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Rietveld refinement of site‐occupancy parameters of Mg 2− x Mn x SiO 4 using a new weight function in least‐squares fitting
Author(s) -
Yamazaki S.,
Toraya H.
Publication year - 1999
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889898010206
Subject(s) - rietveld refinement , octahedron , crystallography , olivine , chemistry , crystal structure , analytical chemistry (journal) , crystal (programming language) , mineralogy , computer science , programming language , chromatography
The crystal structures of olivine‐type MgMn x SiO 4 ( x = 0, 1, 1.4 and 2) were refined using high‐resolution synchrotron radiation data and the Rietveld method, adopting the new weight function with the form ( Y o is the observed profile intensity) [Toraya (1998). J. Appl. Cryst. 31 , 333–343]. Positional parameters were accurately determined by optimizing e in . Derived structures were in accordance with observations on olivine structures, having a constant tetrahedral Si–O distance and octahedral metal–oxygen distances which increase linearly on substitution of octahedral atoms with those having larger atomic radii. Site‐occupancy parameters of octahedral atoms were refined under various refinement conditions and could be determined within ±1.2% under the constraint of chemical composition. Deviations of x from assumed chemical compositions, when the site‐occupancy parameters were refined without the constraint, were 1.0–3.5% using the new weight function; they are comparable with values obtained in single‐crystal studies on Mg–Fe olivine (0.5–2.7%). The use of atomic scattering factors for fully ionized atoms gave better site‐occupancy parameters, by 0.1–2.5%, than those for neutral atoms in the present analysis.