| 1. |
- Dyachenko, O G, et al.
(author)
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Structure and properties of Ba6 − xLnxNb10O30, Ln = La, Ce and Nd compounds
- 1997
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In: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 32:4, s. 409-419
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Journal article (peer-reviewed)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.
(author)
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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
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In: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 29:7, s. 801-809
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Journal article (peer-reviewed)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.
(author)
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SYNTHESIS AND CHARACTERIZATION OF REDUCED NIOBATES [SR1-XLNXNB2O6, LN=LA, ND]
- 1994
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In: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 29, s. 743-749
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Journal article (peer-reviewed)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.
(author)
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Synthesis and characterization of reduced niobates CaLnNb2O7, Ln = Y, Nd with a pyrochlore structure
- 1997
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In: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 32:4, s. 421-430
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Journal article (peer-reviewed)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.
(author)
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Synthesis and characterization of the reduced niobates CaLnNb2O7, Ln = La-Pr, Sm, Gd-Lu, with the pyrochlore-type structure
- 1998
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In: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 33, s. 1251-1256
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Journal article (peer-reviewed)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.
(author)
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A study on the preparation and properties of fibrillar boehmite
- 1986
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In: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 21:10, s. 1159-1166
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Journal article (peer-reviewed)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.
(author)
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Phases in the Mn-Nb-N-O system, formed by ammonolysis of mixtures of Mn acetate tetrahydrate and a Nb xerogel
- 1998
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In: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 33:7, s. 1035-1044
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Journal article (peer-reviewed)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
(author)
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Proton and oxygen ion conduction in nonoxide ceramics
- 2000
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In: Materials research bulletin. - 0025-5408 .- 1873-4227. ; 35:1, s. 47-52
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Journal article (peer-reviewed)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.
(author)
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Application of Eh-pH diagram for room temperature precipitation of zinc stannate microcubes in an aqueous media
- 2014
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In: Materials research bulletin. - : Elsevier. - 0025-5408 .- 1873-4227. ; 49:1, s. 645-650
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Journal article (peer-reviewed)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. |
- Azad, A.K., et al.
(author)
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Structural and magnetic properties of LaFe0.5Cr0.5O3 studied by neutron diffraction, electron diffraction and magnetometry
- 2005
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In: Materials Research Bulletin. - 0025-5408. ; 40(10), s. 1633-1644
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Journal article (peer-reviewed)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
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