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  • 1. Bajwa, Anjali
    et al.
    Balakrishnan, Malini
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Batra, Vidya S.
    Removal of volatile organic compounds over bagasse ash derived activated carbons and monoliths2016In: Journal of Environmental Chemical Engineering, ISSN 2160-6544, E-ISSN 2213-3437, Vol. 4, no 2, p. 1561-1573Article in journal (Refereed)
    Abstract [en]

    The unburned carbon in bagasse ash was separated and used as a starting material for activated carbon and carbon monolith preparation. The separated carbon was steam activated in a rotary kiln under different conditions and compared with carbon activated in limited supply of air. The activated carbon from the rotary kiln showed surface areas ranging from 324 to 601 m(2)/g. Different phenolic resins and cellulosic binders were used to prepare the monoliths using slurry casting method. The effects of different preparation conditions on the properties of the monolith were studied. Upon monolith formation, the surface area was reduced slightly and surface areas in the range 92-479 m(2)/g were achieved. The activated carbons and monoliths were tested for static adsorption of volatile organic compounds (VOCs) using benzene, xylene, hexane and toluene as model compounds. With the activated carbons, adsorption capacities as high as 22.5, 31.1, 27.5 and 25.0 g/100 g sample were obtained for toluene, benzene, xylene and hexane, respectively. The adsorption capacities were reduced for the corresponding monoliths. The waste derived activated carbons and monoliths show promising results as adsorbents for the removal of volatile organic compounds.

  • 2. Bajwa, Anjali
    et al.
    Moraga, Francisca
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Balakrishnan, Malini
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Batra, Vidya S.
    Activated Carbon Monoliths by Pressureless Technique for Environmental Applications2015In: Environmental Progress & Sustainable Energy, ISSN 1944-7442, E-ISSN 1944-7450, Vol. 34, no 5, p. 1420-1426Article in journal (Refereed)
    Abstract [en]

    Carbon monoliths have been prepared through simple procedure by carbonization in inert atmosphere at 550 C from commercial activated carbon and from unburned carbon in it ykste bctgasse fly asb; US nig, In 0 different kin dS phenolic resin binders. The bagasse fly ash was collected ft on; sugar mills where bagasse is used as a biomass based fuel for cogeneration. Commercial actuated carbon based monoliths whet -e 5 and 10 wt % of the actuated carbon had been replaced by iron oxide (hematite) were dic0 prepared. Results indicate that BET sutfac:e area decreases upon carbonization and loading of hematite. Scanning electron microscopy studies shows that the iron oxide is well distributed over the monoliths and X-ray diffraction shows that it is reduced to magnetite during carbonization. Temperature programmed reduction eAperintents show that the iron oxides on the monoliths are redox active. The monoliths based on commercial activated carbon show 80% remotwl of phenol in dihtted phenol based water solutions whereas unburned carbon derived monoliths showed 5-/ % removal in similar solution.

  • 3. Benson, Daryn
    et al.
    Li, Yanling
    Luo, Wei
    Ahuja, Rajeev
    Svensson, Gunnar
    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).
    Lithium and Calcium Carbides with Polymeric Carbon Structures2013In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 11, p. 6402-6406Article in journal (Refereed)
    Abstract [en]

    We studied the binary carbide systems Li2C2 and CaC2 at high pressure using an evolutionary and ab initio random structure search methodology for crystal structure prediction. At ambient pressure Li2C2 and CaC2 represent salt-like acetylides consisting of C-2(2-) dumbbell anions. The systems develop into semimetals (P (3) over bar m1-Li2C2) and metals (Cmcm-Li2C2, Cmcm-CaC2, and Immm-CaC2) with polymeric anions (chains, layers, strands) at moderate pressures (below 20 GPa). Cmcm-CaC2 is energetically closely competing with the ground, state structure. Polyanionic forms of carbon 4 stabilized by electrostatic interactions with surrounding cations add a new feature to carbon chemistry. SemimetallicP (3) over bar m1-Li2C2 displays an electronic structure close to that of graphene. The pi* band, however, is hybridized with Li-sp states and changed into a bonding valence band. Metallic forms are predicted to be superconductors. Calculated critical temperatures may exceed 10 K for equilibrium volume structures.

  • 4.
    Biendicho, Jordi Jacas
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). STFC Rutherford Appleton Laboratory, England.
    Roberts, Matthew
    Noréus, Dag
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lagerqvist, Ulrika
    Smith, Ronald I.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Norberg, Stefan T.
    Eriksson, Sten G.
    Hull, Stephen
    In situ investigation of commercial Ni(OH)(2) and LaNi5-based electrodes by neutron powder diffraction2015In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 30, no 3, p. 407-416Article in journal (Refereed)
    Abstract [en]

    Electrochemical reactions at both positive and negative electrodes in a nickel metal hydride (Ni-MH) battery during charge have been investigated by in situ neutron powder diffraction. Commercially available beta-Ni(OH)(2) and LaNi5-based powders were used in this experiment as positive and negative electrodes, respectively. Exchange of hydrogen by deuterium for the beta-Ni(OH)(2) electrode was achieved by ex situ cycling of the cell prior to in situ measurements. Neutron diffraction data collected in situ show that the largest amount of deuterium contained at the positive electrode is de-intercalated from the electrode with no phase transformation involved up to similar to 100 mA h/g and, in addition, the 110 peak width for the positive electrode increases on charge. The negative electrode of composition MmNi(3.6)Al(0.4)Mn(0.3)Co(0.7), where Mm = Mischmetal, exhibits a phase transformation to an intermediate hydride gamma phase first and then to the beta phase on charge. Unit cell dimensions and phase fractions have been investigated by Rietveld refinement of the crystal structure.

  • 5.
    Biendicho, Jordi Jacas
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). STFC Rutherford Appleton Laboratory, England.
    Roberts, Matthew
    Offer, Colin
    Noréus, Dag
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Widenkvist, Erika
    Smith, Ronald I.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edström, Kristina
    Norberg, Stefan T.
    Eriksson, Sten G.
    Hull, Stephen
    New in-situ neutron diffraction cell for electrode materials2014In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 248, p. 900-904Article in journal (Refereed)
    Abstract [en]

    A novel neutron diffraction cell has been constructed to allow in-situ studies of the structural changes in materials of relevance to battery applications during charge/discharge cycling. The new design is based on the coin cell geometry, but has larger dimensions compared to typical commercial batteries in order to maximize the amount of electrode material and thus, collect diffraction data of good statistical quality within the shortest possible time. An important aspect of the design is its modular nature, allowing flexibility in both the materials studied and the battery configuration. This paper reports electrochemical tests using a Nickel-metal-hydride battery (Ni-MH), which show that the cell is able to deliver 90% of its theoretical capacity when using deuterated components. Neutron diffraction studies performed on the Polaris diffractometer using nickel metal and a hydrogen-absorbing alloy (MH) clearly show observable changes in the neutron diffraction patterns as a function of the discharge state. Due to the high quality of the diffraction patterns collected in-situ (i.e. good peak-to-background ratio), phase analysis and peak indexing can be performed successfully using data collected in around 30 min. In addition to this, structural parameters for the beta-phase (charged) MH electrode obtained by Rietveld refinement are presented.

  • 6.
    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.

  • 7. Chernov, Sergey V.
    et al.
    Dobrovolsky, Yuri A.
    Istomin, Sergey Y.
    Antipov, Evgeny V.
    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).
    Tarakina, Nadezhda V.
    Abakumov, Artem M.
    Van Tendeloo, Gustaaf
    Eriksson, Sten G.
    Rahman, Seikh M. H.
    Sr2GaScO5, Sr10Ga6Sc4O25, and SrGa0.75Sc0.25O2.5: a Play in the Octahedra to Tetrahedra Ratio in Oxygen-Deficient Perovskites2012In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 2, p. 1094-1103Article in journal (Refereed)
    Abstract [en]

    Three different perovskite-related phases were isolated in the SrGa1-xScxO2.5 system: Sr2GaScO5, Sr10Ga6Sc4O25, and SrGa0.75Sc0.25O2.5, Sr2GaScO5 (x = 0.5) crystallizes in a brownrnillerite-type structure [space group (S.G.) Icmm, a = 5.91048(5) angstrom, b = 15.1594(1) angstrom, and c = 5.70926(4) angstrom] with complete ordering of Sc3+ and Ga3+ over octahedral and tetrahedral positions, respectively. The crystal structure of Sr10Ga6Sc4O25 (x = 0.4) was determined by the Monte Carlo method and refined using a combination of X-ray, neutron, and electron diffraction data [S.G. I4(1)/a, a = 17.517(1) angstrom, c = 32.830(3) angstrom]. It represents a novel type of ordering of the B cations and oxygen vacancies in perovskites. The crystal structure of Sr10Ga6Sc4O25 can be described as a stacking of eight perovskite layers along the c axis ...[-(Sc/Ga)O-1.6-SrO0.8-(Sc/Ga)O-1.8-SrO0.8-](2 center dot center dot center dot) Similar to Sr2GaScO5, this structure features a complete ordering of the Sc3+ and Ga3+ cations over octahedral and tetrahedral positions, respectively, within each layer. A specific feature of the crystal structure of Sr10Ga6Sc4O25 is that one-third of the tetrahedra have one vertex not connected with other Sc/Ga cations. Further partial replacement of Sc3+ by Ga3+ leads to the formation of the cubic perovskite phase SrGa0.75Sc0.25O2.5 (x = 0.25) with a = 3.9817(4) angstrom. This compound incorporates water molecules in the structure forming SrGa0.75Sc0.25O2.5 center dot xH(2)O hydrate, which exhibits a proton conductivity of similar to 2.0 x 10(-6) S/cm at 673 K.

  • 8. Dyachenko, O G
    et al.
    Istomin, S Y
    Fedotov, M M
    Antipov, E V
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Holm, W
    Structure and properties of Ba6 − xLnxNb10O30, Ln = La, Ce and Nd compounds1997In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 32, no 4, p. 409-419Article in journal (Refereed)
    Abstract [en]

    Ba6 − xLnxNb10O30 compounds, Ln = La, Ce and Nd, with a tetragonal tungsten bronze-type structure have been synthesized and were characterized by X-ray powder diffraction and EDS analysis. The homogeneity regions of the obtained compounds were found to be 0 ≤ x ≤ 2 for La, and 0 ≤ x ≤ 1.5 for Ce and Nd. The crystal structures of Ba5LaNb10O30 and Ba4La2Nb10O30 were refined using X-ray powder diffraction data. Refinement indicated the presence of vacancies in the positions. This observation was supported by oxidation studies of the La-substituted compounds. The temperature dependence of the normalized resistivity of the compounds showed a nonmetallic behavior. The increase in the ratio with decreasing temperature is less distinct for the phases with the higher concentration of rare-earth cation.

  • 9. Efthimiopoulos, Ilias
    et al.
    Benson, Daryn E.
    Konar, Sumit
    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).
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liebig, Stefan
    Ruschewitz, Uwe
    Vazhenin, Grigory V.
    Loa, Ingo
    Hanfland, Michael
    Syassen, Karl
    Structural transformations of Li2C2 at high pressures2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 6, article id 064111Article in journal (Refereed)
    Abstract [en]

    Structural changes of Li2C2 under pressure were studied by synchrotron x-ray diffraction in a diamond anvilcell under hydrostatic conditions and by using evolutionary search methodology for crystal structure prediction.We show that the high-pressure polymorph of Li2C2, which forms from the Immm ground-state structure (Z = 2)at around 15 GPa, adopts an orthorhombic Pnma structure with Z = 4. Acetylide C2 dumbbells characteristic ofImmm Li2C2 are retained in Pnma Li2C2. The structure of Pnma Li2C2 relates closely to the anticotunnite-typestructure. C2 dumbbell units are coordinated by nine Li atoms, as compared to eight in the antifluorite structureof Immm Li2C2. First-principles calculations predict a transition of Pnma Li2C2 at 32 GPa to a topologicallyidentical phase with a higher Cmcm symmetry. The coordination of C2 dumbbell units by Li atoms is increasedto 11. The structure of Cmcm Li2C2 relates closely to the Ni2 In-type structure. It is calculated that Cmcm Li2C2becomes metallic at pressures above 40 GPa. In experiments, however, Pnma Li2C2 is susceptible to irreversibleamorphization.

  • 10. Eriksson, Annika K.
    et al.
    Tran, Thuy
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Saxin, S
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Effects of A-site substitution on the structure and magnetic properties of Bi0.15Sr0.85-yAeyCo1-xFexO3-? perovskites2009In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 11, no 11, p. 1945-1954Article in journal (Refereed)
    Abstract [en]

    The effects of partial substitution of Sr2+ by Ca2+ and Ba2+ on the A-site of oxygen deficient perovskites, Bi0.15Sr0.85-yAeyCo1-xFexO3-?, where y = 0.29 for Ae = Ba and y = 0.17 for Ae =  Ca, and 0.0 ? x ? 1.0, have been investigated. The differing ionic size of the Ca2+ and Ba2+ cations influences both the crystal structure and the properties of the materials. The smaller Ca2+ cation favoured formation of an oxygen vacancy ordered perovskite superstructure (I4/mmm, a = 2ap, c = 4ap), meanwhile the presence of the larger Ba2+ cation promoted a disordered simple cubic structure (Pm-3m, a = ap) that was also found for all Fe containing samples, i.e. x ? 0.25. The samples were studied with PXRD, NPD, TGA, HREM and magnetic susceptibility measurements. All as-prepared samples exhibited long range G-type antiferromagnetic ordering. The effect of oxygen annealing was dramatic for the Bi0.15Sr0.68Ca0.17Co1-xFexO3-? series with a disappearance of magnetic order for x ? 0.25 linked to increasing spin glass properties. The oxygen content of the Bi0.15Sr0.56Ba0.29Co1-xFexO3-? as-prepared materials was generally higher than their Ca substituted counterparts, and the long range antiferromagnetic order was more resistant to oxygen annealing.

  • 11. Felser, C
    et al.
    Kohler, J
    Simon, A
    Jepsen, O
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cramm, S
    Eberhardt, W
    Metal valence states in Eu0.7NbO3, EuNbO3, and Eu2Nb5O9 by TB-LMTO-ASA band-structure calculations and resonant photoemission spectroscopy1998In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 57, p. 1510-1514Article in journal (Refereed)
    Abstract [en]

    The electronic structures of Eu2Nb5O9, EuNbO3, and Eu0.7NbO3 have been investigated by photoemission and total-yield spectroscopy with synchrotron radiation, and in the case of Eu2Nb5O9 by tight-binding linear muffin-tin orbital (LMTO) band-structure calculations. A central question for reduced europium niobates is that of the valence of Eu and Nb. Both europium and niobium atoms can appear in different valence states so that various electronic configurations in the title compounds are possible. For this reason, the valence band was studied by the resonant Eu 4d⃗4f technique to determine the Eu valence. The final-state 4f6 multiplet of divalent Eu is dominant in all spectra. Since there are no 4f density of states at the Fermi level, valence fluctuations are not expected. The niobium valence states were investigated by core-level spectroscopy. We found only one 3d5/23d3/2 doublet for the Nb 3d core level in EuNbO3 and Eu0.7NbO3, while in Eu2Nb5O9, two 3d doublets have been observed, corresponding to two chemically distinct niobium atoms in this compound. The 3d5/2 peak in EuNbO3 is assigned to the +4 nominal valence state at a binding energy of 209.7 eV. The doublet of Eu0.7NbO3 is observed at 0.5 eV higher binding energy (at 210.2 eV), which then corresponds to a nominal Nb+4+δ chemical state. In Eu2Nb5O9, the valence of Nb in the NbO6 octahedra is less than +5 and in the Nb6O12 clusters is close to +2 as expected. This is in accordance with the LMTO band-structure calculations

  • 12.
    Grins, Jekab
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Esmaeilzadeh, Saeid
    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 James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    High-resolution electron microscopy of a Sr-containing sialon polytypoid phase1999In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 19, p. 2723-2730Article in journal (Refereed)
    Abstract [en]

    A new type of Sr-containing sialon polytypoid phase with the structural formula SrSi10-xAl18+xN32-xOx (x approximate to l) has been found in the Sr-Si-Al-O-N system. The phase was characterised by X-ray powder diffraction (XRPD), and its structure was investigated by electron diffraction (ED) and high resolution electron microscopy (HREM). It is considerably disordered, but the average structure has a rhombohedral unit cell with a=5.335(5)approximate to root 3.a(AIN) and c= 79.1(1)Angstrom approximate to 30.c(AIN). The Sr atoms ave located in layers M-Sr-M, M=(Si/Al), at the origin of the unit cell with 12 X= (O,N) atoms around it, at distances of similar to 3 Angstrom, forming a cubo-octahedron. The X atoms that form a hexagon around the Sr atom in the ab plane are corner shared by M = (Si/Al) tetrahedra with opposite polarity in adjacent layers in which 2/3 of the tetrahedra are occupied. The M-Sr-M layers alternate with normally eight-layer-thick AIN type blocks, although the thickness of these blocks frequently varies. The structural model obtained from the HREM images includes a polarity reversal of the tetrahedra in the AIN blocks, similar to that proposed to occur in Si-Al-O-N polytypoid phases. The model with one Sr layer and 10 M = (Si,Al) layers per 1/3 of the repeat unit agrees with the composition of the phase and experimental HREM images.

  • 13.
    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.

  • 14.
    Grins, Jekabs
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Käll, PO
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and structural characterisation of MnWN2 prepared by ammonolysis of MnWO41995In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 5, p. 571-575Article in journal (Refereed)
    Abstract [en]

    A new ternary transition-metal nitride, the composition of which is close to MnWN2, has been synthesized by ammonolysis of X-ray amorphous MnWO4 at 800 degrees C. The Guinier-Hagg powder pattern could be indexed with a hexagonal cell with a = 2.9213(3) Angstrom and c = 10.957(2) Angstrom. Although no superstructure reflections could be observed in the X-ray powder diffraction pattern, such reflections were revealed by electron diffraction. In most of the crystallites investigated, the relationship between supercell and the hexagonal (sub)cell was found to be a(super) = root 3a(hex). A Rietveld structure determination, based on space group P6(3)me (no. 186), showed that the metal atoms were approximately close-packed in an ABAC... sequence with Mn at site 2(a) and W at site 2(d), The lowest R(F) value (10%) was obtained for an ordered structure model with the Mn and N atoms occupying 2(a) and the W and N at sites 2(b). Measurements of the magnetic susceptibility, and of the electrical resistivity, indicated a metallic behaviour of MnWN2

  • 15.
    GRINS, Jekabs
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    SVENSSON, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    SYNTHESIS OF OXYNITRIDE PEROVSKITES [AZRXTA1-XO2+XN1-X, A=CA, SR, BA AND 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1]1994In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 29, no 7, p. 801-809Article in journal (Refereed)
    Abstract [en]

    Solid solution perovskite phases AZrxTa1-xO2+xN1-x, with A = Ca, Sr, Ba and 0 less-than-or-equal-to x less-than-or-equal-to 1 have been synthesised by ammonolysis of mixtures of Ta-Zr gels and ACO3. The gels were made by the sol-gel technique using TaCl5 and Zr-n-propoxide as precursors. The perovskite phases have been characterised by X-ray powder diffraction and elemental analysis for one composition from each subsystem has been performed. The Ca compounds were found to be orthorhombic for all x. The orthorhombic GdFeO3 type perovskite structure was verified for the composition CaZr0.52Ta0.48O2.52N0.48 by a Rietveld refinement to R(F) = 2.3 %, using CuKalpa1 X-ray powder diffractometer data. According to X-ray powder diffraction data, the Sr compounds are orthorhombic for x greater-than-or-equal-to 0.60 and cubic for lower x values. The Ba compounds were found to be cubic for all x.

  • 16.
    Grins, Jekabs
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wardecki, Dariusz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). University of Warsaw, Poland; Chalmers University of Technology, Sweden.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Carlson, Stefan
    Biendicho, Jordi J.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Catalonia Institute for Energy Research, Spain.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A structural study of Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta with x <= 0.75 by neutron powder diffraction and EXAFS/XANES spectroscopy2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 13, p. 5313-5323Article in journal (Refereed)
    Abstract [en]

    The structures of Ruddlesden-Popper n = 2 member phases Sr3-xYxFe1.25Ni0.75O7-delta with 0 <= x <= 0.75 have been investigated using neutron powder diffraction and K-edge Fe and Ni EXAFS/XANES spectroscopy in order to gain information about the evolution of the oxygen vacancy distribution and Fe/Ni oxidation state with x. Both samples prepared at 1300 degrees C under a flow of N-2(g), with delta = 1.41-1.00, and samples subsequently annealed in air at 900 degrees C, with delta = 0.44-0.59, were characterized. The as-prepared x = 0.75 phase has delta = 1, the O1 atom site is vacant, and the Fe3+/Ni2+ ions have a square pyramidal coordination. With decreasing x the O3 occupancy decreases nearly linearly to 81% for x = 0, while the O1 occupancy increases from 0 for x = 0.4 to 33% for x = 0. The air-annealed x = 0.75 sample has a delta value of 0.59 and the Fe3+/Fe4+/Ni2+/Ni3+ ions have both square pyramidal and octahedral coordination. With decreasing x, the delta value decreases to 0.45 for x = 0, implying an increase in the oxidation states of Fe/Ni ions. EXAFS/XANES data show that for the as-prepared samples the coordination changes are predominantly for Ni2+ ions and that the air-annealed samples contain both Fe3+/Fe4+ and Ni2+/Ni3+ ions.

  • 17.
    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).
    Esmaeilzadeh, Saeid
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekab
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structure and magnetic susceptibility of MnNb3O61999In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 1, p. 567-575Article in journal (Refereed)
    Abstract [en]

    The mixed valence state niobium compound MnNb3O6 was found while studying phase formations in the system MnO-Nb2O5-NbO. It is isostructural with AxNb3O6, x ≤ 1 and A = Na, Ca. Single crystals were obtained by heating MnC2O4 · 2H2O and Nb2O5 in a flow of H2 at 1300 °C. Monophasic samples were also prepared by heating stoichiometric mixtures of MnO, Nb2O5 and Nb in niobium ampoules under Ar(g) at 1100 °C. The crystal structure of MnNb3O6 (Immm, Z = 4, a = 7.1057(5), b = 10.1420(6), c = 6.5341(5) Å) was refined, using singlecrystal MoKα X-ray diffraction data, to a weighted R value of 0.018 for 329 unique reflections. The structure contains undulating layers of NbO6 octahedra of the type α2[NbO6/2]in the ac-plane, with the octahedra sharing edges along [001]and corners along [100]. Between the layers there are columns along [001]of edge-sharing square MnO8 prisms alternating with columns containing Nb2O8 clusters with an Nb-Nb distance of 2.6163(5) Å. The magnetic susceptibility shows a Curie-Weiss behaviour: χM = C/(T+θ) with θ ≈ −22 K and μeff = 6.0(1) μB for T ≥ ca. 35 K, with a small deviation from this dependence at lower temperatures, indicating Mn2+ ions with localised magnetic moments and antiferromagnetic interactions.

  • 18.
    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

  • 19.
    Hörlin, Tom
    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).
    Olsson, E
    Chalmers.
    Extended defect structures in zinc oxide doped with iron and indium1998In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 8, p. 2465-2473Article in journal (Refereed)
    Abstract [en]

    The effects of iron- and indium oxide doping on the structure: and magnetic susceptibility of ZnO have been studied. The nominal compositions were InxFe2-xO3(ZnO)n with 0 less than or equal to x less than or equal to 1 and n= 23, 48 and 98. Magnetic measurements showed the iron-doped samples to be paramagnetic, with a behaviour indicating antiferromagnetic coupling between the iron-ions. HREM studies showed that indium and iron are incorporated as layer defects of two kinds. One type forms cubic close packed (ccp) planes perpendicular to the c axis, and the other appears as-corrugated layers inserted between the former. The folds in the corrugated layers consist of alternating (114) and (11 (4) over bar) planes. Analytical transmission electron microscopy studies revealed that indium prefers the ccp layers, whereas iron can be found in both types of defects. Structural models based upon the experimental results are presented.

  • 20.
    Iftekhar, Shahriar
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Lööf, J.
    Jarmar, T.
    Botton, G.
    Andrei, C.
    Engqvist, H.
    Phase formation of CaAl2O4 from CaCO3-Al2O3 powder mixtures2008In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 28, no 4, p. 747-756Article in journal (Refereed)
    Abstract [en]

    Calcium aluminate is the main constituent in calcium aluminate cements, used in a wide range of applications in construction and mining industries and recently also as biomedical implant. In applications that demand very precise reaction features, such as the biomedical ones, the phase purity is of very high importance.

    In this paper the formation of CaAl2O4 from CaCO3–Al2O3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 °C. Phase formation was studied in samples both quenched from the holding temperatures and in samples slowly cooled. Samples were characterized by X-ray powder diffraction (XRPD), using Guinier-Hägg film data and the Rietveld method, and scanning (SEM) and transmission (TEM) electron microscopy. Samples for TEM with very high site accuracy were produced using focused ion beam microscopy.

    In addition to CA (CaAl2O4) the samples contained major amounts of CA2 (CaAl4O7), C12A7 (Ca12Al14O33) and minor amounts of un-reacted A (Al2O3). Trace amounts of C3A (Ca3Al2O6) were observed only for samples heated to 1500 °C. The amount of the Ca-rich phase C12A7 was found to decrease with time as it reacts with A and, to a less degree, CA2 to form CA. In agreement with previous studies the amount of CA2 formed decreases comparatively slowly with time. Its un-reactivity is due to that it is concentrated in isolated porous regions of sizes up to 100 μm. The formation of the Ca aluminates is found to be in response to local equilibriums within small inhomogeneous regions, with no specific phase acting as an intermediate phase. Samples quenched from 1500 °C were found to contain smaller amounts of poorly crystallized phases. A reaction between C and A takes place already at 900 °C, forming a meta-stable orthorhombic modification of CA. The orthorhombic unit cell with a = 8.732(2) Å, b = 8.078(2) Å, c = √3·a = 15.124(4) Å was verified by electron diffraction, revealing frequent twinning and disorder of the crystallites.

  • 21.
    Istomin, S Y
    et al.
    Moscow State University, Department of Chemistry.
    Dyachenko, O G
    Moscow State University, Department of Chemistry.
    Antipov, E V
    Moscow State University, Department of Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and characterization of reduced niobates CaLnNb2O7, Ln = Y, Nd with a pyrochlore structure1997In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 32, no 4, p. 421-430Article in journal (Refereed)
    Abstract [en]

    The first known reduced niobates with a pyrochlore structure, CaLnNb(2)O(7) Ln = Y, Nd, have been synthesized from Ca2Nb2O7, Ln(2)O(3), and NbO2 in sealed Nb ampoules heated at 1400 degrees C for 6 h. Our studies show that these compounds have a small homogeneity region according to the formula Ca(2-x)Ln(x)Nb(2)O(7), Ln = Nd with x = 0.9, 1.0; and Ln = Y with x = 1.0, 1.1. The prepared compounds were characterized by EDX (energy dispersive X-ray) analysis, X-ray and electron diffraction, and thermogravimetric analysis. The crystal structures of CaNdNb2O7 and CaYNb2O7 were refined using X-ray and neutron powder diffraction data. CaNdNb2O7 and CaYNb2O7 have undistorted pyrochlore structures: space group Fd3m, a = 10.416(1) Angstrom and 10.3159(8) Angstrom, respectively. Resistivity measurements show that CaNdNb2O7 exhibits semiconducting behavior. Copyright (C) 1997 Elsevier Science Ltd.

  • 22.
    Istomin, S Y
    et al.
    Moscow State University, Department of Chemistry.
    D’Yachenko, O G
    Moscow State University, Department of Chemistry.
    Antipov, E V
    Moscow State University, Department of Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lundqvist, B
    Synthesis and characterization of the reduced niobates CaLnNb2O7, Ln = La-Pr, Sm, Gd-Lu, with the pyrochlore-type structure1998In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 33, p. 1251-1256Article in journal (Refereed)
    Abstract [en]

    New reduced niobates, CaLnNb2O7, Ln = La-Pr, Sm, Gd-Lu, with the pyrochlore-type structure were synthesized in sealed Nb ampoules at 1350–1500°C for 6–10 h. The prepared compounds were characterized by powder X-ray diffraction, energy dispersive X-ray analysis, and thermogravimetric analysis. The magnetic measurements showed that all of the samples except the La, Sm, and Lu compounds exhibited Curie-Weiss behavior. The compounds were found to be electrically insulating.

  • 23.
    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.

  • 24. Istomin, S. Ya.
    et al.
    Antipov, E. V.
    Fedotov, Yu. S.
    Bredikhin, S. I.
    Lyskov, N. V.
    Shafeie, S.
    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).
    Liu, Y.
    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).
    Crystal structure and high-temperature electrical conductivity of novel perovskite-related gallium and indium oxides2014In: Journal of Solid State Electrochemistry, ISSN 1432-8488, E-ISSN 1433-0768, Vol. 18, no 5, p. 1415-1423Article in journal (Refereed)
    Abstract [en]

    Novel complex oxides Sr2Ga1+x In1-x O-5, x = 0.0-0.2 with brownmillerite-type structure were prepared in air at T = 1,273 K, 24 h. Study of the crystal structure of Sr2Ga1.1In0.9O5 refined using X-ray powder diffraction data (S.G. Icmm, a = 5.9694(1) , b = 15.2091(3) , c = 5.7122(1) , chi (2) = 2.48, R (F) (2) (=) 0.0504, R (p) = 0.0458) revealed ordering of Ga3+ and In3+ cations over tetrahedral and octahedral positions, respectively. A partial replacement of Sr2+ by La3+ according to formula Sr1-y La (y) Ga0.5In0.5O2.5+y/2, leads to the formation of a cubic perovskite (a = 4.0291(5) ) for y = 0.3. No ordering of oxygen vacancies or cations was observed in Sr0.7La0.3Ga0.5In0.5O2.65 as revealed by electron diffraction study. The trace diffusion coefficient (D (T)) of oxygen for cubic perovskite Sr0.7La0.3Ga0.5In0.5O2.65 is in the range 2.0 Au 10(-9)-6.3 Au 10(-8) cm(2)/s with activation energy 1.4(1) eV as determined by isotopic exchange depth profile technique using secondary ion mass spectrometry at 973-1,223 K. These values are close to those reported for Ca-doped ZrO2. High-temperature electrical conductivity of Sr0.7La0.3Ga0.5In0.5O2.65 studied by AC impedance was found to be nearly independent on oxygen partial pressure. Calculated values of activation energy at T < 1,073 K for hole and oxide-ion conductivities are 0.96 and 1.10 eV, respectively.

  • 25. Istomin, S. Ya.
    et al.
    Karakulina, O. M.
    Rozova, M. G.
    Kazakov, S. M.
    Gippius, A. A.
    Antipov, E. V.
    Bobrikov, I. A.
    Balagurov, A. M.
    Tsirlin, A. A.
    Michau, A.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Biendicho, Jordi Jacas
    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).
    Tuning the high-temperature properties of Pr2NiO4+delta by simultaneous Pr- and Ni-cation replacement2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 40, p. 33951-33958Article in journal (Refereed)
    Abstract [en]

    Novel Pr2-xSrxNi1-xCoxO4 +/-delta (x = 0.25; 0.5; 0.75) oxides with the tetragonal K2NiF4-type structure have been prepared. Room-temperature neutron powder diffraction (NPD) study of x = 0.25 and 0.75 phases together with iodometric titration results have shown the formation of hyperstoichiometric oxide for x = 0.25 (delta = 0.09(2)) and a stoichiometric one for x = 0.75. High-temperature X-ray powder diffraction (HT XRPD) showed substantial anisotropy of the thermal expansion coefficient (TEC) along the a-and c-axis of the crystal structure, which increases with increasing the Co content from TEC(c)/TEC(a) = 2.4 (x = 0.25) to 4.3 (x = 0.75). High-temperature NPD (HT NPD) study of the x = 0.75 sample reveals that a very high expansion of the axial (Ni/Co)-O bonds (75.7 ppm K-1 in comparison with 9.1 ppm K-1 for equatorial ones) is responsible for such behaviour, and is caused by a temperature-induced transition between low- and high-spin states of Co3+. This scenario has been confirmed by high-temperature magnetization measurements on a series of Pr2-xSrxNi1-xCoxO4 +/-delta samples. For compositions with high Ni content (x = 0.25 and 0.5) we synthesised K2NiF4-type oxides Pr2-x-ySrx+y(Ni1-xCox)O-4 +/-delta, y = 0.0-0.75 (x = 0.25); y = 0.0-0.5 (x = 0.5). The studies of the TEC, high-temperature electrical conductivity in air, chemical stability of the prepared compounds in oxygen and toward interaction with Ce2-xGdxO2-x/2 (GDC) at high temperatures reveal optimal behaviour of Pr1.35Sr0.65Ni0.75Co0.25O4+delta. This compound shows stability in oxygen at 900 degrees C and does not react with GDC at least up to 1200 degrees C. It features low TEC of 13 ppm K-1 and high-temperature electrical conductivity in air of 280 S cm(-1) at 900 degrees C, thus representing a promising composition for use as a cathode material in intermediate temperature solid oxide fuel cells (IT-SOFC).

  • 26.
    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.

  • 27.
    Istomin, Sergey Ya.
    et al.
    Chemical Department, Moscow State University.
    Grippa, Alexander Yu.
    Chemical Department, Moscow State University.
    D'yachenko, Oleg G.
    Chemical Department, Moscow State University.
    Antipov, Eugeny V.
    Chemical Department, Moscow State University.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Tholence, Jean L.
    LEPES, CNRS, BP 166, 38042 Grenoble Cedex 9, France.
    A new superconducting sulfide—'EuNb2S5'1998In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 300, p. 67-70Article in journal (Refereed)
    Abstract [en]

    A new low-temperature superconducting (Tc≈3 K) niobium sulfide ‘EuNb2S5' with a hexagonal structure (a=3.3556(8) Å, c=23.440(9) Å) was synthesized from a mixture of EuS, Nb(m) and S in evacuated and sealed silica tubes, heated at 1100°C for 48 h. This superconductor was characterized by EDX analysis, X-ray powder and electron diffraction studies. Electron diffraction revealed the presence of a supercell: asuper=bsuper=√7×a.

  • 28.
    ISTOMIN, SY
    et al.
    Moscow State University.
    DYACHENKO, OG
    Moscow State University.
    ANTIPOV, EV
    Moscow State University.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    NYGREN, M
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    SYNTHESIS AND CHARACTERIZATION OF REDUCED NIOBATES [SR1-XLNXNB2O6, LN=LA, ND]1994In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 29, p. 743-749Article in journal (Refereed)
    Abstract [en]

    Sr1-xLnxNb2O6, Ln = La (x less-than-or-equal-to 0.4), Nd (x less-than-or-equal-to 0.3) solid solutions with a CaTa2O6-type structure have been studied. No superconductivity was found in the prepared samples down to 5K. The CaTa2O6 type crystal structure of Sr0.6La0.4Nb2O6 was refined from X-ray powder diffraction data: R(i)=0.054, R(p)=0.117. The oxidation process of the lanthanum-containing compounds was studied. A drastical decrease of the lanthanum content, accompanied by the formation of the cation vacancies at the Sr/La site occurs during oxidation.

  • 29. Kaban, I.
    et al.
    Jovari, P.
    Escher, B.
    Tran, Dung Trung
    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).
    Webb, M. A.
    Regier, T. Z.
    Kokotin, V.
    Beuneu, B.
    Gemming, T.
    Eckert, J.
    Atomic structure and formation of CuZrAl bulk metallic glasses and composites2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 100, p. 369-376Article in journal (Refereed)
    Abstract [en]

    Cu47.5Zr47.5Al5 metallic glass is studied experimentally by high-energy X-ray diffraction, neutron diffraction with isotopic substitution, electron diffraction and X-ray absorption spectroscopy. The atomic structure of the glass is modeled by reverse Monte-Carlo and molecular dynamics simulations. RMC modeling of seven experimental datasets enabled reliable separation of all partial pair distribution functions for Cu47.5Zr47.5Al5 metallic glass. A peculiar structural feature of the ternary alloy is formation of the strong Al-Zr bonds, which are supposed to determine its high viscosity and enhanced bulk glass formation. Analysis of the local atomic order in Cu47.5Zr47.5Al5 glass and Cu10Zr7, CuZr2 and CuZr B2 crystalline structures elucidates their similarities and differences explaining the phase formation sequence by devitrification of the glass.

  • 30. 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.

  • 31. Keshavarz, Samara
    et al.
    Kontos, Sofia
    Wardecki, Dariusz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Chalmers University of Technology, Sweden; University of Warsaw, Poland.
    Kvashnin, Yaroslav O.
    Pereiro, Manuel
    Panda, Swarup K.
    Sanyal, Biplab
    Eriksson, Olle
    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).
    Gunnarsson, Klas
    Svedlindh, Peter
    Magnetic properties of Ruddlesden-Popper phases Sr3-&: A combined experimental and theoretical investigation2018In: Physical review materials, ISSN 2475-9953, Vol. 2, no 4, article id 044005Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive study of the magnetic properties of Sr3-xYx(Fe1.25Ni0.75)O-7(-delta )(0 <= x <= 0.75). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by a theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the Ned temperature (T-N) with an increase of Y concentrations and O occupancy. The NPD data reveal that all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the three-dimensional magnetic order is stabilized due to finite interlayer exchange couplings. The latter give rise to finite interlayer spin-spin correlations, which disappear above T-N.

  • 32. Knee, CS
    et al.
    Lindberg, F
    Stockholm University.
    Khan, N
    Svensson, G
    Stockholm University.
    Svedlindh, P
    Rundlöf, H
    Eriksson, SG
    Börjesson, L
    Influence of oxygen defects on the structure and magnetic properties of Sr1-xBixCoO3-y (0.1 <= x <= 0.2) supercell perovskites2006In: Chemistry of Materials, Vol. 18, p. 1354-1364Article in journal (Refereed)
  • 33.
    Konar, Sumit
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Häusserman, Ulrich
    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).
    Intercalation Compounds from LiH and Graphite: Relative Stability of Metastable Stages and Thermodynamic Stability of Dilute Stage I-d2015In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 7, p. 2566-2575Article in journal (Refereed)
    Abstract [en]

    The intercalation of lithium into graphite was studied at temperatures between 400 and 550 degrees C by heating mixtures of LiH and graphite powders with molar ratios 4:1, 1:1, and 1:6 under dynamic vacuum for periods between 1 and 72 h. These conditions probe the formation and thermal stability of metastable staged Ligraphite intercalation compounds (Li-GICs) close to the competing formation of the thermodynamically stable carbide Li(2)C2. Li-GICs of stages I (LiC6, A alpha), IIa (Li0.5C6, A alpha A), IIb (Li similar to C-0.33(6), A alpha AB beta B), III (Li similar to C-0.22(6), A alpha AB), IV (Li similar to C-0.167(6)), and dilute stage lithium Id have been identified and characterized by powder X-ray diffraction and Raman spectroscopy. The rate and extent of intercalation (i.e., the achieved stage of Li-GIC) depends on LiH activity and temperature. Stage I was only observed for temperatures above 500 degrees C. At 400 degrees C, the highest intercalation corresponded to stage IIb, which was obtained after 2 and 24 h for 4:1 and 1:1 reaction mixtures, respectively. Lower-staged Li-GICs attained at temperatures below 500 degrees C deintercalate upon prolonged dwelling with the exception of stage IIa, which can be maintained for very long periods (several days) in the presence of LiH. At temperatures above 500 degrees C, the kinetically controlled formation of Li-GICs is followed by Li2C2 carbide formation. It is shown that the Li-GIC I-d coexists with Li2C2 at temperatures up to 800 degrees C and that the Li content of I-d (solubility of Li in graphite) increases between 550 and 800 degrees C. Consequently, I-d with a temperature-dependent homogeneity range should be added as a stable phase in the Li-C phase diagram. A sketch of a revised Li-C phase diagram is provided.

  • 34.
    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.

  • 35. Kravchenko, Ekaterina
    et al.
    Khalyavin, Dmitry
    Zakharchuk, Kiryl
    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).
    Pankov, Vladimir
    Yaremchenko, Aleksey
    High-temperature characterization of oxygen-eficient K2NiF4-type Nd2-xSrxNiO4-delta O4-delta (x=1.0-1.6) for potential SOFC/SOEC applications2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 47, p. 23852-23863Article in journal (Refereed)
    Abstract [en]

    Previously unexplored oxygen-deficient RuddLesden-Popper Nd2-xSrxNiO4-delta (x = 1.0-1.6) nickelates were evaluated for potential use as oxygen electrode materials for solid oxide fuel and electrolysis ceRs, with emphasis on structural stability, oxygen nonstoichiometry, dimensional changes, and electrical properties. Nd2-xSrxNiO4-delta ceramics possess the K2NiF4-type tetragonal structure under oxidizing conditions at 25-1000 degrees C. Acceptor-type substitution by strontium is compensated by the generation of eLectron-hoLes and oxygen vacancies. Oxygen deficiency increases with temperature and strontium doping reaching -1/8 of oxygen sites for x = 1.6 at 1000 degrees C in air. Strongly anisotropic expansion of the tetragonal Lattice on heating correlated with oxygen nonstoichiometry changes results in an anomalous dilatometric behavior of Nd2-xSrxNiO4-delta ceramics under oxidizing conditions. Moderate thermal expansion coefficients, (11-14) x 10(-6) K-1, ensure however thermomechanical compatibility with common solid electrolytes. Reduction in inert atmosphere induces oxygen vacancy ordering accompanied by a contraction of the Lattice and a decrease of its symmetry to orthorhombic. Nd2-xSrxNiO4-delta ceramics exhibit a p-type metallic-Like electrical conductivity at 500-1000 degrees C under oxidizing conditions, with the highest conductivity (290 S cm(-1) at 900 degrees C in air) observed for x = 1.2. The high Lev& of oxygen deficiency in Sr-rich Nd2-xSrxNiO4 impLies enhanced mixed ionic-electronic transport favorable for electrode applications.

  • 36. Kravchenko, Ekaterina
    et al.
    Zakharchuk, Kiryl
    Viskup, Alexander
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Pankov, Vladimir
    Yaremchenko, Aleksey
    Impact of Oxygen Deficiency on the Electrochemical Performance of K2NiF4-Type (La1-xSrx)(2)NiO4-delta Oxygen Electrodes2017In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 3, p. 600-611Article in journal (Refereed)
    Abstract [en]

    Perovskite-related (La1-xSrx)(2)NiO4-delta (x= 0.5-0.8) phases were explored for possible use as oxygen electrodes in solid electrolyte cells with a main focus on the effect of oxygen deficiency on the electrocatalytic activity. (La1-xSrx)(2)NiO4-d solid solutions were demonstrated to preserve the K2NiF4-type tetragonal structure under oxidizing conditions. Acceptor-type substitution by Sr is compensated by the formation of oxygen vacancies and electron holes and progressively increases high-temperature oxygen nonstoichiometry, which reaches as high as d= 0.40 for x= 0.8 at 950 degrees C in air. The electrical conductivity of (La1-xSrx)(2)NiO4-d ceramics at 500-1000 degrees C and p(O-2) >= 10(-3) atm is p-type metallic-like. The highest conductivity, 300 Scm(-1) at 800 degrees C in air, is observed for x= 0.6. The average thermal expansion coefficients, (14.0-15.4) x 10(-6) K-1 at 25900 degrees C in air, are sufficiently low to ensure the thermomechanical compatibility with common solid electrolytes. The polarization resistance of porous (La1-xSrx)(2)NiO4-d electrodes applied on a Ce0.9Gd0.1O2-delta solid electrolyte decreases with increasing Sr concentration in correlation with the concentration of oxygen vacancies in the nickelate lattice and the anticipated level of mixed ionic-electronic conduction. However, this is accompanied by increasing reactivity between the cell components and necessitates the microstructural optimization of the electrode materials to reduce the electrode fabrication temperature.

  • 37.
    Leis, J
    et al.
    Tartu Technologies Ltd., 185 Riia Str., 51014 Tartu, Estonia.
    Perkson, A
    Tartu Technologies Ltd., 185 Riia Str., 51014 Tartu, Estonia.
    Arulepp, M
    Tartu Technologies Ltd., 185 Riia Str., 51014 Tartu, Estonia.
    Kaarik, M
    Tartu Technologies Ltd., 185 Riia Str., 51014 Tartu, Estonia.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Carbon nanostructures produced by chlorinating aluminium carbide2001In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 39, no 13, p. 2043-2048Article in journal (Refereed)
    Abstract [en]

    A number of carbon samples with different nanostructures such as: amorphous, nanoparticles and turbostratic, were synthesised through the reaction between aluminium carbide and gaseous chlorine at fixed temperatures between 300 and 900 degreesC. The synthesised carbon samples were characterised using high-resolution transmission electron microscopy and X-ray powder diffraction techniques, as well as low temperature nitrogen sorption measurements. The carbon produced at T=300 degreesC was amorphous with a surface area of similar to 1400 m(2) g(-1). At 700 degreesC, a large amount of carbon nanoparticles and with a lower surface area similar to 710 m(2) g(-1) was obtained. At 900 degreesC, mainly a turbostratic carbon with a surface area of similar to 680 m(2) g(-1) was produced.

  • 38.
    Leis, J
    et al.
    Tartu Technologies Ltd., 185 Riia Str., 51014 Tartu, Estonia.
    Perkson, A
    Tartu Technologies Ltd., 185 Riia Str., 51014 Tartu, Estonia.
    Arulepp, M
    Tartu Technologies Ltd., 185 Riia Str., 51014 Tartu, Estonia.
    Nigu, P
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Catalytic effects of metals of the iron subgroup on the chlorination of titanium carbide to form nanostructural carbon2002In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 40, no 9, p. 1559-1564Article in journal (Refereed)
    Abstract [en]

    The effect of the reaction temperature and the metals of an iron subgroup on the thermo-chemical treatment of titanium carbide with a chlorine gas and their influence on the carbon structure obtained thereby was studied. Different analytical methods such as porosity measure me tits, X-ray diffraction spectrometry and a high-resolution electron microscopy revealed the catalytic behaviour of the above-mentioned metals. which appeared to support the formation of graphitised carbon at much lower temperatures compared to those needed for the ordinary thermo-chemical chlorination of titanium carbide.

  • 39.
    Lindberg, F
    et al.
    Stockholm University.
    Drozhzhin, OA
    Istomin, SY
    Svensson, G
    Stockholm University.
    Kaynak, FB
    Svedlindh, P
    Warnicke, P
    Wannberg, A
    Mellergard, A
    Antipov, EV
    Synthesis and characterization of Sr0.75Y0.25C1-xMxO2.625+delta (M = Ga, 0.125<= x <= 0.500 and M = Fe, 0.125 <= x <= 0.8752006In: Journal of Solid State Chemistry, Vol. 179, p. 1434-1444Article in journal (Refereed)
  • 40. Mazo, G. N.
    et al.
    Kazakov, S. M.
    Kolchina, L. M.
    Istomin, S. Ya.
    Antipov, E. V.
    Lyskov, N. V.
    Galin, M. Z.
    Leonova, L. S.
    Fedotov, Yu. S.
    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).
    Influence of structural arrangement of R2O2 slabs of layered cuprates on high-temperature properties important for application in IT-SOFC2014In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 257, p. 67-74Article in journal (Refereed)
    Abstract [en]

    Layered cuprates Pr2 - xSrxCuO4-delta with T* (x = 0.3, 0.4) and T (x = 1.0, 13) structures were prepared in air at 1273-1373 K. Oxygen content (4 - delta) of the as-prepared phases decreases from 3.96 (x = 03) and 3.98 (x = 0.4) to 3.69 (x = 1.0) and 3.49 (x = 1.3), respectively, as determined by chemical titration. Dilatometry measurements revealed non-linear expansion with low- and high-temperature regions occurring due to thermogravimetrically detected oxygen loss. Different expansion behaviors in low- and high-temperature regions of T- and T*-phases are attributed to various distributions of oxygen vacancies in their crystal structures. Both x = 0.4 and 1.0 ceramic samples exhibit lower conductivity values at high temperatures in comparison with undoped Pr2CuO4. The temperature dependences of the electrical conductivity at variable oxygen partial pressure (Po-2 = 10(-4)-0.21 atm) reveal different mechanisms of the holes generation in x = 0.4 and 1.0 compounds. The tracer diffusion coefficient of oxygen (D-T) in Pr1.6Sr0.4CuO3.98 determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) is in the range 6.7 x 10(-10)-5.7 x 10(-8) cm(2)/s at 973-1223 K. Obtained values are in between those for La2CuO4 and Pr2CuO4 with pure rock-salt and fluorite slabs in the crystal structure, respectively. This shows the importance of rock-salt slabs for high oxygen conductivity in R2MO4 oxides.

  • 41. 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.

  • 42.
    Nilsson, Göran
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Structural Chemistry.
    Crystal Structure of BaNb6.3(1)Ti3.6(1)O16 containing Nb6O12, fused Ti3O13 Clusters and Ti3O10 Units2000In: Zeitschrift für Anorganische und Allgemeines Chemie, ISSN 0044-2313, E-ISSN 1521-3749, Vol. 626, no 1, p. 160-172Article in journal (Refereed)
    Abstract [en]

    A new phase, BaNb6.3(1)Ti3.6(1)O16, has been synthesised. Electron diffraction studies indicate an hexagonal substructure with unit cell parameters a ≈ 8.9 Å and c ≈ 9.5 Å. In some of the ED patterns superstructure reflections are present, indicating a supercell with a = √3 · asub and c = csub. However, X-ray single-crystal diffraction studies of a crystallite yielding reflections corresponding to the supercell revealed it to be monoclinic, with the unit cell parameters a = 26.811(2) Å, b = 15.4798(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°. The average crystal structure was refined, using the subcell with a = 8.937(2) Å, b = 15.479(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°, space group Cm11, and Z = 4, to RI = 3.24% and RwI = 3.44%. The structure can be described as an hexagonal close packing layers of Nb6 octahedra, Ba, and O atoms (A1, A2) and layers of O atoms (B1, B2), appearing in the packing sequence: A1B1A2B2. The Nb6 octahedra are found in isolated Nb6O12O6 clusters, and the Ti atoms in Ti3O13 and Ti3O10 units in octahedral and tetrahedral voids formed by O atoms, respectively. The Ti positions were found to be only partly occupied. Microanalysis indicates that some Nb atoms are located in the Ti3 triangles. A model is presented that interprets these not fully occupied Ti3 triangles as a result of a superimposing of three different structures. Two of these consist of two fused Ti3O13 units, forming an Ti6O19 unit, and a Ti3O10 unit, while the third consists of alternating Ti3O13 units.

  • 43.
    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.

  • 44.
    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).
    X-ray powder diffraction and high-resolution electron microscopy studies of new intergrowth compounds between Ba(Nb,Zr)O3 and NbO2001In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 314, no 1-2, p. 67-77Article in journal (Refereed)
    Abstract [en]

    The structure of Ba2Nb5O9 can be described as intergrown layers of perovskite (BaNbO3) and NbO. The compound is a member of the BanNbn+3mO3(n+m) homologous series where n and m are the perovskite and NbO slab widths, respectively. The substitution of Zr for Nb according to the formula Ba2Nb5−xZrxO9 has been investigated. The increase of the c axis length as a function of the overall composition shows, in combination with microanalysis in scanning and transmission electron microscopes, that the maximum value of x is approximately 0.6. The microanalysis indicates that Zr prefers the MO6 octahedra in the perovskite slab. The X-ray powder diffraction (XRD) analysis and high-resolution electron microscopy (HREM) images show that for 0.6≤x≤1.5 a disordered intergrowth of Ba(Nb;Zr)O3 and NbO layers is formed. The XRD patterns and microanalyses of cation content showed that a new homologue Ba3(Nb,Zr)6O12 with n:m=3:1 in the series Ban(Nb;Zr)n+3mO3(n+m) is formed in some of these samples. It has the unit cell parameters a=4.1725(6) Å and c=16.429(3) Å and crystallises in space group P4/mmm, Z=1. The structure of this compound was determined by comparing simulated and experimental HREM images.

  • 45.
    Nilsson, Mattias
    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).
    Käll, Per-Olov
    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, structural characterisation and magnetic properties of Gd14W4O33-xNy(0<=x<=17+/-2, 0<=y<=9+/-2), a new fluorite-related oxynitride1996In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 240, no 1-2, p. 60-69Article in journal (Refereed)
    Abstract [en]

    A series of crystalline Gd-W oxides, with Gd:W ratios spanning the values 0.1-3.5, has been prepared and treated with a flow of NH3(g) in the temperature range 700-1100 degrees C. Besides the previously reported formation of GdWO3N and Gd2WO3N2, the following new results were obtained: (i) cubic Gd0.1WO3 upon ammonolysis forms an (oxy)nitride Gd0.1W(O,N)(y) with an f.c.c. lattice; (ii) the previously described Gd2WO3N2 exhibits a solid solubility range Gd3-xW1+x(O,N)(y) with, approximately, 0 less than or equal to x less than or equal to 1; (iii) ammonolysis of Gd14W4O33 yields an oxynitride, the composition of which varies with the synthesis temperature according to Gd14W4O33-xNy(O less than or equal to x less than or equal to 17+/-2, 0 less than or equal to y less than or equal to 9+/-2). All strong diffraction lines, including those of the pure oxide (x = y = 0), can be indexed with a body-centred monoclinic unit cell derived from that of fluorite. For Gd14W4O33 the cell 3 parameters are a = 5.3592(11), b = 3.7295(7), c = 3.8636(8) Angstrom, beta = 92.170(2)degrees and V = 77.17 Angstrom(3). However, strong superstructure reflections in the electron diffraction patterns indicate that the true unit cell is considerably larger. A partial structure determination of Gd14W4O33-xNy has been carried out by the Rietveld method. Magnetic susceptibility measurements in the temperature interval 15-300 K show a Curie-Weiss law behaviour for Gd14W4O33-xNy, with mu(eff) = 8.08+/-0.06 Bohr magntons per Gd3+ and theta = -12.4+/-1.1 K for all compositions.

  • 46.
    Ojwang, Dickson
    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).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The adsorption kinetics of CO2 on copper hexacyanoferrate studied by thermogravimetric analysisManuscript (preprint) (Other academic)
    Abstract [en]

    The CO2 adsorption and CO2 adsorption kinetics were evaluated by thermogravimetry on two Prussian blue analogues, K2x/3CuII[FeIIx FeIII1-x(CN)6]2/3, with nominally K-free x = 0.0 and K-rich x = 1.0. Differential isosteric heats of adsorption were determined from adsorption isotherms using the Clausius-Clapeyron equation and integral values by differential scanning calorimetry. The average differential heats of CO2 adsorption are 28 kJ/mol for x = 0.0 and 33 kJ/mol for x = 1.0.  Both compositions show small maxima in differential heat at ~1 mmol/g.  The integral adsorption heats were determined to be 26 kJ/mol for both x = 0.0 and x = 1.0. The kinetic CO2 adsorption/desorption curves can be modeled by a double exponential function describing two parallel processes with different rate constants. The activation energies for CO2 adsorption on x = 0.0 were 6(1) kJ/mol for the faster component and 16(1) kJ/mol for the slower one, while the corresponding values for x = 1.0 were 9(1) kJ/mol and 7(1) kJ/mol, respectively. The maximum CO2 uptake for both compositions was found to be ~4.5 mmol/g, 19.8 wt %, at 1 bar and 273 K. The materials exhibited fast adsorption kinetics and stable cyclic performance at room temperature. The kinetics were slower for the samples with x = 1.0 than for x = 0.0 which may be attributed to interactions between CO2 molecules and K+ ions.   

  • 47.
    Ojwang, Dickson O.
    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).
    Wardecki, Dariusz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Valvo, Mario
    Renman, Viktor
    Häggström, Lennart
    Ericsson, Tore
    Gustafsson, Torbjörn
    Mahmoud, Abdelfattah
    Hermann, Raphael P.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structure Characterization and Properties of K-Containing Copper Hexacyanoferrate2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 12, p. 5924-5934Article in journal (Refereed)
    Abstract [en]

    Copper hexacyanoferrate, Cu-II[Fe-III(CN)(6)](2/3)center dot nH(2)O, was synthesized, and varied amounts of IC ions were inserted via reduction by K2S2O3 (aq). Ideally, the reaction can be written as Cu-II[Fe-III(CN)(6)](2/3)-nH(2)O + 2x/3K(+) + 2x/3e(-)K(+) <-> K-2x/3 Cu-II[Fe-x(II).Fe-1-x(II),(CN)(6)](2/3)-nH(2)O. Infrared, Raman, and Mossbauer spectroscopy studies show that Fe-II is continuously reduced to Fell with increasing x, accompanied by a decrease of the a-axis of the cubic Fn (3) over barm unit cell. Elemental analysis of K by inductively coupled plasma shows that the insertion only begins when a significant fraction similar to 10% of the Fe-III, has already been reduced. Thermogravimetric analysis shows a fast exchange of water with ambient atmosphere and a total weight loss of similar to 26 wt % upon heating to 180 degrees C, above which the structure starts to decompose. The crystal structures of Cu-III[Fe-III(CN)(6)](2/3)center dot nH(2)O and K2/3Cu[Fe(CN)(6)](2/3)center dot nH(2)O were refined using synchrotron X-ray powder diffraction data. In both, one-third of the Fe(CN)(6) groups are vacant, and the octahedron around Cull is completed by water molecules. In the two structures, difference Fourier maps reveal three additional zeolitic water sites (8c, 32f, and 48g) in the center of the cavities formed by the-Cu-N-C-Fe- framework. The K-containing compound shows an increased electron density at two of these sites (32f and 48g), indicating them to be the preferred positions for the K+ ions.

  • 48. Renman, Viktor
    et al.
    Ojwang, Dickson O.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Valvo, Mario
    Gomez, Cesar Pay
    Gustafsson, Torbjorn
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm Univ, Arrhenius Lab, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden.
    Structural-electrochemical relations in the aqueous copper hexacyanoferrate-zinc system examined by synchrotron X-ray diffraction2017In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 369, p. 146-153Article in journal (Refereed)
    Abstract [en]

    The storage process of Zn2+ in the Prussian blue analogue (PBA) copper hexacyanoferrate (Cu[Fe(CN)(6)](2/3)-nH(2) O-CuHCF) framework structure in a context of rechargeable aqueous batteries is examined by means of in operando synchrotron X-ray diffraction. Via sequential unit-cell parameter refinements of time-resolved diffraction data, it is revealed that the step-profile of the cell output voltage curves during repeated electrochemical insertion and removal of Zn2+ in the CuHCF host structure is associated with a non-linear contraction and expansion of the unit-cell in the range 0.36 < x < 1.32 for Znx/3Cu[Fe(CN)(6)](2/3)-nH(2)O. For a high insertion cation content there is no apparent change in the unit-cell contraction. Furthermore, a structural analysis with respect to the occupancies of possible Zn2+ sites suggests that the Fe(CN)(6) vacancies within the CuHCF framework play an important role in the structural-electrochemical behavior of this particular system. More specifically, it is observed that Zn2+ swaps position during electrochemical cycling, hopping between cavity sites to vacant ferricyanide sites.

  • 49. Renman, Viktor
    et al.
    Ojwang, Dickson O.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Valvo, Mario
    Pay Gomez, Cesar
    Gustafsson, Torbjörn
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structural-electrochemical relations in the aqueous copper hexacyanoferrate-zinc system examined by synchrotron X-ray diffractionManuscript (preprint) (Other academic)
    Abstract [en]

    The storage process of Zn2+ in the Prussian blue analogue (PBA) copper hexacyanoferrate (Cu[Fe(CN)6]2/3·nH2O - CuHCF) framework structure in a context of rechargeable aqueous batteries is examined by means of in-operando synchrotron X-ray diffraction. Via sequential unit-cell parameter refinements of time-resolved diffraction data, it is revealed that the step-profile of the cell output voltage curves during repeated electrochemical insertion and removal of Zn2+ in the CuHCF host structure is associated with a non-linear contraction and expansion of the unit-cell in the range 0.36<x<1.32 for Znx/3Cu[Fe(CN)6]2/3·nH2O. For a high insertion cation content there is no apparent change in the unit-cell contraction.  Furthermore, a structural analysis with respect to the occupancies of possible Zn2+ sites suggest that the Fe(CN)6 vacancies within the CuHCF framework play an important role in the structural-electrochemical behaviour of this particular system. More specifically, it is observed that Zn2+ swaps position during electrochemical cycling, hopping between cavity sites to vacant ferricyanide sites.

  • 50. Roberts, Matthew
    et al.
    Biendicho, Jordi Jacas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hull, Stephen
    Beran, Premysl
    Gustafsson, Torbjörn
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edström, Kristina
    Design of a new lithium ion battery test cell for in-situ neutron diffraction measurements2013In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 226, p. 249-255Article in journal (Refereed)
    Abstract [en]

    This paper introduces a new cell design for the construction of lithium ion batteries with conventional electrochemical performance whilst allowing in situ neutron diffraction measurement. A cell comprising of a wound cathode, electrolyte and anode stack has been prepared. The conventional hydrogen-containing components of the cell have been replaced by hydrogen-free equivalents. The electrodes are fabricated using a PTFE binder, the electrolyte consists of deuterated solvents which are supported in a quartz glass fibre separator. Typical battery performance is reported using the hydrogen-free components with a specific capacity of 140 mA h g(-1) being observed for LiFePO4 at a rate of 0.2 C. Neutron diffraction patterns of full cells were recorded with phase change reactions monitored. When aluminium packaging was used a better signal to noise ratio was obtained. The obtained atomic positions and lattice parameters for all cells investigated were found to be consistent with parameters refined from the diffraction pattern of a powder of the pure electrode material. This paper highlights the pertinent points in designing cells for these measurements and addresses some of the problems.

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