Crystal structure and chemistry of barium-graphite intercalation compounds

Graphite can accommodate various chemical species between graphene layers to form graphite intercalation compounds (GIC) [1]. Alkali metals can easily lead to bulk stage-1 intercalation compounds by vapor transport but for more electronegative elements, such as alkaline-earth metals or lanthanides, only a superficial intercalation is obtained and other synthesis methods have to be envisaged. Molten alloys, formed between an alkali metal and the targeted metal, have demonstrated their efficiency to prepare bulk and homogeneous GIC from these latter elements, for example the superconducting CaC6 phase [2], but some elements remain difficult to intercalate by this method. More recently, our team developed a method based on the work of Hagiwara et al., consisting in using a LiCl-KCl eutectic molten medium [3], which for example allowed to prepare for the first time a bulk SrC6 compound [4]. This work is focused on the intercalation of barium into graphite from the LiCl-KCl molten salts method. A bulk stage-1 BaC6 compound has been prepared and X-ray diffraction measurements confirmed its crystal structure [5]. Moreover, by varying the experimental conditions, two completely novel phases, denoted α and β, have been isolated. From ion beam analyses, Li0,2K0,6Ba0,35C6 and Li0,2K0,75Ba0,6C6 chemical formulae have been determined for α and β phases, respectively, showing that lithium and potassium are intercalated together with barium. X- ray diffraction led to the determination of the stacking sequence of each compound, and their planar unit cells. Lastly, a reaction mechanism is proposed, which explains the formation of the different phases observed in this study

Parenting Culture(s): Ideal-Parent Beliefs Across 37 Countries

What is it to be “an ideal parent”? Does the answer differ across countries and social classes? To answer these questions in a way that minimizes bias and ethnocentrism, we used open-ended questions to explore ideal-parent beliefs among 8,357 mothers and 3,517 fathers from 37 countries. Leximancer Semantic Network Analysis was utilized to first determine parenting culture zones (i.e., countries with shared ideal-parent beliefs) and then extract the predominant themes and concepts in each culture zone. The results yielded specific types of ideal-parent beliefs in five parenting culture zones: being “responsible and children/family-focused” for Asian parents, being “responsible and proper demeanor-focused” for African parents, and being “loving and responsible” for Hispanic-Italian parents. Although the most important themes and concepts were the same in the final two zones—being “loving and patient,” there were subtle differences: English-speaking, European Union, and Russian parents emphasized “being caring,” while French-speaking parents valued “listening” or being “present.” Ideal-parent beliefs also differed by education levels within culture zones, but no general pattern was discerned across culture zones. These findings suggest that the country in which parents were born cannot fully explain their differences in ideal-parent beliefs and that differences arising from social class or education level cannot be dismissed. Future research should consider how these differences affect the validity of the measurements in question and how they can be incorporated into parenting intervention research within and across cultures

Parenting Culture(s): Ideal-Parent Beliefs Across 37 Countries

What is it to be “an ideal parent”? Does the answer differ across countries and social classes? To answer these questions in a way that minimizes bias and ethnocentrism, we used open-ended questions to explore ideal-parent beliefs among 8,357 mothers and 3,517 fathers from 37 countries. Leximancer Semantic Network Analysis was utilized to first determine parenting culture zones (i.e., countries with shared ideal-parent beliefs) and then extract the predominant themes and concepts in each culture zone. The results yielded specific types of ideal-parent beliefs in five parenting culture zones: being “responsible and children/family-focused” for Asian parents, being “responsible and proper demeanor-focused” for African parents, and being “loving and responsible” for Hispanic-Italian parents. Although the most important themes and concepts were the same in the final two zones—being “loving and patient,” there were subtle differences: English-speaking, European Union, and Russian parents emphasized “being caring,” while French-speaking parents valued “listening” or being “present.” Ideal-parent beliefs also differed by education levels within culture zones, but no general pattern was discerned across culture zones. These findings suggest that the country in which parents were born cannot fully explain their differences in ideal-parent beliefs and that differences arising from social class or education level cannot be dismissed. Future research should consider how these differences affect the validity of the measurements in question and how they can be incorporated into parenting intervention research within and across cultures

Utilisation du détecteur courbe CPS 120 INEL en position horizontale ou verticale. Application à l'étude des composés d'insertion graphite-lithium

En utilisant les propriétés texturales des matériaux lamellaires ou fibrillaires hautement orientés, nous pouvons étudier "in-situ" la structure de composés, au cours de leur insertion, selon la méthode du "cristal tournant". Pour cela, nous avons réalisé un diffractomètre muni d'un détecteur courbe (CPS 120 INEL), que l'on peut placer horizontalement ou verticalement de manière à envelopper la sphère d'Ewald pour l'enregistrement des rangées (hkl)* que l'on souhaite étudier. L'échantillon est fixe ; le montage, par transmission. Ce dispositif nous a permis de mettre en évidence la modification de l'empilement des feuillets de graphène dans les composés d'insertion graphite-lithium de deuxième stade et de compléter la caractérisation structurale de ces composés.The textural properties of lamellar or fibrillar highly onented materials permit studying "in-situ" the structure changes which accompany intercalation into them, using the "rotating-crystal" method. To do so, we have used a diffractometer equipped with an INEL CPS 120 detector which can be placed in either a horizontal or vertical position, so as to completely encompass the Ewald sphere and allow recording the (hkl)* rods at any given point of reciprocal space. The sample is fixed in position and we used a transmission setup. We show the expenmental diagrams corresponding to the graphene stacking changes in second stage graphite-lithium intercalation compounds which have allowed completing the structural characterization of these phases

Carbon aerogels prepared by autocondensation of flavonoid tannin

International audienc

Challenges and Prospects of RF Oscillators Using Silicon Resonant Tunneling Diodes

International audienc

Floating hollow carbon spheres for improved solar evaporation

International audienc

Covalent functionalization of polyhedral graphitic particles synthesized by arc discharge from graphite

International audienc

Hydrophobised carbon foams for improved long-term seasonal solar thermal energy storage

International audienceComposites carbon foams based on sucrose-based char matrix and graphite filler were prepared and characterised with the aim of hosting sugar alcohols as phase-change materials (PCMs) in the context of thermal energy storage (TES). Seasonal solar TES demands an excellent undercooling of the molten PCM infiltrated in the foam, so that the heat can be stored as long as possible. The present paper demonstrates how the surface of such composite foams, i.e., comprising two carbon phases of different reactivities, can be modified for promoting undercooling. For that purpose, 8 different hydrophobisation treatments were applied, and the results were compared with those of the non-treated foam, in which heterogeneous nucleation could not be avoided. We show that one kind of functionalisation was successful, i.e., it fully preserved the melting point and the enthalpy of melting of the hosted phase-change material and completely avoided the heterogeneous nucleation of the PCM, while maintaining the thermal conductivity in the range required for this kind of application