Bridging the ruddlesden-popper and the aurivillius phases: Synthesis and structure of a novel series of layered perovskite oxides, (BiO)LnTiO4 (Ln = La, Nd, Sm) [7]

Full text of DOI:10.1021/ja011941u

11496
J. Am. Chem. Soc. 2001, 123, 11496-11497
Table 1. Crystallographic Data for (BiO)LaTiO a
Bridging the Ruddlesden-Popper and the Aurivillius
Phases: Synthesis and Structure of a Novel Series of
Layered Perovskite Oxides, (BiO)LnTiO4 (Ln ) La,
Nd, Sm)
4
Wyckoff
position
atom
x
y
z
occupancy
Bi1
La1
Bi2
La2
Ti
O1
O2
O3
O4
2c
2c
2c
2c
2c
4f
2c
2c
2a
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.75
0.25
0.25
0.75
0.9044(4)
0.9044(4)
0.5961(4)
0.5961(4)
0.257(2)
0.67(2)
0.33(2)
0.33(2)
0.67(2)
1
1
1
1
1
Thathan Sivakumar, Ram Seshadri, and
Jagannatha Gopalakrishnan*
0.236(2)
Solid State and Structural Chemistry Unit
Indian Institute of Science, Bangalore 560 012, India
b
0.367(3)[0.41]
0.027(3)[0.08]b
0
ReceiVed August 10, 2001
a
Space group P4/nmm (No. 129) with origin at (000). a ) 3.8907(2)
Å; c ) 12.161(1) Å. Rwp ) 14.0%; RBragg ) 11.3%. All isotropic thermal
Two series of layered perovskite oxides continue to attract
research attention. One series is the Ruddlesden-Popper (R-P)
2
b
parameters were constrained at B ) 1 Å . Numbers in parentheses
are errors, and numbers in square brackets are the physically reasonable
positions used to make the structure plot.
1
2-4
oxides, A
Ti SrTa
been investigated for a wide variety of properties, which include
2
[An-1
B
n
O
3n+1], whose members such as
K
2
La
2
-
3
O
10, K
2
2 7 4
O , and NaLnTiO (Ln ) La or rare earth) have
members of this series, A(BiO)[An-1
and A layered perovskites for the first time.
We prepared (BiO)LnTiO (Ln ) La, Nd, Sm) starting from
NaLnTiO , which are n ) 1 members of the R-P series exhibiting
a unique ordering of Na and Ln atoms at the alternate interlayer
sites between single perovskite sheets in the sequence Ln
n
B O3n+1], bridging the R-P
2,3
5
5
ion-exchange, intercalation, exfoliation, topochemical dehy-
dration,6 reductive transformation to higher members, and
,7
8,9
4
1
0
photocatalytic activity for decomposition of water. The other
series is the Aurivillius (A) phases,11 (Bi
are well-known high-temperature ferroelectric materials. In recent
times, members of this series, for example, Bi SrTa and La-
substituted Bi Ti 12 in thin-film geometry, have been shown to
4
2
2 n
O )[An-1B O3n+1], which
2
-
2
2
O
9
4
TiO4/2
O
2
-Na
NaLnTiO into (BiO)LnTiO
with BiOCl.
2
-TiO4/2
O
2
-Ln
2
, along the c-axis. We transformed
4
3
O
16
4
4
in the following metathesis reaction
possess nonvolatile ferroelectric memory characteristics that are
promising for computer memory applications.1 Considering that
2,13
n
the 2D-perovskite unit, viz., [An-1B O3n+1], is common for both
NaLnTiO + BiOCl f (BiO)LnTiO + NaCl
(1)
4
4
of the series of oxides, one could envisage the following from a
crystal-chemistry standpoint: Transformation of R-P to A series
and vice versa by exchanging the interlayer entities between the
perovskite sheets, and bridging of the two series by sequentially
arranging the interlayer entities between the perovskite sheets.
We found that the transformation occurs smoothly at 600 °C/6
h. The product oxides, after washing and drying to remove NaCl,
are single-phase materials, as revealed by EDAX analysis and
powder X-ray diffraction (XRD). EDAX analysis showed the
expected 1:1:1 stoichiometry for Bi:La:Ti without chlorine
impurity. Laboratory XRD patterns of the products are indexable
on tetragonal cells with a ) 3.892(2) Å, 3.891(2) Å, 3.890(3) Å;
c ) 12.16(1) Å, 12.15(1) Å, 12.14(1) Å for Ln ) La, Nd, Sm
phases, respectively. Significantly, we could not synthesize these
The R-P f A and A f R-P transformations have recently been
achieved1
4,15
by innovative chemical reactions involving meta-
thesis/selective acid leaching. Bridging of the two series of layered
perovskites wherein structural units of R-P and A phases are
2 2
stacked one over the other to give the layer sequence, [Bi O ]-
[A B O3n+1]A [An-1B O3n+1], has, however, not been reported
n-1 n 2 n
so far. We report in this Communication the synthesis and
structure of new layered perovskite oxides of the formula, (BiO)-
2 3 2 3 2
oxides by direct solid-state reaction of La O , Bi O , and TiO at
elevated temperatures.
Considering that the NaLnTiO
in reaction 1 is similar to the conversion, K
4
f (BiO)LnTiO
4
conversion
Ti
LnTiO (Ln ) La, Nd, Sm), which could be regarded as n ) 1
4
2
La
2
3 10
O f
14
*
Author for correspondence. E-mail: gopal@sscu.iisc.ernet.in.
(Bi
interlayer K atoms are replaced by (Bi
that the structure of (BiO)LnTiO would consist of the layer
sequence Ln -(Bi -Ln
We determined the crystal structure of (BiO)LaTiO
O
2
2 3
)La Ti O10, in the metathesis reaction with BiOCl, wherein
2
(
1) Ruddlesden, S. N.; Popper, P. Acta Crystallogr. 1957, 10, 538-539.
2
O
2
) sheets, we expected
Ruddlesden, S. N.; Popper, P. Acta Crystallogr. 1958, 11, 54-55.
(
(
(
2) Gopalakrishnan, J.; Bhat, V. Inorg. Chem. 1987, 26, 4299-4301.
3) Ollivier, P. J.; Mallouk, T. E. Chem. Mater. 1998, 10, 2585-2587.
4) (a) Byeon, S.-H.; Park, K.; Itoh, M. J. Solid State Chem. 1996, 121,
4
-TiO4/2O
2 2
2 2
O )-TiO4/2
O
2
2
.
4
by Rietveld
4
30-436. (b) Toda, K.; Kameo, Y.; Kurita, S.; Sato, M. J. Alloys Cmpd.
1
7
refinement of powder XRD data. The refinements employed
1
996, 234, 19-25.
XND code18 and used as starting models the P4/nmm structure
(
5) Schaak, R. E.; Mallouk, T. E. Chem. Mater. 2000, 12, 3427-3434.
6) Thangadurai, V.; Subbanna, G. N.; Gopalakrishnan, J. Chem. Commun.
(
1
998, 1299-1300.
(16) NaLnTiO
4
(Ln ) La, Nd, Sm) were prepared, as reported in the
literature, by reacting stoichiometric amounts of the starting materials, Na
CO , Ln , and TiO with 20% molar excess of Na CO at 900 °C for 48 h
with intermediate grindings. (BiO)LnTiO were synthesized by reacting an
intimate stoichiometric mixture of NaLnTiO and BiOCl (Alfa, 99.99%) at
4
(
7) Schaak, R. E.; Mallouk, T. E. J. Solid State Chem. 2000, 155, 46-54.
8) Schaak, R. E.; Mallouk, T. E. J. Am. Chem. Soc. 2000, 122, 2798-
2
-
(
3
O
2 3
2
2
3
2
8
803.
4
(
9) Schaak, R. E.; Guidry, E. N.; Mallouk, T. E. Chem. Commun. 2001,
4
53-854.
450 ° (12 h), 500 ° (6 h) and 600 °C (6 h), with intermediate grindings. The
final product was washed with distilled water to remove NaCl and dried at
110 °C.
(17) XRD data for Rietveld refinement were collected on a Microcontrole
diffractometer mounted on a Rigaku Geigerflex rotating anode operated at
15 kW. Graphite monochromatised Cu Kâ radiation (λ ) 1.39223 Å) was
employed to increase the number of peaks in the pattern. The sample was
mounted using silicone grease on a Si wafer to minimize background and
preferred orientation. Data were scanned using a step size of 0.02° 2θ with
longer times at higher angles.
(18) B e´ rar, J.-F. Program XND; ESRF: Grenoble, France. More information
under: http://www.ccp14.ac.uk; B e´ rar, J.-F.; Proceedings of the IUCr Satellite
Meeting on Powder Diffractometry; Toulouse, France, July 1990; B e´ rar J.-
F.; Garnier, P. II APD conference, NIST (U.S.A.): Gaithersburg, Maryland,
May 1992; B e´ rar J.-F.; Garnier, P. NIST Special Publication 1992, 846, 212.
(10) (a) Takata, T.; Furumi, Y.; Shinohara, K.; Tanaka, A.; Hara, M.;
Kondo, J. N.; Domen, K. Chem. Mater. 1997, 9, 1063-1064. (b) Ikeda, S.;
Hara, M.; Kondo, J. N.; Domen, K.; Takahashi, H.; Okubo, T.; Kakihana, M.
Chem. Mater. 1998, 10, 72-77.
(
11) Aurivillius, B. Ark. Kemi 1949, 1, 463-480. Aurivillius, B. Ark. Kemi
1
950, 2, 519-527.
12) Paz de Araujo, C. A.; Cuchiaro, J. D.; McMillan, L. D.; Scott, M. C.;
Scott, J. F. Nature 1995, 374, 627-629.
13) Park, B. H.; Kang, B. S.; Bu, S. D.; Noh, T. W.; Lee, J.; Jo, W. Nature
999, 401, 682-684.
14) Gopalakrishnan, J.; Sivakumar, T.; Ramesha, K.; Thangadurai, V.;
Subbanna, G. N. J. Am. Chem. Soc. 2000, 122, 6237-6241.
15) Sugimoto, W.; Shirata, M.; Sugahara, Y.; Kuroda, K. J. Am. Chem.
Soc. 1999, 121, 11601-11602.
(
(
1
(
(
1
0.1021/ja011941u CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/27/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 46, 2001 11497
Figure 2. Proposed structure of (BiO)LaTiO
around Ti. Large dark gray spheres are La, while large light gray spheres
are Bi. For comparison, the structures of typical R-P phase, Sr TiO
and A phase, Bi WO , are shown in (b) and (c), respectively.
4
(a). The octahedra are
2
4
,
2
6
Despite these limitations, we find the gross structural features
of (BiO)LaTiO (Figure 2a), namely ReO -like TiO4/2 sheets
2
flanked on one side by La atoms as in R-P phases and by (Bi O )
4
3
O
2
2
sheets on the other side as in A phases, suggest that our
expectations are indeed borne out. The coordinations of La (with
Figure 1. Experimental (top), Rietveld refined (middle), and difference
4
(bottom) XRD profiles of (BiO)LaTiO . The vertical lines are expected
peak positions in the space group P4/nmm. The data have been plotted
separately at low and high angles in order to better visualize the fit.
La-O distances, 2.26-2.82 Å) and Ti (with Ti-O distances,
4
1.96-2.15 Å) are comparable to those in NaLaTiO
4
, while the
[
Bi
2 2
O ] unit (with Bi-O distances 2.27-2.59 Å) is similar to
CuO 19
and LaSrMnO
F.20 During the refinement,
21
of (NdCeSr)
2
4
4
that in A phases. Accordingly, the oxides (BiO)LnTiO could
4
it became clear that there is a mixing of La and Bi atoms in the
two sites; therefore, keeping in mind the chemical composition
of Bi:La:Ti ) 1:1:1, the amount of La and Bi in their respective
sites were allowed to refine, while ensuring that the total ratio
was conserved. The atomic coordinates together with refinement
parameters are given in Table 1, and the experimental, calculated,
and difference profiles are shown in Figure 1. The refinement
reveals that there is some disorder in the structure perhaps arising
from its layered nature and the relatively low temperature of
synthesis. The disorder manifests as a broad background near the
stronger peaks. As a result of this, the final R factors remain rather
high. In the presence of strong scatterers, La and Bi, as well as
the disorder, two of the oxygen atoms refined to unphysical
positions. Therefore, we have moved these oxygen atoms slightly
be regarded as simplest (n ) 1) members of a new series of
layered perovskites, A(BiO)[An-1B O3n+1], that bridge both the
n
R-P and A series. We believe that the significance of the present
work extends beyond the synthesis of a new series of layered
perovskite titanates. Considering that several currently important
materials properties (that include magnetoresistance, supercon-
ductivity, and ferroelectricity) are exhibited by layered perovskites
belonging to R-P and A family of oxides, the present work
suggests the possibility of synergistically combining these proper-
ties in new R-P/A family of layered perovskites.
Acknowledgment. We thank the Department of Science and Tech-
nology, Government of India, and the Council of Scientific and Industrial
Research, New Delhi, for support of this work. We also thank G.
Baldinozzi of the Ecole Centrale, Paris, for help in acquiring the high
resolution powder XRD data and in the analysis.
(
(
Table 1) to obtain a physically reasonable structural model
Figure 2). A neutron diffraction study would help determine the
exact position of oxygen atoms in the structure.
JA011941U
(
19) Izumi, F.; Takayama-Muromachi, E.; Fujimori, A.; Kamiyama, T.;
Asano, H.; Akimitsu, J.; Sawa, H. Physica C 1989, 158, 440-448.
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(
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2