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  • 1.
    Akhtar, Farid
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ojuva, Arto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wirawan, Sang Kompiang
    Hedlund, Jonas
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hierarchically porous binder-free silicalite-1 discs: a novel support for all-zeolite membranes2011In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 24, p. 8822-8828Article in journal (Refereed)
    Abstract [en]

    Thermal expansion mismatch between the zeolite film and the support is an important cause for the formation of defects and cracks during the fabrication and use of zeolite membranes. We have studied how silicalite-1 discs with a permeability comparable to commercially available alumina supports can be produced by pulsed current processing (PCP) as a novel substrate for all-zeolite membranes. Hierarchically porous and mechanically strong membrane supports where the surface area and crystallography of the silicalite-1 particles were maintained could be obtained by carefully controlling the thermal treatment during PCP consolidation. In situ X-ray diffraction and dilatometry showed that the coefficient of thermal expansion (CTE) of the silicalite-1 substrate was negative in the temperature range 200-800 degrees C while the commonly used alumina substrate displayed a positive CTE. The critical temperature variation, Delta T, and thicknesses for crack-free supported zeolite films with a negative CTE were estimated using a fracture energy model. Zeolite films with a thickness of 1 mu m can only sustain a relatively modest Delta T of 100 degrees when supported onto alumina substrates while the all-zeolite membranes can support temperature variations above 500 degrees.

  • 2.
    Andersson, Nina
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Corkery, Robert
    Alberius, Peter
    One-Pot Synthesis of Well-Ordered Mesoporous Magnetic Carriers2007In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 17, p. 2700-2705Article in journal (Refereed)
    Abstract [en]

    The facile preparation of a mesoporous magnetic carrier technology is demonstrated. The micron-sized spherical mesostructured particles are prepared using a newly-developed, one-step, combined emulsion and solvent evaporation (ESE) method. The surfactant-templated silica matrix display a well-ordered internal pore architecture. Very limited pore blocking, and only to a limited degree disordered- or worm-like structures are observed, induced by the iron oxide nanoparticles added to provide the superparamagnetic properties.The iron oxide content was precisely controlled, and the magnetic properties were well preserved during the process. Finally we demonstrate the applicability of the magnetically separable mesoporous material as an adsorbent for specific dissolved materials from dilute aqueous solutions.

  • 3. Bhatt, Aarti Sripathi
    et al.
    Bhat, Denthaje Krishna
    Santosh, Mysore Sridhar
    Tai, Cheuk-wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Chitosan/NiO nanocomposites: a potential new dielectric material2011In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 35, p. 13490-13497Article in journal (Refereed)
    Abstract [en]

    The study of electrochemical behavior of organic-inorganic nanocomposite materials remains a major challenge for application in energy storage devices. Here, new composite materials of chitosan and NiO nanoparticles have been fabricated. The NiO nanoparticles are well characterized by infrared spectroscopy, X-ray diffraction and transmission electron microscopy. The electrical properties of the films are studied by impedance spectroscopy at different temperatures; and thereby permittivity, electric modulus and conductivity data are obtained. By studying the variations in permittivity and electric modulus spectra with respect to applied frequency signal and temperature, the ionic conductivity of the material is investigated. The Correlated Barrier Hopping model is employed to understand the conduction mechanism. An admirable conductivity of 1.4 x 10(-2) S cm(-1) is obtained for a nanocomposite with 4 wt% NiO content. The activation energies of the composite films decrease with increase in NiO content, from 16.5 to 4.8 kJ mol(-1).

  • 4.
    Eriksson, Kristofer
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johansson, Lars Erik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Göthelid, Emmanuelle
    Department of Physics and Astroniomy Uppsala University.
    Nyholm, Leif
    Department of Chemistry, Uppsala Univeristy.
    Oscarsson, Sven
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Manufacturing of Anisotropic Particles by Site Specific Oxidation of Thiols2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 16, p. 7681-7683Article in journal (Refereed)
    Abstract [en]

    A novel method for the manufacturing of functional anisotropic particles based on an inexpensive and straightforward electrochemical approach is presented. The method enables large-scale manufacturing of anisotropic particles as well as fabrication of multifunctional beads which may be used in the design of barcodes for multiplex diagnostics.

  • 5.
    Gao, Chuanbo
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Molecular design of AEC tri-block anionic surfactant towards rational synthesis of targeted thick-walled mesoporous silica2009In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 19, p. 3404-3411Article in journal (Refereed)
    Abstract [en]

    Here we report a new synthesis strategy to synthesize thick-walled two dimensional hexagonal mesoporous silicas, using tri-block surfactant fatty alcohol ether carboxylate [AEC: CnH2n+1O(CH2CH2O)mCH2COONa] with two different hydrophilic head groups of (EO)x-block and anionic carboxylate. The unique formation of double-layer silica wall arose from two types of hydrophilic head groups via the silica source condensation led to an obvious increase in the wall thickness. The successful carbon replication proved the existence of micropores formed by imbedded (EO)x-block and electrostatic bonding of carboxylate head group and organic group of co-structuredirecting agent. The template-free mesoporous silica showed a high hydrothermal stability due to the thick wall.

  • 6.
    Gao, Chuanbo
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Molecular design of the surfactant and the co-structure-directing agent (CSDA) toward rational synthesis of targeted anionic surfactant templatedmesoporous silica2007In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 17, p. 3591-3602Article in journal (Refereed)
    Abstract [en]

    The formation of anionic surfactant templated mesoporous silica (AMS) is investigated from the perspective of the geometrical molecular design of the surfactant and the co-structure-directing agent (CSDA) toward the rational synthesis of the targeted mesostructure. Increasing the geometrical size of two types of head group of the anionic surfactant in the order (i) sulfonate, sulfate and phosphate, and (ii) carboxylate, N-acylalanate/N-acylglycinate and N-acylglutamate, resulted in the mesophase changing from a disordered or lamellar phase to two-dimensional (2D) hexagonal (p6mm) and three-dimensional (3D) cage-type (hexagonal and a modulated cubic phase) with increasing order of the organic/inorganic interface curvature. A change in the chain length of the surfactant also led to different surfactant packing and mesophase interfacial curvatures, and resulted in a change in mesophase from a modulated cage-type mesophase to cubic Fd-3m, cubic Pm-3n and a disordered cage-type mesophase. The geometrical change in the CSDA resulted in an increasing micellar curvature in the order: aminopropyl , N-methylaminopropyl, N,N-dimethylaminopropyl trimethoxysilane, which led to a change of mesophase from bicontinuous cubic Pn-3m to 2D-hexagonal p6mm. An increase in the CSDA/surfactant ratio in the synthesis gave rise to the mesophase change from a disordered cage-type mesophase to cubic Fm-3m or from lamellar to 2D-hexagonal p6mm, and elemental analysis results showed that the mesoporous silicas have an increased loading of organic moieties using the CSDA method.

  • 7.
    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).
    PHASES IN THE ZRXTA1-X(O,N)Y SYSTEM, FORMED BY AMMONOLYSIS OF ZR-TA GELS - PREPARATION OF A BADDELEYITE-TYPE SOLID-SOLUTION PHASE ZRXTA1-XO1+XN1-X, O-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-11994In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 4, p. 1293-1301Article in journal (Refereed)
    Abstract [en]

    Phase formation in the system ZrxTa1-x(O,N)y has been studied by ammonolysis of Zr-Ta gels, prepared by the sol-gel technique, at temperatures between 700 and 1000-degrees-C. The starting gels and observed phases were characterised by X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (SEM and TEM) and thermogravimetric (TG) analysis. Oxynitride phases of compositions ZrxTa1-xO1+xN1-x, 0 less-than-or-equal-to x less-than-or-equal-to 1, with the baddeleyite-type structure, were prepared at 800-degrees-C. The unit-cell volume increased linearly from 127.8 angstrom3 for TaON (x = 0) to 140.9 angstrom3 for ZrO2 (x = 1). The structure was verified for the composition Zr0.4Ta0.6O1.6N0.4 (x = 0.4) by a Rietveld refinement (R(F) = 3.5%) using Cu-Kalpha1 XRPD data. An orthorhombic oxynitride phase was observed in preparations at 700-degrees-C for 0.26 less-than-or-equal-to x less-than-or-equal-to 0.90 in ZrxTa1-xO1+xN1-x. Unit-cell parameters and powder X-ray reflection intensities agree with an orthorhombic ZrO2 type structure. According to X-ray data, a cubic solid solution phase with a fluorite related subcell is present in materials prepared at 900-degrees-C for 0.26 less-than-or-equal-to x less-than-or-equal-to 0.68. However, electron microdiffraction patterns suggest a metrically monoclinic unit cell with a = 6.1 angstrom, b = 14.1 angstrom, c = 7.1 angstrom and beta = 125-degrees. The Ta3N5 type of structure was found to incorporate up to ca. 18 atom% Zr at 900 and 1000-degrees-C.

  • 8.
    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

  • 9.
    Gunawidjaja, Philips N.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Izquierdo-Barba, Isabel
    Mathew, Renny
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Garcia, Ana
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Arcos, Daniel
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Quantifying apatite formation and cation leaching from mesoporous bioactive glasses in vitro: a SEM, solid-state NMR and powder XRD study2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 15, p. 7214-7223Article in journal (Refereed)
    Abstract [en]

    By employing solid-state nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction (PXRD), and scanning electron microscopy coupled with energy-dispersive X-ray (EDX) spectroscopy, we compare the biomimetic growth of calcium hydroxyapatite (HA) from an ordered mesoporous bioactive glass (MBG) in simulated body fluid (SBF) and buffered water solutions. For the latter medium, we also examine the effects of using two different MBG concentrations. We evaluate the predicting powers of PXRD and P-31 NMR for directly quantifying the relative amounts of biomimetic amorphous calcium phosphate (ACP) and HA: we observe a very good agreement between the two analytical techniques. Thanks to their mesoporous channel system, fluids readily penetrate throughout sub-mm sized MBG grains, as evidenced by EDX. The latter revealed distinct element-mappings across the material after its exposure to SBF compared to water. Under our in vitro conditions involving relatively high MBG-loadings in the solutions, the HA formation reduces in SBF relative to buffered water, particularly for increasing MBG concentration. These features stem from a high [Ca2+]/[PO43-] ratio resulting in the fluid medium, which retards the HA crystallization by inducing a rapid ACP precipitation and an accompanying depletion of phosphate ions in the solution. This has bearings on the design of bioactivity comparisons of bioglasses exhibiting significantly different cation compositions.

  • 10.
    Han, Lu
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sakamoto, Yasuhiro
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Li, Y.
    Che, S.
    Synthesis of carboxylic group functionalized mesoporous silicas (CFMSs) with various structures2007In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 17, p. 1216-1221Article in journal (Refereed)
  • 11. Han, Lu
    et al.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Che, Shunai
    Carboxylic group functionalized ordered mesoporous silicas2011In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 30, p. 11033-11039Article in journal (Refereed)
    Abstract [en]

    Many research efforts have focused on the synthesis of organic and inorganic hybrid ordered mesoporous silicas (MSs) with functionalization of the exterior and/or interior surfaces aiming for applications in separation, adsorption, catalysis, drug delivery, and nanotechnology. Among the organic groups, the carboxylic group is a particularly useful reactive group for many applications. This article provides a brief overview of the carboxylic group functionalized MSs and the recent progress in synthetic strategies and applications have been reviewed.

  • 12.
    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.

  • 13.
    Klingstedt, Miia
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Miyasaka, Keiichi
    Kimura, Kosuke
    Gu, Dong
    Wan, Ying
    Zhao, Dongyuan
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Advanced electron microscopy characterization for pore structure of mesoporous materials; a study of FDU-16 and FDU-182011In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 35, p. 13664-13671Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive analysis for pore structures of cage-type ordered mesoporous carbons (OMCs) using various electron microscopy techniques in addition to conventional nitrogen adsorption isotherm studies. The benefits and drawbacks of these techniques are evaluated, and it is shown that they are complementary to each other. Knowledge of the structural properties, pore sizes, and connectivity gives insight into the synthesis strategies and how they are affecting the material properties that are useful within the possible applications. Herein, focus is put on the two OMCs with Im (3) over barm and Fm (3) over barm symmetries specified by FDU-16 and FDU-18. The central techniques used in this study are high resolution scanning electron microscopy combined with cross-section polisher and three-dimensional reconstruction methods (electron tomography and electron crystallography) based on transmission electron microscopy observations.

  • 14.
    Peng, Hong
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Reaction sequences occurring in dense Li-doped sialon ceramics: influence of temperature and holding time2003In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 13, no 9, p. 2285-2289Article in journal (Refereed)
    Abstract [en]

    Spark Plasma Sintering (SPS) has been used to consolidate a lithium-doped duplex α–β sialon with the overall composition Li0.5Si9.5Al2.5O2.0N14. The kinetics of densification has been studied, and the phase transformation, reactions and grain growth occurring in the dense compacts upon further heat treatment have been investigated. Two sources of Si3N4 powders were used, namely α- and β-Si3N4. Green bodies heated at a rate of 100 °C min−1 yielded fully dense compacts at 1450 °C (α-Si3N4) and 1500 °C (β-Si3N4) without holding, and these compacts consisted mainly of a locally formed liquid and precursor Si3N4 particles. Upon further heating it was observed that α-sialon is formed initially, irrespectively of whether α-Si3N4 or β-Si3N4 powder is used as Si3N4 source; and when α-Si3N4 is used as starting powder, almost monophasic α-sialon compacts are formed before any transformation to β-sialon takes place on further heating. When β-Si3N4 is used as starting powder the formation of β-sialon is kinetically promoted, and compacts containing α-sialon, β-sialon and β-Si3N4 are obtained before the equilibrium phase assemblage is reached, i.e. a lithium-doped duplex α–β sialon ceramic. These observations can be interpreted in terms of the Ostwald step rule. Grain growth does not occur until the equilibrium phase assemblage has been established. The separation of grain growth from densification and phase transformation has implications for preparing Si3N4-based nano-ceramics and provides possibility for further studies of the kinetics of grain growth in Si3N4-based ceramics.

  • 15. Prashar, Atul K.
    et al.
    Hodgkins, Robert P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Kumar, Rajiv
    Devi, R. Nandini
    In situ synthesis of Pt nanoparticles in SBA-15 by encapsulating in modified template micelles: size restricted growth within the mesochannels2008In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 18, no 15, p. 1765-1770Article in journal (Refereed)
    Abstract [en]

    A truly in situ and simple method is developed for nanoparticle incorporation within the mesochannels of SBA-15 involving dispersion of metal precursors in surfactant-modified polymer micelles. The diffusion of the precursor within the micellar structure is aided by interaction with the cationic head group of the surfactant leading to a unique method to facilitate the formation of highly disperse, uniform nanoparticles molded by the walls of the mesochannels. The nanoparticle incorporated mesoporous material has a highly enhanced surface area and adsorption capabilities in comparison to its parent materials without any pore blockage which makes this method ideal for the preparation of nanocatalysts.

  • 16.
    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.

  • 17.
    Shen, Zhijian
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yan, Haixue
    Grüner, Daniel
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Belova, Lyubov M.
    Sakamoto, Yasuhiro
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hu, Jianfeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nan, Ce-Wen
    Hoeche, Thomas
    Reece, Michael J.
    Ferroelectric ceramics with enhanced remnant polarization by ordered coalescence of nano- crystals2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 44, p. 23547-23552Article in journal (Refereed)
    Abstract [en]

    An exceptional high ferroelectric remnant polarization (P-r) was observed in BaTiO3 ceramics owing to the formation of micron-sized grains possessing nano-scale mosaicity. Such a structural hierarchy was developed via a novel crystal-growth mechanism, namely ordered coalescence of nano-crystals achieved by synergetic atomic epitaxial growth and self-assembly of nano-crystals. The accommodating lattice defects in sub-grain boundaries due to the imperfect assembly of nano-crystals significantly contribute to the P-r enhancement by stimulating the dynamics of ferroelectric domain formation and switching. This finding defines a new approach to nanopowder sintering leading to enhanced properties sensitive to lattice defects.

  • 18.
    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.

  • 19. Wahlberg, Sverker
    et al.
    Yar, Mazher A.
    Abuelnaga, Mohammad Omar
    Salem, Hanadi G.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Muhammed, Mamoun
    Fabrication of nanostructured W-Y2O3 materials by chemical methods2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 25, p. 12622-12628Article in journal (Refereed)
    Abstract [en]

    A novel method for the fabrication of highly uniform oxide dispersion-strengthened (ODS) materials made by chemical processing is presented. The powders are fabricated by a two-step route starting with a chemical synthesis at room temperature, producing nanocrystalline yttrium doped tungsten trioxide hydrate precursor powders. Thermogravimetric analysis with evolved gas analysis revealed the presence of ammonium nitrate in the precursors. The second step is the reduction of the precursor in a hydrogen atmosphere at 600 and 800 degrees C. The reduced powders, containing W-1.2%Y2O3, showed two types of tungsten particles, cube-shaped with a size less than 250 nm and finer particles (<50 nm) of both spherical and cubic shape. The powder was consolidated by spark plasma sintering at 1100 degrees C, producing a bulk material with a relative density of 88%. Characterization of the sintered materials by high resolution scanning electron microscopy revealed a uniform microstructure with tungsten grains of less than 300 nm and nanosized oxide particles uniformly dispersed at the tungsten grain boundaries, as well as inside the tungsten grains. Experimental determination of the elastic properties was conducted by nanoindentation tests and fracture toughness was studied by radial indentation cracking.

  • 20. Yao, Qingxia
    et al.
    Su, Jie
    Cheung, Ocean
    Liu, Qingling
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Interpenetrated metal-organic frameworks and their uptake of CO2 at relatively low pressures2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 20, p. 10345-10351Article in journal (Refereed)
    Abstract [en]

    Adsorption-driven separation of CO2 from flue gas has the potential to cut the cost for carbon capture and storage. Among the porous physisorbents, metal-organic frameworks (MOFs) are a class of promising candidates for gas separation and storage owing to their extraordinarily high specific surface areas and pore volumes, and predesigned pore structures. Here, we report three interpenetrated MOFs composed of Zn4O clusters and rigid dicarboxylate anions, namely SUMOF-n (SU StockholmUniversity; n = 2, 3, 4). All the interpenetrated MOFs possess small pores of two different types and high pore volumes. SUMOF-2 had a structure similar to interpenetrated MOF-5, but with an extra-framework cation present in one of the two types of pores. SUMOF-3 was an interpenetrated version of IRMOF-8 while SUMOF-4 crystallized with mixed linkers, biphenyl-4,4'-dicarboxylic acid and benzene-1,4-dicarboxylic acid. Among the three SUMOFs, SUMOF-4 had the largest specific surface area (1612 m(2) g(-1)) and pore volume. Single component adsorption of CO2 and N-2 was determined at 273 K. We showed that the interpenetrated SUMOF-2 adsorbedmore CO2 than non-interpenetrated MOF-5 under 273 K and 1 bar. This may be explained by the increased electric field gradients due to the interpenetration in the MOF. The uptake of CO2 for SUMOF-2 and SUMOF-4 was significant at somewhat higher pressure. Their CO2 isotherms were close to linear, which could be beneficial for separation of CO2 via pressure swing adsorption from biogas or natural gas. On the other hand, SUMOF-3 adsorbed most CO2 at pressures relevant for CO2 capture from flue gas.

  • 21. Yu, Jin-Tao
    et al.
    Chen, Zhe
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Huang, Zhi-Tang
    Zheng, Qi-Yu
    Cyclotricatechylene based porous crystalline material: Synthesis and applications in gas storage2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 12, p. 5369-5373Article in journal (Refereed)
    Abstract [en]

    An undulated two-dimensional CTC-based covalent organic framework, CTC-COF, was synthesized through solvothermal reaction for the first time. This mesoporous material stacks in an eclipsed mode in the microcrystalline state. CTC-COF has a surface area of 1710 m(2) g(-1), with a pore width of 2.26 nm calculated by the NL-DFT modelling. The bowl-shaped core unit led to a larger surface area than its analogue, COF-5 constructed by planar subunits. This material has higher low pressure hydrogen uptake than other 2D COFs with similar structures, and even close to the 3D COF materials.

1 - 21 of 21
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