Three-dimensional lanthanide-organic frameworks based on di-, tetra-, and hexameric clusters

Three-dimensional lanthanide-organic frameworks formulated as (CH3)2NH2[Ln(pydc)2] · 1/2H2O [Ln3+ ) Eu3+ (1a) or Er3+ (1b); pydc2- corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H2pydc)], [Er4(OH)4(pydc)4(H2O)3] ·H2O (2), and [PrIII 2PrIV 1.25O(OH)3(pydc)3] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide - DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction, thermogravimetric analysis, vibrational spectroscopy (FT-IR and FT-Raman), electron microscopy, and CHN elemental analysis. While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction of anionic ∞ 3{[Ln(pydc)2]-} frameworks having the channels filled by the charge-balancing (CH3)2NH2 + cations generated in situ by the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3 contain instead tetrameric [Er4(μ3-OH)4]8+ and hexameric |Pr6(μ3-O)2(μ3-OH)6| clusters which act as the building blocks of the networks, and are bridged by the H2-xpydcx- residues. It is demonstrated that this modular approach is reflected in the topological nature of the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 °C with this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core

Helium behavior in implanted B4C boron carbide

International audienc

Impact of disorder on ionic charge in spinel compounds

International audienceIn order to obtain a correlation between the ionic charge and the local environment, the evolution of valence charges of cations in different 2-3 spinel compounds was investigated as a function of the temperature. The evolution of the structural parameters in normal (MgAl(2)O(4)), mixed (MgGa(2)O(4)) and inverse (MgIn(2)O(4)) spinels as a function of the temperature was extracted from X-ray diffraction patterns collected during different thermal annealings. The evolution of these structural parameters as a function of the disorder is analyzed within the bond valence shell model: large variations of the cation valence are observed in these three spinel compounds. From this analysis, a strong correlation between the change of the cation valence and the local disorder is pointed out. Including this dependence in the microscopic models may provide a better agreement between experimental observations and simulations. (C) 2008 Elsevier B.V. All rights reserved

Towards precise evaluation of hydration in protonic and mixed H+/e-conducteurs

International audienc

Insights on the Electrochemical Magnesiation of InSb from Combined Operando X-ray Diffraction and X-ray Absorption Spectroscopy

International audienceThe continued acceleration of the lithium demand combined with its relatively low abundance and uneven concentration on the Earth's crust might dramatically increase its price in a near future. Mg-batteries are promising candidates to replace Li-ion batteries thanks to Mg abundance, theoretical capacity (2.2Ah/g-3.8Ah/cm$^3$), low cost and safety. However, metallic Mg reacts with standard electrolytes to form a blocking layer on its surface, preventing cation exchange, and thus dramatically limiting reversible stripping/deposition. An interesting alternative is to substitute Mg metal with another negative electrode made of p-block elements as they electrochemically alloy with Mg and possess adequate stability in standard electrolytes.In a recent work, we investigated the InSb alloy as a negative electrode in order to fundamentally understand the electrochemical reactions occurring in alloys in Mg batteries. A strong synergy between In and Sb has been evidenced with the promotion of the electrochemical activity of Sb towards magnesiation along few cycles, in contrast to what was already reported in other studies.Using complementary information from operando X-Ray diffraction (XRD) and X-Ray Absorption Spectrosopy (XAS), we further characterized in-depth the peculiar electrochemical behavior of InSb. Operando XRD measurements demonstrate the formation of the Mg$_3$Sb$_2$ phase almost all along the first magnesiation, accompanied by the extrusion of In metal. While crystalline MgIn has always been detected in the case of pure In or InBi electrodes, we observed a kinetically dependent electrochemically-driven amorphization of MgIn. This behavior suggests a possible competition between crystallization and amorphization in the material. EXAFS data, obtained at the In and Sb K-edges at the ROCK beamline of synchrotron Soleil, corroborate the formation of Mg$_3$Sb$_2$ and In crystalline phases but also the formation of MgIn. It gives us further insights on the atomic environment of In and Sb during the first magnesiation. Thanks to the evolution of EXAFS spectra as well as the changes in scattering paths, the phase proportions evolution as function of the number of Mg inserted into InSb has been followed. These results are of paramount importance to shed light on synergetic effects between $p$-block elements and to study the relation between $in\ situ$ amorphization and electrochemical behavior