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  • 1
    Electronic Resource
    Electronic Resource
    X-ray Rietveld Analysis with a Physically Based Background (1995)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 28 (1995), S. 115-120 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: On the basis of known equations for calculating X-ray diffraction intensities from a given number of unit cells of a crystal phase in polycrystalline material, as due to: (i) Bragg reflections; (ii) average diffuse scattering caused by thermal plus first-kind disorder; and (iii) incoherent scattering, a relationship has been found that ties, in the Rietveld analysis, the Bragg scale factor to a scale factor for `disorder' as well as incoherent scattering. Instead of fitting the background with a polynomial function, it becomes possible to describe the background by physically based equations. Air scattering is included in the background simulation. By this means, the refinement can be carried out with fewer parameters (six fewer than when a fifth-order polynomial is used). The DBWS-9006PC computer program written by Sakthivel & Young [(1990), Georgia Institute of Technology, Atlanta, GA, USA] has been modified to follow this approach and it has been used to refine the crystal structures of the cubic form of Y2O3 and of α-Al2O3. Peak asymmetry has been described by a function based on an exponential approximation. The results from refinements using polynomial physically based background function are, in terms of final structural parameters and reliability indices, very close to each other and in agreement with results reported in the literature. The reconstruction and optimization of the background scattering by means of physically based equations helps the implementation in the Rietveld code of other possible specific diffuse scattering contributions, such as that due to an amorphous phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188989401037X
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  • 2
    Electronic Resource
    Electronic Resource
    Stabilization of cubic Na-modified ZrO2: a neutron diffraction study (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 32 (1999), S. 475-480 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Neutron diffraction patterns, collected at room temperature and, with in situ thermal treatment, from 981 to 1173 K, on a zirconia sample containing 3 wt% of sodium, show the presence and the stability of the cubic form of zirconia from 298 to 1073 K. The analysis has also demonstrated the presence of a significant amount of the tetragonal form of zirconia, which cannot be clearly detected using conventional X-ray diffraction. We report and discuss the Rietveld refinements performed on the samples, analysed at 298 and at 981 K. The cubic form appears to be stabilized by the incorporation of sodium ions, which randomly replace the zirconium ions, thus forming a substitutional solid solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889899002344
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  • 3
    Electronic Resource
    Electronic Resource
    Scale Factor in Powder Diffraction (1998)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 219-224 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In this paper, a simple method of obtaining the scale factor that transforms powder intensities from arbitrary units into electron units is proposed. This method, which is suitable for diffraction data collected from polycrystalline single-phase specimens, without fluorescence and preferred-orientation effects, obtains the scale factor analyzing the global scattered intensity in the reciprocal space without the necessity for the peak–background separation. Once the scale factor is found, it is possible to estimate the overall thermal parameter and to trace a physically based background line which is useful in extracting accurate structure factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876739701324X
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  • 4
    Electronic Resource
    Electronic Resource
    Determining the Degree of Crystallinity in Semicrystalline Materials by means of the Rietveld Analysis (1995)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 28 (1995), S. 121-126 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Rietveld analysis has enabled a determination, by an internal approach, of the degree of crystallinity of a sample of polyethylene terephthalate (PET) and three samples of zirconium oxide obtained by precipitation from ZrOCl2 followed by crystallization at a different temperature. After subtraction of the air scattering, a global diffuse scattering produced by the amorphous phase, by the thermal and lattice disorder and, lastly, by the incoherent or Compton scattering, was built up in the frame of the DBWS-9006PC computer program written by Sakthivel & Young [(1990), Georgia Institute of Technology, Atlanta, GA, USA], modified as described by Riello, Fagherazzi, Clemente & Canton [J. Appl. Cryst. (1995), 28, 115–120]. All these contributions (and the corresponding scale factors) were simultaneously optimized, together with the crystalline peak profiles. On the basis of the modified Rietveld analysis, an equation has been suggested that calculates the degree of crystallinity. The value found in the examined PET sample is very close to that already calculated [Polizzi, Fagherazzi, Benedetti, Battagliarin & Asano (1990). J. Appl. Cryst. 23, 359–365] with a nonstructural fitting procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889894010381
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  • 5
    Electronic Resource
    Electronic Resource
    Quantitative Phase Analysis in Semicrystalline Materials Using the Rietveld Method (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 78-82 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new procedure to perform quantitative analysis without any internal standard has been developed within Rietveld analysis. This new approach permits solution of the problem due to the presence of an amorphous phase when its chemical composition or the global sample composition is known. The equations developed, based on a study of the global intensities diffracted by each phase in reciprocal space, reduce to the well known formula of Hill & Howard [J. Appl. Cryst. (1987), 20, 467–474] when applied to completely crystalline materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889897009631
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  • 6
    Electronic Resource
    Electronic Resource
    Detecting palladium nanoparticles in Pd/C catalysts using X‐ray Rietveld method (2000)
    Springer
    Catalysis letters 64 (2000), S. 119-124 
    Details
    ISSN: 1572-879X
    Keywords: Pd/C catalysts ; nanostructural features ; nanoparticles ; nanoclusters ; X‐ray diffraction ; Rietveld analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This study uses X‐ray diffraction (XRD) techniques to investigate the nanostructural features of a series of four Pd/C catalysts, which had the same load, 0.51 ± 0.02 wt%, as palladium, with significantly different dispersions, obtained by applying different temperature ageings up to 873 K. By means of a Rietveld refinement, performed using a special fitting procedure, which takes into account the various contributions to the background scattering, the palladium fraction due to nanoparticles or clusters smaller than about 20–25 Å could be determined. We have compared this Rietveld (absolute) quantitative method with a simpler, but less precise, single‐peak (relative) XRD analysis, interesting for fast industrial applications. The Pd fractions due to nanoparticles, as determined by the two methods, are close each other for all samples investigated, apart from one for which the disagreement is near 20%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019080213448
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  • 7
    Electronic Resource
    Electronic Resource
    In situ wide angle X-ray scattering (WAXS) study of bimetallic Au–Pd catalysts (2000)
    Springer
    Catalysis letters 69 (2000), S. 17-20 
    Details
    ISSN: 1572-879X
    Keywords: X-ray diffraction ; gold ; palladium ; bimetallic catalysts ; metal alloy ; microstructure ; Rietveld method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Aim of the paper is to apply a modified version of the Rietveld method to two Au–Pd/C catalysts prepared by successive impregnation and reduced in situ by a special holder in order to show that a suitable WAXS analysis, performed in routine lab and using an X-ray conventional generator, can be very detailed and rich of information especially when a bimetallic catalyst has to be considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019080714240
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of Nanoporous Lanthanide-Doped YAG Powders Obtained by Propellant Synthesis (2004)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 453-454 (May 2004), p. 251-256 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/08/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.453-454.251.pdf
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  • 9
    Electronic Resource
    Electronic Resource
    Characterization of Nanoporous Lanthanide-Doped Gadolinium Gallium Garnet Powders Obtained by Propellant Synthesis (2005)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 494 (Sept. 2005), p. 143-148 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In the present work we study the nanocrystalline powders of lanthanide-dopedGd3Ga5O12 (GGG, gadolinium gallium garnet) prepared using propellant synthesis. A series of GGG samples containing a number of different trivalent lanthanide ions (Tm, Er, Ho, Eu, Sm, Nd, and Pr) in different quantities (1%, 5%, 10%) were produced. Samples were characterized by X-ray diffraction (pre- and post calcination) for phase identification and line-broadening analysis, and byelectron microscopy (SEM and TEM) for morphological and nanostructural investigation. Thermal behavior of the powder was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The samples have a polycrystalline porous structure. Elemental microanalysis made by energy dispersive X-ray spectroscopy (EDX) detector attached to TEM andXRD unit-cell determinations confirmed that the lanthanides ions entered the structure of GGG. Crystallites have a high degree of disorder
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/10/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.494.143.pdf
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  • 10
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    Ultracool white dwarfs and the age of the Galactic disc (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-12
    Description: We present parallax observations and a detailed model atmosphere analysis of 54 cool and ultracool ( T eff  〈 4000 K) white dwarfs (WDs) in the solar neighbourhood. For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21 pc to 〉100 pc, and include five stars within 30 pc. Contrary to expectations, all but two of them have tangential velocities smaller than 150 km s –1 thus suggesting Galactic disc membership. The oldest WDs in this sample have WD cooling ages of 10 Gyr, providing a firm lower limit to the age of the thick disc population. Many of our targets have uncharacteristically large radii, indicating that they are low-mass WDs. It appears that we have detected the brighter population of cool and ultracool WDs near the Sun. The fainter population of ultracool CO-core WDs remain to be discovered in large numbers. The Large Synoptic Survey Telescope should find these elusive, more massive ultracool WDs in the solar neighbourhood.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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