Masahiro Shikano

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

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Publications (64)144.82 Total impact

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    ABSTRACT: 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 Mn+2 magnetic moments are antiferromagnetically coupled within the chains which are antiferromagnetically coupled to each other.
    Journal of Solid State Chemistry 09/2014; · 2.04 Impact Factor
  • Hamdi Ben Yahia, Masahiro Shikano, Hironori Kobayashi
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    ABSTRACT: The new polymorph of Co2[PO4]F has been synthesized by a hydrothermal route. Its crystal structure was determined from single-crystal X-ray diffraction data. Co2[PO4]F crystallizes with the triplite-type structure, space group C2/c, a = 12.856(2), b = 6.4369(10), c = 9.6742(16) Å, β = 117.40(1) °, V = 710.7(2) Å3 and Z = 8. The structure consists of a 3D-framework buildup of condensed PO4 tetrahedra, and cobalt(II) polyhedra which form chains running along the [101] and [010] directions. The coordina-tion of the cobalt cations and the connectivity between the cobalt polyhedra are not well defined due to the disorder of the fluoride anions which form zigzag chains along [001]. The theoretical ordering of the fluoride anions led to two different structural models, very similar to the triplite Cc-CoFe[PO4]F and the triploidite P21/c-Co2[PO4]F, and in which the cobalt atoms are five and six coordinated.
    Zeitschrift für Kristallographie. 08/2014;
  • Toyoki Okumura, Masahiro Shikano, Hironori Kobayashi
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    ABSTRACT: Bulk and surface structural changes induced in a Li5FeO4 positive electrode with a defect anti-fluorite type structure are examined during its initial charge–discharge cycle by various synchrotron-radiation analysis techniques, with a view to determining the contribution of oxygen to its electrochemical properties. Bulk structural analyses including XRD, Fe K-edge XANES and EXAFS reveal that pseudo-cubic lithium iron oxides (PC-LFOs), in the form of LiαFe(4−α)+O2, are formed during the first charging process instead of the decomposition of pristine Li5FeO4. Moreover, the relative volume of this PC-LFO phase varies nonlinearly according to the charging depth. At the same time, the surface lithium compounds such as Li2O cover over the PC-LFO phase, which also contribute to the overall electrochemical reaction, as measured from the O K-edge XANES operating in a surface-sensitive total-electron yield mode. The ratio of these two different reaction mechanisms changes with the depth during the first charging process, with this tendency causing variation in the subsequent discharge capacity retention in relation to the depth of the charging electron and/or temperature of this “Li-rich” positive electrode. Indeed, such behaviour is noted to be very similar to the specific electrochemical properties of Li2MnO3.
    J. Mater. Chem. A. 07/2014; 2(30).
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    ABSTRACT: The new compound HP-Na2Co[PO4]F was synthesized by high pressure solid state reaction and its crystal structure was determined from single crystal X-ray diffraction data. The physical properties of HP-Na2Co[PO4]F were characterized by magnetic susceptibility, specific heat capacity, galvanometric cycling, and electrochemical impedance spectroscopy measurements. HP-Na2Co[PO4]F crystallizes with the space group P63/m, a = 10.5484(15), c = 6.5261(9) Å, V = 628.87(15) Å3 and Z = 6. The crystal structure consists of infinite chains of edge-sharing CoF2O4 octahedra. The latter are interconnected through the PO4 tetrahedra forming a 3D-Co[PO4]F-framework. The six coordinated sodium atoms are distributed over three crystallographic sites (2b, 6h, and 4f). The structure of HP-[Na11/3Na23/3Na32/3]Co[PO4]F is similar to [Na11/3Na23/3Sr1/3•1/3]Ge[GeO4]O. There is only one difference; Na3 occupies the 4f (1/3, 2/3, 0.0291) atomic position, whereas the Sr occupies the 2c (1/3, 2/3, 1/4) atomic position. The magnetic susceptibility follows a Curie-Weiss behavior above 50 K with Θ = -21 K indicating predominant antiferromagnetic interactions. The specific heat capacity and magnetization measurements show that HP-Na2Co[PO4]F undergoes a three-dimensional magnetic ordering at TN = 11.0(1) K. The ionic conductivity σ, estimated at 350 °C, is 1.5 10−7 S cm−1. The electrochemical cycling indicates that only one sodium ion could be extracted during the first charge in Na half-cell; however, the re-intercalation was impossible due to a strong distortion of the structure after the first charge to 5.0 V.
    Dalton Transactions 07/2014; · 3.81 Impact Factor
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    ABSTRACT: X-ray absorption near-edge structure (XANES) spectroscopy, which reveals the features of the electronic and local structure, of lithium manganese oxides LixMn2O4 (x = 0–2) was examined using first-principles calculations. Both the easily observable parts and the tiny peaks of the theoretical Mn K-edge XANES spectra agreed with the experimental spectra. From the theoretical results of two anti-ferromagnetic LiMn2O4 models, the contributions of the Mn3+ ion and Mn4+ ion centers to the XANES spectra differ due to the difference in the overlap between the Mn 4p partial density of state (PDOS) and the O 2p PDOS. Similar results can be also seen by comparing the theoretical XANES spectra and the PDOS between Li(Mn3+Mn4+)O4 and de-intercalated Li0.5(Mn3+0.5Mn4+1.5)O4 and Mn4+2O4 (λ-MnO2). The XANES spectral changes with the lithium ion displacement (six- to four-coordination) due to the phase transition (cubic Fdm LiMn2O4 to tetragonal I41/amd Li2Mn2O4) can be determined by the indirect contribution of the Li 2p PDOS to the Mn 4p PDOS via the O 2p PDOS.
    J. Mater. Chem. A. 05/2014; 2(21).
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    ABSTRACT: The new compounds Li2Mg[PO4]F and Li9Mg3[PO4]4F3 have been synthesized by a solid state reaction route. The crystal structures were determined from single-crystal X-ray diffraction data. Li2Mg[PO4]F crystallizes with the orthorhombic Li2Ni[PO4]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å, V = 721.13(10) Å3, and Z = 8, whereas Li9Mg3[PO4]4F3 crystallizes with hexagonal symmetry, space group P63, with a = 12.6159(6), c = 5.0082(4) Å, V = 690.32(7) Å3, and Z = 2. A merohedral twinning was taken into account for its structural refinement. The structure of Li2Mg[PO4]F contains MgO3F chains made up of edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg[PO4]F framework. The lithium atoms occupy mainly three distinct crystallographic sites. The structure of Li9Mg3[PO4]4F3 consists of corner-sharing MgO4F2 octahedra forming MgO4F chains running along the c axis. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg3[PO4]4F3 framework with hexagonal and pentagonal tunnels, in which are located the Li atoms. This study reveals also a strong relationship between Li2Mg[PO4]F-, Mg1-xFexAl3[BO3][SiO4]O2- and P21/c-Li5V[PO4]2F2-structures; and between P63-Li9Mg3[PO4]4F3 and P21/c-Na2Mn[PO4]F. The ionic conductivities σ of the composite material Li6Mg4[PO4]3[SO4]F3 and Li9Mg3[PO4]4F3, estimated using electrochemical impedance spectroscopic analyses at 300 °C, are 3.9 10−5 and 10−4 S cm−1 with activation energies of 0.524 eV and 0.835 eV, respectively.
    Journal of Materials Chemistry 01/2014; · 5.97 Impact Factor
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    ABSTRACT: The 5 wt.% Al2O3-coated Li1.20Mn0.55Ni0.16Co0.09O2 was prepared by the mechanochemical reaction. The optimal condition for sample preparation was determined to be the rotation speed of 2000 rpm and the reaction time of 5 min by SEM, XRD, and XANES measurements. Surface analysis using XANES data demonstrated that all the samples were rather uniformly covered with nano-Al2O3 particles. The pristine and 5 wt.% Al2O3-coated samples after the stepwise pre-cycling treatment showed the discharge capacity of 243 and 216 mAh/g at 323 K, respectively. Although the Al2O3-coated sample showed less discharge capacity compared with the pristine sample, the Al2O3-coated sample showed better discharge capacity retention compared with the pristine sample after 35 cycles at 323 K. These results demonstrate that the mechanochemical Al2O3-coating process is an effective way of improving the cycle performance at high temperature.
    Solid State Ionics 01/2014; 262:43–48. · 2.05 Impact Factor
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    ABSTRACT: 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.
    Inorganic Chemistry 12/2013; · 4.59 Impact Factor
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    ABSTRACT: 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 measurements. The magnetic structure and properties of Co(OH)F were characterized by magnetic susceptibility and low-temperature neutron powder diffraction measurements. M(OH)F (M = Fe, Co) crystallizes with structures related to diaspore-type-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 Fe- and Co-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 neutron powder diffraction 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 -FeOOH.
    Inorganic Chemistry 12/2013; · 4.59 Impact Factor
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    ABSTRACT: 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.
    Dalton Transactions 11/2013; · 3.81 Impact Factor
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    ABSTRACT: The new compound LiNaMg[PO4]F has been synthesized by 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 clip1 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 rather long interlayer distance, dmin(Ni+2-Ni+2)~6.8 Å, the material develops 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.
    Dalton Transactions 11/2013; · 3.81 Impact Factor
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    Hamdi Ben Yahia, Masahiro Shikano, Hironori Kobayashi
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    ABSTRACT: The basic structural chemistry of O3-LixCoO2 (0.25 ≤ x ≤ 1) oxides is reviewed. Crystal chemical details of selected compositions and group-subgroup schemes are discussed with respect to phase transitions upon electrochemical or chemical deintercalation of the lithium atoms. Furthermore, the theoretical crystal structures of LixCoO2 supercells (x = 0.75, 0.5, 0.33, and 0.25) are reported for the first time based on the combination of transmission electron microscope (TEM) and X-ray or Neutron diffraction experiments. Li0.75CoO2 and Li0.25CoO2 supercells crystallize with the space group R-3m, a4 = 5.6234 Å and 5.624 Å, and c4 = 14.2863 Å and 14.26 Å, respectively, whereas Li0.5CoO2 supercell crystallizes with the space group P21/m, a7 = 4.865Å, b7 = 2.809 Å, c7 = 9.728 Å, and 7 = 99.59 °. Li0.33CoO2 supercell may crystallize in different unit cells (hexagonal or orthorhombic or monoclinic). For Li0.75CoO2, the TEM superstructure reflexions are due to only one type of lithium and vacancy ordering within the lithium layers, however for x = 0.5, the superstructure reflexions are due to an intergrowth of two Li0.5CoO2 monoclinic structures (P2/m, a5 = 4.865(3) Å, b5 = 2.809(3) Å, c5 = 5.063(3) Å, β5 = 108.68(5) º) with the lithium and vacancies alternating the 1g and 1f atomic positions, in two successive layers, along the c direction. For Li0.33CoO2, in most cases, the Li and vacancy ordering are similar to Li and Mn ordering in Li2MnO3 structure. The phase transition mechanisms from O3-LiCoO2 to O3-Li0.25CoO2 and from O3-LiCoO2 to spinel-Li0.5CoO2 have been determined and the structural relationship between O3-LiCoO2 and Li2MnO3 has been discussed in details.
    Chemistry of Materials 08/2013; · 8.24 Impact Factor
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    ABSTRACT: The new compound MnF2-x(OH)x (x ∼ 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 ∼ 0.8) crystallizes with orthorhombic symmetry, space group Pnn2 (no. 34), a = 4.7127(18), b = 5.203(2), c = 3.2439(13) Å, V = 79.54(5) Å(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-HF bent hydrogen bonds. The magnetic susceptibility measurements indicate an antiferromagnetic ordering at ∼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 Mn(2+). MnF2-x(OH)x (x ∼ 0.8) is expected to be of great interest as a positive electrode for Li cells if the protons could be exchanged for lithium.
    Physical Chemistry Chemical Physics 07/2013; · 4.20 Impact Factor
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    ABSTRACT: The new compounds LiNaFe1-xMnx[PO4]F (x ≤ 1/4) were synthesized by a solid state reaction route. The crystal structure of LiNaFe3/4Mn1/4[PO4]F was determined from single-crystal X-ray diffraction data. LiNaFe3/4Mn1/4[PO4]F crystallizes with the Li2Ni[PO4]F-type structure, space group Pnma, a = 10.9719(13), b = 6.3528(7), c = 11.4532(13) Å, V = 798.31 (16) Å3, and Z = 8. The structure consists of edge-sharing (Fe3/4Mn1/4)O4F2 octahedra forming (Fe3/4Mn1/4)FO3 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 manganese doped phases show poor electrochemical behavior comparing to the iron pure phase LiNaFe[PO4]F.
    Materials Chemistry and Physics 04/2013; · 2.07 Impact Factor
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    Hamdi Ben Yahia, Masahiro Shikano, Hironori Kobayashi
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    ABSTRACT: The new compounds Mn2(OH)2SO3, Mn2F(OH)SO3, and Mn5(OH)4(H2O)2[SO3]2[SO4] were synthesized using a hydrothermal route and their crystal structures were determined using single crystal X-ray diffraction data. Mn2(OH)2SO3 and Mn2F(OH)SO3 crystallized with the space group Pnma, a = 7.3580(14), b = 10.3429(20), c = 5.7611(11) Å, Z = 4; and a = 7.413(4), b = 10.139(5), c = 5.717(3) Å, Z = 4, respectively, whereas Mn5(OH)4(H2O)2[SO3]2[SO4] crystallized with the space group P21/m, a = 7.6117(7), b = 8.5326(7), c = 10.9273(9) Å, β = 101.6005(13)°, Z = 2. Mn2(OH)2SO3 and Mn2F(OH)SO3 consist of a 3D-framework of manganese octahedra sharing corners and edges and giving rise to 1D-tunnels along the a axis in which are located the sulfur atoms, whereas Mn5(OH)4(H2O)2[SO3]2[SO4] consists of a 3D-framework of MnO5, MnO6, SO3, and SO4 polyhedra. Mn5(OH)4(H2O)2[SO3]2[SO4] is the first transition metal mixed sulfate-sulfite inorganic compound. Bent and symmetrically bifurcated hydrogen bonds were observed in these materials.
    Dalton Transactions 03/2013; · 3.81 Impact Factor
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    ABSTRACT: The new compound Li1.65Na0.35Fe[PO4]F with the Li2Ni[PO4]F structure has been prepared from the analogous LiNaFe[PO4]F phase by ion exchange using LiBr in ethanol at 90 °C. The sample was characterized by powder X-ray diffraction, 57Fe Mӧssbauer spectroscopy, and electrochemical measurements. Li1.65Na0.35Fe[PO4]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.5093(5) Å, b = 6.4999(2) Å, c = 11.0483(5) Å, V = 754.70(7) Å3, and Z = 8. The 57Fe Mӧssbauer data collected at different stages of galvanometric cycling confirmed that only 1 mole of alkali metal is extractable between 1.0 V and 5.1 V vs. Li+/Li with a discharge capacity between 135 and 145 mA h g-1. Li/Na electrochemical ion exchange occurs during cycling and leads to a lithium rich phase.
    Journal of Power Sources 01/2013; · 5.26 Impact Factor
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    ABSTRACT: The new compound LiNaFe[PO(4)]F was synthesized by a solid state reaction route, and its crystal structure was determined using neutron powder diffraction data. LiNaFe[PO(4)]F was characterized by (57)Fe Mössbauer spectroscopy, magnetic susceptibility, specific heat capacity, and electrochemical measurements. LiNaFe[PO(4)]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9568(6) Å, b = 6.3959(3) Å, c = 11.4400(7) Å, V = 801.7(1) Å(3) and Z = 8. The structure consists of edge-sharing FeO(4)F(2) octahedra forming FeFO(3) chains running along the b axis. These chains are interlinked by PO(4) 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[PO(4)]F undergoes a three-dimensional antiferromagnetic ordering at T(N) = 20 K. The neutron powder diffraction measurements at 3 K show that each FeFO(3) 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).
    Dalton Transactions 08/2012; 41(38):11692-9. · 3.81 Impact Factor
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    ABSTRACT: The new compound LiNaCo[PO(4)]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[PO(4)]F were characterized by magnetic susceptibility, specific heat, and neutron powder diffraction measurements and also by density functional calculations. LiNaCo[PO(4)]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9334(6), b = 6.2934(11), c = 11.3556(10) Å, and Z = 8. The structure consists of edge-sharing CoO(4)F(2) octahedra forming CoFO(3) chains running along the b axis. These chains are interlinked by PO(4) 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 θ = -21 K. The specific heat and magnetization measurements show that LiNaCo[PO(4)]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 CoFO(3) 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.
    Inorganic Chemistry 08/2012; 51(16):8729-38. · 4.59 Impact Factor
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    ABSTRACT: First-principle calculation was employed to simulate X-ray absorption near-edge structure (XANES) spectroscopy of two typical types of lithium cobalt oxides to clarify the electronic and local structural changes during lithium-ion de-intercalation. The simulated Co K-edge XANES spectra agreed well with the observed spectra. The differences in the shape of the XANES spectra with structural symmetry and/or lithium contents in lithium cobalt oxides were analyzed based on the partial density of state (PDOS) of the excited energy level. First-principle calculation simulations revealed that the cobalt PDOS overlapped with nearby lithium PDOS via oxygen PDOS, and the overlap difference among various Li1−xCoO2 could be detected using both the experimental and theoretical Co K-edge XANES spectra.
    Journal of Materials Chemistry 07/2012; 22(33):17340-17348. · 5.97 Impact Factor
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    ABSTRACT: The new compounds Li(2-x)Na(x)Ni[PO(4)]F (x = 0.7, 1, and 2) have been synthesized by a solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data. Li(1.3)Na(0.7)Ni[PO(4)]F crystallizes with the orthorhombic Li(2)Ni[PO(4)]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å and Z = 8, LiNaNi[PO(4)]F crystallizes with a monoclinic pseudomerohedrally twinned structure, space group P2(1)/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90° and Z = 4, and Na(2)Ni[PO(4)]F crystallizes with a monoclinic twinned structure, space group P2(1)/c, a = 13.4581(8), b = 5.1991(3), c = 13.6978(16) Å, β = 120.58(1)° and Z = 8. For x = 0.7 and 1, the structures contain NiFO(3) chains made up of edge-sharing NiO(4)F(2) octahedra, whereas for x = 2 the chains are formed of dimer units (face-sharing octahedra) sharing corners. These chains are interlinked by PO(4) tetrahedra forming a 3D framework for x = 0.7 and different Ni[PO(4)]F layers for x = 1 and 2. A sodium/lithium disorder over three atomic positions is observed in Li(1.3)Na(0.7)Ni[PO(4)]F structure, whereas the alkali metal atoms are well ordered in between the layers in the LiNaNi[PO(4)]F and Na(2)Ni[PO(4)]F structures, which makes both compounds of great interest as potential positive electrodes for sodium cells.
    Dalton Transactions 03/2012; 41(19):5838-47. · 3.81 Impact Factor