Browsing by Author "Fauth, F"

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    Crystallographic and magnetic structures of the VI3 and LiVI3 van der Waals compounds
    (American Physical Society, 2021-07-12) Marchandier, T; Dubouis, N; Fauth, F; Avdeev, M; Grimaud, A; Tarascon, JM; Rousse, G
    Two-dimensional (2D) layered magnetic materials are generating a great amount of interest for the next generation of electronic devices thanks to their remarkable properties associated with spin dynamics. The recently discovered layered VI3 ferromagnetic phase belongs to this family, although a full understanding of its properties is limited by the incomplete understanding of its crystallographic structure. The motivation of this work is to address this issue. Here, we investigate the VI3 crystal structures at low temperature using both synchrotron x-ray and neutron powder diffraction and provide structural models for the two structural transitions occurring at 76 and 32 K. Moreover, we confirm by magnetic measurements that VI3 becomes ferromagnetic at 50 K and we question the establishment of a long-range magnetic structure by neutron diffraction. We equally determined the magnetic properties of our recently reported LiVI3 phase, which is like the well-known CrI3 ferromagnetic phase in terms of electronic and crystallographic structures and found an antiferromagnetic behavior with a Néel temperature of 12 K. Such a finding provides extra clues for a better understanding of magnetism in these low-dimension compounds. Finally, the easiness of preparing Li-based 2D magnetic materials by chemical/electrochemical means opens wide the opportunity to design materials with exotic properties. ©2021 American Physical Society
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    Extending insertion electrochemistry to soluble layered halides with superconcentrated electrolytes
    (Springer Nature, 2021-07-29) Dubouis, N; Marchandier, T; Rousse, G; Marchini, F; Fauth, F; Avdeev, M; Iadecola, A; Porcheron, B; Deschamps, M; Tarascon, JM; Grimaud, A
    Insertion compounds provide the fundamental basis of today’s commercialized Li-ion batteries. Throughout history, intense research has focused on the design of stellar electrodes mainly relying on layered oxides or sulfides, and leaving aside the corresponding halides because of solubility issues. This is no longer true. In this work, we show the feasibility of reversibly intercalating Li+ electrochemically into VX3 compounds (X = Cl, Br, I) via the use of superconcentrated electrolytes (5 M LiFSI in dimethyl carbonate), hence opening access to a family of LixVX3 phases. Moreover, through an electrolyte engineering approach, we unambiguously prove that the positive attribute of superconcentrated electrolytes against the solubility of inorganic compounds is rooted in a thermodynamic rather than a kinetic effect. The mechanism and corresponding impact of our findings enrich the fundamental understanding of superconcentrated electrolytes and constitute a crucial step in the design of novel insertion compounds with tunable properties for a wide range of applications including Li-ion batteries and beyond. © 2021 Springer Nature Limited
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    Magnetodielectric effects in A-site cation-ordered chromate spinels LiMCr4O8 (M=Ga and In)
    (American Physical Society, 2016-08-15) Saha, R; Fauth, F; Avdeev, M; Kayser, P; Kennedy, BJ; Sundaresan, A
    We report the occurrence of a magnetodielectric effect and its correlation with structure and magnetism in the A-site ordered chromate spinel oxides LiMCr4O8 (M=Ga, In). In addition to magnetic and dielectric measurements, temperature dependent synchrotron and neutron diffraction experiments have been carried out for the Ga compound. The results are compared and contrasted with that of a corresponding conventional B-site magnetic chromate spinel oxide, ZnCr2O4. Like ZnCr2O4, the A-site ordered chromate spinels exhibit a magnetodielectric effect at the magnetic ordering temperature (TN∼13–15K), resulting from magnetoelastic coupling through a spin Jahn-Teller effect. While the presence of a broad magnetic anomaly, associated with a short-range magnetic ordering (TSO∼45K) in ZnCr2O4, does not cause any dielectric anomaly, a sharp change in dielectric constant has been observed in LiInCr4O8 at the magnetic anomaly, which is associated with the opening of a spin gap (TSG∼60K). Contrary to the In compound, a broad dielectric anomaly exists at the onset of short-range antiferromagnetic ordering (TSO∼55K) in LiGaCr4O8. The differences in dielectric behavior of these compounds have been discussed in terms of breathing distortion of the Cr4 tetrahedra. ©2016 American Physical Society
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    Solid-state chemistry shuffling of alkali ions toward new layered oxide materials
    (American Chemical Society, 2024-01-09) Mpanga, EM; Wernert, R; Fauth, F; Suard, E; Avdeev, M; Fraisse, B; Camacho, PS; Carlier, D; Lebedev, O; Cassidy, SJ; Rousse, G; Berthelot, R
    Alkali transition-metal layered compounds usually contain only one type of alkali cation between the edge-shared octahedra layers. Herein, the ternary phase diagram A2Ni2TeO6 (A = Li, Na, K) was explored through solid-state synthesis and new alkali-mixed compositions showing alternation of distinct alkali layers are obtained. Such intergrowth structures are synthesized either by a single high-temperature treatment from raw chemicals or through reaction between layered precursors, the latter involving a solid-state process triggered at moderate temperatures. The in-depth characterization of the multiple cationic orderings is performed by combining powder diffraction techniques (X-rays and neutrons), high-resolution transmission electron microscopy, and solid-state NMR spectroscopy. In addition to the Ni/Te honeycomb ordering, alternation of lithium layers with sodium or potassium layers is observed for compositions (Li/Na)2Ni2TeO6 or (Li/K)2Ni2TeO6, respectively. Crystal structure solving was achieved by stacking building blocks of the respective single alkali layered oxides and unveiled a complex out-of-plane ordering of honeycomb layers. Moreover, a solid-state reaction between Li2Ni2TeO6 and NaKNi2TeO6 enables preparation of the new phase Li∼1Na∼0.5K∼0.5Ni2TeO6, a unique example containing up to three alkali cations and exhibiting a more complex stacking with sodium and potassium cations occupying the same layer. This investigation confirms that the chemical versatility of layered alkali transition-metal compounds could also occur on the alkali layer. Following the research methodology described here, we revisit the crystal chemistry of alkali transition-metal layered materials by exploring alkali ion substitutions previously thought infeasible, in order to find new alkali-mixed compositions. © 2024 American Chemical Society.
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    Superconcentrated electrolytes widens insertion electrochemistry to soluble layered halides
    (Cambridge University Press, 2021-03-25) Dubouis, N; Marchandier, T; Rousse, G; Marchini, F; Fauth, F; Avdeev, M; Iadecola, A; Porcheron, B; Deschamps, M; Tarascon, JM; Grimaud, A
    Insertion compounds provide the fundamental basis of today’s commercialized Li-ion batteries. Throughout history, intense research has focus on the design of stellar electrodes mainly relying on layered oxides or sulfides, and leaving aside the corresponding halides because of solubility issues. This is no longer true. In this work, we show for the first time the feasibility to reversibly intercalate electrochemically Li+ into VX3 compounds (X = Cl, Br, I) via the use of superconcentrated electrolytes, (5 M LiFSI in dimethyl carbonate), hence opening access to a novel family of LixVX3 phases. Moreover, through an electrolyte engineering approach we unambiguously prove that the positive attribute of superconcentrated electrolytes against solubility of inorganic compounds is rooted in a thermodynamic rather than a kinetic effect. The mechanism and corresponding impact of our findings enrich the fundamental understanding of superconcentrated electrolytes and constitute a crucial step in the design of novel insertion compounds with tunable properties for a wide range of applications beyond Li-ion batteries. The content is available under CC BY NC ND 4.0 License CreativeCommons.org.