Search for new superconductors by the Li-intercalation into layered perovskites of the Aurivillius phase

Article abstract of DOI:10.1016/j.physc.2008.05.020

We have succeeded in the Li-intercalation into the layered perovskites of the Aurivillius phase having Bi₂O₂ layers, Bi₂MO₆ (M = Mo, W), Bi₂W₂O₉, Bi₂BaNb₂O<

Full text of DOI:10.1016/j.physc.2008.05.020

Physica C 468 (2008) 1152–1154
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Physica C
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Search for new superconductors by the Li-intercalation into layered perovskites
of the Aurivillius phase
*
H. Tezuka , M. Kato, T. Kajita, T. Noji, Y. Koike
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 21 May 2008
We have succeeded in the Li-intercalation into the layered perovskites of the Aurivillius phase having
Bi O layers, Bi MO (M = Mo, W), Bi W O , Bi BaNb O , Bi SrNaNb O12 and Bi Ti O12, using the electro-
2 2 2 6 2 2 9 2 2 9 2 3 4 3
chemical technique. The host samples have turned from light gray or yellowish white to black through
the Li-intercalation, indicating that electron carriers are doped into the host samples through the Li-inter-
calation. However, no superconductivity has appeared.
PACS:
7
8
4.70.Àb
2.45.Aa
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Layered perovskite
Li-intercalation
Ferroelectric compounds
1
. Introduction
2. Experimental
All of the high-T
c
cuprate superconductors have layered perov-
Polycrystalline host samples of Bi
BaNb , Bi NaSrNb 12 and Bi Ti
lid-state reaction as follow. Bi MoO
ometric amounts of Bi and MoO
mixed, ground and heated in air at 500 °C for 24 h. The products
were pulverized, pressed into pellets and sintered at 580 °C for
2
MO
6 2 2 9
(M = Mo, W), Bi W O ,
skite structures. It is helpful for the elucidation of the mechanism
of high-T superconductivity to discover new superconductors
Bi
2
2
O
9
2
3
O
4
3
O
12 were prepared by so-
c
2
6
3
were prepared from stoichi-
powders. The powders were
with layered perovskite structures not only from among cuprates
but also from among non-cuprates. Figs. 1a–c show crystal
structures of typical layered perovskites. The layered perovsk-
ites consist of interlayer blocks and perovskite-like slabs of
2 3
O
72 h. Bi and Bi
2
WO
6
2 2
W O
9
were prepared from stoichiometric
[
B
nÀ1
M
n
O
3n+1] with n being the number of octahedra stacked along
the direction perpendicular to the MO plane. Based upon the
interlayer blocks, these are classified into Ruddlesden–Popper
phases (A 3n+1]), Dion–Jacobson phases (A[BnÀ1
and Aurivillius phases (Bi [BnÀ1 3n+1]).
amounts of Bi O and WO
2 3
3
powders. The powders were mixed,
2
ground and heated in air at 800 °C for 48 h. Bi
Ti 12 were prepared from stoichiometric amounts of Bi
BaCO , Nb and TiO powders. The powders were mixed, ground
and heated in air at 900–1000 °C for 12–24 h. Bi NaSrNb 12 was
synthesized as follows. First, Bi SrNb was prepared from stoi-
chiometric amounts of Bi and Nb powders. The powders
were mixed, ground and heated in air at 1000 °C for 12 h. Next,
NaNbO was prepared form stoichiometric amounts of Na CO
and Nb powders. The powders were mixed, ground and heated
in air at 1000 °C for 1 h. Finally, the obtained single-phase samples
of Bi SrNb and NaNbO were mixed, ground and heated in air at
1100 °C for 3 h.
2 2 9
BaNb O and Bi4-
3
O
2 3
O ,
2
n
[BnÀ1M O
M
n
O3n+1])
3
2
O
5
2
2
O
2
M
n
O
2
3
O
The alkaline-metal intercalation is a promising method for the
electron doping. Many insulating materials can easily become
metallic or even superconducting through the alkaline-metal inter-
calation, because electrons are transferred from alkaline-metal
atoms to the host compound. So far, we have succeeded in synthe-
sizing the Ruddlesden–Popper phase of Li
3
using the electrochemical Li-intercalation technique. In this paper,
we report the electrochemical Li-intercalation into the Aurivillius
2
2 9
O
2
O
3
2 5
O
3
2
3
2 5
O
x
Sr
2
2 2
CuO X (X = Br, I) [1–
] and the Dion–Jacobson phase of Li ASr
x
2
Nb
3
O10 (A = Rb, Cs) [4]
2
2
O
9
3
The electrochemical Li-intercalation was carried out at room
temperature in an argon-filled glove box using a three-electrode
cell as shown in Fig. 2. The working electrode (WE) was a pelletized
sample with the dimensions of 7 mm in diameter and 1.5 mm in
thickness which was covered with Ni meshes. Li sheets were used
as the counter electrode (CE) and the reference electrode (RE). As
phase of Bi
12 and Bi
2
MO
Ti
6
(M = Mo, W), Bi
2 2 9 2 2 9 2 3
W O , Bi BaNb O , Bi NaSrNb -
O
4
3
O
12
.
*
Corresponding author. Tel.: +81 22 795 7977; fax: +81 22 795 7975.
E-mail address: h.tezuka@teion.apph.tohoku.ac.jp (H. Tezuka).
4
an electrolyte, 1.0 M LiClO dissolved in propylene carbonate (PC)
0
921-4534/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.physc.2008.05.020

H. Tezuka et al. / Physica C 468 (2008) 1152–1154
1153
Li (Bi O )(B M O3n+1)
x
2
2
n-1
n
3
.0
(c)
2
1
.0
.0
0
(
a)
(
e)
(d)
(b)
(f)
Fig. 1. Schematic crystal structures of layered perovskites when n = 3. (a)
Ruddlesden–Popper phase of 3n+1], (b) Dion–Jacobson phase of
A[BnÀ1 3n+1], (c) Aurivillius phase of Bi [BnÀ1 3n+1].
2 n
A [BnÀ1M O
M
n
O
2
O
2
n
M O
0
0.2
0.4
0.6
0.8
x (Li)
Fig. 3. Variation of the potential of the working electrode against the reference
electrode with the Li-content x at a constant current of 50 A in (a) Li Bi MoO , (b)
Bi SrNaNb 12 and (f)
l
x
2
6
Li
Li
x
Bi
Bi
2
WO
Ti
6
,
(c) Li
x
Bi
2 2
W O
9
,
(d) Li
x
Bi
2
BaNb
2
O
9
,
(e) Li
x
2
3
O
x
4
3
O
12
.
electrode with the Li-content x is shown in Fig. 3. The potential
+
rapidly decreases down to ꢀ1–2 V (vs. Li/Li ) and then becomes al-
+
most constant, indicating that Li ions are intercalated. In addition,
all of the samples have turned from light gray or yellowish white to
black through the Li-intercalation, indicating electron carriers were
doped into the host samples thorough the Li-intercalation. For all
compounds, powder X-ray diffraction patterns of the Li-interca-
lated samples were the same as those of the host samples. After
the Li-intercalation, no additional phase were observed, indicating
no formation of byproducts. Moreover, no change in the lattice
parameters through the Li-intercalation was observed within our
experimental accuracy. No superconductivity was observed above
2
K in the magnetic-susceptibility measurement. The absence of
superconductivity is guessed to be partly due to the localization
of electron carriers caused by the structural distortion. These host
samples are well-known ferroelectric compounds with structural
distortion which is characterized by the deformation of the MO
octahedra [5–7]. The deformation of the MO octahedra is caused
by three kinds of components; (i) tilting of the MO octahedra
due to the lattice mismatch between BO and MO planes, (ii)
displacement of M due to the strong covalency of the M–O bond
and (iii) displacement of the apical oxygen of the MO octahedra
6
6
Fig. 2. Schematic diagram of the three-electrode cell for the electrochemical Li-
intercalation.
6
2
6
was used. The total amount of Li intercalated into the sample was
estimated according to the simple Faraday law and also deter-
mined from the ICP analysis. There was a good agreement with
each other.
All products were characterized by powder X-ray diffraction.
Since Li-intercalated samples were unstable in air, they were
mixed with grease in order to avoid the exposure to the moisture
in the atmosphere during the measurements. The magnetic sus-
ceptibility was measured using a superconducting quantum inter-
ference device (SQUID) magnetometer in a magnetic field of 3 Oe.
due to the strong covalency of the Bi–O bond. Reduction of the
hybridization between Md and O2p orbitals in the asymmetric
6
MO octahedra may cause the localization of doped electron
carriers, resulting in the suppression of the appearance of
superconductivity.
4
. Conclusions
We have succeeded in the Li-intercalation into the layered
perovskite of Aurivillius phase, Bi
2
6 2 2 9
MO (M = Mo, W), Bi W O , Bi2-
BaNb , Bi NaSrNb 12 and Bi Ti O
2
O
9
2
3
O
4
3
12, using the electrochemical
3
. Results and discussion
technique. However, no superconductivity has appeared. The local-
ization of doped electron carriers due to the structural distortion in
the ferroelectric compounds may suppress the appearance of
superconductivity.
The Li-intercalation was carried out at a constant current of
0 lA for all samples. The variation of the potential of the working
5

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H. Tezuka et al. / Physica C 468 (2008) 1152–1154
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