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



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ID: 192980.0, MPI für Festkörperforschung / FKF Publikationen 2004
Synthesis, structure and magnetic properties of Na6Co2O6
Authors:Sofin, M.; Peters, E.-M.; Jansen, M.
Language:English
Date of Publication (YYYY-MM-DD):2004
Title of Journal:Journal of Solid State Chemistry
Volume:177
Issue / Number:7
Start Page:2550
End Page:2556
Review Status:not specified
Audience:Not Specified
Abstract / Description:Na6Co2O6 was synthesized via the azide/nitrate route by reaction
between NaN3, NaNO3 and Co3O4. Stoichiometric mixtures of the starting
materials were heated in a special regime up to 500degreesC and
annealed at this temperature for 50 It in silver crucibles. Single
crystals have been grown by subsequent annealing of the reaction
product at 500degreesC for 500 It in silver crucibles, which were
sealed in glass ampoules under dried Ar. According to the X-ray
analysis of the crystal structure (P (1) over bar, Z = 1, a =
5.7345(3), b = 5.8903(3), c = 6.3503(3) Angstrom, alpha = 64.538(2),
beta = 89.279(2), gamma = 85.233(2)degrees, 1006 independent
reflections, R-1 = 8.34% (all data)), cobalt is tetrahedrally
coordinated by oxygen. Each two CoO4 tetrahedra are linked through a
common edge forming Co2O66- anions. Cobalt ions within the dimers,
being in a high spin state (S = 2), are ferromagnetically coupled (J =
17 cm(-1)). An intercluster spin exchange (zJ' = -4.8 cm(-1)) plays a
significant role below 150 K and leads to an antiferromagnetically
ordered state below 30 K. Heat capacity exhibits a lambda-type anomaly
at this temperature and yields a value of 19.5 J/mol K for the
transition entropy, which is in good agreement with the theoretical
value calculated for the ordering of the ferromagnetic-coupled dimers.
In order to construct a model for the spin interactions in Na6Co2O6,
the magnetic properties of Na5CoO4 have been measured. This compound
features isolated CoO4 tetrahedra and shows a Curie-Weiss behavior (mu
= 5.14 mu(B), Theta = -20 K) down to 15 K. An antiferromagmetic
ordering is observed in this compound below 10 K. (C) 2004 Published by
Elsevier Inc.
Free Keywords:azide/nitrate route; sodium cobalt oxide; crystal structure; magnetic
properties; heat capacity
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:000222314700045 [ID No:1]
ISSN:0022-4596 [ID No:2]
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