2006 APS March Meeting
Monday–Friday, March 13–17, 2006;
Baltimore, MD
Session N3: Insulating Cobaltates: Mottness on a Triangular Lattice
8:00 AM–11:00 AM,
Wednesday, March 15, 2006
Baltimore Convention Center
Room: Ballroom I
Sponsoring
Unit:
DCMP
Chair: Philip Phillips, University of Illinois
Abstract ID: BAPS.2006.MAR.N3.3
Abstract: N3.00003 : Sodium Ion Ordering in double-layered and triple-layered Na$_{x}$CoO$_{2}$
9:12 AM–9:48 AM
Preview Abstract
Abstract
Author:
Henny Zandbergen
(Dept. of Chemistry and Princeton Materials Inst., Princeton University; National Centre for HREM, Dept. of Nanoscience, Delft University of Technology)
The layered sodium cobalt oxide Na$_{x}$CoO$_{2}$ is studied by
electron
diffraction for a wide range of sodium contents, 0.15$<$x$<$0.75.
This range
in compositions is obtained by removal of Na by various methods
for the
starting materials Na$_{0.7}$CoO$_{2}$, and Na$_{1.0}$CoO$_{2 }$ The
structure of Na$_{x}$CoO$_{2}$ is based the stacking of
triangular O-Co-O
layers with Na planes. The Co atoms are in edge-sharing CoO$_{6}$
octahedra.
For the starting compound Na$_{0.7}$CoO$_{2}$, the Na$^{+}$ ions
are in a
trigonal prismatic coordination whereas for Na$_{1.0}$CoO$_{2 }$ the
Na$^{+}$ coordination is octahedral. Prismatic coordination
occurs when the
close packed oxygen planes directly adjacent to the Na plane have
the same
projection into the basal plane (A-Na-A), whereas octahedral
coordination of
Na occurs when the directly adjacent oxygen planes have different
projections (A-Na-B) into the basal plane. Due to this difference in
stacking the a axis is about 1.08 nm and 1.65 nm for
Na$_{0.7}$CoO$_{2}$ and
Na$_{1.0}$CoO$_{2 }$respectively. For Na$_{0.7}$CoO$_{2}$ as well as
Na$_{1.0}$CoO$_{2 }$a series of superstructures are observed,
which can be
explained with ordered Na ion-Na vacancy superlattices. The
structural
principle for some of the observed ordering schemes, particularly
near
x=0.5, is, surprisingly, the presence of lines of Na ions and
vacancies
rather than simply maximized Na-Na separations. With
Na$_{0.7}$CoO$_{2}$ as
starting material, the most strongly developed superlattice is
found for the
composition Na$_{0.5}$CoO$_{2}$. With Na$_{1,0}$CoO$_{2}$ as
starting
material, the most strongly developed superlattice is found for the
compositions Na$_{0.75}$CoO$_{2 }$and Na$_{0.5}$CoO$_{2}$. In
particular the
superstructure Na$_{0.75}$CoO$_{2 }$of is very complicated.
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In collaboration with M.L. Foo, Department of Chemistry and
Princeton Materials Institute, Princeton University, Princeton,
NJ 08544 USA; Q. Xu and V. Kumar, National Centre for HREM,
Department of Nanoscience, Delft University of Technology,
Rotterdamseweg 137, 2628 AL Delft, The Netherlands ; L. Viciu,
Department of Chemistry and Princeton Materials Institute,
Princeton University; Q. Huang, NIST Center for Neutron Research,
NIST, Gaithersburg, MD 20899; and R.J. Cava, Department of
Chemistry and Princeton Materials Institute, Princeton University.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2006.MAR.N3.3