University of Groningen
Prediction and Verification of the Structural Chemistry of New One-Dimensional
Barium/Copper/Iridium Oxides
Blake, Graeme R.; Sloan, Jeremy; Vente, Jaap F.; Battle, Peter D.
Published in:
Chemistry of Materials
DOI:
10.1021/cm980317m
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Blake, G. R., Sloan, J., Vente, J. F., & Battle, P. D. (1998). Prediction and Verification of the Structural
Chemistry of New One-Dimensional Barium/Copper/Iridium Oxides.
Chemistry of Materials
,
10
(11), 3536-
3547. https://doi.org/10.1021/cm980317m
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Prediction and Verification of the Structural Chemistry
of New One-Dimensional Barium/Copper/Iridium Oxides
Graeme R. Blake,
†
Jeremy Sloan,
†,‡
Jaap F. Vente,
†
and Peter D. Battle*
,†
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR,
U.K., and Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K.
Received April 30, 1998. Revised Manuscript Received August 4, 1998
We propose a classification scheme for the commensurate phases in the family of pseudo
one-dimensional structures formed from the mixed hcp stacking of A
3
O
9
and oxygen-deficient
A
3
A′O
6
layers. We envisage these compounds as composites of two substructures having
common a and b unit cell parameters but different parameters c
1
and c
2
. Use of the ratio
c
1
/c
2
facilitates the prediction of new commensurate structures while allowing for the
commonly incommensurate nature of materials in this family. The structures of the new
commensurate phases Ba
5
CuIr
3
O
12
,Ba
14
Cu
3
Ir
8
O
33
,Ba
16
Cu
3
Ir
10
O
39
, and Ba
9
Cu
2
Ir
5
O
21
are
predicted and subsequently verified by powder X-ray diffraction and HRTEM. Ba
5
CuIr
3
O
12
has a 10 layer structure with space group P321, a ) 10.143 82(8) Å, c ) 21.6553(2) Å; Ba
14
-
Cu
3
Ir
8
O
33
has a 14 layer structure with space group P321, a ) 10.145 85(8) Å, c ) 29.9574-
(3) Å; Ba
16
Cu
3
Ir
10
O
39
has a 16 layer structure with space group P321, a ) 10.136 43(7) Å; c
) 35.0616(3) Å; Ba
9
Cu
2
Ir
5
O
21
has an 18 layer structure with space group R32, a ) 10.144 64-
(11) Å, c ) 38.2455(6) Å. Sequences of trigonal prismatic sites and octahedral sites run in
chains parallel to z, with Ba cations located between the chains; the distribution of iridium
and copper cations in the octahedral and trigonal prismatic sites is disordered in each case.
Electron diffraction patterns and lattice images show evidence for modulation in the
structures of Ba
5
CuIr
3
O
12
,Ba
14
Cu
3
Ir
8
O
33
, and Ba
16
Cu
3
Ir
10
O
39
but not in that of Ba
9
Cu
2
Ir
5
O
21
.
The magnetic susceptibilities of all four phases obey a modified Curie-Weiss law above 150
K, with no long-range magnetic order observed between 5 and 300 K. They are all electrical
insulators.
Introduction
We have recently reported the crystal structures of
Ba
6
CuIr
4
O
15
1
and Sr
4
CuIr
2
O
9
.
2
It is convenient to think
of these structures (Figure 1) as being derived from an
hcp stack (aba) of pseudo close packed layers of stoi-
chiometry A
3
O
9,
(A ) Sr, Ba). If the octahedral inter-
stices between such layers are filled by cations, B, then
the 2H perovskite structure of, for example, BaNiO
3
,
3
results. An ordered removal of groups of three oxide ions
from one of these layers modifies the stoichiometry of
that layer to A
3
O
6
, while creating potential cation sites
within the layer. These new sites are equidistant from
three anions in each of the neighboring layers, and they
consequently have trigonal prismatic coordination ge-
ometry. When the trigonal prismatic sites are occupied
by a cation A′, the stoichiometry of the layer is changed
to A
3
A′O
6
(Figure 2). Darriet and Subramanian
4
dis-
cussed the stoichiometries that can arise when a mixed
stack of A
3
O
9
layers and A
3
A′O
6
layers forms the basis
of a crystal structure, the octahedral interstices being
occupied by B cations. They described these compounds
with the general formula A
3n+3
A′
n
B
n+3
O
6n+9
, where the
layer sequence is (A
3
A′O
6
)
n
(A
3
O
9
); that is, an A
3
O
9
layer
is inserted after every n (A
3
A′O
6
) layers. Ba
6
CuIr
4
O
15
then corresponds to an n ) 1 structure, Sr
4
CuIr
2
O
9
has
n ) 3 and Sr
4
IrO
6
(A ) A′ ) Sr)
5
is the n ) ∞ end-
* To whom correspondence should be addressed.
†
Inorganic Chemistry Laboratory.
‡
Department of Materials.
(1) Battle, P. D.; Blake, G. R.; Darriet, J.; Gore, J. G.; Weill, F. J.
Mater. Chem. 1997, 7, 1559.
(2) Battle, P. D.; Blake, G. R.; Sloan, J.; Vente, J. F. J. Solid State
Chem. 1998, 136, 103.
(3) Lander, J. J. Acta Crystallogr. 1951, 4, 148.
(4) Darriet, J.; Subramanian, M. A. J. Mater. Chem. 1995, 5, 543.
Figure 1. Crystal structures of (a) Sr
4
CuIr
2
O
9
and (b) Ba
6
-
CuIr
4
O
15
. IrO
6
octahedra are shaded; Cu-containing trigonal
prismatic sites are unshaded. Black circles represent Sr or Ba.
3536 Chem. Mater. 1998, 10, 3536-3547
10.1021/cm980317m CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/15/1998
member of the series; examples involving other transi-
tion elements are known and have been listed else-
where.
6
In an alternative but equivalent view, each of
these structures can be described in a trigonal unit cell
with three chains of cation-containing polyhedra run-
ning parallel to the z axis. All of the chains contain the
same sequence of BO
6
octahedra and A′O
6
prisms, but
there is an offset between neighboring chains. The
atoms A occupy coordination sites between the chains.
Both descriptions of the structure type can be recognized
in the structure of Sr
4
CuIr
2
O
9
, as drawn in Figure 1.
In a number of cases, for example Ba
6
ZnIr
4
O
15
and Ba
4
-
CuIr
2
O
9
,
1,2
the descriptions of the structures presented
above have proved to be inadequate. X-ray and electron
diffraction studies have shown these compounds to be
incommensurate along [001], with the precise periodicity
strongly dependent on synthesis conditions. Their struc-
tures can be described as composites containing two
substructures, with the same unit cell parameters a and
b but with differentparameters c
1
and c
2
; c
1
is associated
with the columns of A cations and is the mean separa-
tion of equivalent, (i.e. alternate) pseudo close packed
planes in the aba hcp stack, and c
2
is the mean spacing
of the cations within the polyhedral chains. The unit
cell is commensurate when pc
1
) qc
2
, that is, c
1
/c
2
)
q/p (p, q are integers), and incommensurate when c
1
/c
2
is not a rational fraction. Consistent with these defini-
tions, there are 2p layers, either A
3
O
9
or A
3
A′O
6
,inthe
unit cell and q polyhedra. Each A
3
O
9
layer generates
one octahedral site per chain, but the insertion of an
A
3
A′O
6
layer generates a prismatic site which takes up
twice the space (parallel to [001]) of an octahedral site.
If we assume that all of the sites in a chain are to be
filled, then if q e 2p, we must utilize 2p - q prismatic
sites and 2q - 2p octahedral sites in order to have a
total of q sites, all filled. The unit cell of the 2H
perovskite (n ) 0) has two layers and two transition
metal cations per chain per unit cell, and therefore p )
1, q ) 2, and q ) 2p; no prismatic sites are formed, and
the structure contains only A
3
O
9
layers. At the other
extreme, Sr
3
A′IrO
6
(n ) ∞) has six layers and four
cations per chain per unit cell;
5
therefore p ) 3, q ) 4,
q ) 4p/3, and equal numbers of octahedral and pris-
matic sites are utilized. These two limiting cases
demonstrate that (4p/3) e q e 2p. For the A
4
A′Ir
2
O
9
(n
) 3) compounds, p ) 2, q ) 3, and we expect c
1
/c
2
) 3/2
for a commensurate phase; deviations from this value
indicate an incommensurate structure. In a similar way,
the n ) 1 structure adopted by Ba
6
CuIr
4
O
15
has c
1
/c
2
)
5/3,
1
whereas the related incommensurate compound
Ba
6
ZnIr
4
O
15
has c
1
/c
2
) 1.63.
The use of the parameters p and q allows us to
account for all compounds in the series formulated as
A
3n+3
A′
n
B
n+3
O
6n+9
by Darriet and Subramanian (DS),
and, in addition, it establishes criteria for (in)com-
mensurability among these phases. Furthermore, it
enables us to predict new phases which lie outside the
original formulation. The description of the stacking
sequence as (A
3
A′O
6
)
n
(A
3
O
9
) limits the model to com-
positions in which only single A
3
O
9
layers occur, but it
is easy to conceive of stuctures where multiple (A
3
O
9
)
layers separate sequences of (A
3
A′O
6
) layers. This paper
describes our attempts to predict and subsequently
prepare and characterize new phases within this gen-
eral structural framework. Understanding the crystal
chemistry of these complex oxides was a major part of
the motivation of this work, but we were also aware that
the polyhedral chains might have interesting 1D elec-
tronic properties if they could be made with the opti-
mum cation distribution. The principal aim of our
experimental program was to prepare new phases which
cannot be described by the DS formula and to charac-
terize their electronic properties. To do this, we at-
tempted to occupy the B sites with a transition metal
which readily takes oxidation states up to IV and the
prismatic sites with a relatively small, divalent transi-
tion metal cation. Iridium was selected for the former
role, and preliminary experiments led us to conclude
that Cu is best suited to occupy the trigonal sites.
Experimental Section
Our attempts to synthesize polycrystalline samples (∼1g)
of selected compositions employed the standard methods of
solid-state chemistry, with BaCO
3
, CuO, and Ir metal as
starting materials. All syntheses were carried out by heating
(5) Powell, A. V.; Battle, P. D.; Gore, J. G. Acta Crystallogr. 1993,
C49, 189.
(6) Darriet, J.; Grasset, F.; Battle, P. D. Mater. Res. Bull. 1997,
32, 139.
Figure 2. Layers of different stoichiometry in
A
3n+3
A′
n
B
n+3
O
6n+9
: (a) an A
3
O
9
layer, (b) an A
3
O
6
layer with
trigonal prismatic sites (A′) marked by lightly shaded circles.
The two-dimensional unit cells of both layer types are shown,
with a′ ) x3a.
Table 1. Preparation of Ba/Cu/Ir/O Phases
compd temps/°C (firing times/days)
Ba
5
CuIr
3
O
12
1200 °C (3 days) + 1250 °C (1 day)
Ba
14
Cu
3
Ir
8
O
33
1200 °C (2 days) + 1250 °C (8 days)
Ba
16
Cu
3
Ir
10
O
39
1200 °C (4.5 days)
Ba
9
Cu
2
Ir
5
O
21
1200 °C (3 days) + 1250 °C (11 days) + 1300 °C
(19 days) + 1310 °C (5 days) + 1320 °C (2 days)
Structural Chemistry of 1D Ba/Cu/Ir Oxides Chem. Mater., Vol. 10, No. 11, 1998 3537
alumina crucibles containing pelletized, stoichiometric mix-
tures of the appropriate reactants in air, initially at 800 °C
and subsequently as described in Table 1. The progress of the
reactions was followed by X-ray powder diffraction (XRD), and
they were deemed to be complete when the measured diffrac-
tion pattern could be accounted for by the presence of one
commensurate phase having trigonal or rhombohedral sym-
metry. The XRD data were collected at room temperature over
the angular range 5 e 2θ/deg e 120, with a step size of ∆2θ )
0.02°, on a Siemens D5000 diffractometer operating with Cu
KR
1
radiation in Bragg-Brentano geometry. The data were
analyzed by the Rietveld method,
7
as implemented in the
GSAS program suite.
8
Further structural characterization of
the products was carried out using a JEOL-4000EX HRTEM
operated at 400 kV. This microscope has a point resolution of
1.7 Å and a spherical aberration coefficient of 9 Å. Finely
ground specimens were dispersed in chloroform in an ultra-
sonic bath and then placed, dropwise, onto lacey carbon-coated
copper grids (Agar 200 mesh). Lattice images were recorded
under optimum Scherzer defocus conditions from crystal
fragments with their [010] or [11h0] zone axes aligned parallel
to the electron beam. Image simulations were calculated using
the multislice program in the EMS program package.
9
The
metal contentof the products was analyzed using an Atomscan
25 ICP emission spectrometer. Magnetic measurements were
made on a sample contained in a gelatin capsule using a
Quantum Design MPMS-5 SQUID magnetometer. Data were
recorded while warming the sample through the temperature
range 5 e T/K e 300 after cooling in zero field (ZFC) and after
cooling inthe measuring fields (100 and 1000 G, FC). Electrical
conductivity measurements were attempted using the stan-
dard four-probe technique, copper wires being attached to a
sintered bar of the sample with conducting silver paint.
Results
Two assumptions were made in predicting possible
target structures; first, in any one chain, trigonal
prismatic sites are always separated by at least one
octahedral site and, second, no layer has more than one-
third of the oxide ions absent, thus eliminating the
possibility that, for a given layer, trigonal prismatic sites
can occur in more than one chain. Use of the relation-
ship (4p/3) e q e 2p for p e 9 generates the possible
stoichiometries listed in Table 2. The choice p
max
) 9is
arbitrary; there is no limit to the number of structures
that can be envisaged with a greater number of layers
in the unit cell. By way of example, some of the possible
10 layer (p ) 5) structures are drawn in Figure 3;
A
10
A′
3
B
4
O
21
(Figure 3a) can be recognized as a DS n )
9 structure with c
1
/c
2
) 7/5, whereas A
5
A′B
3
O
12
(Figure
3b) has c
1
/c
2
) 8/5 and cannot be described in the DS
(7) Rietveld, H. M. J. Appl. Crystallogr. 1969, 2, 65.
(8) Larson, A. C. and von Dreele, R. B. General Structure Analysis
System (GSAS); Report LAUR 86-748, Los Alamos National Labora-
tories: Los Alamos, NM, 1990.
(9) Stadelman, P. A. Ultramicroscopy 1987, 21, 131.
Table 2. Possible Stoichiometries of Compounds Based on the Mixed Stacking of A
3
A′O
6
and A
3
O
9
Layers
a
layers per
unit cell pq
octahedra
per chain
prisms
per chain comments c
1
/c
2
sequence of polyhedra:
translation of (
1
/
3
,
2
/
3
, z) chain
b
212 2 0ABO
3
2o
2
: a,0(n ) 0, 2H structure)
424 4 02 × 2H structure 2
23 2 1 A
4
A′B
2
O
9
3/2 opo: a, c/4 (n ) 3)
635 4 1A
6
A′B
4
O
15
5/3 o
2
po
2
: a, c/3 (R, n ) 1); b, c/6
34 2 2 A
3
A′BO
6
4/3 popo: a, c/3 (R, n ) ∞)
847 6 1A
8
A′B
6
O
21
7/4 o
3
po
3
: a,3c/8; b, c/4; c, c/8
46 4 2 2 × A
4
A′B
2
O
9
3/2
10 5 9 8 1 A
10
A′B
8
O
27
9/5 o
4
po
4
: a,2c/5; b,3c/10; c, c/5; d, c/10
58 6 2 A
5
A′B
3
O
12
8/5 po
3
po
3
: a, c/5; b, c/10
57 4 3 A
10
A′
3
B
4
O
21
7/5 opopopo: a, c/10 (n ) 9)
12 6 11 10 1 A
12
A′B
10
O
33
11/6 o
5
po
5
: a,5c/12; b, c/3 (R); c, c/4; d, c/6; e, c/12
610 8 2 2 × A
6
A′B
4
O
15
5/3
69 6 3 3 × A
4
A′B
2
O
9
3/2
68 4 4 2 × A
3
A′BO
6
4/3
14 7 13 12 1 A
14
A′B
12
O
39
13/7 o
6
po
6
: a,3c/7; b,5c/14; c,2c/7; d,3c/14; e, c/7; f, c/14
712 10 2 A
7
A′B
5
O
18
12/7 po
5
po
5
: a,3c/14; b, c/7; c, c/14
711 8 3 A
14
A′
3
B
8
O
33
11/7 opo
3
po
3
po: a,3c/7; b,3c/14; c, c/14
710 6 4 A
7
A′
2
B
3
O
15
10/7 opopo
2
popo: a, c/14 (n ) 6)
popo
2
po
2
po: b, c/14
16 8 15 14 1 A
16
A′B
14
O
45
15/8 o
7
po
7
: a,7c/16; b,3c/8; c,5c/16; d, c/4; e,3c/16;
f, c/8; g, c/16
814 12 2 2× A
8
A′B
6
O
21
7/4
813 10 3 A
16
A′
3
B
10
O
39
13/8 o
2
po
3
po
3
po
2
: a,7c/16; b, c/4; c, c/8; d, c/16
812 8 4 4 × A
4
A′B
2
O
9
3/2
811 6 5 A
16
A′
5
B
6
O
33
11/8 opopopopopo: a, c/16 (n ) 15)
18 9 17 16 1 A
18
A′B
16
O
51
17/9 o
8
po
8
: a,4c/9; b,7c/18; c, c/3 (R); d,5c/18; e,2c/9;
f, c/6; g, c/9; h, c/18
916 14 2 A
9
A′B
7
O
24
16/9 po
7
po
7
: a, c/3 (R); b, c/9; c, c/18
915 12 3 3 × A
6
A′B
4
O
15
5/3
914 10 4 A
9
A′
2
B
5
O
21
14/9 opo
3
po
2
po
3
po: a, c/3 (R, n ) 2); b, c/18
po
3
po
2
po
2
po
3
: c, c/3 (R); d, c/6; e, c/18
913 8 5 A
18
A′
5
B
8
O
39
13/9 po
2
popo
2
popo
2
: a, c/3 (R, n ) 5); b, c/18
popo
2
po
2
po
2
po: c, c/18
912 6 6 3× A
3
A′BO
6
4/3
a
Compositions which can be described as DS phases (A
3
A′O
6
)
n
(A
3
O
9
) are shown in italics. c
1
/c
2
is given for a commensurate structure.
b
Sequence of polyhedra (o
n
) n adjacent face-sharing octahedra) for the chain along (0,0,z) is given, followed by relative translations of
the (
1
/
3
,
2
/
3
, z) chain to give structures a-c, etc. (R) denotes rhombohedral structures; all others are trigonal except for 2H.
Table 3. Observed (Calculated) Metal Content of Ba/Cu/
Ir/O Phases
compd % Ba % Cu % Ir
Ba
5
CuIr
3
O
12
45.02 (45.21) 4.00 (4.18) 38.13 (37.97)
Ba
14
Cu
3
Ir
8
O
33
46.77 (46.01) 4.41 (4.56) 37.46 (36.80)
Ba
16
Cu
3
Ir
10
O
39
45.56 (44.53) 3.66 (3.86) 39.73 (38.96)
Ba
9
Cu
2
Ir
5
O
21
49.31 (46.46) 4.87 (4.78) 35.54 (36.13)
3538 Chem. Mater., Vol. 10, No. 11, 1998 Blake et al.
scheme. However, further consideration shows that a
second 10 layer structure (Figure 3c) with trigonal
symmetry is also consistent with the unit cell dimen-
sions and the composition of the latter phase. In fact,
Figure 3. Idealized crystal structures of the 10 layer compounds: (a) A
10
A′
3
B
4
O
21
; (b) A
5
A′B
3
O
12
(model a); (c) A
5
A′B
3
O
12
(model
b).
Figure 4. [010] zone electron diffraction patterns of (a) Ba
5
CuIr
3
O
12
, (b) Ba
14
Cu
3
Ir
8
O
33
, (c) Ba
16
Cu
3
Ir
10
O
39
, and (d) Ba
9
Cu
2
Ir
5
O
21
.
Table 4. Unit Cell Parameters of Ba/Cu/Ir/O Phases from X-ray Diffraction
compd a/Å c/Å c
1
/Å c
2
/Å c
1
/c
2
Ba
5
CuIr
3
O
12
10.143 82(8) 21.6553(2) 4.3292(7) 2.7063(3) 1.5997(5)
Ba
14
Cu
3
Ir
8
O
33
10.145 85(8) 29.9574(3) 4.2800(3) 2.7225(3) 1.5721(3)
Ba
16
Cu
3
Ir
10
O
39
10.136 43(7) 35.0616(3) 4.3826(8) 2.6963(4) 1.6254(5)
Ba
9
Cu
2
Ir
5
O
21
10.144 64(11) 38.2455(6) 4.2454(6) 2.7284(3) 1.5560(4)
Structural Chemistry of 1D Ba/Cu/Ir Oxides Chem. Mater., Vol. 10, No. 11, 1998 3539
![Figure 5. [11h0] zone electron diffraction patterns of (a) Ba5CuIr3O12, (b) Ba14Cu3Ir8O33, (c) Ba16Cu3Ir10O39, and (d) Ba9Cu2Ir5O21.](/figures/figure-5-11h0-zone-electron-diffraction-patterns-of-a-16by6b02.webp)
