Experimental and theoretical investigations of friction properties of graphite intercalated compounds.

It is classically admitted that the goodfriction properties of lamellar compounds are strongly related to their anisotropic structure and especially to the existence of weak interlayer interactions through the van der Waals gap separating the basal layers. As it is also known, the presence of the van der Waals gap in the structure of lamellar compounds will allow lot of chemical species to be intercalated in the structure leading both to the expansion of structure parameters and inter layer interactions modifications. The present work is concerned with the experimental and theoretical study of friction propertiesof Graphite Intercalated Compounds (GICs) in order to better understand thetribologiclamellar compounds. In order to modulate the interlayer interactions, two types of intercalated species were used, electrophylic species (AlCl3, FeCl3, SbCl5) and nucleophilic species (Li, K, Rb)

Complexation of Nickel Ions by Boric Acid or (Poly)borates

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Deciphering the epigenetic alphabet involved in transgenerational stress memory in crops

Although epigenetic modifications have been intensely investigated over the last decade due to their role in crop adaptation to rapid climate change, it is unclear which epigenetic changes are heritable and therefore transmitted to their progeny. The identification of epigenetic marks that are transmitted to the next generations is of primary importance for their use in breeding and for the development of new cultivars with a broad-spectrum of tolerance/resistance to abiotic and biotic stresses. In this review, we discuss general aspects of plant responses to environmental stresses and provide an overview of recent findings on the role of transgenerational epigenetic modifications in crops. In addition, we take the opportunity to describe the aims of EPI-CATCH, an international COST action consortium composed by researchers from 28 countries. The aim of this COST action launched in 2020 is: (1) to define standardized pipelines and methods used in the study of epigenetic mechanisms in plants, (2) update, share, and exchange findings in epigenetic responses to environmental stresses in plants, (3) develop new concepts and frontiers in plant epigenetics and epigenomics, (4) enhance dissemination, communication, and transfer of knowledge in plant epigenetics and epigenomics

Pressure-dependent Raman scattering of polycrystalline KNb1-xTaxO3 solid solutions

International audienceWe report experimental and calculated Raman scattering investigations of KNb 1-x Ta x O 3 (x = 0.4, 0.5, 0.6) solid solutions as a function of hydrostatic pressure. The observed phase transitions sequence in the range from room pressure to 12 GPa is similar to the temperature-induced structural phase transformations: orthorhombic (ferroelectric) to tetragonal (ferroelectric (ferroelectric) to cubic (paraelectric). Furthermore, it was observed that the domain of stability of ferroelectricity at high pressures increases with Nb-content. For the first time, some DFT calculations of theoretical Raman spectra are reported in order to support the experimental observations of pressure-induced phase transitions

First-principles investigation of CO2, CO, and O2 adsorptions on the (001)-reconstructed surfaces of CsPbX3 (X = Cl, Br, and I) perovskites

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A comment on ‘‘The interaction of X 2 (X = F, Cl, and Br) with active sites of graphite” [Xu et al., Chem. Phys. Lett., 418, 413 (2006)]

International audienceA comment on "The interaction of X2 (X = F, Cl, and Br) with active sites of graphite" [Xu et al., Chem. Abstract In their article, Xu et al. [1] present the adsorption energies for the chemisorption of the three halogens F 2, Cl 2, and Br 2 on the active sites of graphite. The three investigated systems are the three most stable surfaces, (001), (100), and (110); the latter two are also called zigzag and armchair surface, respectively. Due to some inconsistencies in their article, we re-evaluated the results of Xu et al. in order to investigate the impact on the adsorption energies of the halogens. For the (001) surface, our results agree with Xu et al. However, for the other two surfaces, we find major differences. Contrary to Xu et al., we find that the halogens adsorb the strongest on the zigzag surface. The second strongest adsorption is found on the armchair surface for the symmetric configurations, the third strongest for the asymmetric configurations. Several reasons are given which explain this discrepancy. The most striking source of error in the work of Xu et al. is due to the fact that they did not choose the correct spin multiplicities for the model systems which means that they performed the calculations in excited states. This leads to errors between 50-600% for the zigzag surface and 3-42% for the armchair surface

Adsorption of Atomic Hydrogen on Defect Sites of Graphite: Influence of Surface Reconstruction and Irradiation Damage

International audienceThe influence of surface reconstruction and defects due to irradiation damage on the trapping of hydrogen in nuclear graphite has been investigated at the ab initio level. Several models of defects and surfaces have been studied and compared with previously proposed traps, i.e. the zig-zag edge of dislocation loops and reconstructed surfaces of graphite crystallites. The relative stabilities of hydrogen adsorption on the (100), (110), and (001) graphite basic planes have been evaluated for different amounts of hydrogen coverage and various types of reconstruction. The unreconstructed (100) surface adsorbs hydrogen the strongest. The (100) and (110) surface reconstructions result in decreased stability for H adsorption compared to unrelaxed surfaces. Point defects caused by irradiation, such as mono-and divacancies, also trap hydrogen. We find that extended defects are weaker traps than monovacancies. This is true for surface defects as well as for bulk defects. The obtained results show that the existing hypothesis for trapping at dislocation loops has to be refined. Finally, an agreement with experiments is obtained for trapping on the reconstructed surfaces

Phase transformation in SrTi0.6Zr0.4O3 : a high-pressure Raman and X-ray diffraction study

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