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  • 1. Ali, Sk Imran
    et al.
    Zhang, Weiguo
    Halasyamani, P. Shiv
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zn3Sb4O6F6: Hydrothermal synthesis, crystal structure and nonlinear optical properties2017In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 256, p. 158-161Article in journal (Refereed)
    Abstract [en]

    Zn3Sb4O6F6 has been synthesized hydrothermally at 230 degrees C. The crystal structure was determined from single crystal X-ray diffraction data. It crystallizes in the cubic non-centrosymmetric space group I-43m with the unit cell parameter a = 8.1291(4) angstrom and is isostructural with M3Sb4O6F6 (M = Co, Ni). The new compound is the first oxofluoride containing Zn2+ and a p-element cation with a stereochemically active lone pair. The crystal structure is made up by [ZnO2F4] octahedra forming a network via corner sharing at F-atoms and [SbO3] trigonal pyramids that form [Sb4O6] cages that connect via the O-atoms to the Zn-atoms. Powder second harmonic generation (SHG) measurements using 1064 nm radiation on Zn3Sb4O6F6 indicate an SHG intensity of approximately 40 x alpha-SiO2.

  • 2.
    Becker, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Three new tellurite halides with unusual Te4+ coordinations and iron honeycomb lattice variants2007In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 180, no 5, p. 1750-1758Article in journal (Refereed)
    Abstract [en]

    The crystal structure of three new iron and copper-iron tellurite halides are presented; (I) Cu3Fe8Te12O32Cl10 that crystallizes in the orthorhombic space group Pmmn, (II) Fe8Te12O32Cl3Br3 that crystallizes in the monoclinic space group P21/c, and (III) Fe5(TeO3)6Cl2 that crystallizes in the triclinic space group P-1. The crystal structures were solved from single crystal X-ray diffraction data. All three compounds have layered crystal structures where the Fe atoms form variants of the honeycomb lattice. Highly unusual Te4+ coordination polyhedra are exemplified: [TeO3+1E], [TeO3XE], [TeO3+1XE], and [TeO3X2E] (X=halide ion, E=the lone–pair valence electrons). The crystal structures contain large non-bonding volumes occupied by the stereochemically active lone–pair electrons on Te4+.

  • 3.
    Becker, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Prester, Mladen
    Berger, Helmuth
    Lin, Ping Hui
    Johnsson, Mats
    Drobac, Djuro
    Zivkovic, Ivica
    Crystal structure and magnetic properties of two new cobalt selenite halides: Co5(SeO3)4X2 (X=Cl, Br) 2007In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 180, no 3, p. 1051-1059Article in journal (Refereed)
    Abstract [en]

    Two new isostructural cobalt selenite halides Co5(SeO3)4Cl2 and Co5(SeO3)4Br2 have been synthesized. They crystallize in the triclinic system space group P−1 with the following lattice parameters for Co5(SeO3)4Cl2: a=6.4935(8) Å, b=7.7288(8) Å, c=7.7443(10) Å, α=66.051(11)°, β=73.610(11)°, γ=81.268(9)°, and Z=1. The crystal structures were solved from single-crystal X-ray data, R1=3.73 and 4.03 for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively. The new compounds are isostructural to Ni5(SeO3)4Br2.

    Magnetic susceptibility measurements on oriented single-crystalline samples show anisotropic response in a broad temperature range. The anisotropic susceptibility is quantitatively interpreted within the zero-field splitting schemes for Co2+ and Ni2+ ions. Sharp low-temperature susceptibility features, at TN=18 and 20 K for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively, are ascribed to antiferromagnetic ordering in a minority magnetic subsystem. In isostructural Ni5(SeO3)4Br2 magnetically ordered subsystem represents a majority fraction (TN=46 K). Nevertheless, anisotropic susceptibility of Ni5(SeO3)4Br2 is dominated at low temperatures by a minority fraction, subject to single-ion anisotropy effects and increasing population of Sz=0 (singlet) ground state of octahedrally coordinated Ni2+.

  • 4.
    Berastegui, P.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hull, S.
    Eriksson, S. G.
    A high temperature superionic phase of CsSn2F52010In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 183, no 2, p. 373-378Article in journal (Refereed)
    Abstract [en]

    The compound CsSn2F5 has been investigated over the temperature range from ambient to 545 K using differential scanning calorimetry, impedance spectroscopy and neutron powder diffraction methods. A first-order phase transition is observed from DSC measurements at 510(2) K, to a phase possessing a high ionic conductivity (σ2.5×10−2 Ω−1 cm−1 at 520 K). The crystal structure of the high temperature superionic phase (labelled α) has been determined to be tetragonal (space group I4/mmm, a=4.2606(10) Å, c=19.739(5) Å and Z=2) in which the cations form layers perpendicular to the [001] direction, with a stacking sequence CsSnSnCsSnSn… All the anions are located in two partially occupied sites in the gap between the Cs and Sn layers, whilst the space between the Sn cations is empty, due to the orientation of the lone-pair electrons associated with the Sn2+. The structure of α-CsSn2F5 is discussed in relation to two other layered F conducting superionic phases containing Sn2+ cations, α-RbSn2F5 and α-PbSnF4 and, to facilitate this comparison, an improved structural characterisation of the former is also presented. The wider issue of the role of lone-pair cations such as Sn2+ in promoting dynamic disorder within an anion substructure is also briefly addressed.

  • 5.
    Biendicho, Jordi Jacas
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). STFC Rutherford Appleton Laboratory, England.
    Shafeie, Samrand
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Frenck, Louise
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Pierre & Marie Curie University, France.
    Gavrilova, Daria
    Böhme, Solveigh
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Chemnitz University of Technology, Germany.
    Bettanini, A. M.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Universita Ca Foscari Venezia, Italy.
    Svedlindh, Peter
    Hull, Steve
    Zhe, Zhao
    Istomin, S. Y.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and characterisation of perovskite SrxY1-xFeO3-d (=.63≤x<1) and Sr0.75Y0.25Fe1-yMyO3-d (M=Cr, Mn, Ni) (y= 0.2, 0.33, 0.5)2013In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 200, p. 30-38Article in journal (Refereed)
    Abstract [en]

    Oxygen-deficient ferrates with the cubic perovskite structure SrxY1-xFeO3-d were prepared in air (0.71 ≤ x ≤ 0.91) as well as in N2 (x=0.75 and 0.79) at 1573K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-δ=2.79(2) for x=0.75 to 3-δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along <100>p with G± ~0.4<100>p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5-390K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm K-1 in air at 298-673K. At 773-1173K TEC increases up to 17.2 ppm K-1 due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1-yMyO3-δ (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79.

  • 6.
    Grins, Jekabs
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Käll, Per-Olov
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis, Structure and Magnetic Susceptibility of the Oxynitride Spinel Mn2(MnTa3)N6-δO2+δ, 0 ≤ δ ≤ 11995In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 117, no 1, p. 48-54Article in journal (Refereed)
    Abstract [en]

    The oxynitride spinel Mn-2(MnTa3)N6-deltaO2+delta, with 0 less than or equal to delta less than or equal to 1, has been synthesized at 1175 K by ammonolysis of a mixture of a Ta-containing xerogel and Mn(OAc)(2) . 4H(2)O. The N content was determined by combustion analysis and thermogravimetric oxidation, yielding a composition confined between Mn-2(MnTa3)N6O2 (delta = 0) and Mn-2(MnTa3)N5O3 (delta = 1). The structure is cubic, with space group Fd3m and a = 8.8353(3) Angstrom. It was refined using the Rietveld technique and neutron powder diffraction data collected at room temperature and 15 K, to R(F) = 2.9 and 3.8%, respectively. The tetrahedral sites are occupied only by Mn atoms and the octahedral sites statistically by 25% Mn and 75% Ta atoms. The N and O atoms are randomly distributed over the anion sites. The magnetic susceptibility exhibits a maximum at 29 K and a Curie-Weiss behavior at higher temperatures with theta(a) = -250(20) K and mu(eff) = 5.7(2) Bohr magnetons per Mn atom. The neutron powder diffraction data collected at 15 K showed no evidence of magnetic ordering. A NaCl-type phase with a = 4.4382(2) Angstrom and tentative composition Mn0.8Ta0.2(O,N) was observed in preparations at 1175 K. A hexagonal Mn4Ta2(O,N)(x) phase with cell dimensions a = 5.3024(4) Angstrom, c = 14.493(2) Angstrom was obtained at 973 K. (C) 1995 Academic Press, Inc.

  • 7.
    Hannerz, H
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Istomin, S Y
    Moscow State University, Department of Chemistry.
    D’Yachenko, O G
    Moscow State University, Department of Chemistry.
    Transmission electron microscopy and neutron powder diffraction studies of GdFeO3 type SrNbO31999In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 147, p. 421-428Article in journal (Refereed)
    Abstract [en]

    Stoichiometric SrNbO3; with a GdFeO3 type structure was synthesized between 1300 and 1550°C in Ar-filled and sealed niobium ampoules. Its crystal structure was refined using time-of-flight neutron diffraction data. Space group Pnma: a=√2·ap=5.6894(2) Å; b=2·ap=8.0684(1) Å; c=√2·ap=5.6944(2) Å; RF2=0.020; and RP=0.034. High-resolution electron microscopy and electron diffraction studies frequently revealed structural defects in SrNbO3. X-ray and electron diffraction studies showed cubic symmetry for SrNbO3 synthesized below 1300°C and for compounds with nominal composition Sr0.8NbO3 synthesized between 1200 and 1550°C. SrNbO3 was found to be temperature independently paramagnetic

  • 8.
    Istomin, S Y
    et al.
    Moscow State University, Department of Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    D’Yachenko, O G
    Moscow State University, Department of Chemistry.
    Holm, W
    KTH.
    Antipov, E V
    Moscow State University, Department of Chemistry.
    Perovskite-Type Ca1−xSrxNbO3(0≤x≤1) Phases: a synthesis, structure, and electron microscopy study1998In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 141, p. 514-521Article in journal (Refereed)
    Abstract [en]

    Reduced niobates Ca1−xSrxNbO3(0≤x≤1) with perovskite-type structures have been synthesized at 1500°C in niobium ampoules sealed under argon gas. The prepared compounds were characterized by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy, and energy-dispersive X-ray analysis. The structure of CaNbO3(GdFeO3type) was refined using X-ray powder diffraction data. Electron diffraction studies showed that complex superstructures of the perovskite-type structure occur forx>0 in Ca1−xSrxNbO3: (i) forx=0.2 and 0.3 reflections corresponding to a supercell witha≈2×√2×aper,b≈4×aper, andc≈2×√2×aper(per=ideal perovskite) were observed, (ii) forx=0.5, 0.6, and 0.7 a cubic supercell was found witha=4×aper, whereas (iii) forx=0.8 and 0.9 the supercell is probably orthorhombic withac≈√2×aperandb≈2×aper. Forx=1.0 a new orthorhombic modification of SrNbO3withac≈√2×aperandb≈2×aperwas found. Resistivity measurements showed CaNbO3to have a nonmetallic type of conductivity, whereas the Sr-containing samples were metallic.

  • 9.
    Istomin, S. Ya.
    et al.
    Moscow State University, Department of Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hannerz, H
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kohler, J
    Max Planck Institute - Solid State Chemistr, Stuttgart, Germany.
    An X-ray powder and electron diffraction study of reduced tantalates with the perovskite structure, Na1-xSrxTaO3, 0 < x <= 0.42000In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 154, p. 427-434Article in journal (Refereed)
    Abstract [en]

    Single-phase perovskite-type reduced tantalates, Na1-x SrxTaO3 with 0 < x 0.4, have been synthesized by heating mixtures of NaTaO3, Sr5Ta4O15 and Ta in sealed tantalum ampules at 1400 degreesC for 20-24 h. At Sr contents of 0.5 less than or equal to x less than or equal to 0.8 and above 1400 degreesC, polyphasic samples were obtained. X-ray powder diffraction (XRD) and transmission electron microscopy studies (selected area (SAED) and convergent beam electron diffraction (CBED)) showed an orthorhombic distortion of the x = 0.1 sample (GdFeO3 type, space group Pnma). The interpretation of the XRD, SAED, and CBED studies indicates the crystallites found in the x = 0.2 and 0.3 samples to consist of domains with tetragonal and orthorhombic symmetry having the unit Cell parameters of a = b approximate to root (2a(per)) and c approximate to 2a(per) and a approximate to b approximate to root (2a(per)) and c approximate to a(per) (a(per) cell axis in the ideal perovskite structure), respectively. The x 0.4 sample was cubic (space group Pm3m) with a = a(per). Resistivity measurements showed that all samples are semiconducting and that the conductivity increases with Sr content. Magnetic measurements of Na0.6Sr0.4TaO3 revealed a diamagnetic behavior down to 20 K. Below this temperature a slight paramagnetism arises. (C) 2000 Academic Press.

  • 10.
    Jalilian, Ehsan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lidin, Sven
    Lunds universitet, Polymer- och materialkemi.
    Dual graphs realized in the compounds di-μ3-4-mercaptopyridine catena-di-μ2-iodo-di-μ3-iodo-μ4-iodo penta copper(I) and di-μ3-4-mercaptopyridine-di-catena-iodo-di-μ3-iodo tri copper(I)2010In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 183, no 11, p. 2656-2661Article in journal (Refereed)
    Abstract [en]

    Two compounds, [Cu5I5](SNC5H4)2 [i] and [Cu3I3](SNC5H4)2 [ii], were synthesized under hydrothermal conditions and the crystal structures were solved. Both compounds crystallized in space group I41/a. The iodide and the sulphur from mercaptopyridine are connected to copper atom, giving the copper atoms tetrahedral coordination geometry. The pyridine end of the organic moiety is non-bonding and fills the empty space around the tetrahedra formed from copper, sulphur and iodide.

  • 11. Kal, Subhadeep
    et al.
    Stoyanov, Emil
    Belieres, Jean-Philippe
    Groy, Thomas L.
    Norrestam, Rolf
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Haussermann, Ulrich
    High-pressure modifications of CaZn2, SrZn2, SrAl2, and BaAl2: Implications for Laves phase structural trends2008In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 181, no 11, p. 3016-3023Article in journal (Refereed)
    Abstract [en]

    High-pressure forms of intermetallic compounds with the composition CaZn2, SrZn2, SrAl2, and BaAl2 were synthesized from CeCu2-type precursors (CaZn2, SrZn2, SrAl2) and Ba21Al40 by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl2 and BaAl2), X-ray single-crystal diffraction (CaZn2), and electron microscopy (SrZn2). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu2 (C15) structure, the dizincides adopt the hexagonal MgZn2 (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions.

  • 12. Kaluzhskikh, M. S.
    et al.
    Kazakov, S. M.
    Mazo, G. N.
    Istomin, S. Ya.
    Antipov, E. V.
    Gippius, A. A.
    Fedotov, Yu.
    Bredikhin, S. I.
    Liu, Yi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    High-temperature crystal structure and transport properties of the layered cuprates Ln(2)CuO(4), Ln=Pr, Nd and Sm2011In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 184, no 3, p. 698-704Article in journal (Refereed)
    Abstract [en]

    High-temperature crystal structure of the layered cuprates Ln(2)CuO(4), Ln = Pr, Nd and Sm with tetragonal T'-structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a- and c-axis changing from TEC(a)/TEC(c)approximate to 1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln(2)CuO(4) shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO(2)-planes (TEC(Pr-O1)= 11.7 ppm K(-1)) in comparison with other cuprates: TEC (Nd-O1)=15.2 ppm K(-1) and TEC (Sm-O1)= 15.1 ppm K(-1). High-temperature electrical conductivity of Pr(2)CuO(4) is the highest one in the whole studied temperature range (298-1173 K): 0.1-108 S/cm for Pr(2)CuO(4), 0.07-23 S/cm for Nd(2)CuO(4) and 2 X 10(-4)-9 S/cm for Sm(2)CuO(4). The trace diffusion coefficient (D(T)) of oxygen for Pr(2)CuO(4) determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2 X 10(-13) Cm(2)/S (973 K) and 3.8 X 10(-10) Cm(2)/S (1173 K) which are in between those observed for the manganese and cobalt-based perovskites.

  • 13.
    Konar, Sumit
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nylén, Johanna
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bernin, Diana
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ruschewitz, Uwe
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The many phases of CaC22016In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 239, p. 204-213Article in journal (Refereed)
    Abstract [en]

    Polymorphic CaC2 was prepared by reacting mixtures of CaH2 and graphite with molar ratios between 1:1.8 and 1:2.2 at temperatures between 700 and 1400 degrees C under dynamic vacuum. These conditions provided a well controlled, homogeneous, chemical environment and afforded products with high purity. The products, which were characterized by powder X-ray diffraction, solid state NMR and Raman spectroscopy, represented mixtures of the three known polymorphs, tetragonal CaC2-I and monoclinic CaC2-II and -III. Their proportion is dependent on the nominal C/CaH2 ratio of the reaction mixture and temperature. Reactions with excess carbon produced a mixture virtually free from CaC2-I, whereas high temperatures (above 1100 degrees C) and C-deficiency favored the formation of CaC2-I. From first principles calculations it is shown that CaC2-I is dynamically unstable within the harmonic approximation. This indicates that existing CaC2-I is structurally/dynamically disordered and may possibly even occur as slightly carbon-deficient phase CaC2-delta. It is proposed that monoclinic II is the ground state of CaC2 and polymorph III is stable at temperatures above 200 degrees C. Tetragonal I represents a metastable, heterogeneous, phase of CaC2. It is argued that a complete understanding of the occurrence of three room temperature modifications of CaC2 will require a detailed characterization of compositional and structural heterogeneities within the high temperature form CaC2-IV, which is stable above 450 degrees C. The effect of high pressure on the stability of the monoclinic forms of CaC2 was studied in a diamond anvil cell using Raman spectroscopy. CaC2-II and -III transform into tetragonal CaC2-I at about 4 and 1GPa, respectively.

  • 14. Lin, Sen
    et al.
    Shi, Lei
    Yoshida, Hisao
    Li, Mingrun
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Synthesis of hollow spherical tantalum oxide nanoparticles and their photocatalytic activity for hydrogen production2013In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 199, p. 15-20Article in journal (Refereed)
    Abstract [en]

    Nano-particles consisting of hollow spherical tantalum oxide (referred to as HSTaO in this work) were synthesized by using the nonionic triblock copolymer F127 as the structure-directing agent in an ethanol aqueous medium. The HSTaO had a large surface area (higher than 100 m(2)/g), and relatively uniform particle size, in the range of 50-200 nm. The wall thickness of the hollow spherical particles was measured to be about 15-17 nm and contained ultrafine Ta2O5 crystallites. The band gap of HSTaO (4.3 eV) is clearly wider than that of bulk Ta2O5 (3.9 eV), which can be attributed to the quantum size of the ultrafine Ta2O5 crystallites. In addition, HSTaO with core-shell Ni/NiO particles (co-catalyst) exhibited similar photocatalytic activity as bulk Ta2O5 with co-catalyst in hydrogen generation from methanol aqueous solution under photoirradiation, with the HSTaO photocatalyst showing higher stability than the bulk.

  • 15. Mayerhoefer, Thomas G.
    et al.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    SUBLeonova, Ekaterina
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Physical Chemistry.
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Physical Chemistry.
    Kriltz, Antje
    Popp, Juergen
    Consolidated silica glass from nanoparticles2008In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 181, no 9, p. 2442-2447Article in journal (Refereed)
    Abstract [en]

    A dense silica glass was prepared by consolidating a highly dispersed silicic acid powder (particle size < 10 nm) with the Spark Plasma Sintering (SPS) technique. The glass was characterized by ellipsometry, transmission electron microscopy (TEM), infrared reflectance and transmittance spectroscopy, as well as by Raman, UV-Vis-NIR and solid-state nuclear magnetic resonance (NMR) spectroscopy. The prototypic sample showed a transmittance of about 63% compared to silica glass in the UV-Vis spectral range. Based on the results of infrared transmittance spectroscopy this lower transparency is due to the comparably high water content, which is about 40 times higher than that in silica glass. H-1 magic-angle spinning (MAS) NMR confirmed an increase in hydroxyl groups in tie sample prepared by SPS relative to that of the conventional SiO2 reference glass. Aside from the comparably high water content, we conclude from the similarity of the IR-reflectance and the Si-29 MAS NMR spectra of the SPS sample and the corresponding spectra of the conventionally prepared silica glass, that the short- and medium-range order is virtually the same in both materials. Raman spectroscopy, however, Suggests that the number of three- and four-membered rings is significantly smaller in the SPS sample compared to the conventionally prepared sample. Based on these results we conclude that it is possible to prepare glasses by compacting amorphous powders by the SPS process. The SPS process may therefore enable the preparation of glasses with compositions inaccessible by conventional methods. 

  • 16. Napolsky, Ph S.
    et al.
    Drozhzhin, O. A.
    Istomin, S. Ya
    Kazakov, S. M.
    Antipov, E. V.
    Galeeva, A. V.
    Gippius, A. A.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Abakumov, A. M.
    Van Tendeloo, G.
    Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O3-y perovskites - perspective cathode materials for IT-SOFC2012In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 192, p. 186-194Article in journal (Refereed)
    Abstract [en]

    Oxygen deficient perovskites Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=root 2 x a(per), b=2 x a(per), c=root 2 x a(per) (a(0)b(-)b(-) tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 <= x <= 0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573 K for 48 h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) angstrom, R-p=0.057, R-wp=0.056, chi(2)=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1-xMnxO3-y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8 ppm K-1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3-y, and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 <= y <= 0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the sigma value from similar to 1 to similar to 50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E-p) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6.

  • 17.
    Nedumkandathil, Reji
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Benson, Daryn E.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Spektor, Kristina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The 3R polymorph of CaSi22015In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 222, p. 18-24Article in journal (Refereed)
    Abstract [en]

    The Zintl phase CaSi2 commonly occurs in the 6R structure where puckered hexagon layers of Si atoms are stacked in an AA'BB'CC' fashion. In this study we show that sintering of CaSi2 in a hydrogen atmosphere (30 bar) at temperatures between 200 and 700 degrees C transforms 6R-CaSi2 quantitatively into 3R-CaSi2. In the 3R polymorph (space group R-3m (no. 166), a=3.8284(1), c=15.8966(4), Z=3) puckered hexagon layers are stacked in an ABC fashion. The volume per formula unit is about 3% larger compared to 6R-CaSi2. First principles density functional calculations reveal that 6R and 3R-CaSi2 are energetically degenerate at zero Kelvin. With increasing temperature 6R-CaSi2 stabilizes over 3R because of its higher entropy. This suggests that 3R-CaSi2 should revert to 6R at elevated temperatures, which however is not observed up to 800 degrees C. 3R-CaSi2 may be stabilized by small amounts of incorporated hydrogen and/or defects.

  • 18.
    Nedumkandathil, Reji
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kranak, Verina F.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johansson, Robert
    Ångström, Jonas
    Balmes, Oliver
    Andersson, Mikael S.
    Nordblad, Per
    Scheicher, Ralph H.
    Sahlberg, Martin
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hydrogenation induced structure and property changes in GdGa2016In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 239, p. 184-191Article in journal (Refereed)
    Abstract [en]

    Hydrides GdGaH were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50 bar and temperatures from 50 to 500 degrees C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50 bar and temperatures below 500 degrees C afford a uniform hydride phase with the NdGaH1.66 structure (Cmcm, a=3.9867(7) angstrom, b=12.024(2) angstrom, c=4.1009(6) angstrom) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH1.66 structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH1.66. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200 degrees C affords a hydride with x approximate to 1.3, which is stable up to 500 degrees C, and that additional H absorption, yielding GdGaH1.66, takes place at lower temperatures. Consequently, GdGaH1.66 desorbs H above T=200 degrees C. Without the presence of hydrogen, hydrides GdGaHx decompose at temperatures above 300 degrees C into GdH2 and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie Weiss constant and effective magnetic moment of GdGaH1.66 were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of similar to 8 mu B which is typical for compounds containing Gd3+ ions.

  • 19.
    Nilsson, Göran
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Single-Crystal X-Ray Diffraction Studies of Homologues in the Series nBa(Nb,Zr)O3+3mNbO with n=2, 3, 4, 5 and m=12001In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 156, p. 75-83Article in journal (Refereed)
    Abstract [en]

    Single crystals of four homologues in the series nBa(Nb,Zr)O3+3mNbO, with n:m=2:1, 3:1, 4:1, and 5:1, were found in the reduced Ba–Nb–Zr–O system. Single-crystal X-ray diffraction data were collected for all the crystals. For all homologues the space group was found to be P4/mmm. The structures can be described as intergrowths of Ba(Nb,Zr)O3 perovskite and NbO slabs. The refined cell parameters and compositions of the 2:1, 3:1, and 4:1 homologues are a=4.1768(5) Å and c=12.269(2) Å for Ba2Nb4.5(1)Zr0.5(1)O9, a=4.1769(5) Å and c=16.493(3) Å for Ba3+δNb4.8(2)−δ Zr1.2(2)O12−δ (δ=0.098(4)), and a=4.1747(6) Å and c= 20.619(4) Å for Ba4+δNb5.1(4)−δZr1.9(4)O15−δ (δ=0.270(9)). The refined cell parameters of the 5:1 homologue are a=4.1727(3) Å and c=24.804(3) Å. Zr replaces Nb only in the NbO6 octahedra found in the perovskite slabs.

  • 20.
    Samain, Louise
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Amshoff, Philipp
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Biendicho, Jordi J.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). STFC Rutherford Appleton Laboratory, England.
    Tietz, Frank
    Mahmoud, Abdelfattah
    Hermann, Raphael P.
    Istomin, Sergey Ya.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Lomonosov Moscow State University, Russia.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Crystal structure and high-temperature properties of the Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta (0 <= x <= 0.75)2015In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 227, p. 45-54Article in journal (Refereed)
    Abstract [en]

    Ruddlesden-Popper n=2 member phases Sr3-xYxFe1.25Ni0.75O7-delta, 0 <= x <= 0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mossbauer spectroscopy. Both samples as-prepared at 1300 degrees C under N-2(g) flow and samples subsequently air-annealed at 900 degrees C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with delta=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mossbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a delta value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mossbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K-1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.

  • 21.
    Samain, Louise
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ladd, Danielle M.
    Seo, Dong-Kyun
    Javier Garcia-Garcia, F.
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structural analysis of highly porous gamma-Al2O32014In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 217, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Two highly porous gamma-aluminas, a commercial catalyst obtained from the calcination of boehmite and a highly mesoporous product obtained from amorphous aluminum (oxy)hydroxide via a sol-gel-based process were investigated by Al-27 nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and atomic pair distribution function (PDF) analysis of synchrotron powder diffraction data. NMR data showed for both materials a distribution of tetrahedrally and octahedrally coordinated Al at a 0.30:0.70 ratio, which is typical for gamma-aluminas. TEM studies revealed that rod-shaped particles with about 5 nm in thickness are the building blocks of the porous structure in both materials. These particles often extend to a length of 50 nm in the commercial catalyst and are considerably shorter in the sol-gel-based material, which has a higher surface area. Refinement of PDFs revealed the presence of a similar to 1 nm scale local structure and the validity of a tetragonal average structure for both materials. This tetragonal average structure contains a substantial fraction of non-spinel octahedral Al atoms. It is argued that the presence of local structure is a general feature of gamma-alumina, independent of precursor and synthesis conditions. The concentration of non-spinel Al atoms seems to correlate with surface properties, and increases with increasing pore size/surface area. This should have implications to the catalytic properties of porous gamma-alumina.

  • 22. Shafeie, S.
    et al.
    Dreyer, B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Awater, R. H. P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Golod, Taras
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Biendicho, J. J.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Istomin, S. Ya.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Crystal structure, thermal expansion and high-temperature electrical conductivity of A-site deficient La2-zCo1+y(MgxNb1-x)(1-y)O-6 double perovskites2015In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 229, p. 243-251Article in journal (Refereed)
    Abstract [en]

    New La-deficient double perovskites with P2(1)/n symmetry, La-similar to 1.90(Co1-x2+Mgx2+)(Co1/33+Nb2/35+)O-6 with x=0, 0.13 and 0.33, and La-2(Co1/22+Mg1/22+) (Co1/23+Nb1/25+)O-6 were prepared by solid state reaction at 1450 degrees C. Their crystal structures were refined using time-of-flight neutron powder diffraction data. Our results show that certain cations such as Nb5+, with very strong B-O bonds in the perovskite structure, can induce A-site vacancies in double perovskites. Upon heating in N-2 gas atmosphere at 1200 degrees C similar to 1% O atom vacancies are formed together with a partial reduction of the Co3+ content. The average thermal expansion coefficient between 25 and 900 degrees C of La-1.90(Co2/32+Mg1/32+)(Co1/33+Nb2/35+)O-6 was determined to be 17.4 ppm K-1. Four-point electronic conductivity measurements showed that the compounds are semiconductors, with conductivities varying between 3.7.10(-2) and 7.7.10(-2) S cm(-1) at 600 degrees C and activation energies between 0.77 and 0.81 eV. Partial replacement of La3+ with Sr2+ does not lead to any increase of conductivity, while replacement of Mg2+ with Cu2+ in La1.9CoCu1/3Nb2/3O6 and La1.8CoCu1/2Nb1/2O6 leads to similar to 100 times larger conductivities at 600 degrees C, 0.35 and 1.0 S cm(-1), respectively, and lower activation energies, 0.57 and 0.73 eV, respectively.

  • 23.
    Shafeie, Samrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Istomin, S. Y.
    Karvonen, L.
    Chen, S. A.
    Chen, T. H.
    Chen, J. M.
    Weidenkaff, A.
    Karppinen, M.
    Sirtl, T.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Phase formation, crystal structures and magnetic properties of perovskite-type phases in the system La2Co1+z(MgxTi1-x)1-zO62011In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 184, no 1, p. 177-190Article in journal (Refereed)
    Abstract [en]

    Perovskite-type cobaltates in the system La(2)Co(1+z) (Mg(x)Ti(1-x))(1-z)O(6) were studied for z=0 <= x <= 0.6 and 0 <= x <= 0.9, using X-ray and neutron powder diffraction, electron diffraction (ED), magnetic susceptibility measurements and X-ray absorption near-edge structure (XANES) spectroscopy. The samples were synthesised using the citrate route in air at 1350 degrees C. The space group symmetry of the structure changes from P2(1)/n via Pbnm to R (3) over barc with both increasing Mg content and increasing Co content. The La(2)Co(Mg(x)Ti(1-x))O(6) (z=0) compounds show anti-ferromagnetic couplings of the magnetic moments for the Co below 15 K for x=0, 0.1 and 0.2. XANES spectra show for the compositions 0 <= x <= 0.5 a linear decrease in the L(3)/(L(3)+ L(2))Co-L(2.3) edge branching ratio with x, in agreement with a decrease of the average Co ion spin-state, from a high-spin to a lower-spin-state, with decreasing nominal Co(2+) ion content.

  • 24.
    Spektor, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Tran, Dung Trung
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Leinenweber, Kurt
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Transformation of rutile to TiO2-II in a high pressure hydrothermal environment2013In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 206, p. 209-216Article in journal (Refereed)
    Abstract [en]

    The high pressure transformation of rutile to TiO2-II with the α-PbO2 structure is known to be kinetically hindered. In this study we show that a hydrothermal environment at 6 GPa and 650 °C provides appreciable rates for producing single phase bulk samples of TiO2-II. So obtained TiO2-II was characterized by scanning electron microscopy, powder X-ray diffraction, Raman and Far-IR spectroscopy. The structural properties are identical to TiO2-II from dry transitions. Transmission electron microscopy studies strongly indicate that Ostwald ripening processes play an important role in the hydrothermally assisted transformation and subsequent growth of TiO2-II crystals. TiO2-II is thermally stable to about 550 °C. At 600 °C the onset of the transformation to rutile is observed. The thermal expansion in the temperature range from room temperature to 500 °C is highly anisotropic, virtually affecting only the c unit cell parameter (αc=7.1(2)×10−6 °C−1). The pressure–temperature conditions for the hydrothermally assisted transformation of rutile are viable for industrial production settings, and in light of the large technological significance of TiO2, TiO2-II may present an interesting target for large-scale synthesis.

  • 25.
    Svensson, Gunnar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    ERIKSSON, LARS
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The Crystal Structure of SrNb4O61995In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 114, p. 301-307Article in journal (Refereed)
    Abstract [en]

    Single crystals of SrNb4O6 were obtained by heat treatment of a pelleted mixture of Sr5Nb4O15, Nb2O5, and Nb at 1670 degrees C in sealed Nb tubes. High-resolution electron microscopy (HREM) studies showed the structure to be an intergrowth of alternating slabs of SrNbO3 (perovskite-type structure) and NbO (ordered deficient NaCl-type structure), both two unit cells wide. SrNb4O6 has a tetragonal unit cell with a = 4.1655(3) Angstrom and c = 16.223(1) Angstrom and space group P4/mmm, Z = 2. The structure model obtained from the HREM images was refined, using single-crystal diffraction data, to R(f) = 3.0%

  • 26.
    Söderberg, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Kubota, Yoshiki
    Muroyama, Norihiro
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grüner, Daniel
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Yoshimura, Arisa
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Electron charge distribution of CaAl2−xZnx: Maximum Entropy Method combined with Rietveld analysis of High-resolution-synchrotron X-ray powder diffraction data2008In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 181, no 8, p. 1998-2005Article in journal (Refereed)
    Abstract [en]

    Using short wavelength X-rays from synchrotron radiation (SPring-8), high-resolution powder diffraction patterns were collected. In order to study both the structural relationship and the mechanism of stability in the CaAl2−xZnx system, among the Laves phases (MgCu2 and MgNi2 type) and KHg2-type structures, the charge density distribution of CaAl2−xZnx as a function of x was obtained from the diffraction data by Rietveld analysis combined with the maximum entropy method (MEM). In the MEM charge density maps overlapping electron densities were clearly observed, especially in the Kagomé nets of the Laves phases. In order to clarify the charge redistribution in the system, the deformation charge densities from the densities formed by the constituent free atoms are discussed. In the ternary MgNi2-type phase, partial ordering of Al and Zn atoms is observed, a finding that is supported by ab-initio total energy calculations.

  • 27.
    Tengå, Andreas
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Garcia-Garcia, Javier
    Lehrstuhl für Festkörperchemie,Institutfür Physik,Universität Augsburg.
    Yang, Wu
    Department of Chemistry and Biochemistry, Arizona State University.
    Newman, Nathan
    Department of Chemistry and Biochemistry, Arizona State University.
    Häussermann, Ulrich
    Department of Chemistry and Biochemistry, Arizona State University.
    Metal–nonmetal transition in the sphalerite-type solid solution [ZnSnSb2]1-x[2(InSb)]x2009In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 182, no 6, p. 1438-1442Article in journal (Refereed)
    Abstract [en]

    Samples of the solid solution [ZnSnSb2]1-x[2(InSb)]x have been prepared over the whole range of composition by tin flux synthesis. The lattice parameter of the sphalerite-type average structure varies linearly between that of the end members ZnSnSb2 and InSb, a = 6.2849(2) and 6.4776(15), respectively. Electron diffraction shows different kinds of structured diffuse scattering for Zn and In rich samples, respectively. The former is attributed to compositional short range ordering, the latter to thermally excited phonon modes. A metal-nonmetal transition takes place between the compositions x = 0.8 and x = 0.9.

  • 28. Verchenko, V. Yu
    et al.
    Likhanov, M. S.
    Kirsanova, M. A.
    Gippius, A. A.
    Tkachev, A. V.
    Gervits, N. E.
    Galeeva, A. V.
    Buettgen, N.
    Kraetschmer, W.
    Lue, C. S.
    Okhotnikov, Kirill S.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shevelkov, A. V.
    Intermetallic solid solution Fe1-xCoxGa3: Synthesis, structure, NQR study and electronic band structure calculations2012In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 194, p. 361-368Article in journal (Refereed)
    Abstract [en]

    Unlimited solid solution Fe1-xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P4(2)/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and Ga-69,Ga-71 nuclear quadrupole resonance (NRQ) spectroscopy clearly shows that the Fe-Fe and Co-Co dumbbells are preferred to the Fe-Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x > 0. The solid solution is metallic for x > 0.025. The study of the nuclear spin-lattice relaxation shows that the rate of the relaxation, 1/T-1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N-2(E-F).

  • 29.
    Wu, Yang
    et al.
    Department of Chemistry and Biochemistry, Arizona State University.
    Lidin, Sven
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Tengå, Andreas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Newman, Nathan
    School of Materials, Arizona State University.
    Häussermann, Ulrich
    Department of Chemistry and Biochemistry, Arizona State University.
    Phase relations and structural properties of the ternary narrow gap semiconductors Zn5Sb4In2-δ (δ = 0.15) and Zn9Sb6In22010In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 183, no 7, p. 1574-1581Article in journal (Refereed)
    Abstract [en]

    A systematic study of the Zn-rich corner of the ternary system Zn-Sb-In revealed the presence of two ternary compounds, stable Zn5Sb4In2-δ(δ = 0.15) and metastable Zn9Sb6In2, with closely related crystal structures. Their common motif is a tetragonal basic structure of 32434 nets formed by the Sb atoms that are stacked in antiposition to yield layers of square antiprisms sharing edges plus intervening tetracapped tetrahedra (tetreadersterns). The majority of Zn atoms occupy peripheral tetrahedra of such tetraedersterns which produces frameworks with a composition “ZnSb”. These frameworks represent orthorhombic superstructures, (2×1×1) for Zn5Sb4In2-δ (Z = 4) and (2×3×1) for Zn9Sb6In2 (Z = 8), with respect to the tetragonal arrangement of Sb atoms. The In and remaining Zn atoms are distributed in the channels formed by the square antiprisms. Phase relations in the Zn-Sb-In system are complex. Crystals of metastable Zn9Sb6In2 are regularly intergrown with various amounts of Zn5Sb4In2-δ. Additionally, a monoclinic variant to orthorhombic Zn9Sb6In2 could be identified. Zn9Sb6In2 decomposes exothermically into a mixture of Zn5Sb4In2-δ, Zn4Sb3 and elemental Zn at around 480 K. Both Zn5Sb4In2-δ and Zn9Sb6In2 are poor metals with resistivity values that are characteristic of heavily doped or degenerate semiconductors (0.2 to 3 mW cm at room temperature).

  • 30. Yang, Tao
    et al.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Croft, Mark
    Nowik, Israel
    Ignatov, Alexander
    Cong, Rihong
    Greenblatt, Martha
    Ca4Fe3-xMnxO8-delta Cl2: A new n=3 Ruddlesden-Popper oxychloride2010In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 183, no 6, p. 1215-1220Article in journal (Refereed)
    Abstract [en]

    Solid state solutions of Ca4Fe3-xMnxO8-delta Cl2 (0 92 <= x <= 1.79 (delta similar to 0.1) single crystals were synthesized in CaCl2-flux in air. The structure, determined by single-crystal X-ray diffraction, is related to the n = 3 Ruddlesden-Popper phase in space group I4/mmm with strong deviations from the ideal structure Mn and Fe are disordered over two transition metal sites. Due to the positional disordering of the equatorial oxygen atoms in the MO6 octahedra in Ca4Fe3-xMnxO8-delta Cl2 both tilting (similar to 9 degrees) along the c-axis and rotation (similar to 10 5 degrees) within the ab-plane are observed All the Fe ions are trivalent, as confirmed by Fe-57 Mossbauer spectroscopy and X-ray absorption near edge spectroscopy (XAS), while the formal valence state of Mn varies from very close to 4+ in the x = 0.92 to mix-valent 3+/4+ in the x = 179 member, as indicated by XAS Magnetic investigations evidence short-range antiferromagnetic ordering already at room temperature and spin-glass behavior at low temperature due to the structural disordering of Mn/Fe.

  • 31.
    Zimmermann, Iwan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kremer, Reinhard K.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis, crystal structure and magnetic properties of the open framework compound Co3Te2O2(PO4)2(OH)42011In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 184, no 11, p. 3080-3084Article in journal (Refereed)
    Abstract [en]

    The new compound Co(3)Te(2)O(2)(PO(4))(2)(OH)(4) was synthesized using hydrothermal techniques. It crystallizes in the monoclinic space group C2/m with the unit cell a=19.4317(10) angstrom, b=6.0249(3) angstrom, c=4.7788(2) angstrom, beta=103.139(5)degrees. The crystal structure is an open framework having chains of edge sharing [Co(1)O(6)] octahedra. Other building blocks are [TeO(3)(OH)(2)], [PO(4)] and [Co((2))O(2)(OH)(4)] connected mainly via corner sharing. The -OH groups protrude into channels in the structure. The magnetic susceptibility measured from 2 to 300 K shows two broad anomalies at around 21 K and 4 K. respectively. The peak at similar to 20 K is ascribed to a two-dimensional antiferromagnetic ordering of linear [Co(1)O(6)] chains coupled by interchain interaction via [PO(4)] groups in the Co(1) sheets. The second transition at 4 K is ascribed to a second antiferromagnetic ordering of the moments of the Co(2) entities via super-super exchange involving [PO(4)] and [TeO(3)(OH)(2)] groups. This assignment is strongly supported by low-temperature heat capacity measurements indicating an entropy removal within the high-temperature transition of about twice the magnitude of the low-temperature transition.

  • 32.
    Zimmermann, Iwan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kremer, Reinhard K.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Two isostructural layered oxohalide compounds containing Mn2+, Te4+ and Si4+; crystal structure and magnetic susceptibility2014In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 218, p. 6-9Article in journal (Refereed)
    Abstract [en]

    The new compounds Mn-4(TeO3)(SiO4)X-2 (X=Br, Cl) were synthesized by solid state reactions in sealed evacuated silica tubes. The compounds crystallize in the monoclinic space group P2(1)/m with the unit cell parameters a=5.5463(3) angstrom (5.49434(7) angstrom), b= 6.4893(4) angstrom (6.44184(9) angstrom), c=12.8709(7) A (12.60451 (18) angstrom), beta=93.559(5)degrees (94.1590(12)degrees) and Z=2 for the respective Br and Cl analogues. Manganese adopts various distorted coordination polyhedra; [MnO6] octahedra, [MnO5] tetragonal pyramids and [MnO2X2] tetrahedra. Other building blocks are [SiO4] tetrahedra and [TeO3] trigonal pyramids. The structure is made up from layers having no net charge that are connected via weak Van der Waal interactions. The layers that are parallel to (1 1 0) consist of two manganese oxide sheets which are separated by [Siad tetrahedra. On the outer sides of the sheets are the [MnO2X2] tetrahedra and the [TeO3] trigonal pyramids connected so that the halide ions and the stereochemically active lone pairs on the tellurium atoms protrude from the layers. Magnetic susceptibility measurements reveal a Curie law with a Weiss temperature of theta=-153(3) K for temperatures >= 100 K and indicate antiferromagnetic ordering at TN similar to 4 K. Possible structural origins of the large frustration parameter of f=38 are discussed.

1 - 32 of 32
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