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- Title
Structural Assessment of Fluorine, Chlorine, Bromine, Iodine, and Hydroxide Substitutions in Lead Arsenate Apatites (Mimetites)–Pb5(AsO4)3X.
- Authors
Sordyl, Julia; Puzio, Bartosz; Manecki, Maciej; Borkiewicz, Olaf; Topolska, Justyna; Zelek-Pogudz, Sylwia
- Abstract
Five lead-arsenate apatites (mimetites)-Pb5(AsO4)3X—where X denotes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and hydroxide (OH)—were synthesized via precipitation from aqueous solutions. The crystal structures were determined through Rietveld refinement of powder synchrotron X-ray data. All the compounds crystallized in the hexagonal class symmetry (space group P63/m). The Rietveld refinement indicated that mimetite-Cl, -Br, -I, and -OH had an anion deficiency at position X. Substitution of halogens in a mimetite structure brought about systematic changes in unit-cell parameters, interatomic distances, and metaprism twist angles φ, proportional to the substituted halogen's ionic radius. Mimetite-OH did not follow the linear correlations determined within the series. Twist angle φ, a useful device for monitoring changes in apatite topology, ranged from 20.34° for mimetite-F to 11.42° for mimetite-I. The geometric method has been proposed for determining the diameter of hexagonal channels hosting halogens in apatites. A comparison of the results with halogenated pyromorphites showed similar systematic trends: the substitutions in mimetites have comparable effect on the interatomic distances as in their phosphorous analogues.
- Subjects
APATITE; BROMINE; CHLORINE; FLUORINE; IODINE; RIETVELD refinement; INTERATOMIC distances
- Publication
Minerals (2075-163X), 2020, Vol 10, Issue 6, p494
- ISSN
2075-163X
- Publication type
Article
- DOI
10.3390/min10060494