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International audience; Aperiodic crystals possess long-range order without translational symmetry. They constitute a state of matter that has forced a profound paradigm shift in solid-state physics. A common feature of aperiodic crystals is that they recover periodicity in higher dimensional spaces, the so-called crystallographic superspaces. Much work has been dedicated to the structural order within these superspaces and also to their specific dynamics. This paper focuses on the phase transitions within crystallographic superspaces. Aperiodic crystals are divided into three families: incommensurately modulated crystals, composite crystals, and quasicrystals. Incommensurately modulated crystals have been studied heavily and appear now to be relatively well understood, since they possess a periodic high-symmetry phase. The other two members of the family are aperiodic by construction. In this paper, we present a comprehensive and systematic study of a prototype composite host-guest family of n-alkane/urea inclusion compounds [$n−$ C$_n$H$_{2n+2}$/CO(NH$_2$)$_2$]. For these materials, which exhibit a rich sequence of phases, the phase transitions are described in terms of group/subgroup symmetry breaking within crystallographic superspaces. Such phase transitions may decrease, increase, or maintain the dimension of the crystallographic superspace. These results highlight the multiplicity of specific structural solutions thataperiodicity offers.

International audience; Skim milk ultrafiltration is worldwide used in dairy. Its management at industrial scale is based on the permeate flux mastering, the first bottleneck, and consequently on the nature of the overall fouling which is not yet fully understood with respect to the membrane lifespan. The second bottleneck is the mastering and control of the cleaning efficiency aiming at the full removal of the initial irreversible fouling mainly made of proteins. In this study, we have deliberately chemically aged several spiral wound membrane elements by filtering NaOCl solution (400 ppm in total free chlorine at pH 8.0 and 50 °C) up to a cumulative chlorine dose of 2,800 ppm.d. The critical/threshold and limiting fluxes have been proven to increase with the membrane ageing together with a decrease in their related transmembrane pressure. This suggest that, at industrial scale, UF might be managed with respect to the chlorine dose received by the membrane during its service life. SEM and Raman spectroscopy have been used to localise the initial irreversible fouling whereas ATR-FTIR was the tool to quantify proteins on membrane. Membrane cleaning was achieved by a non-oxidative alkaline detergent removing the hereafter called “removable fouling” whereas a “residual fouling” remained on/in the membrane. However, the following NaOCl treatment (achieved for disinfection purpose at industrial scale) also acts both as cleaner (polishing the alkaline step by removing part of the residual fouling) and as degradation agent toward the membrane. Unambiguously NaOCl induced a significant decrease in the membrane intrinsic hydraulic resistance associated with an increase of the irreversible fouling, either initial or residual, build during the following skim milk UF. This paper shows how degradation and fouling can transiently compensate each other and lead to the impression of an initial water flux recovery. This phenomenon can lead to misinterpretation of the membrane cleanliness in the specific case of aged membranes. Indeed, for a received chlorine dose close to 400 ppm.d at pH = 8.0, an irreversible residual fouling can remain, strongly anchored in/on the membrane with a water flux recovery after cleaning only 15% less than that of the pristine membrane. This residual fouling favours the rapid build-up of more and more irreversible fouling during the next skim milk filtration steps. However, with respect to the accuracy on flux measurement, the amplitude of the problem will be underestimated, preventing from getting rid of the first and crucial accumulated layers and consequently leading to an irreversible accelerated degrading process. Relationships have been found between the received chlorine dose and the aged membrane resistance and the residual irreversible fouling that could be used for management at industrial scale.

Aiming to improve the characterization of Carbonate Reservoirs from resource assessment to optimization of the static and dynamic modeling, we describe a holistic flowchart for an integrated approach by using the capillary pressure measurements. Its most innovative steps from pore scale to field scale is illustrated on a Super Giant Carbonate Reservoir from the Middle East. The flowchart relies on patented, published and proven "data driven" algorithmic techniques (k-NN, Histogram Upscaling and MRGC-CFSOM clustering) devoid of any user’s bias. Its capability to integrate Static and Dynamic, from Pore Scale to Log scale, stems from the integration, prediction and upscaling at log scale, over cored and un-cored intervals of MICP curves together with all core and log material. Predictions by means of "k-NN multiple modeling" of SCAL & RCA plug measurements allows a reliable and accurate characterization of the rock matrix at log scale, while quantifying its degree of heterogeneity. By revealing to the geoscientists, the pore scale rock texture, its stratigraphic evolution and its heterogeneities, the continuous profile of upscaled Pore Size Distribution (PSD) curves vs logs provides invaluable information on the rock forming processes controlling the matrix Porous Network. By applying the Purcell theory onto the upscaled PSD, the "Log scale" Permeability and the true FZI and Rmh are computed which are then used as input to a e-Facies model (MRGC-CFSOM) by integrating to other logs and core material. The e-Facies model is interpreted in terms of "matrix" storage and flow parameters as well as in terms of depositional mechanisms and diagenetic overprints, in the light of the core descriptions whose Petrophysical pertinence is thoroughly and quantitatively validated with all the Petrophysical material. By reversing the method used to derive PSD from MICP saturation curves and using the Pc equating the buoyancy forces at any depth increment, the saturation at any depth increment above the actual Free Water Level (or a scenario of FWL), is computed from the continuous profile of upscaled PSD. Production data, RSTs and PLTS provide the information on total flow and by subtracting matrix contribution to the total flow, the location and quantification of the contribution of the depth intervals with large vugs and fractures is greatly eased, particularly if Borehole imagery is available. The contribution of Matrix, large vugs and fractures are then merged into a single model used for robust well to well correlations, zonation of the reservoir, 3D gridding and volumetric evaluation. Using this innovative flowchart approach, characterization of high permeability streaks, saturation height function and chemical polymer EOR processes were greatly improved as input to the static and dynamic model history match exercise.

International audience; The understanding of the symmetry breakings within crystals that are aperiodic by construction is actually very limited. Quasicrystals and incommensurate composite crystals may potentially allow such studies. We focus on the phase transitions of the aperiodic n-nonadecane/urea which recovers a translational symmetry within a four-dimensional space at room temperature. High-resolution neutron and synchrotron studies are reported as a function of the temperature on this organic crystal which presents an exceptional mosaicity. They reveal the richness of such approach, showing the appearance of very long wavelength supplementary intermodulations. This work generalizes the Landau theory to incommensurate composite crystals.

International audience; This study aimed at studying the impact of alcohol presence in water/alcohol mixtures on the performances of the NF 270 polypiperazine amide nanofiltration membrane (Dow Filmtec). Three alcohols of different physico-chemical characteristics were selected methanol, ethanol and isopropanol. NF was achieved for several water/alcohol mixtures of different viscosity (up to twice that of water) and dielectric constant, both known to play a role in separation performances. In presence of alcohol (up to 23 vol%, 30 vol% and 21 vol% for methanol, ethanol and isopropanol, respectively) the flux significantly decreased when compared to that of water. This study provides insights in the alcohol transfer mechanisms allowing to select Spiegler and Kedem and reject Solution-Diffusion, both coupled with the film theory. Discussion highlights how surprisingly the membrane swelling can sometimes have no significant impact on the membrane resistance because opposite phenomena can be compensated such as pore radius increase simultaneously with membrane thickness increase. © 2020

International audience

The discovery in materials of long range order without lattice periodicity has generated a very broad field of research with the introduction of totally new concepts. The common feature of this new state of matter is the translational symmetry recovered by adding supplementary dimensions to the physical space, defining a crystallographic superspace. Along these supplementary directions, specific low excitations, so-called phasons, are predicted and observed. These quasi-periodic crystals may present phase transitions as function of external parameters, which have then to be described as symmetry breakings within these crystallographic superspaces. Three different families of quasi-periodic crystals are usually considered: incommensurate modulated crystals, aperiodic composites and quasicrystals. Their crystallography and dynamics are discussed.

This paper reports on symmetry breaking in the aperiodic inclusion compound $n\text{-octadecane/urea}$ and its isotopomer $n\text{-octadecane/urea-}{d}_{4}$. The high-symmetry phase is described by a hexagonal rank-4 superspace group. Pretransitional phenomena in this crystallographic superspace reveal competing short-range-ordering phenomena within the high-symmetry phase. Very high-resolution diffraction data show that critical scattering appears at inequivalent points within the four-dimensional Brillouin zone, although the first phase transition at ${{T}_{c}}_{1}$ near 158 K implies the condensation at only one of those points. The resulting superspace group remains of dimension 4. Two other phase transitions are reported at ${{T}_{c}}_{2}\phantom{\rule{4pt}{0ex}}=152.8(4)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and ${{T}_{c}}_{3}=109(4)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ in $n\text{-octadecane/urea-}{d}_{4}$. The two low-symmetry phases that arise are described by rank-5 superspace groups.

Accurate structure factors are extracted from synchrotron powder diffraction data measured on crystalline diamond based on a novel multipole model division of overlapping reflection intensities. The approach limits the spherical-atom bias in structure factors extracted from overlapping powder data using conventional spherical-atom Rietveld refinement. The structure factors are subsequently used for multipole electron-density modelling, and both the structure factors and the derived density are compared with results from ab initio theoretical calculations. Overall, excellent agreement is obtained between experiment and theory, and the study therefore demonstrates that synchrotron powder diffraction can indeed provide accurate structure-factor values based on data measured in minutes with limited sample preparation. Thus, potential systematic errors such as extinction and twinning commonly encountered in single-crystal studies of small-unit-cell inorganic structures can be overcome with synchrotron powder diffraction. It is shown that the standard Hansen-Coppens multipole model is not flexible enough to fit the static theoretical structure factors, whereas fitting of thermally smeared structure factors has much lower residuals. If thermally smeared structure factors (experimental or theoretical) are fitted with a slightly wrong radial model (s2p2 instead of sp3) the radial scaling parameters (`' parameters) are found to be inadequate and the `error' is absorbed into the atomic displacement parameter. This directly exposes a correlation between electron density and thermal parameters even for a light atom such as carbon, and it also underlines that in organic systems proper deconvolution of thermal motion is important for obtaining correct static electron densities.

The intergrowth crystal of n-tetracosane/urea presents a misfit parameter, defined by the ratio γ = ch/cg (chost/cguest), that is very close to a commensurate value (γ ≅ 1/3). High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of γ = 0.3369, which is found to be constant at all temperatures studied. A complex sequence of structural phases is reported. The high temperature phase (phase I) exists in the four-dimensional superspace group P6122(00γ). At Tc1 = 179(1) K, a ferroelastic phase transition increases the dimension of the crystallographic superspace. This orthorhombic phase (phase II) is characterized by the five-dimensional (5D) superspace group C2221(00γ)(10δ) with a modulation vector ao* + cm* = ao* + δ · ch*, in which the supplementary misfit parameter is δ = 0.025(1) in host reciprocal units. This corresponds to the appearance of a modulation of very long period (about 440 ± 16 Å). At Tc2 = 163.0(5) K, a 5D to 5D phase transition leads to the crystallographic superspace group P212121(00γ)(00δ) with a very similar value of δ. This phase transition reveals a significant hysteresis effect.

The quasiparticle band structures within the GW approximation of the possible superconductors LiBC and NaBC are presented. The GW correction to the LDA is shown to be strongly dependent on the degree of orbital localization, and the overall correction cannot be reproduced by a rigid band shift as in conventional semiconductors. Precise values of the interband transitions for high-symmetry points in the Brillouin zone are given. The imaginary part of the self-energy which is related to the lifetime of quasiparticles, is presented in order to be compared with future experiments. Moreover, the ground-state properties of LiBC and NaBC are studied and it is shown that the bonding is partly covalent.

The experimental electron density of the high-performance thermoelectric material Zn4Sb3 has been determined by maximum entropy (MEM) analysis of short-wavelength synchrotron powder diffraction data. These data are found to be more accurate than conventional single-crystal data due to the reduction of common systematic errors, such as absorption, extinction and anomalous scattering. Analysis of the MEM electron density directly reveals interstitial Zn atoms and a partially occupied main Zn site. Two types of Sb atoms are observed: a free spherical ion (Sb3-) and Sb2(4-) dimers. Analysis of the MEM electron density also reveals possible Sb disorder along the c axis. The disorder, defects and vacancies are all features that contribute to the drastic reduction of the thermal conductivity of the material. Topological analysis of the thermally smeared MEM density has been carried out. Starting with the X-ray structure ab initio computational methods have been used to deconvolute structural information from the space-time data averaging inherent to the XRD experiment. The analysis reveals how interstitial Zn atoms and vacancies affect the electronic structure and transport properties of beta-Zn4Sb3. The structure consists of an ideal A12Sb10 framework in which point defects are distributed. We propose that the material is a 0.184:0.420:0.396 mixture of A12Sb10, A11BCSb10 and A10BCDSb10 cells, in which A, B, C and D are the four Zn sites in the X-ray structure. Given the similar density of states (DOS) of the A12Sb10, A11BCSb10 and A10BCDSb10 cells, one may electronically model the defective stoichiometry of the real system either by n-doping the 12-Zn atom cell or by p-doping the two 13-Zn atom cells. This leads to similar calculated Seebeck coefficients for the A12Sb10, A11BCSb10 and A10BCDSb10 cells (115.0, 123.0 and 110.3 microV K(-1) at T=670 K). The model system is therefore a p-doped semiconductor as found experimentally. The effect is dramatic if these cells are doped differently with respect to the experimental electron count. Thus, 0.33 extra electrons supplied to either kind of cell would increase the Seebeck coefficient to about 260 microV K(-1). Additional electrons would also lower sigma, so the resulting effect on the thermoelectric figure of merit of Zn4Sb3 challenges further experimental work.

Aperiodic composite crystals present long-range order without translational symmetry. These materials may be described as the intersection in three dimensions of a crystal which is periodic in a higher-dimensional space. In such materials, symmetry breaking must be described as structural changes within these crystallographic superspaces. The increase in the number of superspace groups with the increase in the dimension of the superspace allows many more structural solutions. This is illustrated inn-nonadecane–urea, revealing a fifth higher-dimensional phase at low temperature.

n-Dodecane/urea is a member of the prototype series of n-alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases. Below Tc=248 K there appears a phase with rank four superspace group P61 22(00γ), the one typically observed at room temperature in n-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio γ= c h/c g (c host/c guest), is found to be 0.632±0.005. Below Tc1=123 K, a monoclinic modulated phase is created with a constant shift along c of the guest molecules in adjacent channels. The maximal monoclinic space group for this structure is P121 1(α0γ). Analogies and differences with n-heptane/urea, which also presents a monoclinic, modulated low-temperature phase, are discussed.

Resume Depuis 1994, le GBEA s'impose aux laboratoires d'analyses de biologie medicale publics et prives. A l'instar de tous les autres referentiels normatifs il peut etre approche de deux facons fort differentes. La premiere consiste a se conformer aux exigencies supplesmentaires en les appliquant litteralement, mais sans reflexion en profondeur ce qui genere des couts supplementaires, mais pas necessairement une amelioration durable. La deuxieme, certes plus ambitieuse, mais beaucoup plus profitable sur le long terme, a pour finalite d'ameliorer les performances globales du service ou de l'entreprise dans un contexte devenu concurrentiel, meme dans le secteur public. C'est cette deuxieme approche que nous presentons ici. Elle est fondee sur la modelisation et l'analyse approfondie des processus-cles du laboratoire et des differentes activites qui composent ce processus. Cette analyse permet de poursuivre une reflexion de groupe sur les caracteristiques de chaque activite, dysfonctionnements, risques, existence d'une documentation qualite et bien entendu conformite au GBEA. Ce type de demarche est motivante pour le personnel. Par ailleurs, la meme analyse des processus-cles sert de fil conducteur a une etude economique comme il est montre dans l'article suivant.

Summary The facies and core data prediction techniques have not yet found their way in the CBM/CSG business, despite having been used successfully for more than a decade in the conventional O/G business; but we believe this new technique signals that the time has come for this to happen. The method described here is based on the Facimage facies-prediction software run under Geolog. Reasonable qualitative estimates can be generated immediately from a full suite of logs but for each new basin or coal sequence, gas and ash content from cores are required to derive a predictive model and deliver calibrated, quantitative results - by tying core measurements to their log signature, as is done for conventional O/G analysis. Once blind testing has proven the model is satisfactory, gas and ash content together with the different facies can be predicted quantitatively from logs without cores. Rigorous quality control measures ensure that the prediction models used are applicable or, where there is a difference, that there may/must be changes in the geology or a log acquisition problem. The processes used are designed to be devoid of operator bias and can be run as soon as logs are run to allow on-site decisions about testing, suspension or P&A. We demonstrate the principles and methods used to derive gas and ash content without core data, but assuming calibration has been achieved, and how we build the quality control model and how we address the problems of spatial resolution mismatch between core and logs and of shoulder-bed effects.

PACS number(s): 61.44.Fw, 64.60.−i, 61.05.cf.-- et al., Upon cooling, the aperiodic inclusion compound n-nonadecane/urea presents a hexagonal-to-orthorhombic group-subgroup phase transition at Tcl that increases the structure's superspace dimensionality from four to five. This paper reports on pretransitional phenomena in such a high-dimensional space, generalizing the critical results previously reported at a lower dimensionality. Very high-resolution diffraction data reveal anomalously large correlation lengths along the aperiodic direction, with all correlation lengths diverging at Tcl. This could be explained by low-frequency phason excitations that soften at Tcl at the critical wave vector, in accordance with an increase in the critical diffuse scattering intensity. © 2013 American Physical Society.

Aperiodic alkane/urea inclusion compounds (UIC) are prototype composites which exhibit complex sequences of phases that can clearly be described in the (3+d) dimension crystallographic superspace. By simply changing the length of the guest alkane molecules (C n H2n+2) which pile up in the channels of the host urea honeycomb-like framework, it is, for instance, possible to have phase-ordering phase transition from 3 to (3+1) dimension in the case of n-heptane/urea (n=7), or as in the case of n-hexadecane/urea (n=16) or n-nonadecane/urea (n=19), a generalization to higher dimensions of the phase transitions found in modulated structures. Such results are successfully obtained with the help of high resolution diffraction methods.

International audience; n-Heptane/urea is an aperiodic inclusion compound in which the ratio of host and guest repeats along the channel axis is very close to unity and is found to have a constant value (0.981) from 280 K to 90 K. Below 280 K, two phase transitions are observed. The first (T(c1) = 145 K) is a ferroelastic phase transition that generates superstructure reflections for the host while leaving the guest with 1D order. The second (T(c2) = 130 K) is a "phase ordering" transition to a four-dimensional structure (P2(1)11(0βγ)) with pronounced host-guest intermodulation and a temperature dependent phase shift between guests in adjacent channels.

International audience; This letter reports on the structural instabilities of an aperiodic composite crystal under pressure. The (P, T) phase diagram up to 0.55GPa of nonadecane-urea is reported showing various symmetry breakings in crystallographic superspaces, towards three different orthorhombic phases. These structural phase transitions are characterized by a change in the intermodulation and are described by increasing the rank of the crystallographic superspaces.

National audience; La gestion raisonnée du phosphore dans les zones d’élevage en situation d’excédent phosphaté par rapport aux besoins des cultures, sera ici traitée par le développement de trois thèmatiques complémentaires : la gestion des cycles des éléments nutritifs, la gestion de la fertilité des sols, l’activité biologique des sols et la nutrition. L’objectif étant de tendre vers une agriculture durable, économe des ressources naturelles et de mettre en oeuvre la fertilisation raisonnée des cultures.

International audience; High-resolution studies of the host-guest inclusion compound n-hexadecane/urea are reported at atmospheric pressure, using both cold neutrons and x-ray diffraction. This intergrowth crystal presents a misfit parameter, defined by the ratio c(h)/c(g) (c(host)/c(guest)), which is temperature independent and irrational (γ = 0.486 ± 0.002) from 300 to 30 K. Three different structural phases are reported for this aperiodic crystal over this temperature range. The crystallographic superspaces are of rank 4 in phases I and II, whereas phase III is associated with an increase in rank to 5, with a supplementary misfit parameter (δ = 0.058 ± 0.002) that is constant throughout this phase. The superspace group of phase I is hexagonal P6(1)22(00γ) down to T(c1) = 149.5 ± 0.5 K; phase II, which persists down to T(c2) = 127.8 ± 0.5 K is orthorhombic P2(1)2(1)2(1)(00γ), and phase III is orthorhombic P2(1)2(1)2(1)(00γ)(00δ).

The exploration for stratigraphic traps, especially in carbonates, is challenging and requires carefully detailed analysis of petroleum system elements. Accurately defining the spatial and temporal distribution of source rock, reservoir, and seal facies is essential for exploring stratigraphic traps. This study presents an integrated approach for evaluating reservoir and seal capacity of Jurassic carbonates to explore stratigraphic traps using the Facimage electrofacies prediction and calibrated seismic facies modeling techniques. Core-based rock types were generated for selected Jurassic carbonate reservoir formations by integrating core descriptions, thin-section petrographic data, core plug porosity/permeability, and capillary pressure (MICP) measurements. Reservoir quality and sealing capacity were thoroughly evaluated using core-derived pore-throat size and capillary pressure data from a full spectrum of reservoir and sealing facies. This was followed by calibration of core-derived reservoir and seal facies to well-log responses by constructing Facimage models for selected “Reference Wells” that are extensively cored and analyzed. The Facimage models were rigorously tested by validating predicted electrofacies/capillarity and core-derived rock types, and their sealing capacity. The optimized Facimage model was used to predict electrofacies that represent rock types of varying reservoir quality and seal capacity for all the selected “Application Wells” within the area of interest. The derived electrofacies (rock types) of reservoirs and seals can be upscaled to a seismically detectable level. The upscaled facies were then output as numerical codes into the calibrated seismic facies modeling of 3D seismic volumes using state-of-the-art technologies for analysis, integration, and visualization. The calibrated seismic facies, rock types and porosity models provide lateral and vertical facies changes of reservoirs and seals within 3D volumes. These are critical elements for exploring stratigraphic traps. The Middle and Upper Jurassic reservoirs have been taken as examples for the above approach. Preliminary results have demonstrated that existing stratigraphic trap analogue and potential new stratigraphic traps can be successfully predicted, as shown in the Upper Fadhili and Arab- D reservoirs.

The search for stratigraphic traps especially in carbonates is a challenging task and requires careful detailed analysis of the petroleum system elements. Understanding the spatial relation between source, reservoir and seal layers constitutes a critical success factor. Building a workflow that transforms well and seismic data into 3D models allows stratigraphic traps prediction and better understanding of the stratigraphic trapping components. With the acquisition of modern 3D seismic data and the advancement in data analysis software, we are able to build 3D seismic and electrofacies and porosity models that are tied to well based information such as cores and well logs. The built 3D models allow the investigation of the spatial relations of source, reservoir and seal units. A corner stone of our workflow for targeting carbonate stratigraphic traps is to integrate all available data into 3D models of seismic facies, electrofacies and core data. These models were also transformed to porosity models using relations from seismic (AI), core measured and well log derived porosities. This allows analysis of the stratigraphic trap in great details. Highly detailed core data and well log defined electrofacies, are upscaled and used to calibrate seismic waveform based facies. The seismic facies volume generated from a combination of seismic attributes allowed lateral stratigraphic prediction. A workflow for the deliberate search for carbonate stratigraphic traps includes: ● Stratigraphic and sedimentologic analysis from cores and well-logs and building of depositional architecture. ● Stratigraphic modeling and Wheeler diagram construction to track lateral and temporal shifts of depositional facies and electrofacies modeling, which uses a combined analysis of well logs and cores, for facies definition. ● Seismic modeling and analysis to investigate the link of the facies response to seismic. ● Hybrid clustering classification. ● Seismic trace based 3D model integration of the core lithofacies, the electrofacies, and the seismic facies to produce facies and porosity models. ● Integration of other petroleum systems elements and visualization of the results. Application of this workflow to a Jurassic interval in an area in the eastern Saudi Arabia have proven that carbonate stratigraphic trap can be predicted thus giving us confidence in pursuing these type of traps.

The reactivity of the niobium antidiffusion barrier at the time of heat treatment is presented in the case of NbCu-sheathed, in situ PbMo6S8 (PMS-) based wires doped with 2.6 at.% Sn. As a result of this reactivity, a lamellar layer grows axially towards the centre of the wire, consuming a significant amount of sulphur at the expense of the formation of the superconducting PMS phase. Investigation of the growth kinetics by scanning electron microscopy under variable experimental conditions indicates that slightly decreasing the heat treatment temperature or increasing the powder densification can considerably minimize the niobium reactivity. In the light of results from electron microprobe analysis together with X-ray powder diffraction data, the possible existence of a new Pb0.15Nb2S3 compound is discussed.

The paper presents a workflow to predict a Middle Jurassic carbonate stratigraphic trap in Northern Saudi Arabia.

This paper presents different aspects of x-ray diffraction techniques for material science: investigation of symmetry breaking, electron density analysis, diffuse scattering, aperiodic systems and time-resolved experiments.

Different methods were employed to synthesize a series of high quality PbMo 6 S 8 Chevrel-phase compounds. All the samples were characterized by means of X-ray diffraction, Auger electron spectroscopy, specific heat, acsusceptibility, resistivity, scanning electron spectroscopy and microprobe analysis. A marked decrease in the superconducting transition temperature (T c ) and the hexagonal lattice constant ratio (c/a) were noticed on the samples prepared in quartz tubes. Based on a simple correlation between T c and c/a ratio, we present some of the significant structure-property relations and phase purity of the samples. This interdependence is discussed mainly in terms of oxygen content in the phase. For instance, oxygen-free samples have T c invariably above 14.5 K. Interestingly, the optimal T c is found in samples having rather different, from each other, crystallographic parameters, but with a same c/a ratio. On the other hand, the wide variation of T c and structural parameters of PbMo 6 S 8 observed in the present investigation and those of many earlier works are explained by the presence of varying amounts of oxygen in the ternary phase. These results are checked in parallel with the oxygen-doped (PbMo 6 S 8−x O x ; x ≥ 0.2) samples.

Colourless block crystals of the title compound, Cs(3)[Lu(dipic)(3)]·8H(2)O [dipic is dipicolinate or pyridine-2,6-dicarboxyl-ate, C(7)H(3)NO(4)] were synthesized by slow evaporation of the solvent. The crystal structure of this Lu(III)-complex, isostructural with the Dy(III) and Eu(III) complexes, was determined from a crystal twinned by inversion and consists of discrete [Lu(dipic)(3)](3-) anions, Cs(+) cations and water mol-ecules involving hydrogen bonding. The Lu atom lies on a twofold rotation axis and is coordinated by six O atoms and three N atoms of three dipicolinate ligands. One Cs atom is also on a twofold axis. The unit cell can be regarded as successive layers along the crystallographic c-axis formed by [Lu(dipic)(3)](3-) anionic planes and [Cs(+), H(2)O] cationic planes. In the crystal structure, although the H atoms attached to water mol-ecules could not be located, short O-O contacts clearly indicate the occurrence of an intricate hydrogen-bonded network through contacts with other water mol-ecules, Cs cations or with the O atoms of the dipicolinate ligands.

International audience; A Reply to the Comment by Ludger Wirtz et al..

International audience; Density functional calculations have been carried out on three families of lanthanide complexes of D3 or C4 symmetry, namely [Ln(H2O)9]3+, [Ln(DPA)3]3-, and [Ln(DOTAM)]3+ (Ln = Y, La, Lu; DPA = pyridine-2,6-dicarboxylate; DOTAM = 1,4,7,10-tetracarbamoylmethyl-1,4,7,10-tetraazacyclododecane), to get some insights concerning the sensitivity of 4f electrons to the surrounding ligands. We show that the electron density accumulations found within 0.7 A of the metal center, that precisely give the opposite image of the coordination sphere as they are located trans with respect to the Ln-ligand bonds, are almost exclusively due the f electrons. This polarization of the 4f electrons in lanthanides complexes has therefore to be considered as a general feature that plays a crucial role in some experimentally observed phenomenons such as the dependency of quadratic hyperpolarizability to the number of f electrons in [Ln(DPA)3]3- complexes that we have evidenced.

International audience; Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid-solid phase transition of an incommensurate host-guest system: the channel inclusion compound of nonadecane/urea. Strikingly, this phase transition generates a unit cell doubling that concerns only the modulation of one substructure by the other-an internal variable available only in superspace. This unanticipated pathway for degrees of freedom to rearrange leads to a second phase transition, which again is controlled by the higher dimensionality of superspace. These results reveal nature's capacity to explore the increased number of phases allowed in aperiodic crystals.

The calculated quasiparticle band structure of bulk hexagonal boron nitride using the all-electron GW approximation shows that this compound is an indirect-band-gap semiconductor. The solution of the Bethe-Salpeter equation for the electron-hole two-particle Green function has been used to compute its optical spectra and the results are found in excellent agreement with available experimental data. A detailed analysis is made for the excitonic structures within the band gap and found that the excitons belong to the Frenkel class and are tightly confined within the layers. The calculated exciton binding energy is much larger than that obtained by Watanabe {\it et al} using a Wannier model to interpret their experimental results and assuming that h-BN is a direct-band-gap semiconductor., Comment: 4 pages, 3 figures

International audience; We report on striking evidence for a room temperature structural phase instability in p-hexaphenyl, inducing a nonplanar conformation of the molecules. Solid state proton NMR and single crystal x-ray diffraction allow the analysis of the organization, the individual dynamics and the involved symmetry breaking. The analysis of Raman spectra above and below room temperature reveals a singular behavior suggesting a modification of the overlap between the electronic wave function induced by the non-planarity. These results provide a new basis to answer fundamental issues related to molecular and electronic materials and, in particular, luminescent organic devices.

International audience; A detailed theoretical study based on first-principles DFT calculations is reported for the charge transfer complex 2,6-dimethyltetrathiafulvalene-p-chloranil (DMTTF−CA). Charge transfer estimates reveal that no periodic ordering of neutral and ionic layers is obtained in the low-temperature phase of DMTTF−CA. Similarities and differences with other mixed-stack charge transfer complexes are discussed with the help of a topological analysis of the electron density. Our results also show that the most popular model in this field, which is based on the balance between the cost of ionization and the gain in Madelung energy, should be used with great care. These molecules are far from being point charges, and molecular deformation and polarization should not be ignored.

International audience; Topological analysis of electron densities sampled on 3D grids have been performed on two different crystalline compounds-ammonium dihydrogen phosphate and urea-using the software package InteGriTy and the results are compared to that of analytical derivation from the software Newprop and TOPOND. Both critical points and integrated quantities are considered with emphasis put on bond critical points and atomic charges.

We report the direct observation by x-ray diffraction of a photoinduced paraelectric-to-ferroelectric structural phase transition using monochromatic 100-picosecond synchrotron pulses. It occurs in tetrathiafulvalene- p -chloranil, a charge-transfer molecular material in which electronic and structural changes are strongly coupled. An optical 300-femtosecond laser pulse switches the material from a neutral to an ionic state on a 500-picosecond time scale and, by virtue of intrinsic cooperativity, generates self-organized long-range structural order. The x-ray data indicate a macroscopic ferroelectric reorganization after the laser irradiation. Refinement of the structures before and after laser irradiation indicates structural changes at the molecular level.

Claudine Katan ‘s present address : CNRS UMR6082 FOTON, INSA de Rennes, 20 avenue des Buttes de Coësmes, CS 70839, 35708 RENNES cedex 7, France; International audience; InteGriTy is a software package that performs topological analysis following the AIM (atoms in molecules) approach on electron densities given on three-dimensional grids. Tricubic interpolation is used to obtain the density, its gradient and the Hessian matrix at any required position. Critical points and integrated atomic properties have been derived from theoretical densities calculated for the compounds NaCl and TTF-(2,5)Cl(2)BQ (tetrathiafulvalene-2,5-dichlorobenzoquinone), thus covering the different kinds of chemical bonds: ionic, covalent, hydrogen bonds and other intermolecular contacts.

The prototype compound for the neutral-ionic phase transition, namely TTF-CA, is theoretically investigated by first-principles density functional theory calculations. The study is based on three neutron diffraction structures collected at 40, 90 and 300 K (Le Cointe et al., Phys. Rev. B 51, 3374 (1995)). By means of a topological analysis of the total charge densities, we provide a very precise picture of intra and inter-chain interactions. Moreover, our calculations reveal that the thermal lattice contraction reduces the indirect band gap of this organic semi-conductor in the neutral phase, and nearly closes it in the vicinity of the transition temperature. A possible mechanism of the neutral-ionic phase transition is discussed. The charge transfer from TTF to CA is also derived by using three different technics., Comment: 11 pages, 9 figures, 7 tables

Small molecules, such as urea, thiourea, perhydrotriphenylene can be co-crystallised with long-chain hydrocarbon molecules to form inclusion compounds. The guest chains are confined to narrow, approximately cylindrical, channels created by the host small-molecule lattice. The stoichiometry and the conformations of the chains included inside the channels are function of internal interactions such as intra-chain interaction, but also of overall co-operative properties of the resulting three dimensionally ordered single crystal. These intergrowth compounds may form incommensurate composite crystals. A prototype example of such uniaxial intergrowth aperiodic crystals is n-alkane (CnH2n+2)/urea (CO(NH2)2). In these supra-molecular systems, urea molecules are connected by H-bonds and form helical ribbons, which repeat every six urea molecules to form a series of linear, hexagonal tunnels that can accommodate linear alkanes. Because the channels (~0.53 nm) are larger than the hydrocarbon chains, guests are held loosely and can undergo substantial motions. A significant amount of diffuse scattering of the first and second kinds can be depicted in scattering experiments, static or dynamic. These materials undergo a large variety of continuous or weakly first order structural phase transitions when changing the alkane molecule length and giving place to large pre-transitional effects. The talk will give an overview of the diffuse scattering in these compounds and will focus on connection with aperiodicity.

Modern crystallography makes intense use of large scale facilities: neutron reactors, synchrotron sources, free electron lasers, where sources, optics and detectors allow for a wide range of possible experiments putting forwards the limits of the analysis of the structure and dynamics of matter and materials. Giving the large scale facilities a major role in the teaching of crystallography and material science, allowing for intense practice, requires to gather different skills which is more often done through summer school or intensive programs at PhD or junior scientist level. The Erasmus Mundus Master Course MaMaSELF (Master in Material Science Exploring Large Scale Facilities) is a unique European master program focused on the use of large scale facilities to investigate intimate nature of matter and materials where the five consortium higher education institutions (University of Rennes 1, France; Technische Universität München and Ludwig Maximilian University in München, Germany; University of Torino, Italy and University of Montpellier 2, France) have managed, together with Large Scale Facilities partners (ESRF, ILL, FRMII, DESY, LLB, SOLEIL, PSI) and third country partners spread out all over the world (Brazil, India, Japan, Russia, Switzerland , USA), to offer to the students a two years program at the master level including large amount of crystallography and spectroscopy teaching and an intensive summer-school totally dedicated to large scale facilities and including a large proportion of lessons and labs taught by experts, as well as many internship and master thesis opportunities at the large scale facilities.