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

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

  • 2.
    GRINS, Jekabs
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    SVENSSON, Gunnar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    SYNTHESIS OF OXYNITRIDE PEROVSKITES [AZRXTA1-XO2+XN1-X, A=CA, SR, BA AND 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1]1994In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 29, no 7, p. 801-809Article in journal (Refereed)
    Abstract [en]

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

  • 3.
    Istomin, S Y
    et al.
    Moscow State University, Department of Chemistry.
    Dyachenko, O G
    Moscow State University, Department of Chemistry.
    Antipov, E V
    Moscow State University, Department of Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis and characterization of reduced niobates CaLnNb2O7, Ln = Y, Nd with a pyrochlore structure1997In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 32, no 4, p. 421-430Article in journal (Refereed)
    Abstract [en]

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

  • 4.
    Istomin, S Y
    et al.
    Moscow State University, Department of Chemistry.
    D’Yachenko, O G
    Moscow State University, Department of Chemistry.
    Antipov, E V
    Moscow State University, Department of Chemistry.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lundqvist, B
    Synthesis and characterization of the reduced niobates CaLnNb2O7, Ln = La-Pr, Sm, Gd-Lu, with the pyrochlore-type structure1998In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 33, p. 1251-1256Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    ISTOMIN, SY
    et al.
    Moscow State University.
    DYACHENKO, OG
    Moscow State University.
    ANTIPOV, EV
    Moscow State University.
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    NYGREN, M
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    SYNTHESIS AND CHARACTERIZATION OF REDUCED NIOBATES [SR1-XLNXNB2O6, LN=LA, ND]1994In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 29, p. 743-749Article in journal (Refereed)
    Abstract [en]

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

  • 6.
    Jalilian, Ehsan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liao, Rong-Zhen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lidin, Sven
    Luminescence properties of monoclinic Cu4I4(Piperidine)42011In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 46, no 8, p. 1192-1196Article in journal (Refereed)
    Abstract [en]

    A new modification of Cu4I4Pip4 has been synthesized under hydrothermal conditions. X-ray crystallography revealed that this compound crystallized in the monoclinic system and consists of a tetrahedral core with composition Cu4I4, in which each Cu atom is coordinated by a piperidine molecule via the N atom. In contrast to a previously reported modification of Cu4I4Pip4, the present modification shows luminescent properties when exposed to UV-light. In addition, we have used time-dependent density functional theory calculations to characterize both compounds in term of both absorption and emission.

  • 7. Kars, Mohammed
    et al.
    Fredrickson, Daniel C.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Gomez-Herrero, A.
    Lidin, Sven
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Rebbah, Allaoua
    Otero-Diaz, L. C.
    Structural study by X-ray diffraction and transmission electron microscopy of the misfit compound (SbS1-xSex)(1.16)(Nb1.036S2)(2)2010In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 45, no 8, p. 982-988Article in journal (Refereed)
    Abstract [en]

    In the Sb-Nb-S-Se system, a new misfit layer compound (MSL) has been synthesized and its structure was determined by combining single crystal X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It presents a composite crystal structure formed by (SbS1-xSex)slabs stacking alternately with double NbS2 layers and both can be treated as separate monoclinic subsystems. The (SbS1-xSex) slabs comprise a distorted, two-atom-thick layer with NaCl-type structure formed by an array of (SbX5) square pyramids joined by edges (X: S, Se); the NbS2 layers consist of (SbX5) trigonal prisms linked through edge-sharing to form sheets, just as in the 2H-NbS2 structure type. Both sublattices have the same lattice parameters a = 5.7672(19) angstrom, c = 17.618(6) angstrom and beta = 96.18(3)degrees, with incommensurability occurring along the b direction: b(1) = 3.3442(13) angstrom for the NbS2 subsystem and b(2) = 2.8755(13) angstrom for the (SbS1-xSex) subsystem. The occurrence of diffuse scattering intensity streaked along c* indicates that the (SbS1-xSex) subsystem is subjected to extended defects along the stacking direction.

  • 8.
    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.

  • 9.
    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.

  • 10.
    Wang, Cao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhao, Zhe
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Transparent polycrystalline ruby ceramic by spark plasma sintering2010In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 45, no 9, p. 1127-1131Article in journal (Refereed)
    Abstract [en]

    Fine-grained and transparent polycrystalline ruby ceramics (Cr2O3-doped Al2O3) were successfully prepared by spark plasma sintering (SPS). The effect of Cr2O3 concentration on the grain size, hardness, fracture toughness and thermal conductivity of ruby ceramics was investigated systematically. For 0.05 wt.% Cr2O3, high in-line transmittance of 85% at 2000 nm can be reached, further increase of Cr2O3 concentration leads to the decrease in transmittance. High hardness of 23.95-25.05 GPa can be achieved due to the fine grain size in all ruby ceramics. The fracture toughness of 1.9-2.29 MPa m(1/2) indicates that no improvement in fracture toughness over pure Al2O3 can be obtained by Cr2O3 doping in these submicron grained ruby ceramics. High thermal conductivity of 28-29.8 W/(m K) at room temperature, close to that of single crystal sapphire, can be achieved. The change in grain size for different Cr2O3 concentrations is the major reason for the change in mechanical and thermal properties, but not for the change in optical properties.

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