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1.
  • Dyachenko, O G, et al. (författare)
  • Structure and properties of Ba6 − xLnxNb10O30, Ln = La, Ce and Nd compounds
  • 1997
  • Ingår i: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 32:4, s. 409-419
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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2.
  • GRINS, Jekabs, et al. (författare)
  • 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]
  • 1994
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 29:7, s. 801-809
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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3.
  • ISTOMIN, SY, et al. (författare)
  • SYNTHESIS AND CHARACTERIZATION OF REDUCED NIOBATES [SR1-XLNXNB2O6, LN=LA, ND]
  • 1994
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 29, s. 743-749
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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4.
  • Istomin, S Y, et al. (författare)
  • Synthesis and characterization of reduced niobates CaLnNb2O7, Ln = Y, Nd with a pyrochlore structure
  • 1997
  • Ingår i: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 32:4, s. 421-430
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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5.
  • Istomin, S Y, et al. (författare)
  • Synthesis and characterization of the reduced niobates CaLnNb2O7, Ln = La-Pr, Sm, Gd-Lu, with the pyrochlore-type structure
  • 1998
  • Ingår i: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 33, s. 1251-1256
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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6.
  • Sterte, Johan, et al. (författare)
  • A study on the preparation and properties of fibrillar boehmite
  • 1986
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 21:10, s. 1159-1166
  • Tidskriftsartikel (refereegranskat)abstract
    • Effects of temperature, time and Al2O3 Cl molar ratio on the structure and porous nature of synthetic fibrillar boehmite prepared by hydrothermal treatment of aluminum chlorohydrate solutions were investigated. Fibrillar boehmite crystallized at temperatures above 120°C in a solution with an Al2O3 Cl ratio of 0.93 employing a reaction time of 24 h. The ultimate particles in a sample prepared at 160°C had a length of approximately 1000 Å and a diameter of about 50 Å. Increasing crystallinity with increasing temperature up to 220°C and with increasing reaction time up to 24 h was observed while differences in Al2O3 Cl ratio resulted in minor effects. The deionized and freeze dried or directly freeze dried products possessed surface areas in the range 50-250 m2/g and pore volumes in the range 0.1-1.0 cm3/g. Pore volume distributions were calculated for some samples. Effects of deionization are discussed.
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7.
  • Tyutyunnik, A P, et al. (författare)
  • Phases in the Mn-Nb-N-O system, formed by ammonolysis of mixtures of Mn acetate tetrahydrate and a Nb xerogel
  • 1998
  • Ingår i: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 33:7, s. 1035-1044
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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8.
  • Zhu, Bin (författare)
  • Proton and oxygen ion conduction in nonoxide ceramics
  • 2000
  • Ingår i: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 35:1, s. 47-52
  • Tidskriftsartikel (refereegranskat)abstract
    • By directly examining fuel cell performances, it was discovered that nonoxide containing materials such as chlorides and fluorides exhibit significant proton and oxygen ion conduction. Ionic transport measurements showed that both proton and oxygen ion conduction are present, with proton conduction predominant in most cases. Steady-state current output under fuel-cell operation indicates that the transport process in both chloride and fluoride electrolytes is dominated by the source ions, protons, and oxygen ions. These new materials have significant importance for both fundamental and applied research.
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9.
  • Al-Hinai, A. T., et al. (författare)
  • Application of Eh-pH diagram for room temperature precipitation of zinc stannate microcubes in an aqueous media
  • 2014
  • Ingår i: Materials research bulletin. - : Elsevier. - 0025-5408 .- 1873-4227. ; 49:1, s. 645-650
  • Tidskriftsartikel (refereegranskat)abstract
    • Potential-pH diagram assisted-design for controlled precipitation is an attractive method to obtain engineered binary and ternary oxide particles. Aqueous synthesis conditions of zinc stannate (ZnSnO3) particles at low temperature were formulated with the assistance of potential-pH diagram. The pH of a solution containing stoichiometric amounts of Zn2+ and Sn4+ was controlled for the precipitation in a one pot synthesis step at room temperature (25 degrees C). The effect of the concentration of the reactants on the particle size was studied by varying the concentration of the precursor (Zn2+ + Sn4+) solution. Scanning electron micrographs show that the particles are monodispersed micron sized cubes formed by the self-organization olnano-sized crystallites. The obtained microcubes characterized by X-ray Diffraction and thermo gravimetric analysis (TGA) show that the particles are in ZnSnO3.3H(2)O form.
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10.
  • Baykal, A., et al. (författare)
  • Effect of ionic liquids on the electrical and magnetic performance of polyaniline-nickel ferrite nanocomposite
  • 2013
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 48:2, s. 378-382
  • Tidskriftsartikel (refereegranskat)abstract
    • Polyaniline-NiFe2O4 nanofiber composites were successfully synthesized at the interface of water and ionic liquid via in situ polymerization using cetyl trimethylammonium bromide (CTAB) as surfactant. Both TG analysis and FT-IR measurements proved the presence of organic layer on the surface of NiFe2O4 nanoparticles. The influence of 1-butyl-3-methyl-imidazolium bromide [BMIM]Br as ionic liquid on the structure, conductivity and magnetic property of polyaniline-NiFe2O 4-CTAB nanocomposite were studied in detail. The results show that imidazolium-based ionic liquids BMIMBr acts as an anchor agent for the formation of morphology in polyaniline-NiFe2O4-CTAB nanocomposite. Introduction of ionic liquids obviously improves the conductivity but weakens the magnetization of polyaniline-NiFe2O4 nanocomposite.
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11.
  • Bourajoini, Hasna, et al. (författare)
  • Calcium manganese oxide catalysts for water oxidation : Unravelling the influence of various synthesis strategies
  • 2016
  • Ingår i: Materials research bulletin. - : Elsevier. - 0025-5408 .- 1873-4227. ; 79, s. 133-137
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract Three different mixed oxide catalysts primarily consisting of calcium and manganese oxides targeting artificial photosynthesis were synthesized and studied. According to the results, their catalytic activity for water oxidation was enhanced by the presence of mixed valence states of Mnn+ ions (3.0 ≤ n ≪ 4.0), while the specific surface area had negligible effect.
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12.
  • Cabioch, Thierry, et al. (författare)
  • Ti2AlN thin films synthesized by annealing of (Ti plus Al)/AlN multilayers
  • 2016
  • Ingår i: Materials research bulletin. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0025-5408 .- 1873-4227. ; 80, s. 58-63
  • Tidskriftsartikel (refereegranskat)abstract
    • Single-phase Ti2AlN thin films were obtained by annealing in vacuum of (Ti + Al)/AIN multilayers deposited at room temperature by magnetron sputtering onto single-crystalline (0001) 4H-SiC and (0001) Al2O3 substrates. In-situ X-ray diffraction experiments combined with ex-situ cross-sectional transmission electron microscopy observations reveal that interdiffusion processes occur in the multilayer at a temperature of similar to 400 degrees C leading to the formation of a (Ti, Al, N) solid solution, having the hexagonal structure of alpha-Ti, whereas the formation of Ti2AlN occurs at 550-600 degrees C. Highly oriented (0002) Ti2AlN thin films can be obtained after an annealing at 750 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.
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13.
  • Chandar, Nagamuthu Krishna, et al. (författare)
  • Structural, morphological and optical properties of solvothermally synthesized Pr(OH)(3) nanoparticles and calcined Pr6O11 nanorods
  • 2014
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 50, s. 417-420
  • Tidskriftsartikel (refereegranskat)abstract
    • The structural, morphological and optical properties of solvothermally synthesized Pr(OH)(3) nanoparticles and calcined Pr6O11 nanorods have been studied. Pr6O11 nanorods were grown by subsequent thermal decomposition of the synthesized Pr(OH)(3) nanoparticles at 700 degrees C for 2 h. Structural analysis showed that the synthesized Pr(OH)(3) nanoparticles possess hexagonal phase and calcined Pr6O11 nanorods have cubic fluorite phase. HRSEM images revealed that the Pr6O11 sample contains well-defined rod-like morphology. The UV-vis absorbance study of Pr6O11 nanorods showed shapedependent absorption edge toward higher wavelength as compared to Pr(OH)(3) nanoparticles. The PL spectrum of Pr6O11 nanorods reveals the enhanced near-band-edge emission in the blue region, with significant defect level green emission. The mechanism for the formation of Pr6O11 nanorods from Pr(OH)(3) nanoparticles has been proposed.
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14.
  • Deligoz, H., et al. (författare)
  • Synthesis, structural and electrical properties of triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs
  • 2012
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:3, s. 537-543
  • Tidskriftsartikel (refereegranskat)abstract
    • Triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs was synthesized by a glycothermal reaction. XRD analysis identified the product as Mn0.2Co0.8Fe2O4 with a high phase purity. Nano-sized particles with an average size of about 6-8 nm were obtained with nearly single crystalline nature with TEM analysis. Superparamagnetic-like behavior of TREG stabilized Mn0.2Co0.8Fe2O4 NPs was observed by VSM. The binding between TREG and Mn0.2Co0.8Fe2O4 NPs was investigated with FT-IR and found to be via O on the TREG and NP surface. TG analysis indicated that the Mn0.2Co0.8Fe2O4 NP content was about 40%, with a TREG-shell content to be around 60%. Overall conductivity of the nanocomposite is in the range of 10(-10) to 10(-7) S cm(-1) with a strong dependence on temperature and frequency, indicating ionic conductivity. The nanocomposite exhibited lower epsilon' and epsilon '' compared to TREG stabilized Mn0.2Co0.8Fe2O4 NPs due to the doping of co-doping of manganese and cobalt.
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15.
  • Deligöz, H., et al. (författare)
  • Synthesis, structural, magnetic and electrical properties of Co 1-xZnxFe2O4 (x = 0.0, 0.2) nanoparticles
  • 2013
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 48:2, s. 646-654
  • Tidskriftsartikel (refereegranskat)abstract
    • Co1-xZnxFe2O4 spinel nanoparticles with Zn concentrations of x = 0.0, 0.2 were prepared by a hydrothermal route in the presence of triethylene glycol (TEG). The structural, magnetic, electrical and dielectric properties of the prepared nanoparticles were studied. The XRD results confirmed the formation of single spinel ferrite structure with crystallite size 9 and 10 nm for x = 0.0 and 0.2 compositions respectively. The lattice parameter (a) increased with increasing Zn concentration. Temperature and frequency dependent electrical and dielectric properties of the prepared ferrites have also been investigated. Our findings show that overall conductivity of Co0.8Zn0.2Fe 2O4 nanoparticle is lower than that of CoFe 2O4 and roughly in the range of 10-11-10 -7 S cm-1 depending strongly temperature and frequency owing to the formation of stable electric bonds between the Zn2+ and Fe2+ ions, which localizes Fe2+ charge carriers. The ac conductivity showed a temperature dependent behavior at low frequencies and temperature independent behavior at high frequencies, which is an indication of ionic conductivity. dc conductivity of Co0.8Zn0.2Fe 2O4 nanoparticle are found to obey the Arrhenius plot and can be classified into two regions over with activation energy of 0.113 and 0.163 eV in the ranges of 20-40 °C and 70-120 °C, respectively when CoFe2O4 has an activation energy of 0.245 eV.
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16.
  • Dom, R., et al. (författare)
  • Deposition of nanostructured photocatalytic zinc ferrite films using solution precursor plasma spraying
  • 2012
  • Ingår i: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 47:3, s. 562-570
  • Tidskriftsartikel (refereegranskat)abstract
    • Deposition of pure spinel phase, photocatalytic zinc ferrite films on SS-304 substrates by solution precursor plasma spraying (SPPS) has been demonstrated for the first time. Deposition parameters such as precursor solution pH, concentration, film thickness, plasma power and gun-substrate distance were found to control physico-chemical properties of the film, with respect to their crystallinity, phase purity, and morphology. Alkaline precursor conditions (7 < pH ≤ 10) were found to favor oxide film formation. The nanostructured films produced under optimized conditions, with 500 mM solution at pH ∼ 8.0, yielded pure cubic phase ZnFe 2O 4 film. Very high/low precursor concentrations yielded mixed phase, less adherent, and highly inhomogeneous thin films. Desired spinel phase was achieved in as-deposited condition under appropriately controlled spray conditions and exhibited a band gap of ∼1.9 eV. The highly porous nature of the films favored its photocatalytic performance as indicated by methylene blue de-coloration under solar radiation. These immobilized films display good potential for visible light photocatalytic applications. © 2012 Elsevier Ltd. All rights reserved.
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17.
  • Erdemi, H., et al. (författare)
  • Synthesis and conductivity studies of piperidine-4-carboxylic acid functionalized Fe 3O 4 nanoparticles
  • 2012
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:9, s. 2193-2199
  • Tidskriftsartikel (refereegranskat)abstract
    • Piperidine-4-carboxylic acid (PPCA) functionalized Fe 3O 4 nanoparticles as a novel organic-inorganic hybrid was fabricated and characterized by XRD, FT-IR, VSM, and TEM techniques. Its detailed electrical properties are also presented. Composition was determined as Fe 3O 4, while particles were observed to have spherical morphology. VSM measurement proved the super-paramagnetic property of the as synthesized nanocomposite. ac and dc conductivity measurements indicated semiconductor characteristics and changing trends with temperature because of reorganization of the nanocomposite. dc conductivity is strongly temperature dependent and is classified into three regions. Analysis of the real and imaginary parts of the permittivity of nanocomposite showed the ionic polarization mechanism consisting of ionic conductivity and interfacial polarization.
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18.
  • Günay, M., et al. (författare)
  • Triethylene glycol stabilized MnFe2O4 nanoparticle : Synthesis, magnetic and electrical characterization
  • 2013
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 48:3, s. 1057-1064
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, triethylene glycol (TEG) stabilized superparamagnetic MnFe2O4 nanoparticle (TEG@Mn-Fe2O4) was synthesized via a simple polyol route. Composition of nanoparticle was confirmed as MnFe2O4 and surface conjugation of TEG was confirmed by Fourier transform infrared spectroscopy to be via oxygens on TEG covalently attached to metal centers on the NPs: Vibrating sample magnetometer measurements confirmed the superparamagnetic character of these nanoparticles without reaching to a saturation, and has no coercivity. The TEG@MnFe2O4 nanocomposite showed thermally activated conductivity, significant interfacial polarization effect also in the dielectric permittivity evaluations. Temperature dependency of conductivity is a strong evidence for thermally activated polarization mechanism. dc conductivity is classified into two regions over a limited temperature range and shows maximum conductivity of about 4 x 10(-7) S cm(-1) at 120 degrees C. Temperature and frequency dependence of dielectric permittivity indicated interfacial polarization and temperature-assisted-reorganization effects.
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19.
  • Ivanov, Sergey A., et al. (författare)
  • Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn3-xCoxTeO6
  • 2014
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 50, s. 42-56
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of Co2+ doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn3TeO6 have been investigated. Ceramic samples of the solid solution series Mn3-xCoxTeO6 were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x <= 2.4 adopt the trigonal corundum-related structure of pure Mn3TeO6 (space group 18) in the temperature range 5-295 K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co2+ concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co2+ concentration x. Curie-Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn3TeO6 can be described as an incommensurately modulated magnetic spin state with k = [0, 0, k(z)] and an elliptical spin-spiral order of spins within the chains of MnO6 octahedra. With increasing Co2+ concentration the propagation vector kz changes from 0.453 (x = 0) to 0.516 (x = 2.4). The magnetic anisotropy changes as well, leading to a reorientation of the spiral-basal plane. A possible coexistence of long-range order of electrical dipoles and magnetic moments in Mn3-xCoxTeO6 is discussed.
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20.
  • Ivanov, Sergey A., et al. (författare)
  • New type of incommensurate magnetic ordering in Mn(3)TeO(6)
  • 2011
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 46:11, s. 1870-1877
  • Tidskriftsartikel (refereegranskat)abstract
    • The complex metal oxide Mn(3)TeO(6) exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group R (3) over bar with a = 8.8679(1) angstrom. c = 10.6727(2) angstrom. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis.
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21.
  • Ivanov, Sergey A., et al. (författare)
  • Preparation, structural, dielectric and magnetic properties of LaFeO3-PbTiO3 solid solutions
  • 2012
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:11, s. 3253-3268
  • Tidskriftsartikel (refereegranskat)abstract
    • Solid solutions of (1−x)LaFeO3–(x)PbTiO3 (0 < x < 1) have been prepared by conventional solid-state reaction. These complex perovskites have been studied by means of X-ray (XRPD) and neutron powder (NPD) diffraction, complemented with dielectric, magnetic, heat capacity and Mössbauer measurements. Complete solubility in the perovskite series was demonstrated. The NPD and XRPD patterns were successfully refined as orthorhombic (x ≤ 0.7) and tetragonal (x ≥ 0.8). A composition-driven phase transformation occurs within the interval 0.7 < x < 0.8. The samples with x < 0.5 showed evidence of long-range magnetic ordering with an G-type antiferromagnetic arrangement of the magnetic moments of the Fe3+ cations in the B-site with propagation vector k = (0,0,0). Based on the obtained experimental data, a combined structural and magnetic phase diagram has been constructed. The factors governing the structural, dielectric and magnetic properties of (1−x)LaFeO3–(x)PbTiO3 solid solutions are discussed, as well as their possible multiferroicity.
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22.
  • Ivanov, Sergey A., et al. (författare)
  • Temperature-dependent multi-k magnetic structure in multiferroic Co3TeO6
  • 2012
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:1, s. 63-72
  • Tidskriftsartikel (refereegranskat)abstract
    • A complex magnetic order of the multiferroic compound Co(3)TeO(6) has been revealed by neutron powder diffraction studies on ceramics and crushed single crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied temperature range 2-300 K but exhibits successive antiferromagnetic transitions at low temperature. Incommensurate antiferromagnetic order with the propagation vector k(1) = (0, 0.485, 0.055) sets in at 26 K. A transition to a second antiferromagnetic structure with k(2) = (0, 0, 0) takes place at 21.1 K. Moreover, a transition to a commensurate antiferromagnetic structure with k(3) = (0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined by neutron powder diffraction using group theory analysis as a preliminary tool. Different coordinations of the Co(2+) ions involved in the low-symmetry C2/c structure of Co(3)TeO(6) render the exchange-interaction network very complex by itself. The observed magnetic phase transformations are interpreted as an evidence of competing magnetic interactions. The temperature dependent changes in the magnetic structure, derived from refinements of high-resolution neutron data, are discussed and possible mechanisms connected with the spin reorientations are described.
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23.
  • Ivanov, Sergey, et al. (författare)
  • Neutron powder diffraction and magnetic study of perovskites Pb(Mn1/2Nb1/2)O3 and Pb(Mn1/4Fe1/4Nb1/2)O3
  • 2008
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 43:11, s. 3074-3087
  • Tidskriftsartikel (refereegranskat)abstract
    • The structural and magnetic properties of the complex metal oxides Pb(Mn1/2Nb1/2)O3 (PMNO) and Pb(Mn1/4Fe1/4Nb1/2)O3 (PMFNO), which belong to a class of disordered perovskites have been studied. The magnetic susceptibilities of PMNO showed hysteresis between field cooled and zero-field cooled conditions below the transition of 15 K, suggesting that the material has a spin-glass feature. Neutron diffraction patterns of PMNO showed no evidence of a long-range magnetic ordering at 1.5 K, which is consistent with spin-glass behavior. Rietveld refinements of neutron powder diffraction data collected at different temperatures between 1.5 and 700 K have been carried out in order to extract structural information. The crystal structure of this compound is cubic (space group Pmm) within the whole temperature interval. The Mn and Nb ions were found to be disordered over the perovskite B-sites. The main feature of this structure is the positional disorder at the Pb site, the importance of which in connection with the ferroic transitions is briefly discussed. The Pb cations show a positional disorder shifting from their high-symmetry positions along the [1 1 1] direction. The effect of Fe-doping on PMNO has been studied. The substitution of Fe at the Mn site in PMFNO results in a small changes of the magnetic properties without significant differences in the crystal structures. The factors governing the observed structural and magnetic properties of PMNO and PMFNO are discussed and compared with those of other quaternary Mn-containing perovskites. For the PbB3+1/2Nb1/2O3 series with the isomorphous substitution B3+, graphs of average lattice parameters of the perovskite phase and the temperatures of ferroelectric and magnetic phase transitions as functions of the B3+ cation radius were constructed and are discussed. Influence of A-cation sublattice on magnetic properties is also considered.
  •  
24.
  • Ivanov, Sergey, et al. (författare)
  • Temperature evolution of structure and magnetic properties in the perovskite Sr2MnSbO6
  • 2009
  • Ingår i: Materials research bulletin. - : Elsevier Ltd. - 0025-5408 .- 1873-4227. ; 44:4, s. 822-830
  • Tidskriftsartikel (refereegranskat)abstract
    • The structural and magnetic properties of the perovskite Sr2MnSbO6 have been studied. Combining neutron and X-ray powder diffraction data, the temperature evolution of the structural parameters was investigated with the Rietveld method between 2 and 1000 K. The crystal structure is tetragonal (space group I4/m) within the temperature interval of 2–750 K and cubic (space group Fm-3m) above 750 K. Both octahedral B-site positions were found to be partially occupied by Mn and Sb, but with different Mn/Sb ratios. The magnetic susceptibilities showed irreversibility between field cooled and zero-field cooled (ZFC) conditions and spin glass like magnetic dynamics including aging and memory phenomena at temperatures below 30 K; all appearing well above a broad maximum at 13 K in the ZFC susceptibility curves. This suggests that the material reaches an unconventional spin-glass state at low temperatures, possibly arising from a competitive situation between the double exchange (ferromagnetism) and the super-exchange (antiferromagnetism). Neutron diffraction patterns showed no evidence of a long-range magnetic ordering at 2 K which is consistent with spin glass behavior. The factors governing the observed structural and magnetic properties of Sr2MnSbO6 are discussed and compared with those of other quaternary Mn- and Sb-containing perovskites. Graphs of the temperature of magnetic phase transitions as functions of the cation size were constructed and are discussed for the AB3+1/2B5+1/2O3 series with isomorphous substitution of B3+ and B5+ cations. Possible influence of the A-cation sublattice on magnetic properties is also shortly considered.
  •  
25.
  • Ivanov, Sergey, et al. (författare)
  • The magnetoelectric perovskite Sr3Fe2TeO9 : An insight from magnetic measurements and neutron powder diffraction
  • 2007
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 42:4, s. 776-789
  • Tidskriftsartikel (refereegranskat)abstract
    • A study of the crystallographic and magnetic structures of the double perovskite Sr3Fe2TeO9 has been carried out on a polycrystalline sample using neutron powder diffraction (NPD) data between 10 and 650 K. An analysis of the NPD patterns at room temperature has shown that this compound crystallises in the tetragonal space group I4/m with a = 5.5614(7) Å and c = 7.867(1) Å and has a partially ordered arrangement of Fe and Te at the B-sites. The compound undergoes an I4/m → Fm-3m improper ferroelectric phase transition near 460 K. A low-temperature ferrimagnetic ordering (below TN = 260 K) has been followed from the magnetisation measurements and sequential NPD data analysis. In good agreement with magnetic measurements the ferrimagnetic structure with very weak magnetisation is defined by the propagation vector k = (0, 0, 0). In addition to the obtained experimental results on magnetic and electric properties some aspects of magnetoelectricity in this perovskite are also discussed and compared with those of another quaternary oxide Sr3Fe2B6+O9.
  •  
26.
  • Jalilian, Ehsan, et al. (författare)
  • Luminescence properties of monoclinic Cu4I4(Piperidine)4
  • 2011
  • Ingår i: Materials research bulletin. - : Elsevier Ltd.. - 0025-5408 .- 1873-4227. ; 46:8, s. 1192-1196
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
27.
  • Jeon, So-hyoun, et al. (författare)
  • Selective control of wetting on various substrates
  • 2014
  • Ingår i: Materials research bulletin. - : Elsevier Ltd. - 0025-5408 .- 1873-4227. ; 58, s. 32-34
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective control of wetting is highly demanded for a broad window of applications. To selectively control wetting a surface should be locally modified by structuring surfaces or modulating surface chemistry. However, the local modifications are still challenging due to their complex and expensive processes. In this report we demonstrate the development of a facile approach for selective control of wetting on various substrates. Taking superhydrophobic polypropylene particles and hydrophilic silica nanoparticles, we here show that the locally controlled wetting can be achieved by coating the particles on a wide range of substrates including metal and paper and be applied to microfluidic channels. Furthermore, we represent that the coating method can be applied to any surfaces regardless of compositions and geometries.
  •  
28.
  • Karaoglu, E., et al. (författare)
  • Synthesis and characterization of Piperidine-4-carboxylic acid functionalized Fe 3O 4 nanoparticles as a magnetic catalyst for Knoevenagel reaction
  • 2012
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:9, s. 2480-2486
  • Tidskriftsartikel (refereegranskat)abstract
    • Piperidine-4-carboxylic acid (PPCA) functionalized Fe 3O 4 nanoparticles as a novel organic-inorganic hybrid heterogeneous catalyst was fabricated and characterized by XRD, FT-IR, TGA, TEM and VSM techniques. Composition was determined as Fe 3O 4, while particles were observed to have spherical morphology. Size estimations using X-ray line profile fitting (10 nm), TEM (11 nm) and magnetization fitting (9 nm) agree well, revealing nearly single crystalline character of Fe 3O 4 nanoparticles. Magnetization measurements reveal that PPCA functionalized Fe 3O 4 NPs have superparamagnetic features, namely immeasurable coercivity and absence of saturation. Small coercivity is established at low temperatures. The catalytic activity of Fe 3O 4-PPCA was probed through one-pot synthesis of nitro alkenes through Knoevenagel reaction in CH 2Cl 2 at room temperature. The heterogeneous catalyst showed very high conversion rates (97%) and could be recovered easily and reused many times without significant loss of its catalytic activity.
  •  
29.
  • Kars, Mohammed, et al. (författare)
  • Structural study by X-ray diffraction and transmission electron microscopy of the misfit compound (SbS1-xSex)(1.16)(Nb1.036S2)(2)
  • 2010
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 45:8, s. 982-988
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
30.
  • Lane, Nina J., et al. (författare)
  • High-temperature stability of alpha-Ta(4)AlC(3)
  • 2011
  • Ingår i: Materials research bulletin. - : Elsevier Science B.V., Amsterdam.. - 0025-5408 .- 1873-4227. ; 46:7, s. 1088-1091
  • Tidskriftsartikel (refereegranskat)abstract
    • Cold-pressed alpha-Ta(4)AlC(3) powders were annealed up to 1750 degrees C to test first-principles predictions of alpha-beta phase-stability reversal at 1600 degrees C. Up to 1600 degrees C, the alpha-Ta(4)AlC(3) samples were stable with no indications of any alpha-beta transformation, as shown by the strong characteristic X-ray diffraction peaks of alpha-Ta(4)AlC(3) and the zigzag stacking observed by transmission electron microscopy. These results show that, in this experimental situation, high temperature alone is not sufficient to cause the alpha-beta transformation.
  •  
31.
  • Leone, Stefano, 1978-, et al. (författare)
  • Growth of smooth 4H-SiC epilayers on 4° off-axis substrates with chloride-based CVD at very high growth rate
  • 2011
  • Ingår i: Materials research bulletin. - : Elsevier. - 0025-5408 .- 1873-4227. ; 46:8, s. 1272-1275
  • Tidskriftsartikel (refereegranskat)abstract
    • 4H-SiC epilayers grown on 4º off-axis substrates at high rates usually suffer from step-bunching (very high surface roughness) or of extended triangular defects, both detrimental for device performance. In this study we developed a novel in situ pre-growth surface preparation based on hydrogen chloride (HCl) addition at a temperature higher than that used for the growth. This pre-growth etching procedure minimizes the density of triangular defects which usually occur at low temperatures and simultaneously enables growth at a temperature low enough to avoid stepbunching. Thanks to this surface preparation step, chloride-based CVD could be used for rapid epitaxial growth of high quality layers. In this study, layers were grown at rates of 100 μm/h yielding defect free epitaxial layers with very smooth surface (RMS value of 8.9 Å on 100x100 μm2 area).
  •  
32.
  • Nissinen, T., et al. (författare)
  • Comparison of preparation routes of spinel catalyst for alkaline fuel cells
  • 2004
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 39:9, s. 1195-1208
  • Tidskriftsartikel (refereegranskat)abstract
    • MnCo2O4 has been used as a catalyst for oxygen reduction reaction (ORR) in alkaline fuel cells due to easier production and lower costs compared to noble metals. A novel method using a microwave-assisted route of synthesis in the presence of amorphous carbon was developed resulting in MnCo2O4 with particle sizes
  •  
33.
  • Rehman, Adil, et al. (författare)
  • Effect of ultraviolet light on 1/f noise in carbon nanotube networks
  • 2021
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 134
  • Tidskriftsartikel (refereegranskat)abstract
    • Noise defines the minimum level of the operational signal and is an important figure of merit for various devices. Here, we studied the low-frequency (1/f) noise characteristics of randomly oriented networks of carbon nanotubes and examined the effect of ultraviolet (UV) light on it. The amplitude of 1/f noise in our devices was strongly affected by the quality of nanotubes. This makes noise spectroscopy an effective tool to characterize the structural quality of carbon nanotube devices. UV illumination increased the device resistance and noise amplitude preserving the spectra shapes. This effect remained for tens of minutes even after the UV light was turned off. We observed a completely different trend of noise spectra and resistance with temperature as compared to UV illumination. These results indicated at least two important components of resistance that contribute to the total resistance of the device and are essential to describe the nanotube networks correctly.
  •  
34.
  • Saoud, K., et al. (författare)
  • Synthesis of supported silver nano-spheres on zinc oxide nanorods for visible light photocatalytic applications
  • 2015
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 63, s. 134-140
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the synthesis of silver (Ag) nano-spheres (NS) supported on zinc oxide (ZnO) nanorods through two step mechanism, using open vessel microwave reactor. Direct reduction of ZnO from zinc nitrates was followed by deposition precipitation of the silver on the ZnO nanorods. The supported Ag/ZnO nanoparticles were then characterized by electron microscopy, X-ray diffraction, FTIR, photoluminescence and UV-vis spectroscopy. The visible light photocatalytic activity of Ag/ZnO system was investigated using a test contaminant, methylene blue (MB). Almost complete removal of MB in about 60 min for doses higher than 0.5 g/L of the Ag/ZnO photocatalyst was achieved. This significant improvement in the photocatalytic efficiency of Ag/ZnO photocatalyst under visible light irradiation can be attributed to the presence of Ag nanoparticles on the ZnO nanoparticles which greatly enhances absorption in the visible range of solar spectrum enabled by surface plasmon resonance effect from Ag nanoparticles.
  •  
35.
  • Seed Ahmed, H. A. A., et al. (författare)
  • Concentration quenching of Eu2+ doped Ca2BO3Cl
  • 2016
  • Ingår i: Materials research bulletin. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0025-5408 .- 1873-4227. ; 75, s. 47-50
  • Tidskriftsartikel (refereegranskat)abstract
    • With the aim of determining the concentration quenching mechanism of Eu2+ doped Ca2BO3Cl, a series of phosphors with a varied Eu2+ concentration (Ca2-xBO3Cl:xEu(2+)) was synthesized by the solid state reaction method. The phase structure was determined by X-ray diffraction. Photoluminescence (PL) measurements showed broad excitation and emission signatures of the allowed f-d transition of Eu2+ ions. The PL emission intensity was found to be increased by increasing the concentration of Eu2+ ions up to x=0.03 and then decreased as a result of the concentration quenching effect. The lifetime of the emission from the Eu2+ ions was measured and the decrease in the lifetime with increasing Eu2+ concentration confirmed that non-radiative energy transfer occurred between Eu2+ ions. From the luminescence data, the value of the critical transfer distance was calculated as 1.5 nm and the corresponding concentration quenching mechanism was verified to be a dipole-dipole interaction. (C) 2015 Elsevier Ltd. All rights reserved.
  •  
36.
  • Shafiu, S., et al. (författare)
  • Facile synthesis of PVA-MnFe2O4 nanocomposite : Its magnetic investigation
  • 2013
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 48:10, s. 4066-4071
  • Tidskriftsartikel (refereegranskat)abstract
    • Manganese ferrite (MnFe2O4)-polyvinyl alcohol (PVA) nanocomposite was prepared by a PVA assisted sot-gel auto-combustion method. The magnetic core of the carriers was manganese ferrite (MnFe2O4), with average crystallite size of 9.1 +/- 2.1 nm. The PVA-MnFe2O4 nanocomposite exhibited superparamagnetic behavior at room temperature and ferromagnetic behavior at low temperatures. Zero-field-cooled and field-cooled measurements further confirm the superparamagnetic behavior with a blocking temperature of 160 K. The lower reduced remanent magnetization values than theoretical value of 0.5 indicate that the PVA/MnFe2O4 nanocomposite used in this study has uniaxial anisotropy rather than the expected cubic anisotropy according to the Stoner-Wohlfarth model. The calculated magnetic anisotropy constant of the sample is similar to 1.45 x 10(6) erg/cm(3) which is significantly higher than that of the bulk MnFe2O4 due to the strong magnetic coupling between magnetic core and surface spins.
  •  
37.
  • Shtender, Vitalii, et al. (författare)
  • Impact of the R and Mg on the structural, hydrogenation and magnetic properties of R3-xMgxCo9 (R = Pr, Nd, Tb and Y) compounds
  • 2022
  • Ingår i: Materials research bulletin. - : Elsevier. - 0025-5408 .- 1873-4227. ; 156
  • Tidskriftsartikel (refereegranskat)abstract
    • R2MgCo9 (R = Pr, Nd, Tb and Y) compounds have been synthesized by a powder sintering method and the corresponding hydrides have been prepared by a solid gas method. Their crystal structures and magnetic properties have been systematically studied. X-ray diffraction analysis showed that all R2MgCo9 compounds belong to the PuNi3-type structure. The elements Tb, Y, Nd, Pr yield a lowering of the equilibrium pressure which correlates well with the increase in cell volume. The R2MgCo9H(D)x (R = Pr, Nd, Tb and Y; (9.4 <= x <= 12)) hydrides (deuterides) preserve the PuNi3-type structure with hydrogenation-induced volume expansion ranging from 14.7 to 19.6%. The substitution of deuterium for hydrogen in R2MgCo9-(H,D)(2) (R = Tb and Y) prevents fast desorption at room temperature and ambient pressure. As for the magnetic properties, all the studied interme-tallic compounds show ferromagnetic or ferrimagnetic behavior, and in some cases a temperature dependent spin reorientation. Hydrogen insertion reduces the magnetization and decreases the magnetic ordering temperature (TC), whereas Mg for R substitution increases TC.
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38.
  • Svensson, Gunnar, 1960-, et al. (författare)
  • Synthesis and characterisation of the novel double perovskites La2CrB2/3Nb1/3O6, B = Mg, Ni, Cu
  • 2012
  • Ingår i: Materials Research Bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:9, s. 2449-2454
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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39.
  • Wang, Cao, et al. (författare)
  • Transparent polycrystalline ruby ceramic by spark plasma sintering
  • 2010
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 45:9, s. 1127-1131
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
40.
  • Wang, Dandan, et al. (författare)
  • Ultrafast carrier dynamics of near-band-edge emission in single-crystal ZnO nanorods
  • 2011
  • Ingår i: Materials research bulletin. - : Elsevier Science B.V., Amsterdam.. - 0025-5408 .- 1873-4227. ; 46:6, s. 937-940
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on rational synthesis and optical characteristics of highly crystallined ZnO nanorods which were grown by a facile chemical vapor transport method. Temperature-dependent photoluminescence spectra of as-fabricated ZnO nanorods are dominated by near-band-edge emission with a characteristic fine structure due to high crystallinity. Furthermore, the recombination emission involving carrier dynamics of near-band-edge emission in ZnO nanorods was systematically investigated by temperature-dependent time-resolved photoluminescence spectroscopy. Recombination peaks pertaining to the exciton emissions are monitored and resolved in both temporal and spatial regimes.
  •  
41.
  • Yao, Wenjun, et al. (författare)
  • Solid-State Synthesis of Li4Ti5O12 Whiskers from TiO2-B
  • 2016
  • Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 75, s. 204-210
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, Li4Ti5O12 (LTO) was synthesized from the precursors of TiO2-B and anatase whiskers, respectively. The synthesized LTO whiskers from TiO2-B whiskers via a solid state reaction at 650 °C have a high degree of crystallinity with an average diameter of 300 nm. However, when anatase whiskers were used as the precursor, only particle morphology LTO was produced at 750 °C. The further analysis of the precursors, the intermediate products and the final products reveal that the crystal structure of the anatase hinders the diffusion of lithium, leading to a typical reaction-diffusion process. Under this condition, only particle morphology LTO can be produced. However, the crystal structure of the TiO2-B is easy for lithium diffusion and the process is performed in two separated steps (i.e. diffusion and reaction), which makes it possible to decrease the solid-state reaction temperature down to 650 °C and then maintain the morphologies of whiskers.
  •  
42.
  • Azad, A.K., et al. (författare)
  • Structural and magnetic properties of LaFe0.5Cr0.5O3 studied by neutron diffraction, electron diffraction and magnetometry
  • 2005
  • Ingår i: Materials Research Bulletin. - 0025-5408. ; 40(10), s. 1633-1644
  • Tidskriftsartikel (refereegranskat)abstract
    • The structural and magnetic properties of the perovskite type compound LaFe0.5Cr0.5O3 have been studied by temperature dependent neutron powder diffraction and magnetization measurements. Rietveld refinement of the neutron diffraction data shows that the compound crystallizes in an orthorhombic perovskite structure with a random positioning of the Fe and Cr cations at the B sublattice. The magnetic structure at 10 K is a collinear antiferromagnetic one with the magnetic moment per site being equal to 2.79(4) mu(B). Magnetisation measurements confirm the overall antiferromagnetic behaviour. Moreover, it indicates a weak uncompensated magnetic moment close to the transition temperature T-N approximate to 265 K. This moment can be described by a magnetic cluster state, which remains up to 550 K. Electron diffraction patterns along with high-resolution transmission electron microscopy images reveal that the crystallites are composed by domains of different orientation, which share the same cubic perovskite sub-cell reflections. (C) 2005 Elsevier Ltd. All rights reserved
  •  
43.
  • Azad, A. K., et al. (författare)
  • Structural, magnetic and electrochemical characterization of La(0.83)A(0.17)Fe(0.5)Cr(0.5)O(3-delta) (A = Ba, Ca) perovskites
  • 2009
  • Ingår i: Materials Research Bulletin. - : Elsevier BV. - 0025-5408. ; 44:7, s. 1451-1457
  • Tidskriftsartikel (refereegranskat)abstract
    • The structural, magnetic and electrical properties of the perovskite-type compound La(0.83)A(0.17)Fe(0.5)Cr(0.5)O(3-delta) (A = Ba, Ca) have been investigated by neutron diffraction, magnetization measurements and conductivity measurements. Rietveld refinement of X-ray and neutron diffraction data shows that the compound adopts an orthorhombic crystal structure with Pbnm symmetry with a random positioning of the iron and chromium cations on the B sublattice. The magnetic structures at 10 K are collinear antiferromagnetic with the magnetic moment per site being equal to 2.91(2)mu(B) (for Ba) and 3.05(2)mu(B) (for Ca). Magnetization measurements confirm the overall antiferromagnetic behavior. The magnetic structure is based Oil a unit cell related to that of the nuclear structure and the magnetic cell can be considered the same as nuclear cell. Barium doped samples show lower oxygen deficiency and higher conductivity than calcium doped samples. At low oxygen pressure, both compounds show p-type electronic conduction. (c) 2009 Elsevier Ltd. All rights reserved.
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44.
  •  
45.
  • Azad, AK, et al. (författare)
  • Nuclear and magnetic structure of Ca2MnWO6: A neutron powder diffraction study
  • 2001
  • Ingår i: MATERIALS RESEARCH BULLETIN. - 0025-5408. ; 36:13-14, s. 2485-2496
  • Tidskriftsartikel (refereegranskat)abstract
    • The nuclear and magnetic structures of the double provskite compound Ca2MnWO6 have been determined by neutron powder diffraction. Rietveld refinement shows that the compound adopts a monoclinic crystal structure with P2(1)/n symmetry. Magnetic refinement
  •  
46.
  • Azad, AK, et al. (författare)
  • Synthesis, crystal structure, and magnetic characterization of the double perovskite Ba2MnWO6
  • 2001
  • Ingår i: MATERIALS RESEARCH BULLETIN. - 0025-5408. ; 36:12, s. 2215-2228
  • Tidskriftsartikel (refereegranskat)abstract
    • The double perovskite Ba2MnWO6 has been prepared as a pure powder by a conventional solid-state reaction process and studied by X-ray, neutron powder diffraction (NPD), magnetization, and AC susceptibility measurements. NPD, magnetization, and AC suscepti
  •  
47.
  • Eriksson, Annika, 1975, et al. (författare)
  • High temperature phase transition of the magnetoelectric double perovskite Sr2NiMoO6 by neutron diffraction
  • 2006
  • Ingår i: Materials Research Bulletin. - 0025-5408. ; 41, s. 144-157
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetic ferroelectric double perovskite Sr2NiMoO6 has been characterised using neutron powder diffraction (NPD) data and magnetic susceptibility measurements. High temperature NPD data indicate that the material undergoes a continuous structural phase transition from tetragonal (I4/m) to cubic (Fm(3) over barm) at approximately 550 K. The transition is linked to the level of rotation of the NiO6 and MoO6 octahedra, which form perfectly segregated sub-lattices in the material. The reduction in symmetry at 550 K is linked to the onset of a spontaneous dipole in the material allowing the structural perturbation to be described as an improper ferroelectric phase transition. The appearance of low angle reflections in the 20 K dataset indicates the presence of an antiferromagnetic ordered around state. The magnetic moment was refined to 1.88(8) mu(B) confirming that the magnetism originates from the Ni2+ (S = 1) ions. (C) 2005 Elsevier Ltd. All rights reserved.
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48.
  • Eriksson, Annika, 1975, et al. (författare)
  • Phase stability study of Bi0.15Sr0.85-xAexCoO3-δ (x = 0 and Ae = Ba0.28; Ca0.17) perovskites by in-situ neutron diffraction
  • 2010
  • Ingår i: Materials Research Bulletin. - : Elsevier BV. - 0025-5408. ; 45:12, s. 1875-1882
  • Tidskriftsartikel (refereegranskat)abstract
    • The oxygen deficient perovskites, Bi0.15Sr0.85-xAexCoO3-δ, x = 0 and Aex = Ba0.28, Ca0.17, were studied with in-situ neutron powder diffraction and combined TGA/DSC in order to investigate their behaviour at elevated temperatures in oxidising conditions. The phase stability of the I4/mmm supercell structure adopted by Bi0.15Sr0.85CoO3-δ is shown to be dependent on temperature and the oxygen content of the phase, with three structural events, at T 250, 590 and 880 °C, detected. The first transition occurs as the perovskite supercell vanishes due to oxygen absorption; the second transition is also associated with oxidation and involves the decomposition of the perovskite phase via an exothermic process to yield a dominant hexagonal phase. Finally, at T 900 °C the perovskite phase re-forms. For the Ba and Ca containing materials the decomposition to the hexagonal phase occurs at T 600 °C and 650 °C respectively. The presence of Ca at the A-site is found to stabilise the I4/mmm supercell structure in the range RT - 650 °C. The antiferromagnetic to paramagnetic transitions occur at TN 250 °C, TN 175 °C and TN 145 °C for the samples with Aex = Ba0.28, x = 0 and Aex = Ca0.17, respectively.
  •  
49.
  • Eriksson, G, et al. (författare)
  • The reduction of Co2+ by polyalcohols in the presence of WC surfaces studied by XPS
  • 1997
  • Ingår i: MATERIALS RESEARCH BULLETIN. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0025-5408. ; 32:5, s. 491-499
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Cemented carbides, widely used in cutting tools, are made by sintering fine particles of WC and Co. So far the production of the sintering material has utilized a time and energy consuming grinding and mixing step. An alternative process to chemically pre
  •  
50.
  • Gheitaghy, Amir Mirza, et al. (författare)
  • Infrared absorbance of vertically-aligned multi-walled CNT forest as a function of synthesis temperature and time
  • 2020
  • Ingår i: Materials Research Bulletin. - : Elsevier BV. - 0025-5408. ; 126
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the growth of optimized vertically aligned multi-walled carbon nanotube (VA-MWCNT) forests by LPCVD method for use in a large-area absorber in infrared detectors is presented. The effect of synthesis temperature (500−700 °C) and time (1−10 min) on the optical absorption coefficient in the infrared (2−20 μm) is investigated by FT-IR measurement at various incident angles (15-80°). The structural properties of VA-MWCNT are characterized by SEM, TEM and Raman spectroscopy. Spectral measurements show an increasing absorption with the height of the forest that results at increased synthesis time and temperature. However, the absorption coefficient decreases with increasing synthesize time and temperature, while it is also affected by other properties, such as diameter, density, alignment, and uniformity. Moreover, the reduction in absorption at oblique incident angles demonstrates the relevance of surface properties. Finally, a circular graphite waveguide system is used to model the absorption characteristics of an MWCNT forest.
  •  
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