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  • 51.
    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.   

  • 52.
    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).
    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 analysis2018In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 272, p. 70-78Article in journal (Refereed)
    Abstract [en]

    The CO2 adsorption and CO2 adsorption kinetics were evaluated by thermogravimetry on two Prussian blue analogues, K2x/3CuII [Fe-x(II) Fe-1-x(III) (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 similar to 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 CO(2 )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 similar to 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.

  • 53.
    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.

  • 54. Rajappa Prakasha, Kunkanadu
    et al.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Thersleff, Thomas
    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).
    Jøsang, Leif Olav
    Dalager Dyrli, Anne
    Paulus, Andreas
    De Sloovere, Dries
    D'Haen, Jan
    Van Bael, Marlies K.
    Hardy, An
    Avireddy, Hemesh
    Ramon Morante, Joan
    Jacas Biendicho, Jordi
    Temperature-Driven Chemical Segregation in Co-Free Li-Rich-Layered Oxides and Its Influence on Electrochemical Performance2022In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 34, no 8, p. 3637-3647Article in journal (Refereed)
    Abstract [en]

    Co-free Li-rich layered oxides are gaining interest as feasible positive electrode materials in lithium-ion batteries (LIBs) in terms of energy density, cost reduction, and alleviating safety concerns. Unfortunately, their commercialization is hindered by severe structural degradation that occurs during electrochemical operation. The study at hand demonstrates advanced structural engineering of a Li-rich Co-free oxide with composition Li1.1Ni0.35Mn0.55O2 by spray pyrolysis and subsequent calcination of an aqueous precursor, creating a segregated structure of two distinct layered phases with space groups R3̅m (rhombohedral) and C2/m (monoclinic). This particular structure was investigated with powder neutron diffraction, high-resolution analytical transmission electron microscopy imaging, and electron energy loss spectroscopic characterization. This complex structure contributes to the high electrochemical stability and good rate capability observed for this compound (160 mAh/g at C/3 and 100 mAh/g at 1C). These results provide new insights into the feasibility of developing and commercializing cobalt-free positive electrode materials for LIBs. 

  • 55. Renman, Viktor
    et al.
    Ojwang, Dickson O.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gómez, Cesar Pay
    Gustafsson, Torbjörn
    Edström, Kristina
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Valvo, Mario
    Manganese Hexacyanomanganate as a Positive Electrode for Nonaqueous Li-, Na-, and K-Ion Batteries2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 36, p. 22040-22049Article in journal (Refereed)
    Abstract [en]

    K2Mn[Mn(CN)(6)] is synthesized, characterized, and evaluated as possible positive electrode material in nonaqueous Li-, Na-, and K-ion batteries. This compound belongs to the rich and versatile family of hexacyanometallates displaying distinctive structural properties, which makes it interesting for ion insertion purposes. It can be viewed as a perovskite-like compound in which CN-bridged Mn(CN)(6) octahedra form an open framework structure with sufficiently large diffusion channels able to accommodate a variety of insertion cations. By means of galvanostatic cycling and cyclic voltammetry tests in nonaqueous alkali metal half-cells, it is demonstrated that this material is able to reversibly host Li+, Na+, and K+ ions via electrochemical insertion/deinsertion within a wide voltage range. The general electrochemical features are similar for all of these three ion insertion chemistries. An in operando X-ray diffraction investigation indicates that the original monoclinic structure is transformed into a cubic one during charging (i.e., removal of cations from the host framework) and that such a process is reversible upon subsequent cell discharge and cation reuptake.

  • 56. 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).
    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.

  • 57. 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.

  • 58. 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.

  • 59.
    Rosenthal-Aizman, Katri
    et al.
    Stockholm University, Faculty of Science, Department of Neurochemistry and Neurotoxicology.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Undén, Anders
    Stockholm University, Faculty of Science, Department of Neurochemistry and Neurotoxicology.
    Self-assembling peptide nanotubes from enantiomeric pairs of cyclic peptides with alternating D and L amino acid residues2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 11, p. 3372-3373Article in journal (Refereed)
    Abstract [en]

    Cyclic peptides with alternating d- and l-amino acid residues containing tert-leucine residues in every second position can form peptide nanotubes only when both enantiomers of the peptide are present in the solution. These results strongly indicate the formation of peptide nanotubes that assemble with one enantiomer in every second position, thereby forming a lamellar structure.

  • 60.
    Samain, Louise
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Amshoff, Philipp
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Biendicho, Jordi J.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). STFC Rutherford Appleton Laboratory, England.
    Tietz, Frank
    Mahmoud, Abdelfattah
    Hermann, Raphael P.
    Istomin, Sergey Ya.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Lomonosov Moscow State University, Russia.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Crystal structure and high-temperature properties of the Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta (0 <= x <= 0.75)2015In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 227, p. 45-54Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 62.
    Shafeie, Samrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Istomin, S. Y.
    Karvonen, L.
    Chen, S. A.
    Chen, T. H.
    Chen, J. M.
    Weidenkaff, A.
    Karppinen, M.
    Sirtl, T.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Phase formation, crystal structures and magnetic properties of perovskite-type phases in the system La2Co1+z(MgxTi1-x)1-zO62011In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 184, no 1, p. 177-190Article in journal (Refereed)
    Abstract [en]

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

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    FULLTEXT01
  • 63.
    Shafeie, Samrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Istomin, S. Ya
    Gippius, A. A.
    Karvonen, L.
    Populoh, S.
    Weidenkaff, A.
    Koehler, J.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tracking of high-temperature thermal expansion and transport properties vs. oxidation state of cobalt between +2 and +3 in the La2Co1+z(Ti1-xMgx)(1-z)O-6-system2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 32, p. 16269-16276Article in journal (Refereed)
    Abstract [en]

    The high-temperature thermal expansion and electronic transport properties of the B-site substituted LaCoO3 with both variable oxidation state of cobalt between +2 and +3 (La2Co(Ti1-xMgx)O-6, 0 <= x <= 0.5) and variable Co3+-content relative to the other B-cations (La2Co1+z(Ti0.5Mg0.5)(1-z)O-6, 0.2 <= z <= 0.6) have been investigated. Based on the temperature dependence of the thermal expansion, electronic transport properties and Seebeck coefficient, three different groups of compositions according to their symmetries can be allocated. It was found that the thermal expansion coefficients (TECs) of the studied compounds are mainly dependent on the proportion of Co2+/Co3+. For La2Co(Ti1-xMgx)O-6, the TEC increases from similar to 9 (x = 0) to similar to 19 ppm K-1 (x = 0.5) with an increase of the oxidation state of cobalt from +2 to +3, respectively. The TECs of La2Co1+z(Ti0.5Mg0.5)(1-z)O-6, z = 0.2-0.6 with Co3+-only, remain constant at similar to 21 ppm K-1 independent of the cobalt content. Thermoelectric measurements of the system indicate that all samples in the system, except La2Co1.6(Ti0.5Mg0.5)(0.4)O-6, are p-type conductors over the whole temperature range, 300 < T < 1175 K. The conductivities were found to increase with an increase of both Co3+ and total cobalt content and are described with a small polaron hopping model. Due to an insignificant number of oxygen vacancies of La2Co1+z(Ti1-xMgx)(1-z)O-6 samples prepared in air at elevated temperatures, the investigated system is proposed as an excellent model system for the investigation of the influence of the Co oxidation state and stoichiometry on different properties in perovskite cobalt oxides.

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    La2CoMgTiO6_HT_fin
  • 64.
    Svengren, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Roos, Per
    DTU Nutech, Centre for Nuclear Technologies, Frederiksborgvej 399, 4000 Roskilde, 10 Denmark.
    Daniel, Koros
    WWF-Kenya, Naivasha Landscape Office, P. O. Box 993 – 2117 Naivasha, Kenya.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Radioisotope and metal content in a Lake Nakuru sediment core – accumulation rate and 3  inventoriesManuscript (preprint) (Other academic)
    Abstract [en]

    The Nakuru environment is a hot spot both for human population and for biological conservation with a large number of species protected in the well visited Lake Nakuru  National Park. Reoccurring mass die-off of the Lesser Flamingo in Lake Nakuru as well as  cases of intoxication of humans within the water catchment area have gained attention and dedicated a significant amount of research over the recent decades. The toxicological histories of natural and anthropogenic activities are reflected by accumulated compounds in the water body sediments. In this study, a sediment core obtained from the central and deepest point of Lake Nakuru was sliced with 5 mm resolution and analyzed with the 210Pb dating method. The results show a linear accumulation rate of 1.3 mm y-1 and a mass accumulation rate of 0.027 g cm-2 y-1. Further analysis resulted in core profiles of organic material decay, phosphorus concentration gradient and total content of heavy metals in the lake water and in the sediment. In addition, analysis of 226Ra, 137Cs, 239+240Pu, 228Th/232Th was performed. 

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    fulltext
  • 65.
    Svensson, Gunnar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    BaNb4-xTixO6 (x = 0.53)1999In: Acta Crystallographica Section C: Crystal Structure Communications, ISSN 0108-2701, E-ISSN 1600-5759, Vol. C55, p. 17-19Article in journal (Refereed)
    Abstract [en]

    The title compound, barium niobium titanium oxide, is isostructural with BaNb4O6, i.e. it contains alternating NbO and perovskite-type single slabs. The NbO slabs can alternatively be described as layers of Nb6O12 clusters, condensed via corner sharing among the central Nb6 octahedra.

  • 66.
    Svensson, Gunnar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    ERIKSSON, LARS
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The Crystal Structure of SrNb4O61995In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 114, p. 301-307Article in journal (Refereed)
    Abstract [en]

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

  • 67.
    Svensson, Gunnar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Olofsson, Christer
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Holm, William
    Studies on Ba2Nb5−xTixO9 (0≤x≤1.75)1997In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 248, no 1-2, p. 33-41Article in journal (Refereed)
    Abstract [en]

    The structure of Ba2Nb5O9 can be described as an intergrowth between perovskite- (BaNbO3) and NbO-type slabs. The substitution of Ti for Nb according to the formula Ba2Nb5−xTixO9 (0.00≤x≤1.75) has been investigated. The decrease in unit cell parameters as a function of overall composition determined by microanalysis shows the maximum value of x to be around 0.9. At higher x values increasing amounts of BaNb1−xTixO3 and Nb were found. Rietveld refinements of the structure using X-ray powder diffraction data show Ti to prefer Nb positions in the perovskite slab (NbO6 octahedra) and the Nb positions in the NbO slab closest to the perovskite slabs. This latter Nb is five-fold coordinated by oxygen atoms, forming a square pyramid. The third Nb position, in the middle of the NbO slab with a square planar coordination of oxygen atoms, remains undoped.

    The electrical resistivity and magnetic susceptibility of the x = 0.0, 0.25, 0.50 and 0.75 samples were measured. All samples were found to be metallic conductors and temperature-independent paramagnetic.

  • 68.
    Svensson, Gunnar
    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).
    Shafeie, Samrand
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Masson, D.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Norberg, S. T.
    Eriksson, S.
    Hull, S.
    Zakharov, K. V.
    Volkova, O. S.
    Vasil'ev, A. N.
    Istomin, S. Ya.
    Synthesis and characterisation of the novel double perovskites La2CrB2/3Nb1/3O6, B = Mg, Ni, Cu2012In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 47, no 9, p. 2449-2454Article in journal (Refereed)
    Abstract [en]

    The novel perovskites La2CrB2/3Nb1/3O6, B = Mg, Ni, and Cu have been synthesised at 1350 degrees C in air via the citrate route. Rietveld refinements using neutron powder diffraction (NPD) data showed that the compounds adopt the GdFeO3 type structure with space group Pbnm, and unit cell parameters a approximate to b approximate to root 2 x a(p) and c approximate to 2 x a(p), where a(p) approximate to 3.8 angstrom. Selected area electron diffraction (SAED) of B = Ni and Cu samples confirmed space group Pbnm. However, distinct reflections forbidden in Pbnm symmetry, but allowed in the monoclinic sub-group P2(1)/n and unit cell parameters a approximate to b approximate to root 2 x a(p) and c approximate to 2 x a(p), beta approximate to 90 degrees were present in SAED patterns of B = Mg sample. This indicates an ordering of the B-cations within the crystal structure of La2CrMg2/3Nb1/3O6. High-resolution electron microscopy (HREM) study indicating uniform, without formation of clusters, ordering of B-cations in the crystallites of La2CrMg2/3Nb1/3O6. Magnetic susceptibility measurements show that the compounds are antiferromagnetic (with some glass or spin clustering effects due to additional ferromagnetic interactions between the B-cations) with T-N for La2CrB2/3Nb1/3O6, B = Mg, Ni, Cu being 90, 125 and 140K, respectively.

  • 69.
    Svensson, Gunnar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Samain, Louise
    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). Catalonia Institute for Energy Research, Spain; STFC Rutherford Appleton Laboratory, UK.
    Mahmoud, Abdelfattah
    Hermann, Raphaël P.
    Istomin, Sergey Ya.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Crystal Structure and Coordination of B-Cations in the Ruddlesden-Popper Phases Sr3-xPrx(Fe1.25Ni0.75)O7- (0 x 0.4)2018In: Inorganics, ISSN 2304-6740, Vol. 6, no 3, article id 89Article in journal (Refereed)
    Abstract [en]

    Compounds Sr3-xPrxFe1.25Ni0.75O7- with 0 x 0.4 and Ruddlesden-Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mossbauer spectroscopy. Both samples, prepared at 1300 degrees C under N-2(g) flow and samples subsequently air-annealed at 900 degrees C, were studied. The structures contained oxygen vacancies in the perovskite layers, and the Fe/Ni cations had an average coordination number less than six. The oxygen content was considerably higher for air-annealed samples than for samples prepared under N-2, 7 - = similar to 6.6 and similar to 5.6 per formula unit, respectively. Mossbauer data collected at 7 K, below magnetic ordering temperatures, were consistent with X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) results. The electrical conductivity was considerably higher for the air-annealed samples and was for x = 0.1 similar to 30 Scm(-1) at 500 degrees C. The thermal expansion coefficients were measured in air between room temperature and 900 degrees C and was found to be 20-24 ppmK(-1) overall.

  • 70.
    Svensson, Gunnar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Weil, K S
    Observations of defects in the layered ternary nitride, CrWN2, using transmission electron microscopy1999In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 9, no 10, p. 2709-2714Article in journal (Refereed)
    Abstract [en]

    Investigation of the local structure of CrWN2 by electron diffraction, medium resolution electron microscopy, and image simulation verify that this nitride possesses the same rhombohedral-based structure and AA’BB’CC’AA’BB’CC’... layered stacking sequence as found for LiMoN2. Two distinctive types of defects were observed in this compound, including twinning and intergrowth defects, which probably arise as an inherent consequence of this crystal structure type. An analysis and a description of the relationship between the crystal structure and common defects in CrWN2 are discussed.

  • 71.
    Thersleff, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Biendicho, Jordi Jacas
    Prakasha, Kunkanadu Rajappa
    Moreno, Elias Martinez
    Jøsang, Leif Olav
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Exploring the Nanoscale Origin of Performance Enhancement in Li1.1Ni0.35Mn0.55O2 Batteries Due to Chemical Doping2023In: Advanced Energy Materials, ISSN 1614-6832, E-ISSN 1614-6840, Vol. 13, no 16, article id 2203889Article in journal (Refereed)
    Abstract [en]

    Despite significant potential as energy storage materials for electric vehicles due to their combination of high energy density per unit cost and reduced environmental and ethical concerns, Co-free lithium ion batteries based on layered Mn oxides presently lack the longevity and stability of their Co-containing counterparts. Here, a reduction in this performance gap is demonstrated via chemical doping, with Li1.1Ni0.35Mn0.54Al0.01O2 achieving an initial discharge capacity of 159 mAhg−1 at C/3 rate and a corresponding capacity retention of 94.3% after 150 cycles. The nanoscale origins of this improvement are subsequently explored through a combination of advanced diffraction, spectroscopy, and electron microscopy techniques, finding that optimized doping profiles lead to an improved structural and chemical compatibility between the two constituent sub-phases that characterize the layered Mn oxide system, resulting in the formation of unobstructed lithium ion pathways between them. A structural stabilization effect of the host compound is also directly observed near the surface using aberration corrected scanning transmission electron microscopy and integrated differential phase contrast imaging. 

  • 72.
    Tran, Dung
    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).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    TEM-based pair distribution function study of bimetallic nanoparticles2014In: XV International Conference on Electron Microscopy, 2014Conference paper (Other academic)
  • 73.
    Tran, Dung Trung
    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).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    SUePDF: a program to obtain quantitative pair distribution functions from electron diffraction data2017In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 50, p. 304-312Article in journal (Refereed)
    Abstract [en]

    SUePDF is a graphical user interface program written in MATLAB to achieve quantitative pair distribution functions (PDFs) from electron diffraction data. The program facilitates structural studies of amorphous materials and small nanoparticles using electron diffraction data from transmission electron microscopes. It is based on the physics of electron scattering as well as the total scattering methodology. A method of background modeling is introduced to treat the intensity tail of the direct beam, inelastic scattering and incoherent multiple scattering. Kinematical electron scattering intensity is scaled using the electron scattering factors. The PDFs obtained after Fourier transforms are normalized with respect to number density, nanoparticle form factor and the non-negativity of probability density. SUePDF is distributed as free software for academic users.

  • 74.
    Tran, Dung-Trung
    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).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Atomistic computation of the finite size effect in pair distribution function of nanoparticlesManuscript (preprint) (Other academic)
  • 75.
    Tran, Dung-Trung
    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).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    TEM-based total scattering method for studying disorder of nanoparticles2014Conference paper (Other academic)
  • 76.
    Tyutyunnik, A P
    et al.
    Institute of Solid State Chemistry, Russian Academy of Science, Ekaterinburg, Russia.
    Grins, Jekab
    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).
    Phases in the Mn-Nb-N-O system, formed by ammonolysis of mixtures of Mn acetate tetrahydrate and a Nb xerogel1998In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 33, no 7, p. 1035-1044Article in journal (Refereed)
    Abstract [en]

    Phase formation in the system Mn-Nb-O-N has been studied by ammonolysis of mixtures of Mn acetate tetrahydrate and an Nb xerogel at 600-900 degrees C. Observed phases were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, combustion analysis, and thermogravimetric analysis. An Nb4N5-related phase, with a metal content of less than or equal to 15 at% Mn, was obtained pure at 650-700 degrees C. A new hexagonal phase MnNb2(N,O)(3) was obtained at 750-900 degrees C, Its structure is related to, but not isotypic with, that of Nb5N6. In addition, the preparations contained cubic NaCl-type (Mn, Nb)(N,O) phases. The Mn-free Nb4-y(N,O)(5) and Nb5-y(N,O)(6) (y signifying metal vacancies), with Nb4N5- and Nb5N6-type structures, respectively, were synthesized, to make possible structural comparisons with the Mn-containing phases. A black trigonal phase Mn-3.66(6)Nb-2.34(6)(O,N)(9) with a structure closely related to that of Mn4Nb2O9 was obtained at 700 degrees C. (C) 1998 Elsevier Science Ltd.

  • 77.
    Tyutyunnik, A P
    et al.
    Institute of Solid State Chemistry, Russian Academy of Science, Ekaterinburg, Russia.
    Grins, Jekab
    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).
    Rietveld refinement studies of Nb4N5- and Nb5N6-related phases in the (Mn)-Nb-O-N system1998In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 278, no 1-2, p. 83-91Article in journal (Refereed)
    Abstract [en]

    The structures of two Nb and two Mn–Nb (oxy)nitrides have been refined from Cu Kα1 powder diffractometer data by the Rietveld method and have been characterised by electron diffraction. The phases Nb3.49N4.56O0.44 and Mn0.54Nb3.07N4.40O0.60 have structures related to that of Nb4N5, an NaCl type with ordered metal vacancies. Refinements in space group I4/m, with RF=1.3% and 1.1%, respectively, have shown that they are disordered and that metal atoms partially occupy both the nominally filled 8h position and the nominally empty 2a position in the Nb4N5 type. The observed bond lengths indicate that the 2a position is occupied only by Mn atoms in Mn0.54Nb3.07N4.40O0.60. The Nb5N6 type structure of Nb5(N,O)6 and the related structure of MnNb2(N,O)3 has been refined in space group P63/mcm to RF=1.5% and 2.9%, respectively. In the latter, the trigonal prism sites 6g are found to be occupied only by Nb, the octahedral 4d sites by approximately equal amounts Mn and Nb and the octahedral 2a site, empty in the Nb5N6 type structure, only by Mn. The Nb (oxy)nitride structures exhibit short Nb–Nb distances which indicates localised bonding between Nb atoms. Magnetic susceptibility and electrical conductivity measurements of the tetragonal phases at 15–300 K show, respectively, small magnetic moments which are coupled in an antiferromagnetic manner at low temperatures and poor, nearly temperature-independent, conductivities.

  • 78. Tyutyunnik, A P
    et al.
    Zubkov, V G
    Kellerman, D G
    Pereliaev, V A
    Karkin, A E
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis, superconducting properties and structural (including electron diffraction) studies of Na chi NbO2 and Li chi NbO21996In: European Journal of Solid State and Inorganic Chemistry, ISSN 0992-4361, E-ISSN 1873-3751, Vol. 33, p. 53-65Article in journal (Refereed)
    Abstract [en]

    Monophasic NaxNbO2 (x = 0.5 - 0.6), T-c approximate to 4.1 K was prepared by solid state reaction between Na3NbO4 and Nb. X-ray powder diffraction data from a monophasic sample were used for a refinement of the structure of Na0.5NbO2 (R(p) = 7.4 % and R(I) = 5.3 %), using the Rietveld method. At low x-values a closely related second phase can occur. Rietveld refinement using X-ray powder diffraction data showed this phase to be isostructural with NaNbO2 but with the chemical formula Na0.1NbO2. Transmission electron microscopy studies of NaxNbO2 and LixNbO2 revealed the presence of superstructures in some crystallites. The electron diffraction patterns resemble to some extent those reported for transformations among tantalum chalcogenides.

  • 79. Tyutyunnik, A. P.
    et al.
    Zubkov, V. G.
    Krasil'nikov, V. N.
    Berger, I. F.
    Perelyaeva, L. A.
    Baklanova, I. V.
    Skripkin, M. Yu
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    CRYSTAL STRUCTURE AND VIBRATIONAL SPECTRA OF M[VO(2)(SeO(4))(H(2)O)(2)]center dot H(2)O (M = K, Rb, NH(4))2011In: Journal of Structural Chemistry, ISSN 0022-4766, E-ISSN 1573-8779, Vol. 52, no 2, p. 350-357Article in journal (Refereed)
    Abstract [en]

    By the hydration of MVO(SeO(4))(2) with saturated water vapors at room temperature a series of isostructural complex compounds of vanadium(V) of the composition M[VO(2)(SeO(4))(H(2)O)(2)]center dot H(2)O (K, Rb, NH(4)) are synthesized and their physicochemical properties are studied. Based on the X-ray and neutron diffraction data, it is found that their crystal structure is composed of VO(6) octahedra linked in infinite chains by bridging SeO(4) tetrahedra. Each of the VO(6) octahedra has two short terminal V-O bonds forming a bent dioxovanadium group VO(2)(+). Two water molecules are coordinated by vanadium and one molecule is out of the first coordination sphere in the interchain space. The vibrational spectra of the studied compounds are completely consistent with their structural features.

  • 80. Tyutyunnik, AP
    et al.
    Zubkov, VG
    Tarakina, NV
    Krasilnikov, VN
    Perelyaeva, LA
    Baklanova, IV
    Svensson, G
    Stockholm University.
    Synthesis, crystal structure and vibrational spectra of KCrV2O7 and RbCrV2O72006In: Solid State Sciences, Vol. 8, p. 1344-1352Article in journal (Refereed)
  • 81.
    Urbonaite, Sigita
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Juarez-Galan, Juan M.
    Leis, Jaan
    Rodriguez-Reinoso, Francisco
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Porosity development along the synthesis of carbon from metal carbides2008In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 113, no 1-3, p. 14-21Article in journal (Refereed)
    Abstract [en]

    Carbide derived carbons (CDCs) are materials containing a wide range of pore size, their properties and applications being a function of the pore structure. For this reason it is important to find the relationship between synthesis parameters, such as initial carbide and temperature, and resulting structure. In this work, CDCs were prepared from VC, TiC, WC, TaC, NbC, HfC and ZrC at different temperatures and they have been characterized by means of gas adsorption. Nitrogen at −196 °C and carbon dioxide at 0 °C adsorptions were used to obtain structural information such as apparent surface area (SBET), micropore volume (Vmicro) and pore size distribution (PSD). These studies show that these parameters vary strongly depending on synthesis temperature (700–1200 °C) and initial carbide. Since the size of micropores is near the range suggested as being ideal for methane (CH4) storage, the high-pressure methane adsorption at 25 °C was performed to check the possible use of CDCs as storage material. The CH4 adsorption capacity of CDCs can compete with other carbons on a gravimetric basis, though the volumetric one is far from desired due to their low packing density.

  • 82.
    Urbonaite, Sigita
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Wachtmeister, Staffan
    Stockholm University, Faculty of Science, Department of Physics.
    Mirguet, Claude
    Coronel, Ernesto
    Zou, W.Y.
    Csillag, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    EELS studies of carbide derived carbons2007In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 45, no 10, p. 2047-2053Article in journal (Refereed)
    Abstract [en]

    Carbide derived carbons (CDCs) have been synthesized from VC, WC, TaC, NbC, HfC and ZrC at T = 1000 °C, and from TiC at T = 700–1200 °C via a chlorination reaction. The CDCs have been studied by means of high resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS). These studies show that the structures of CDCs are strongly dependent upon the nature of the starting carbide and the synthesis temperature. The structures range from very disordered nanoporous carbon, consisting of randomly curved graphene layers, to compact spherical entities of compactly packed graphitic layers. EELS studies of carbon core-loss spectra show that the relative sp2 content in these carbons varies between 83% and 98%. The low-loss part of the EEL spectra shows that the positions of the π-plasmons and the bulk plasmons are more dependent on the carbide precursor, than the synthesis temperature. The densities of the CDC particles have been estimated using the bulk plasmon positions as well as the sp3 content determined from the C-K edge spectra. The densities calculated from sp3 are close to the pycnometric ones, while the densities calculated from bulk plasmon positions are lower and reflects the nanostructure of CDCs.

  • 83.
    Wang, Xia
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wenming, Hao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Taiyuan University of Technology, China.
    Peng, Zhang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Szego, Anthony E.
    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).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Macroscopic rods from assembled colloidal particles of hydrothermally carbonized glucose and their use as templates for silicon carbide and tricopper silicide2021In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 602, p. 480-489Article in journal (Refereed)
    Abstract [en]

    Self-aggregated colloids can be used for the preparation of materials, and we studied long rod-like aggregates formed on the evaporation of water from dispersed particles of colloidal hydrochar. The monodispersed hydrochar particles (100–200 nm) were synthesized by the hydrothermal carbonization ofglucose and purified through dialysis. During the synthesis they formed colloidal dispersions which wereelectrostatically stable at intermediate to high pH and at low ion strengths. On the evaporation of water,macroscopically large rods formed from the dispersions at intermediate pH conditions. The rods formedat the solid-water interface orthogonally oriented with respect to the drying direction. Pyrolysis renderedthe rods highly porous without qualitatively affecting their shape. A Cu-Si alloy was reactively infiltratedinto the in-situ pyrolyzed hydrochars and composites of tricopper silicide (Cu3Si)-silicon carbide(SiC)/carbon formed. During this process, the Si atoms reacted with the C atoms, which in turned causedthe alloy to wet and further react with the carbon. The shape of the underlying carbon template wasmaintained during the reactions, and the formed composite preparation was subsequently calcined intoa Cu3Si-SiC-based replica of the rod-like assemblies of carbon-based colloidal particles. Transmission andscanning electron microscopy, and X-ray diffraction were used to study the shape, composition, andstructure of the formed solids. Further studies of materials prepared with reactive infiltration of alloysinto self-aggregated and carbon-based solids can be justified from a perspective of colloidal science, aswell as the explorative use of hydrochar prepared from real biomass, exploration of the compositionalspace in relation to the reactive infiltration, and applications of the materials in catalysis. 

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  • 84.
    Wardecki, Dariusz
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ojwang, Dickson O.
    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).
    Neutron Diffraction and EXAFS Studies of K2x/3Cu[Fe(CN)(6)](2/3)center dot nH(2)O2017In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 17, no 3, p. 1285-1292Article in journal (Refereed)
    Abstract [en]

    The crystal structure of copper hexacyanoferrate (CuHCF), K2x/3Cu[Fe-(CN)(6)](2/3)center dot nH(2)O, with nominal compositions x = 0.0 and x = 1.0 was studied by neutron powder diffraction (NPD) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The compound crystallizes in space group Fm (3) over barm, with a = 10.1036(11) angstrom and a = 10.0588(5) angstrom for x = 0.0 and x = 1.0, respectively. Difference Fourier maps for x = 0.0 show that the coordinated water molecules are positioned at a site 1921 close to vacant N positions in the -Fe-C-N-Cu- framework, while additional zeolitic water molecules are distributed over three sites (8c, 32f, and 48g) in the -Fe-C-N-Cu- framework cavities. The refined water content for x = 0.0 is 16.8(8) per unit cell, in agreement with the ideal 16 (n = 4). For x = 1.0, the refinement suggests that 2.6 K atoms per unit cell (x = 0.98) are distributed only over the sites 8c and 32f in the cavities, and 13.9(7) water per unit cell are distributed over all the four positions. The EXAFS data for Fe, Cu, and K K-edges are in agreement with the NPD data, supporting a structure model with a linear -Fe-C-N-Cu- framework and K+ ions in the cavities.

  • 85. Zeng, Lunjie
    et al.
    Tran, Dung Trung
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tai, Cheuk-Wai
    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, Eva
    Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions2016In: Scientific Reports, E-ISSN 2045-2322, Vol. 6, article id 29679Article in journal (Refereed)
    Abstract [en]

    Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

  • 86. Zubkov, V G
    et al.
    Pereliaev, V A
    Institute of Solid State Chemistry, Russian Academy of Science, Ekaterinburg, Russia.
    Tyutyunnik, A P
    Institute of Solid State Chemistry, Russian Academy of Science, Ekaterinburg, Russia.
    Kohler, J
    Max Planck Institute - Solid State Chemistr, Stuttgart, Germany.
    Simon, A
    Max Planck Institute - Solid State Chemistr, Stuttgart, Germany.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Condensed cluster phases in reduced oxoniobates: synthesis and studies of Sr4−xNb17O26 (x=0.0(1), 0.3(1)) and Eu4−xNb17O26 (x=0.3(1)):  1997In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 256, p. 129-139Article in journal (Refereed)
    Abstract [en]

    Sr4−xNb17O26 (x=0.0, 0.3) and Eu4−xNb17O26 (x = 0.3) were synthesised from SrCO3/Eu2O3 and Nb2O5 in a vacuum furnace at temperatures up to 1600°C (1500°C for Eu) using acetylene soot or Nb as reducing agents. The synthetic studies show that these phases are only formed via an intermediate disordered ‘phase’ (or phasoid). Sr4−xNb17O26 and Eu4−xNb17O26 are isostructural with Ba4Nb17O26 and crystallise in space group P 4/m (83) with the unit cell parameters for   and and , respectively. The crystal structure can be described as an intergrowth between ANbO3 and NbO. Characteristic building blocks are quadruple chains of corner-sharing Nb6-octahedra. ?The structures of Sr4−xNb17O26 and Eu4−xNb17O26 were refined using X-ray powder diffraction and neutron diffraction data (only Sr4−xNb17O26). The Rietveld refiniments and microanalyses showed x in Eu4−xNb17O26 to be 0.3(l) while the Sr analogue both x= 0.0(1) and 0.3(1) were found. High resolution electron microscopy studies showed that the compounds frequently contained structural defects. The magnetic susceptibility of Eu4−xNb17O26 (x=0.3) shows a Curie-Weiss behaviour, with a magnetic moment in good agreement with the expected μeff=7.9 μB for Eu2+/ The Sr analogie is temperature-independent paramagnetic at room temperature, Sr4−xNb17O26 (x=0.3) and Eu4−xNb17O26 (x=0.3) are metallic, with a resistivity increasing with temperature.

  • 87. Zubkov, V. G.
    et al.
    Surat, L. L.
    Tyutyunnik, A. P.
    Berger, I. F.
    Tarakina, N. V.
    Slobodin, B. V.
    Kuznetsov, M. V.
    Denisova, T. A.
    Zhuravlev, N. A.
    Perelyaeva, L. A.
    Baklanova, I. V.
    Shein, I. R.
    Ivanovskii, A. L.
    Shulgin, B. V.
    Ishchenko, A. V.
    Tcherepanov, A. N.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Forslund, Bertil
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Skripkin, M. Yu.
    Structural, vibrational, electronic, and luminescence properties of the cyclotetravanadates A(2)M(VO3)(4) (A=Na,Ag; M=Ca,Sr)2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 17, p. 174113-Article in journal (Refereed)
    Abstract [en]

    The physical properties of the family of cyclotetravanadates A(2)M(VO3)(4), where A=Na,Ag and M=Ca,Sr, have been studied by means of x-ray powder diffraction, neutron diffraction, electron diffraction, infrared, Raman, NMR, photoexcitation and pulse cathode beam excitation, and x-ray photoelectron spectroscopies, and band structure calculations. The differences between the structural, vibrational, luminescence, and electronic properties of the alkali metal-containing [Na2Ca(VO3)(4) and Na2Sr(VO3)(4)] and the d metal-containing cyclotetravanadates [Ag2Ca(VO3)(4) and Ag2Sr(VO3)(4)] are analyzed. Na2Ca(VO3)(4), Ag2Ca(VO3)(4), Na2Sr(VO3)(4), and Ag2Sr(VO3)(4) have tetragonal structures, P4/nbm, with a=10.438 49(6), 10.445 24(5), 10.634 49(4), and 10.625 74(6), and c=4.938 73(5), 4.968 45(5), 4.962 05(4), and 4.979 30(4) angstrom, respectively. The main structural feature of A(2)M(VO3)(4) is the tetracyclic [V4O12] units. The hybridized O 2p-V 3d states of the tetracyclic [V4O12] units have a dominant influence on the electronic structure of these compounds. The compounds are semiconducting with a local density approximation band gap increasing, from 1.85 eV for Ag2Ca(VO3)(4) to 3.02 eV for Na2Ca(VO3)(4). The prospects of these compounds as advanced materials for detectors of photon and corpuscular radiation as well as for color correction of light emission sources such as lamp and light emitting diode sources are discussed.

  • 88. ZUBKOV, VG
    et al.
    PERELEYAEV, VA
    TYUTYUNNIK, AP
    KONTSEVAYA, IA
    VORONIN, VI
    SVENSSON, G
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    SYNTHESIS, HIGH-RESOLUTION ELECTRON-MICROSCOPY AND CRYSTAL-STRUCTURE REFINEMENT OF THE CLUSTER COMPOUND BA3NB16O23 BY X-RAY AND NEUTRON-DIFFRACTION1994In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 203, p. 209-216Article in journal (Refereed)
    Abstract [en]

    Ba3Nb16O23 was prepared by reducing a mixture of BaCO3 and Nb2O5 with acetylene soot under vacuum at 1550-1600-degrees-C. The structure was determined from high resolution electron microscopy images and was refined by the Rietveld technique using X-ray and neutron powder diffraction data. The unit cell parameters are a = 20.9301(4) angstrom, b = 12.4785(3) angstrom and c = 4.1619(1) angstrom, space group Cmmm, Z = 2. The crystal structure can be described as an intergrowth of BaNbO3 and NbO. Characteristic building units are quadruple chains of corner-sharing Nb6 octahedra connected via columns with a perovskite-type structure to form a three-dimensional network.

  • 89. ZUBKOV, VG
    et al.
    TYUTYUNNIK, AP
    PERELIAEV, VA
    SHVEIKIN, GP
    KOHLER, J
    KREMER, RK
    SIMON, A
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and Structural, Magnetic and Electrical Characterization of the Reduced Oxoniobates BaNb8O14, EuNb8O14, Eu2Nb5O9 and EuxNbO3 (x = 0.7, 1.0).1995In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 226, p. 24-30Article in journal (Refereed)
    Abstract [en]

    Powder samples of the reduced oxoniobates Eu0.7NbO3, EuNbO3, Eu2Nb5O9, EuNb8O14 and BaNb8O14 have been synthesised. EuNbO3 and Eu0.7NbO3 adopt the perovskite type structure (space group Pm3m) with unit cell parameters a = 4.021 (1) and 3.981 (3) Angstrom, respectively. Eu,Nb,Og exhibits an intergrowth structure which can be described as alternating slabs of NbO and EuNbO3. It crystallises in P4/mmm with a = 4.131(1) and c = 12.043(5) Angstrom. EuNb8O14 and the here synthesised modification of BaNb8O14 is isostructural with SrNb8O14. The structures of EuNb8O14 and BaNb8O14 have been refined from X-ray powder diffraction data with the Rietveld technique, They have the unit cell parameters a = 9.2272(1), b = 10.2647(2), c = 5.9381(1) and a = 9.3451(1), b = 10.2689(2), c = 5.9470(4) Angstrom, (space group Pbam), respectively. In all the studied compounds AO(12) cuboctahedra (A = Eu, Ba) form either chains (in ANb(8)O(14)), double layers (in Eu2Nb5O9) or three-dimensional nets (in EuNbO3 and Eu0.7NbO3). Magnetic susceptibility measurements show temperature independent paramagnetism for BaNb8O14, while the susceptibilities of the Eu niobates follow Curie-Weiss laws with effective magnetic moments in good agreement with the expected mu(eff)=7.9 mu(B) for EU(2+). Eu0.7NbO3 and Eu1.0NbO3 exhibit ferromagnetic ordering below 4 K. BaNb8O14 and EuNb8O14 are semiconductors, while Eu2Nb5O9, EuNbO3 and Eu0.7NbO3 are metallic.

  • 90. Zubkov, VG
    et al.
    Tyutyunnik, AP
    Tarakina, NV
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Forslund, Bertil
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Synthesis, crystal structure and luminescent properties of pyrovanadates A(2)CaV(2)O(7) (A = Rb, Cs)2009In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 11, no 3, p. 726-732Article in journal (Refereed)
    Abstract [en]

    The novel vanadium oxides Rb2CaV2O7 and Cs2CaV2O7 have been prepared by solid-state reaction and their crystal structures determined and refined using X-ray, neutron powder and electron diffraction data. Rb2CaV2O7 and Cs2CaV2O7 are isostructural, crystallizing in space group P21/n with unit cell parameters: a = 13.8780(1), b = 5.96394(5), c = 10.3376(1) Å, ? = 104.960(1)º and a = 14.0713(2), b = 6.0934(1), c = 10.5944(1) Å, ? = 104.608(1)º, respectively. Their crystal structures can be described as a framework of CaO6 octahedra and V2O7 pyrogroups with alkaline metals found in the tunnels formed. Photoluminescence (PL) and PL excitation spectra of the concerned pyrovanadates have been studied in the vacuum ultraviolet (VUV) to visible light (VIS) range as well as their pulse cathode luminescence (PCL) spectra and the kinetic parameters of PCL. In the PL and the PCL spectra of both pyrovanadates recorded at T = 300 K a broad band with maxima at 2.38, 2.2 eV and a shoulder (band) at 2.08 eV have been observed. At T = 10 K the band at 2.08 eV becomes the main band in the spectra. Two types of luminescence centers for each pyrovanadates, with very similar excitation bands at 3.75, 4.84, 6.2, 7.3 and 9.1 eV, have been found. The nature of the luminescence centers connected with the band 2.08 eV (center I) and the bands 2.2 and 2.38 eV (center II) is discussed

  • 91.
    Åkerblom, Ida E.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ojwang, Dickson O.
    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).
    A thermogravimetric study of thermal dehydration of copper hexacyanoferrate by means of model-free kinetic analysis2017In: Journal of thermal analysis and calorimetry (Print), ISSN 1388-6150, E-ISSN 1588-2926, Vol. 129, no 2, p. 721-731Article in journal (Refereed)
    Abstract [en]

    The kinetics of thermal dehydration of K2x/3Cu[Fe(CN)6]2/3·nH2O was studied using thermogravimetry for x = 0.0 and 1.0. Data from both non-isothermal and isothermal measurements was used for model-free kinetic analysis by the Friedman and KAS methods. The water content was determined to be n = 2.9 – 3.9, with an additional ~10% of water, likely surface adsorbed, that leaves very fast when samples are exposed to a dry atmosphere. The determined activation energies are 19 kJ (mol H2O)-1 for x = 0.0 and 16 kJ (mol H2O)-1 for x = 1.0. The dehydration is adequately described as a diffusion controlled single step reaction following the D3 Jander model. The determined dehydration enthalpy is, 11 kJ (mol H2O)-1 for x = 0.0 and 27 kJ (mol H2O)-1 for x = 1.0, relative to that of water. The increase with increasing x is evidence for that the H2O molecules form bonds to the incorporated K+ ions.

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