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          Institute: MPI für Festkörperforschung     Collection: FKF Publikationen 2004     Display Documents

ID: 192765.0, MPI für Festkörperforschung / FKF Publikationen 2004
Synthesis, structure and magnetic properties of Na9Co2O7, a new mixed-valent sodium cobaltate(II,III)
Authors:Sofin, M.; Peters, E.-M.; Jansen, M.
Date of Publication (YYYY-MM-DD):2004
Title of Journal:Solid State Sciences
Issue / Number:4
Start Page:339
End Page:344
Review Status:not specified
Audience:Not Specified
Abstract / Description:Na9CO2O7 was prepared via the azide/nitrate route. Stoichiometric
mixtures of the precursors (Co3O4, NaN3 and NaNO3) were heated in a
special regime up to 450 degreesC and annealed at this temperature for
100 h in specially designed silver containers. Single crystals have
been grown by annealing a Na2O/Na9CO2O7 mixture (molar ratio 1:2) at
500 degreesC for 2000 h in silver crucibles, which were sealed in glass
ampoules under dried Ar. According to the X-ray analysis of the crystal
structure (Pca2(1), Z = 4, a = 9.5477(6) Angstrom, b = 9.9040(6)
Angstrom, c = 10.1919(7) Angstrom, 4103 independent reflections, R-1 =
5.23% (all data)) there are isolated (CoO4)-O-III tetrahedra and
(CoO3)-O-II triangles. Na9Co2O7 is isostructural to Na9Fe2O7, and shows
Curie-Weiss behaviour down to similar to 25 K. The best fit (for Co-II
(S = 3/2) and Co-III (S = 2)) yields an average value of the magnetic
moment (per cobalt) mu = 3.23mu(B) (g = 2.07) and Theta = -6 K. At 20 K
one observes an onset of ferromagnetic order. (C) 2004 Elsevier SAS.
All rights reserved.
Free Keywords:azide/nitrate-route; sodium cobalt oxide; crystal structure; magnetic
properties; mixed-valent compounds
External Publication Status:published
Document Type:Article
Communicated by:Michaela Asen-Palmer
Affiliations:MPI für Festkörperforschung
External Affiliations:Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
Identifiers:ISI:000221199700004 [ID No:1]
ISSN:1293-2558 [ID No:2]
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