction to the system at $250\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ promotes neither N diffusion into the Nb matrix nor the formation of new surface layers. Upon further heating to $500\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in a nitrogen atmosphere, the growth of a new subsurface ${\mathrm{Nb}}_{x}{\mathrm{N}}_{y}$ layer was detected. These results shed light on the composition of the near-surface region of Nb after low-temperature nitrogen treatments, which are reported to lead to a performance enhancement of SRF cavities.

Sorption of trace elements onto poorly-crystalline Al-hydroxysulphate minerals from acid mine drainage (AMD) has received less attention compared to similar Fe(III)-phases because the former are less abundant in many mine drainage environments. In addition, Al-hydroxysulphates precipitate at a higher pH, so their sorption characteristics could be masked or less significant after sorption of trace elements to Fe minerals, which form at lower pH. In this study, oxidation and titration experiments were conducted with Fe(II)-rich AMD solutions under atmospheric and anoxic conditions to elucidate, individually, the sorption capacity of trace elements in solution by Fe and Al-hydroxysulphates. Under atmospheric conditions, precipitation of Fe(III) as schwertmannite, led to total removal of Fe, As, Cr and Pb in solution and 50% of Al. Subsequently, contaminant-depleted solution began to be controlled by precipitation of basaluminite, which acted as an effective sink for the remaining Al, Cu and Si. On the contrary, under anoxic conditions, neutralisation of Fe(II)-rich solutions led first to the basaluminite precipitation, keeping all Fe available in solution and unveiling a heretofore unknown affinity for As and Cr. Basaluminite retains 60% of As in solution compared to 100% removal of As by schwertmannite. However, the sorption capacity of basaluminite is even more significant than that of Fe-phases, considering that Al concentrations in solution were much lower than those of Fe. These findings give new insights into the processes controlling contaminant mobility in anoxic environments (e.g., the bottom of AMD-affected water reservoirs) and pose new opportunities for treatment strategies.

International audience; In a series of salts of ethane-1,2-diamine with acetic (1), trifluoroacetic (2), trichloroacetic (3), and dichloroacetic (4) acids, the amine is doubly protonated so the cation:anion stoichiometry is 2:1. In 1 and 2, dications are lying across the center of symmetry (Z' = 1/2), in 4 dication is nonsymmetric (Z' = 1), while the structure of 3 contains both symmetric and nonsymmetric cations (Z' = 3/2). All dications, either symmetric or not, are in extended (trans) form, by far the most popular among the salts of ethane-1,2-diamine. Strong hydrogen N-H center dot center dot center dot O bonds constitute the main specific, directional force determining the crystal packing. In 1, one of the N-H hydrogen atoms is involved in bifurcated hydrogen bonds, and in this case, four alresaacceptor oxygen atoms are almost equally involved in accepting the hydrogen bonds; in consequence, the C-O bond lengths are almost equal. In all other cases, the C-O bonds with oxygen atoms involved in more hydrogen bonds are systematically longer than those which accept less such interactions. Halogen C-Cl center dot center dot center dot O interactions are observed in two (out of five) symmetry-independent anions of 3 and 4, suggesting that at least in this series, the roles of these interactions are only secondary in nature. No significant involvement of fluorine atoms in directional interactions is detected, however. The hydrogen-bond networks are described by means of graph-set method. In addition, Hirshfeld surfaces are used to detect and visualize the differences between similar moieties, and fingerprint plots are presented in order to analyze the mutual importance of different kinds of interactions

High-resolution crystal structure determination and spherical and multipolar refinement enabled an organic solid solution of 1-(4′-chlorophenyl)-2-methyl-4-nitro-1H-imidazole-5-carbonitrile and 5-bromo-1-(4′-chlorophenyl)-2-methyl-4-nitro-1H-imidazole to be found, which would not normally be revealed using only standard resolution data (ca0.8 Å), as the disordered part is only visible at high resolution. Therefore, this new structure would have been reported as just another polymorphic form, even more reasonably as isostructural with other derivatives. To the best of our knowledge this is the first example of organic solid solution modelledviacharge density Hansen–Coppens formalism and analysed by means of quantum theory of atoms in molecules (QTAIM) theory.

Multi-temperature single-crystal and powder diffraction experiments on 1-(2′-aminophenyl)-2-methyl-4-nitroimidazole show that this crystal undergoes an isomorphic phase transition with the coexistence of two phase domains over a wide temperature range. The anharmonic approach was the only way to model the resulting disorder., The harmonic model of atomic nuclear motions is usually enough for multipole modelling of high-resolution X-ray diffraction data; however, in some molecular crystals, such as 1-(2′-aminophenyl)-2-methyl-4-nitro-1H-imidazole [Paul, Kubicki, Jelsch et al. (2011 ▶). Acta Cryst. B67, 365–378], it may not be sufficient for a correct description of the charge-density distribution. Multipole refinement using harmonic atom vibrations does not lead to the best electron density model in this case and the so-called ‘shashlik-like’ pattern of positive and negative residual electron density peaks is observed in the vicinity of some atoms. This slight disorder, which cannot be modelled by split atoms, was solved using third-order anharmonic nuclear motion (ANM) parameters. Multipole refinement of the experimental high-resolution X-ray diffraction data of 1-(2′-aminophenyl)-2-methyl-4-nitro-1H-imidazole at three different temperatures (10, 35 and 70 K) and a series of powder diffraction experiments (20 ≤ T ≤ 300 K) were performed to relate this anharmonicity observed for several light atoms (N atoms of amino and nitro groups, and O atoms of nitro groups) to an isomorphic phase transition reflected by a change in the b cell parameter around 65 K. The observed disorder may result from the coexistence of domains of two phases over a large temperature range, as shown by low-temperature powder diffraction.

The long-chain members of the lead(II) alkanoate series or soaps, from octanoate to octadecanoate, have been thoroughly characterized by means of XRD, PDF analysis, DSC, FTIR, ssNMR and other techniques, in all their phases and mesophases. The crystal structures at room temperature of all of the members of the series are now solved, showing the existence of two polymorphic forms in the room temperature crystal phase, different to short and long-chain members. Only nonanoate and decanoate present both forms, and this polymorphism is proven to be monotropic. At higher temperature, these compounds present a solid mesophase, defined as rotator, a liquid crystal phase and a liquid phase, all of which have a similar local arrangement. Since some lead(II) soaps appear as degradation compounds in oil paintings, the solved crystal structures of lead(II) soaps can now be used as fingerprints for their detection using X-ray diffraction. Pair distribution function analysis on these compounds is very similar in the same phases and mesophases for the different members, showing the same short range order. This observation suggests that this technique could also be used in the detection of these compounds in disordered phases or in the initial stages of formation in paintings, Partial support of this research by the DGICYT of the Spanish ‘‘Ministerio de Educacio ́ n y Ciencia’’ (Grants in aid for Scientific Research CTQ2008-06328, CTQ2013-41781-P and CTQ2015- 67755-C2-1-R) is gratefully acknowledged. LG acknowledges financial support provided by CSIC. The authors wish to thank the beamlines BM25-Spline and ID31 (ESRF, Grenoble, France), I711 (Max II ring, MAX IV Laboratory, Lund, Sweden), the Center of Scientific Instrumentat ion at the University Complutense of Madrid (CAI of XRD, Centro de Asistencia a la Investigacio ́ n), and the Laboratory for Crystallographic Studies (IACT, CSIC-UGR), and their staff, for the use of their technical facilities and help.

We present an X-ray Compton scattering study on aqueous trimethylamine N-oxide (TMAO) and guanidine hydrochloride solutions (GdnHCl) as a function of temperature. Independent from the concentration of the solvent, Compton profiles almost resemble results for liquid water as a function of temperature. However, the number of hydrogen bonds per water molecule extracted from the Compton profiles suggests a decrease of hydrogen bonds with rising temperature for all studied samples, and the differences between water and the solutions are weak. Nevertheless, the data indicate a reduced bond weakening with rising TMAO concentration up to 5 M of 7.2% compared to 8% for pure water. In contrast, the addition of GdnHCl appears to behave differently for concentrations up to 3.1 M with a weaker impact on the temperature response of the hydrogen bond structure.

Quantitative analysis of the X-ray pair distribution function collected on calcium silicate hydrates having Ca/Si ratios ranging between 0.57 and 1.47 was applied. With increasing Ca/Si ratio, Si bridging tetrahedra are omitted and Ca(OH)2 is detected at the highest ratios., The structural evolution of nanocrystalline calcium silicate hydrate (C–S–H) as a function of its calcium to silicon (Ca/Si) ratio has been probed using qualitative and quantitative X-ray atomic pair distribution function analysis of synchrotron X-ray scattering data. Whatever the Ca/Si ratio, the C–S–H structure is similar to that of tobermorite. When the Ca/Si ratio increases from ∼0.6 to ∼1.2, Si wollastonite-like chains progressively depolymerize through preferential omission of Si bridging tetrahedra. When the Ca/Si ratio approaches ∼1.5, nanosheets of portlandite are detected in samples aged for 1 d, while microcrystalline portlandite is detected in samples aged for 1 year. High-resolution transmission electron microscopy imaging shows that the tobermorite-like structure is maintained to Ca/Si > 3.

International audience; We have investigated the amorphization of β-trehalose by high energy milling using in situ and ex situ synchrotron powder diffraction and PDF analysis. From this analysis we show that amorphization takes place through a two-phase process involving an amorphous and a long-range ordered phase. The proportion and coherent domain size of the latter rapidly decrease with milling time until the whole sample appears amorphized. The PDF describing the local structure of the amorphous phase after two hours of milling is very close to that of a sample quenched from the liquid, and seems to continue to evolve for longer milling times. Their differences with the PDF expected for a rigid THL molecule confirm the existence of a conformational disorder of the torsion angles from the glycosidic linkage between the two cycles forming the molecule.

International audience; Three models of charge-density distribution – Hansen–Coppens multipolar, virtual atom and kappa – of different complexities, different numbers of refined parameters, and with variable levels of restraints, were tested against theoretical and high-resolution X-ray diffraction structure factors for 2-methyl-4-nitro-1-phenyl-1H-imidazole-5-carbonitrile. The influence of the model, refinement strategy, multipole level and treatment of the H atoms on the dipole moment was investigated. The dipole moment turned out to be very sensitive to the refinement strategy. Also, small changes in H-atom treatment can greatly influence the calculated magnitude and orientation of the dipole moment. The best results were obtained when H atoms were kept in positions determined by neutron diffraction and anisotropic displacement parameters (obtained by SHADE, in this case) were used. Also, constraints on kappa values of H atoms were found to be superior to the free refinement of these parameters. It is also shown that the over-parametrization of the multipolar model, although possibly leading to better residuals, in general gives worse dipole moments.

Background Vernadite is a nanocrystalline and turbostratic phyllomanganate which is ubiquitous in the environment. Its layers are built of (MnO6)8− octahedra connected through their edges and frequently contain vacancies and (or) isomorphic substitutions. Both create a layer charge deficit that can exceed 1 valence unit per layer octahedron and thus induces a strong chemical reactivity. In addition, vernadite has a high affinity for many trace elements (e.g., Co, Ni, and Zn) and possesses a redox potential that allows for the oxidation of redox-sensitive elements (e.g., As, Cr, Tl). As a result, vernadite acts as a sink for many trace metal elements. In the environment, vernadite is often found associated with tectomanganates (e.g., todorokite and cryptomelane) of which it is thought to be the precursor. The transformation mechanism is not yet fully understood however and the fate of metals initially contained in vernadite structure during this transformation is still debated. In the present work, the transformation of synthetic vernadite (δ-MnO2) to synthetic cryptomelane under conditions analogous to those prevailing in soils (dry state, room temperature and ambient pressure, in the dark) and over a time scale of ~10 years was monitored using high-energy X-ray scattering (with both Bragg-rod and pair distribution function formalisms) and transmission electron microscopy. Results Migration of Mn3+ from layer to interlayer to release strains and their subsequent sorption above newly formed vacancy in a triple-corner sharing configuration initiate the reaction. Reaction proceeds with preferential growth to form needle-like crystals that subsequently aggregate. Finally, the resulting lath-shaped crystals stack, with n × 120° (n = 1 or 2) rotations between crystals. Resulting cryptomelane crystal sizes are ~50–150 nm in the ab plane and ~10–50 nm along c*, that is a tenfold increase compared to fresh samples. Conclusion The presently observed transformation mechanism is analogous to that observed in other studies that used higher temperatures and (or) pressure, and resulting tectomanganate crystals have a number of morphological characteristics similar to natural ones. This pleads for the relevance of the proposed mechanism to environmental conditions. Electronic supplementary material The online version of this article (doi:10.1186/s12932-015-0028-y) contains supplementary material, which is available to authorized users.

Functionalisation of silica catalysts (e.g. MCF) supported by anchoring of organosilanes (e.g. aminopropylalkoxysilanes) may change the catalytic properties of the system and also can be used for the further grafting of noble metals [1-2]. In the case of metal loading, in the following calcination process thermal activation and thermal transformation take place leading to the sintering of metal particles, which results in creation of bigger metal crystals. The pair distribution function (PDF) technique is a powerful tool for studying amorphous, crystalline and partially crystalline materials [3]. It bases on model free Fourier transform of X-ray powder diffraction data, and gives the probability of finding any two atoms at a given interatomic distance. A long range order is not necessary and nanostructured materials may be investigated without constraints of conventional crystallographic methods. Structural changes of support (mesoporous cellular foams(MCF))and active sites of new series of metal catalysts (Au, Mo, Nb, Zr) were investigated using PDF technique. All data were collected at ID15 beamline at ESRF: a)catalysts at different steps of synthesis, before and after reactions – measurements in static conditions; b) calcinations processes and in-situ oxidation reactions – measurements at different temperature and with gas flow at ambient pressure. Acknowledgements: National Science Centre in Poland (Project NCN–reg.no.2013/10/ST5/00642) is acknowledged for the partial financial support.