Browsing by Author "Ben Yahia, H"

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    Magnetic structure of some battery materials and why it matters
    (International Battery Materials Association, 2014-03-02) Avdeev, M; Ling, CD; Mohamed, Z; Barpanda, P; Yamada, A; Ben Yahia, H; Shikano, M
    Operation of batteries with insertion cathodes is typically based on a redox reaction Mn+/Mn+p (p=1,2) of transition metals. The motivation to increase gravimetric energy density and reduce cost naturally drives research to the light, i.e. 3d, transition metals M=V-Ni, which in turn are also paramagnetic ions and may order magnetically. Using neutron diffraction and magnetometry we explored magnetic structure and properties of some materials recently synthesized in search of better cathode materials: Na2CoP2O7, maricite- and triphylite-NaFePO4, Na2FePO4F, M(OH)xF2-x (M=Co,Fe), Li2MnSiO4, Li2CoSiO4, LiNaCoPO4F, LiNaFePO4F. The detailed magnetic structures will be presented and features of crystal structures affecting the type of magnetic ordering will be discussed. Although polyanionic materials (phosphates and silicates) are magnetically low density systems and thus order at low temperature (< 50 K), the information on magnetic structure is important for accurate DFT calculations. The effect of neglecting magnetic order on the DFT based quantitative predictions will be illustrated.
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    Neutron diffraction studies of the Na-ion battery electrode materials NaCoCr2(PO4)3, NaNiCr2(PO4)3, and Na2Ni2Cr(PO4)3
    (Elsevier, 2016-06-01) Ben Yahia, H; Essehli, R; Avdeev, M; Park, JB; Sun, YK; Al-Maadeed, MA; Belharouak, I
    The new compounds NaCoCr2(PO4)3, NaNiCr2(PO4)3, and Na2Ni2Cr(PO4)3 were synthesized by sol-gel method and their crystal structures were determined by using neutron powder diffraction data. These compounds were characterized by galvanometric cycling and cyclic voltammetry. NaCoCr2(PO4)3, NaNiCr2(PO4)3, and Na2Ni2Cr(PO4)3 crystallize with a stuffed α-CrPO4-type structure. The structure consists of a 3D-framework made of octahedra and tetrahedra that are sharing corners and/or edges generating channels along [100] and [010], in which the sodium atoms are located. Of significance, in the structures of NaNiCr2(PO4)3, and Na2Ni2Cr(PO4)3 a statistical disorder Ni2+/Cr3+ was observed on both the 8g and 4a atomic positions, whereas in NaCoCr2(PO4)3 the statistical disorder Co2+/Cr3+ was only observed on the 8g atomic position. When tested as negative electrode materials, NaCoCr2(PO4)3, NaNiCr2(PO4)3, and Na2Ni2Cr(PO4)3 delivered specific capacities of 352, 385, and 368 mA h g−1, respectively, which attests to the electrochemical activity of sodium in these compounds. © 2016 Elsevier Inc.
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    The novel stairs-like layered compound Co5(OH)6(H2O)2[SO3]2
    (De Gruyter, 2017-02-15) Ben Yahia, H; Shikano, M; Avdeev, M; Belharouak, I
    The new compound Co5(OH)6(H2O)2[SO3]2 was synthesized by a hydrothermal route and its crystal structure was determined from the combination of sin-gle crystal X-ray- and neutron powder-diffraction data. Co5(OH)6(H2O)2[SO3]2 crystallizes with the space group P21/c, a= 7.0229(19) Å, b= 5.4722(15) Å, c= 15.833(4), β= 106.34(1)°, V= 583.9(3) Å3 and Z= 4. The crystal struc-ture consists of a 2D-framework of cobalt octahedra shar-ing corners and edges and giving rise to a stairs-like layers, interconnected through O–H···O–S4 + hydrogen bonds. © Walter de Gruyter GmbH 2021
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    Single crystal and magnetic structures of maricite-type AgMnVO4
    (Elsevier, 2015-01) Ben Yahia, H; Shikano, M; Gaudin, E; Avdeev, M; Ling, CD
    Single crystals of the ternary manganese vanadate AgMnVO4, were grown using AgVO3 flux. The structure was determined from single crystal X-ray diffraction data. The magnetic structure and properties of AgMnVO4 were characterized by magnetic susceptibility, specific heat, and low-temperature neutron powder diffraction measurements. AgMnVO4 crystallizes in the maricite-type structure with space group Pnma, a=9.5393(12), b=6.8132(9), c=5.3315(7) Å and Z=4. AgMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra, and these chains are interlinked by the VO4 and AgO4 tetrahedra. The specific heat measurements indicate a 3D-antiferromagnetic ordering at ~12.1 K and the neutron powder diffraction measurements at 5 K show that the Mn2+magnetic moments are antiferromagnetically coupled within the chains which are antiferromagnetically coupled to each other. © 2014, Elsevier Inc.
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    Structural relationships among LiNaMg[PO4]F and Na2M[PO4]F (M = Mn-Ni, and Mg), and the magnetic structure of LiNaNi[PO4]F
    (Royal Chemistry of Society, 2013-11) Ben Yahia, H; Shikano, H; Kobayashi, M; Avdeev, M; Liu, S; Ling, CD
    The new compound LiNaMg[PO4]F has been synthesized by a wet chemical reaction route. Its crystal structure was determined from single-crystal X-ray diffraction data. LiNaMg[PO4]F crystallizes with the monoclinic pseudomerohedrally twinned LiNaNi[PO4]F structure, space group P21/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90.00(1)° and Z = 4. The structure contains [MgO3F]n chains made up of zigzag edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming 2D-Mg[PO4]F layers. The alkali metal atoms are well ordered in between these layers over two atomic positions. The use of group–subgroup transformation schemes in the Bärnighausen formalism enabled us to determine precise phase transition mechanisms from LiNaNi[PO4]F- to Na2M[PO4]F-type structures (M = Mn–Ni, and Mg) (see video clip 1 and 2). The crystal and magnetic structure and properties of the parent LiNaNi[PO4]F phase were also studied by magnetometry and neutron powder diffraction. Despite the rather long interlayer distance, dmin(Ni+2–Ni+2) ∼ 6.8 Å, the material develops a long-range magnetic order below 5 K. The magnetic structure can be viewed as antiferromagnetically coupled ferromagnetic layers with moments parallel to the b-axis.
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    Synthesis and characterization of the crystal and magnetic structures and properties of the hydroxyfluorides Fe(OH)F and Co(OH)F
    (Americal Chemical Society, 2013-12-16) Ben Yahia, H; Shikano, M; Tabuchi, M; Kobayashi, H; Avdeev, M; Tan, TT; Liu, S; Ling, CD
    The title compounds were synthesized by a hydrothermal route from a 1:1 molar ratio of lithium fluoride and transition-metal acetate in an excess of water. The crystal structures were determined using a combination of powder and/or single-crystal X-ray and neutron powder diffraction (NPD) measurements. The magnetic structure and properties of Co(OH)F were characterized by magnetic susceptibility and low-temperature NPD measurements. M(OH)F (M = Fe and Co) crystallizes with structures related to diaspore-type α-AlOOH, with the Pnma space group, Z = 4, a = 10.471(3) Å, b = 3.2059(10) Å, and c = 4.6977(14) Å and a = 10.2753(3) Å, b = 3.11813(7) Å, and c = 4.68437(14) Å for the iron and cobalt phases, respectively. The structures consist of double chains of edge-sharing M(F,O)6 octahedra running along the b axis. These infinite chains share corners and give rise to channels. The protons are located in the channels and form O–H···F bent hydrogen bonds. The magnetic susceptibility indicates an antiferromagnetic ordering at ∼40 K, and the NPD measurements at 3 K show that the ferromagnetic rutile-type chains with spins parallel to the short b axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of goethite α-FeOOH. © 2014, American Chemical Society
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    Synthesis and characterization of the crystal structure and magnetic properties of the hydroxyfluoride MnF2-x(OH)x (x similar to 0.8)
    (Royal Society of Chemistry, 2013-01-01) Ben Yahia, H; Shikano, M; Kobayashi, H; Avdeev, M; Liu, S; Ling, CD
    The new compound MnF2-x(OH)(x) (x similar to 0.8) was synthesized by a hydrothermal route from a 1 : 1 molar ratio of lithium fluoride and manganese acetate in an excess of water. The crystal structure was determined using the combination of single crystal X-ray and neutron powder diffraction measurements. The magnetic properties of the title compound were characterized by magnetic susceptibility and low-temperature neutron powder diffraction measurements. MnF2-x(OH)(x) (x similar to 0.8) crystallizes with orthorhombic symmetry, space group Pnn2 (no. 34), a = 4.7127(18), b = 5.203(2), c = 3.2439(13) angstrom, V = 79.54(5) angstrom(3) and Z = 2. The crystal structure is a distorted rutile-type with [Mn(F,O)(4)] infinite edge-sharing chains along the c-direction. The protons are located in the channels and form O-H center dot center dot center dot F bent hydrogen bonds. The magnetic susceptibility measurements indicate an antiferromagnetic ordering at similar to 70 K and the neutron powder diffraction measurements at 3 K show that the ferromagnetic chains with spins parallel to the c-axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of tetragonal rutile-type MnF2 with isoelectronic Mn2+. MnF2-x(OH)(x) (x similar to 0.8) is expected to be of great interest as a positive electrode for Li cells if the protons could be exchanged for lithium. © 2013, Royal Society of Chemistry.
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    Synthesis and characterization of the crystal structure and magnetic properties of the new fluorophosphate LiNaCo[PO4]F
    (American Chemical Society, 2012-08-02) Ben Yahia, H; Shikano, M; Koike, S; Tatsumi, K; Kobayashi, H; Kawaji, H; Avdeev, M; Miiller, W; Ling, CD; Liu, J; Whangbo, MH
    The new compound LiNaCo[PO4]F was synthesized by a solid state reaction route, and its crystal structure was determined by single-crystal X-ray diffraction measurements. The magnetic properties of LiNaCo[PO4]F were characterized by magnetic susceptibility, specific heat, and neutron powder diffraction measurements and also by density functional calculations. LiNaCo[PO4]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9334(6), b = 6.2934(11), c = 11.3556(10) angstrom, and Z = 8. The structure consists of edge-sharing CoO4F2 octahedra forming CoFO3 chains running along the b axis. These chains are interlinked by PO4 tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The magnetic susceptibility follows the Curie Weiss behavior above 60 K with theta = -21 K. The specific heat and magnetization measurements show that LiNaCo[PO4]F undergoes a three-dimensional magnetic ordering at T-mag = 10.2(5) K. The neutron powder diffraction measurements at 3 K show that the spins in each CoFO3 chain along the b-direction are ferromagnetically coupled, while these FM chains are antiferromagnetically coupled along the a-direction but have a noncollinear arrangement along the c-direction. The noncollinear spin arrangement implies the presence of spin conflict along the c-direction. The observed magnetic structures are well explained by the spin exchange constants determined from density functional calculations. © 2012, American Chemical Society.
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    Synthesis and characterization of the crystal structure, the magnetic and the electrochemical properties of the new fluorophosphate LiNaFe[PO4]F
    (Royal Society of Chemistry, 2012-8-16) Ben Yahia, H; Shikano, M; Sakaebe, H; Koike, S; Tabuchi, M; Kobayashi, H; Kawaji, H; Avdeev, M; Miiller, W; Ling, CD
    The new compound LiNaFe[PO4]F was synthesized by a solid state reaction route, and its crystal structure was determined using neutron powder diffraction data. LiNaFe[PO4]F was characterized by 57Fe Mossbauer spectroscopy, magnetic susceptibility, specific heat capacity, and electrochemical measurements. LiNaFe[PO4]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9568(6) A, b = 6.3959(3) A, c = 11.4400(7) A, V = 801.7(1) A3 and Z = 8. The structure consists of edge-sharing FeO4F2 octahedra forming FeFO3 chains running along the b axis. These chains are interlinked by PO4 tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The specific heat and magnetization measurements show that LiNaFe[PO4]F undergoes a three-dimensional antiferromagnetic ordering at TN = 20 K. The neutron powder diffraction measurements at 3 K show that each FeFO3 chain along the b-direction is ferromagnetic (FM), while these FM chains are antiferromagnetically coupled along the a and c-directions with a non-collinear spin arrangement. The galvanometric cycling showed that without any optimization, one mole of alkali metal is extractable between 1.0 V and 5.0 V vs. Li+/Li with a discharge capacity between 135 and 145 mAh g-1. © 2012, Royal Society of Chemistry.
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    Synthetic, structural, and electrochemical study of Monoclinic Na4Ti5O12 as a sodium-ion battery anode material
    (ACS Publications, 2014-12-04) Avdeev, M; Naeyaert, PJP; Sharma, N; Ben Yahia, H; Ling, CD
    The monoclinic phase of Na4Ti5O12 (M-Na4Ti5O12) has been investigated as a potential sodium-ion battery anode material. In contrast to the previously investigated trigonal phase (T-Na4Ti5O12), M-Na4Ti5O12 has continuous two-dimensional (2D) channels with partially occupied Na sites, providing broader pathways and more space for the intercalation of excess sodium. Electrochemical measurements show that it exhibits a comparable or higher reversible capacity than T-Na4Ti5O12. Neutron powder diffraction reveals the preferred sites and occupancies of the excess sodium. In situ synchrotron X-ray diffraction under electrochemical cycling shows that the crystal lattice undergoes strongly anisotropic volume changes during cycling. © 2014, American Chemical Society.