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M1-site occupancy in 3T and 2M (sub 1) phengites by low temperature neutron powder diffraction; reality or artefact?

Alessandro Pavese, Giovanni Ferraris, Vittoria Pischedda and Francois Fauth
M1-site occupancy in 3T and 2M (sub 1) phengites by low temperature neutron powder diffraction; reality or artefact? (in Mica 2000, Annibale Mottana (prefacer) and Paolo Francesco Sassi (prefacer))
European Journal of Mineralogy (December 2001) 13 (6): 1071-1078

Abstract

Two low temperature (15 K) neutron powder diffraction data sets from 2M (sub 1) and 3T phengite samples were collected on the D2B beamline at ILL (Grenoble, France), to investigate the cation ordering and the occurrence of fractional occupants at the M1-site. Low temperature has been used in order to reduce the thermal motion. The complexity of this study poses problems to properly quantify our results, but on the basis of the issues from several refinement schemes we obtained indications in favour of occupancy factors other than zero for the formally empty in dioctahedral micas M1-sites (roughly nearly equal 0.12 and nearly equal 0.18 atom per M1-site, in case of 2M (sub 1) and 3T polytype, respectively). The atomic displacement parameters, and the large uncertainties upon the M1-O bond lengths, suggest the large M1 site to be positionally disordered in both polytypes. These results are to be taken up with due care as stacking faults resulting in staggering of the TOT layers might mimic a fictitious M1 site occupancy.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 13
Serial Issue: 6
Title: M1-site occupancy in 3T and 2M (sub 1) phengites by low temperature neutron powder diffraction; reality or artefact?
Title: Mica 2000
Author(s): Pavese, AlessandroFerraris, GiovanniPischedda, VittoriaFauth, Francois
Author(s): Mottana, Annibaleprefacer
Author(s): Sassi, Paolo Francescoprefacer
Affiliation: Universita degli Studi di Milano, Dipartimento Scienze della Terra, Milan, Italy
Pages: 1071-1078
Published: 200112
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
Meeting name: Advances on micas; problems, methods, applications in geodynamics
Meeting location: Rome, ITA, Italy
Meeting date: 20001102Nov. 2-3, 2000
References: 32
Accession Number: 2002-012289
Categories: Mineralogy of silicates
Document Type: Serial Conference document
Bibliographic Level: Analytic
Annotation: Includes appendix
Illustration Description: illus. incl. 2 tables
N45°10'60" - N45°10'60", E05°43'00" - E05°43'00"
Secondary Affiliation: Universita degli Studi di Torino, ITA, ItalyInstitut Laue Langevin, FRA, France
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200205
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