1,721,041 research outputs found
Order-disorder, Polytypes and Twinning in the Crystal Structure of vurroite
No full textVurroite, ideally Pb20Sn2(Bi,As)22S54Cl6, is a complex mineral type, where the two minor chemical components, Sn and Cl, act as essential constituents together with Pb, Bi, As and S 1, 2. X-ray single crystal data on vurroite strongly indicate an orthorhombic Fcentred symmetry 1, 3. In this study the crystal structure of vurroite is interpreted as an OD structure belonging to the category III of OD structures composed of equivalent layers 4. The application of the OD procedures allowed the derivation of the OD-groupoid family (λ and σ operations), as well as the MDO (Maximum Degree of Order) structures. The layer symmetry (λ) is A(2)mm, the interlayer symmetry (σ) consists of a glide plane n1/2,1/2 and two-fold screw axes parallel to 010 and 001 with the translation components 1⁄4 b and 1⁄4 c, respectively. For this OD family two MDO polytypes exists. The former has monoclinic symmetry, C12/c1, whereas the latter is monoclinic, P12/c1. The OD treatment of the crystal structure of vurroite allowed to prove that the true symmetry of this mineral is monoclinic and that the apparent orthorhombic symmetry observed for the X-ray pattern of the measured crystal is due to a twinning phenomenon. Prof. S. Merlino is gratefully acknowledged for his contribution on the OD interpretation of the structure of vurroite. 1 Pinto D., PhD thesis, University of Bari, 2004, 165. 2 Garavelli A.,Mozgova N.N., Orlandi P., Bonaccorsi E., Pinto D., Borodaev Y., Canadian Mineralogist, 2005, in press. 3 Pinto D., Balić-Žunić T., Bonaccorsi E., Makovicky E., 26th Nordic Geological Winter Meeting, Uppsala, Sweden,2004, 106-107, abstract. 4 Dornberger-Schiff K., Abh. Dtsch. Akad. Wiss. Berlin. Kl. Chem. Geol. Biol., 1964, 3, 1-107
Description of phase V as a combination of modules from pavonite and lillianite homologous series
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The crystal structure of vurroite, Pb20Sn2(Bi,As)22S54Cl6: OD-character, polytypism, twinning and modular description
No full textStructural investigation on the Ag-free lillianite from Vulcano (Aeolian Island, southern Italy)
No full textStructural investigations on natural Ag-free lillianite and galenobismutite samples. A comparative study
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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