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  • Electronic Resource  (5)
  • 1980-1984  (5)
  • 1983  (5)
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  • Electronic Resource  (5)
Years
  • 1980-1984  (5)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Crystal-structure refinement by profile fitting and least-squares analysis of powder diffractometer data (1983)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 16 (1983), S. 611-622 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The refinement of crystal structures using X-ray powder data in a two-stage method is described. (1) The integrated intensities of the individual reflections are derived by a profile fitting method in which the profile shapes are accurately defined using an experimentally determined instrument function and the sum of Lorentzian curves. (2) These values are then used in a powder least-squares refinement for structure determination. The results obtained with three simple structures (silicon, quartz and corundum) gave R(Bragg) values of 0.7 to 2.5%. The necessity of correcting for preferred orientation and the importance of proper specimen preparation are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889883011176
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  • 2
    Electronic Resource
    Electronic Resource
    The chemical bonding in lithium metaborate, LiBO2. Charge densities and electrostatic properties (1983)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 175-185 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768183002256
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  • 3
    Electronic Resource
    Electronic Resource
    The nature of the chemical bonding in boron carbide. IV. Electronic band structure of boron carbide, B13C2, and three models of the structure B12C3 (1983)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 324-329 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768183002487
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  • 4
    Electronic Resource
    Electronic Resource
    The crystal structure of reinhardbraunsite, Ca5(SiO4)2(OH,F)2, a new mineral of the calcio-chondrodite type (1983)
    Springer
    Mineralogy and petrology 31 (1983), S. 137-150 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Die Kristallstruktur von Reinhardbraunsit, Ca5(SiO4)2(OH,F)2, wurde mit Diffraktometerdaten bestimmt und bis zuR=0.033 für 1585 unabhängige Reflexe verfeinert. Reinhardbraunsit kristallisiert monoklin,P21/a, mita=11.458(2),b=5.052(1),c=8.840(1) Å, β=108.91(1)o,Z=2. Die Struktur ist der von synthetischem Calcio-Chondrodit, Ca5(SiO4)2(OH)2, sehr ähnlich. Durch den teilweisen Ersatz von OH durch F sind, das SiO4-Tetraeder ausgenommen, alle mittleren Kation-Anion- und Anion-Anion-Abstände leicht verkürzt. Ein Vergleich der Mg-, Mn- und Ca-Glieder der Chondroditgruppe zeigt eine lineare Abhängigkeit der mittleren M-O-Abstände und der Zell-Volumina von den effektiven Ionenradien. Die Verzerrungen der Kationpolyeder sind ebenfalls annähernd linear abhängig von den mittleren M-O-Abständen.
    Notes: Summary The crystal structure of reinhardbraunsite, Ca5(SiO4)2(OH,F)2, was determined from diffractometer data and refined toR=0.033 for 1585 independent reflections. Reinhardbraunsite crystallizes monoclinic,P21/a, witha=11.458(2),b=5.052(1),c=8.840(2) Å, β=108.91(1)o,Z=2. The structure is very similar to the structure of synthetic calciochondrodite, Ca5(SiO4)2(OH)2. Except of the SiO4 tetrahedron all mean cation-anion and anion-anion distances are slightly decreased due to the partial replacement of OH by F. A comparison of the Mg, Mn and Ca members of the chondrodite group shows that mean M-O distances and cell volumes are linearly related to the effective ionic radii. Polyhedral distortions are also approximately linearly related to the mean M-O distances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01084766
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  • 5
    Electronic Resource
    Electronic Resource
    Untersuchungen zur Elektronendichteverteilung im Dolomit CaMg(CO3)2 (1983)
    Springer
    Mineralogy and petrology 31 (1983), S. 151-164 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Summary Studies of the electron density distribution of dolomite, CaMg(CO3)2 (a hex =4.808(1) Å,c hex =16.022(3) Å, space group $$R\bar 3$$ ,Z=3) were carried out on natural material by X-ray diffraction (810 symmetry independent reflexions with sin ϑ/λ⩽1.180 Å−1 andI 〉 2.5 σ I ) as well as by neutron diffraction (684 symmetry independent reflexions with sin ϑ/λ⩽1.085 Å−1 andI 〉 2.5 σ I ).The conventional structure refinement coverged atR(X)=0.018 (R w (X)=0.022) andR(N)=0.030 (R w (N)=0.034) respectively. Dynamic deformation densitiesF o (X)−F c HO (X) andF o (X)−F c (N) difference Fourier summations were used for the interpretation of the electron density distribution. Additionally static deformation densities were calculated from the parameters of a multipole model refinement (Hirshfeld, 1971). Close to the middle of the C−O bond there is a maximum of the electron density; two other maxima are observed in the lone-pair region of the O atom. It seems that the Mg atoms have a more polarising effect compared with the Ca atoms.
    Notes: Zusammenfassung Die Untersuchungen der Elektronendichteverteilung im Dolomit, CaMg(CO3)2, (a hex =4,808(1) Å,c hex =16,022(3) Å, Raumgruppe $$R\bar 3$$ ,Z=3) erfolgten an natürlichem Material mit Röntgenbeugung (810 symmetrieunabhängige Reflexe mit sin ϑ/λ⩽1,180 Å−1 undI 〉 2,5 σ I ) sowie Neutronenbeugung (684 symmetrieunabhängige Reflexe mit sin ϑ/λ⩽1,085 Å−1 undI 〉 2,5 σ I ).Die konventionelle Strukturverfeinerung konvergierte beiR(X)=0,018 (R w (X)=0,022) bzw.R(N)=0,030 (R w (N)=0,034). Dynamische DeformationsdichtenF o (X)−F c HO (X) undF o (X)−F c (N) Differenzfouriersummationen wurden zur Interpretation der Elektronendichteverteilung herangezogen. Weiters wurden statische Deformationsdichten aus den Parametern einer Verfeinerung mit dem Multipol-Modell (Hirshfeld, 1971) berechnet. Nahe dem Mittelpunkt der C-O-Bindung liegt ein Maximum der Elektronendichte; zwei weitere liegen in den “lone-pair”-Bereichen des O-Atoms. Die Mg-Atome scheinen eine im Vergleich mit den Ca-Atomen stärker polarisierende Wirkung auf das O-Atom zu haben.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01084767
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