Conditions Extrêmes et Matériaux Haute Température et Irradiation

Abstract With the description of more and more complex one‐ and two‐dimensional NMR experiments comes the need to develop methods to make a comprehensive interpretation of the various different experiments that can be carried out on the same sample or series of related samples. We present some examples of modelling one‐ and two‐dimensional solid‐state NMR spectra of I = ½ spin and quadrupolar nuclei, using laboratory‐developed software that is made available to the NMR community. Copyright © 2001 John Wiley & Sons, Ltd.

We report the realization of a quantum circuit in which an ensemble of electronic spins is coupled to a frequency tunable superconducting resonator. The spins are nitrogen-vacancy centers in a diamond crystal. The achievement of strong coupling is manifested by the appearance of a vacuum Rabi splitting in the transmission spectrum of the resonator when its frequency is tuned through the nitrogen-vacancy center electron spin resonance.

BACKGROUND: Disordered compounds are crucially important for fundamental science and industrial applications. Yet most available methods to explore solid-state material properties require ideal periodicity, which, strictly speaking, does not exist in this type of materials. The supercell approximation is a way to imply periodicity to disordered systems while preserving "disordered" properties at the local level. Although this approach is very common, most of the reported research still uses supercells that are constructed "by hand" and ad-hoc. RESULTS: This paper describes a software named supercell, which has been designed to facilitate the construction of structural models for the description of vacancy or substitution defects in otherwise periodically-ordered (crystalline) materials. The presented software allows to apply the supercell approximation systematically with an all-in-one implementation of algorithms for structure manipulation, supercell generation, permutations of atoms and vacancies, charge balancing, detecting symmetry-equivalent structures, Coulomb energy calculations and sampling output configurations. The mathematical and physical backgrounds of the program are presented, along with an explanation of the main algorithms and relevant technical details of their implementation. Practical applications of the program to different types of solid-state materials are given to illustrate some of its potential fields of application. Comparisons of the various algorithms implemented within supercell with similar solutions are presented where possible. CONCLUSIONS: The all-in-one approach to process point disordered structures, powerful command line interface, excellent performance, flexibility and GNU GPL license make the supercell program a versatile set of tools for disordered structures manipulations.

Abstract A novel microporous templated carbon material doped with nitrogen is synthesized by using a two‐step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na–Y zeolite as a scaffold. Liquid‐phase impregnation and in situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas‐phase impregnation with propylene, enables pore‐size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore‐size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area ( S BET = 1680 m 2 g –1 ), the templated carbon material displays a large gravimetric capacitance (340 F g –1 ) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2 V in an aqueous medium with good cycleability—‐beyond 10 000 cycles—and is extremely promising for use in the development of high‐energy‐density supercapacitors.

The local structure of carbon spheres obtained via the hydrothermal carbonization process is characterized by using a combination of advanced solid-state 13C NMR techniques. Glucose was chosen as the starting product because it offers the possibility of 13C isotopic enrichment and is regarded as a model compound for more complex polysaccharides and biomass, as reported in recent studies. A number of 13C solid-state MAS NMR techniques (single-pulse, cross-polarization, inversion recovery cross-polarization, INEPT, 13C−13C proton-driven magnetization exchange, and 13C−13C double-quantum−single-quantum correlation experiments) were combined to retrieve information about binding motifs and C−C closest neighbor relations. We found that the core of the carbonaceous scaffold is composed of furan rings cross-linked by domains containing short keto-aliphatic chains instead of otherwise expected graphene-type sheets, as mainly reported either for hydrothermal carbon spheres or for biomass-related carbons obtained by low-temperature (<350 °C) pyrolysis treatment.

The red long-lasting luminescence properties of the ZnGa2O4:Cr3+ spinel material are shown to be much improved when germanium or tin is substituted to the nominal composition. The resulting Zn1+xGa2–2x(Ge/Sn)xO4 (0 ≤ x ≤ 0.5) spinel solid solutions synthesized here by a classic solid state method have been structurally characterized by X-ray and neutron powder diffraction refinements coupled to 71Ga solid state NMR studies. In contrast to ZnGa2O4:Cr3+ for which long lasting luminescence properties have been reported to arise from tetrahedral positively charged defects resulting from the spinel inversion, our results show that a different mechanism occurs complementary for Zn1+xGa2–2x(Ge/Sn)xO4. Here, the great enhancement of the brightness and decay time of the long lasting luminescence properties is directly driven by the substitution mechanism which creates distorted octahedral sites surrounded by octahedral Ge and Sn positive substitutional defects which likely act as new efficient traps.

Transparent ceramics have various potential applications such as infrared (IR) windows/domes, lamp envelopes, opto-electric components/devices, composite armors, and screens for smartphones and they can be used as host materials for solid-state lasers. Transparent ceramics were initially developed to replace single crystals because of their simple processing route, variability in composition, high yield productivity, and shape control, among other factors. Optical transparency is one of the most important properties of transparent ceramics. In order to achieve transparency, ceramics must have highly symmetric crystal structures; therefore, the majority of the transparent ceramics have cubic structures, while tetragonal and hexagonal structures have also been reported in the open literature. Moreover, the optical transparency of ceramics is determined by their purity and density; the production of high-purity ceramics requires high-purity starting materials, and the production of high-density ceramics requires sophisticated sintering techniques and optimized sintering aids. Furthermore, specific mechanical properties are required for some applications, such as window materials and composite armor. This review aims to summarize recent progress in the fabrication and application of various transparent ceramics.

Glass-ceramics are noted for their unusual combination of properties and manifold commercialized products for consumer and specialized markets. Evolution of novel glass and ceramic processing routes, a plethora of new compositions, and unique exotic nano- and microstructures over the past 60 years led us to review the definition of glass-ceramics. Well-established and emerging processing methods, such as co-firing, additive manufacturing, and laser patterning are analyzed concerning the core requirements of processing glass-ceramics and the performance of the final products. In this communication, we propose a revised, updated definition of glass-ceramics, which reads “Glass-ceramics are inorganic, non-metallic materials prepared by controlled crystallization of glasses via different processing methods. They contain at least one type of functional crystalline phase and a residual glass. The volume fraction crystallized may vary from ppm to almost 100%”.

Drying natural gas efficiently Natural gas must be purified before it can be transported. The preparation process also includes a drying step to remove water. Microporous adsorbents such as zeolites are used for this purpose, but they often need to be heated to temperatures up to 250°C to remove the water so that they can be reused. Cadiau et al. describe a fluorinated metal-organic framework containing nickel metal centers that can remove water from gas streams but that can be regenerated by heating to only 105°C. Science , this issue p. 731

Abstract Proton conductive materials are of significant importance and highly desired for clean energy-related applications. Discovery of practical metal-organic frameworks (MOFs) with high proton conduction remains a challenge due to the use of toxic chemicals, inconvenient ligand preparation and complication of production at scale for the state-of-the-art candidates. Herein, we report a zirconium-MOF, MIP-202(Zr), constructed from natural α-amino acid showing a high and steady proton conductivity of 0.011 S cm −1 at 363 K and under 95% relative humidity. This MOF features a cost-effective, green and scalable preparation with a very high space-time yield above 7000 kg m −3 day −1 . It exhibits a good chemical stability under various conditions, including solutions of wide pH range and boiling water. Finally, a comprehensive molecular simulation was carried out to shed light on the proton conduction mechanism. All together these features make MIP-202(Zr) one of the most promising candidates to approach the commercial benchmark Nafion.

Electrically conductive regions in Earth's mantle have been interpreted to reflect the presence of either silicate melt or water dissolved in olivine. On the basis of laboratory measurements, we show that molten carbonates have electrical conductivities that are three orders of magnitude higher than those of molten silicate and five orders of magnitude higher than those of hydrated olivine. High conductivities in the asthenosphere probably indicate the presence of small amounts of carbonate melt in peridotite and can therefore be interpreted in terms of carbon concentration in the upper mantle. We show that the conductivity of the oceanic asthenosphere can be explained by 0.1 volume percent of carbonatite melts on average, which agrees with the carbon dioxide content of mid-ocean ridge basalts.

Batteries for electrical storage are central to any future alternative energy paradigm. The ability to probe the redox mechanisms occurring at electrodes during their operation is essential to improve battery performances. Here we present the first report on Electron Paramagnetic Resonance operando spectroscopy and in situ imaging of a Li-ion battery using Li2Ru0.75Sn0.25O3, a high-capacity (>270 mAh g(-1)) Li-rich layered oxide, as positive electrode. By monitoring operando the electron paramagnetic resonance signals of Ru(5+) and paramagnetic oxygen species, we unambiguously prove the formation of reversible (O2)(n-) species that contribute to their high capacity. In addition, we visualize by imaging with micrometric resolution the plating/stripping of Li at the negative electrode and highlight the zones of nucleation and growth of Ru(5+)/oxygen species at the positive electrode. This efficient way to locate 'electron'-related phenomena opens a new area in the field of battery characterization that should enable future breakthroughs in battery research.

An homogeneous stirred reactor designed for kinetic studies of hydrocarbon oxidation in the intermediate temperature range is described. The originality of this reactor lies in its ability to operate under pressure up to 10 atm ( approximately 1 MPa). The design of the injectors makes it possible to move a thermocouple and a sampling probe throughout a whole diameter of the reactor.

The structural and electrochemical features of layered 0.5Li2MnO3·0.5LiMO2 electrodes, in which M = Mn0.5−xNi0.5−xCo2x (0 ≤ x ≤ 0.5), have been studied by powder X-ray diffraction, electrochemical differential-capacity measurements, 7Li magic-angle-spinning nuclear magnetic resonance, and X-ray absorption near-edge spectroscopy. Li2MnO3-like regions in the as-prepared samples were observed for all values of x, with transition-metal cation disorder between the LiMO2 and Li2MnO3 components increasing with cobalt content (i.e., the value of x). The structural disorder and complexity of the electrochemical redox reactions increase when the Li2MnO3-like regions within the electrode are activated to 4.6 V in lithium cells; interpretations of structural and electrochemical phenomena are provided.

UNLABELLED: The search for traces of life is one of the principal objectives of Mars exploration. Central to this objective is the concept of habitability, the set of conditions that allows the appearance of life and successful establishment of microorganisms in any one location. While environmental conditions may have been conducive to the appearance of life early in martian history, habitable conditions were always heterogeneous on a spatial scale and in a geological time frame. This "punctuated" scenario of habitability would have had important consequences for the evolution of martian life, as well as for the presence and preservation of traces of life at a specific landing site. We hypothesize that, given the lack of long-term, continuous habitability, if martian life developed, it was (and may still be) chemotrophic and anaerobic. Obtaining nutrition from the same kinds of sources as early terrestrial chemotrophic life and living in the same kinds of environments, the fossilized traces of the latter serve as useful proxies for understanding the potential distribution of martian chemotrophs and their fossilized traces. Thus, comparison with analog, anaerobic, volcanic terrestrial environments (Early Archean >3.5-3.33 Ga) shows that the fossil remains of chemotrophs in such environments were common, although sparsely distributed, except in the vicinity of hydrothermal activity where nutrients were readily available. Moreover, the traces of these kinds of microorganisms can be well preserved, provided that they are rapidly mineralized and that the sediments in which they occur are rapidly cemented. We evaluate the biogenicity of these signatures by comparing them to possible abiotic features. Finally, we discuss the implications of different scenarios for life on Mars for detection by in situ exploration, ranging from its non-appearance, through preserved traces of life, to the presence of living microorganisms. KEY WORDS: Mars-Early Earth-Anaerobic chemotrophs-Biosignatures-Astrobiology missions to Mars.

Herein we show that hydrazine intercalation into 2D titanium carbide (Ti3C2-based MXene) results in changes in its surface chemistry by decreasing the amounts of fluorine, OH surface groups and intercalated water. It also creates a pillaring effect between Ti3C2Tx layers pre-opening the structure and improving the accessability to active sites. The hydrazine treated material has demonstrated a greatly improved capacitance of 250 F g(-1) in acidic electrolytes with an excellent cycling ability for electrodes as thick as 75 μm.

Abstract Order‐disorder phenomena in binary oxides with fluorite‐related structures were studied by Raman spectroscopy. Raman spectra of disordered phases show broad bands, defects leading to selection rule breakdown. For well‐ordered structures, the scattering active modes observed are those allowed by crystal symmetry. Broadening of Raman peaks occurs when order defects are present: antiphase boundaries, distribution of different cations on equivalent crystallographic positions.

We present measurements of longitudinal ultrasonic velocity on single crystals of the heavy-fermion superconductor ${\mathrm{UPt}}_{3}$. The measurements show clear signatures of second-order phase transitions in the superconducting state, with the velocity anomalies well accounted for by Ginzburg-Landau theory. From these signatures we construct a phase diagram for ${\mathrm{UPt}}_{3}$ that reveals all the boundary lines that have been identified as possible phase transitions. We are able to track the phase transition lines to a tetracritical point, located on the upper-critical-field curve, to within the width of the normal-superconducting transition.

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible.

Abstract Developing multielectron reaction electrode materials is essential for achieving high specific capacity and high energy density in secondary batteries; however, it remains a great challenge. Herein, Na 3 MnTi(PO 4 ) 3 /C hollow microspheres with an open and stable NASICON framework are synthesized by a spray‐drying‐assisted process. When applied as a cathode material for sodium‐ion batteries, the resultant Na 3 MnTi(PO 4 ) 3 /C microspheres demonstrate fully reversible three‐electron redox reactions, corresponding to the Ti 3+/4+ (≈2.1 V), Mn 2+/3+ (≈3.5 V), and Mn 3+/4+ (≈4.0 V vs Na + /Na) redox couples. In situ X‐ray diffraction results reveals that both solid‐solution and two‐phase electrochemical reactions are involved in the sodiation/desodiation processes. The high specific capacity (160 mAh g −1 at 0.2 C), outstanding cyclability (≈92% capacity retention after 500 cycles at 2 C), and the facile synthesis make the Na 3 MnTi(PO 4 ) 3 /C a prospective cathode material for sodium‐ion batteries.