DSpace at VNU: Properties of the bi-surplus superconducting Bi2.1-xPbxSr2Ca2Cu3Oy compounds

Journal of Magnetism and Magnetic Materials 262 (2003) 514–519

Properties of the Bi-surplus superconducting
Bi2.1ÀxPbxSr2Ca2Cu3Oy compounds
N.H. Sinh*
Cryogenics Laboratory, Faculty of Physics, College of Natural Science, Hanoi National University,
334 Nguyen Trai Road, Thanh Xuan, Hanoi, Viet Nam

Abstract
Properties of the Bi-surplus superconducting Bi2.1ÀxPbxSr2Ca2Cu3Oy (x ¼ 0:0020:60) compounds have been
investigated. It is found that Pb plays a very important role in the formation of the superconducting phases with high
purity and especially in promoting and enhancing the stability of the 2223 phase in (Bi,Pb)–Sr–Ca–Cu–O compounds.
By increasing the duration of the heat treatment, the single-phase region will be widened, while the transition
temperatures and values of zero-resistance remain nearly unchanged. With suitable heat treatment, the 120 K high-TC
phase can be synthesized by the solid-state reaction method. The superconducting fraction reaches a maximum in the
compounds with x ¼ 0:3020:60: Special attention is paid that the superconducting state is destroyed by annealing in
vacuum for the compound with x ¼ 0:40:
r 2003 Elsevier Science B.V. All rights reserved.
PACS: 74.72.Hs
Keywords: Superconductors; High-T C; Heat treatment; Role of Pb; Superconducting fraction

1. Introduction
Many studies have been made on the high
temperature superconductivity in the 2223 phase
of the Bi–Sr–Ca–Cu–O system, but most of the
studies have been carried out using samples
including a small portion of this phase, because
the 2223 phase was difficult to prepare as a single
phase. Some authors [1–3] pointed out that the
addition of Pb to the superconducting (Bi,Pb)–Sr–
Ca–Cu–O compounds leads to higher TC values,

because Pb might increase the ratio of Cu3+ to
*Corresponding author. Tel.: +84-4-8585281; fax: +84-48584438.
E-mail address: (N.H. Sinh).

Cu2+. On the other hand, Pb improves the
connectivity between regions of the 2223 structure
[4,5], and promotes the formation of a 2223 nearly
single-phase sample.
The Bi-based superconductors offer potential
advantages in comparison to the Y -based superconductors. These include a better resistance to
reactions with water or carbon dioxide and being
stable in terms of oxygen stoichiometry. There are
three superconducting phases, denoted as 2201,
2212 and 2223 in the Bi-based high temperature
superconductors. The structure similarity of these
three phases suggests the phase intergrowth of
2212 from 2201 and 2223 from 2212 through an
intercalation-diffusion of Ca and Cu atoms over a
short distance. The addition of Pb enables the

0304-8853/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0304-8853(03)00088-X


N.H. Sinh / Journal of Magnetism and Magnetic Materials 262 (2003) 514–519

synthesis of an almost pure 2223 phase, especially,
with a surplus of Bi as in Bi2.1ÀxPbxSr2Ca2Cu3Oy.
The present work, studies the properties and the
formation of the Bi-2223 phase in nominal

compositions of Bi2.1ÀxPbxSr2Ca2Cu3Oy.

2.1. Relation between formation of the
superconducting phases and heat treatment process
Samples with nominal compositions of
Bi2.1ÀxPbxSr2Ca2Cu3Oy (x ¼ 0:0020:60) were prepared in air by the solid-state reaction method.
The starting materials were powders of Bi2O3,
PbO, SrCO3 and CuO (all of 3N purity). Our aim
was to set-up a reproducible procedure for
preparing a 2223 phase as pure as possible. The
powders were manually mixed and ground for
60 min and then pressed into pellets of about
20 mm in diameter and 2 mm in thickness. Sintering took place in air at 840–860 C during times
varying from 24 to 144 h, followed by annealing at
500–520 C for the same time variation. Finally,
the samples were furnace cooled to room temperature. A sample of Bi1.7Pb0.4Sr2Ca2Cu3Oy was
quenched after the heat treatment in vacuum and
in flowing oxygen.
The sintering temperature versus time in range
of 750–910 C establishes the diagram on the
formation of the superconducting phase as
presented in Fig. 1. This diagram shows the
relation between the formation of the superconducting phases and the heat treatment in
the Bi-surplus Bi2.1ÀxPbxSr2Ca2Cu3Oy compounds
(x ¼0:1020:60). As suggested in Ref. [3] the
formation of the 2223 phase is associated with
the formation of Bi/Pb rich mobile liquid droplets,
which migrate over the growing platelets.
This phenomenon may correspond to a fast
chemical reaction with an interconnection of 2212

platelets in the presence of the liquid phase [4]. The
presence of this liquid phase would enhance
significantly the diffusion process of Ca2+ and
Cu2+ ions by dissolution of the impurity phases.
Still the role of Pb, present in Ca2PbO4 and PbO,
is important in enhancing the stability and

1000
Liquid State
900

Unstable Superconducting + Liquid State
2201 + 2212 2212 + 2223 2223 + 2212 (little)

Sintering temperature (T °C)

2. Results and discussion

515

Unstable mixed phases

800

2201

2201 + 2212 (little)

700

600

500

No Superconductivity

400
Insulating
300
0

24

48

72

96

120 144 168

Sintering time (t hours)
Fig. 1. The formation of the superconducting phases in
Bi2.1ÀxPbx Sr2Ca2Cu3Oy compounds.

promoting the formation of the 2223 phase in
the (Bi, Pb)–Sr–Ca–Cu–O system.
With respect to the solubility, we can suggest
that the solubility region of Pb into compositions
to form the 2223 single phase is shifted to Bisurplus concentrations with a Bi content smaller

than or equal to 2.1 with sintering-temperatures
in the range of 840–860 C. There is an optimum in
the (Bi+Pb):Cu concentration. In our case the
ratio of 2.1:3 dropped into the 2223 single-phase
range.
2.2. X-ray powder diffraction
Fig. 2 shows XPD patterns, which are typical
for the prepared samples. From the X-ray diffraction patterns, we can see that the samples with
x ¼ 0:00 and 0:10 containing two different superconducting phases, which belong to the 2212 and
2223 phases. The results reveal that the amount of
the 2223 phase increases and that the amount


516

N.H. Sinh / Journal of Magnetism and Magnetic Materials 262 (2003) 514–519
Table 1
Lattice
parameters
(x ¼ 0:0020:60) system

of

the

Bi2.1ÀxPbxSr2Ca2Cu3Oy

X

(2 2 1 2) phase

Pb

(
a;b (A)

(
c (A)

(
a; b (A)

(
c (A)

0.00
0.10
0.20
0.30
0.40
0.50
0.60

5.410
5.408
5.405
—
—
—
—

30.815
30.825
30.840
—
—
—
—

5.410
5.408
5.405
5.398
5.392
5.384
5.380

37.110
37.150
37.225
37.243
37.258
37.281
37.290

(2 2 2 3) phase

a

37.30

°

c
°

5.42

37.25

37.20

5.40

37.15

5.38
37.10
0.00

0.40

0.80

Concentration
Fig. 3. Lattice parameters of Bi2.1ÀxPbxSr2Ca2Cu3Oy compounds as a function of Pb-concentration (Pb=0.00–0.60).

increasing the Pb concentration. No structure
transformation due to the high Pb-concentration
has been observed in this system.

Fig. 2. XPD patterns for samples of composition: (a) Bi2Sr2Ca2Cu2Oy, and (b) Bi1.7Sr0.4Ca2Cu2Oy.

2.3. Resistivity and AC susceptibility

of the 2212 phase decreases with increasing
calcination temperatures and Pb concentrations.
The 2223 phase occupies nearly 100% of the
sample for x ¼ 0:3020:60:
The structure of the 2223 phase is tetragonal as
determined and presented in Table 1. The influence
of the substituted Pb concentration on the lattice
parameters of the single 2223 phase is illustrated in
Fig. 3. The lattice parameters slightly change by

Results of resistance and AC susceptibility
measurements are shown in Fig. 4a and b. It is
clearly observed that there are two phases in the
samples with x ¼ 0:00 and 0.10. For the samples
with x ¼ 0:3020:50 (x ¼ 0:20 and 0.60 was not
shown in the figure), the transitions from metallic
to superconducting state with decreasing temperature very sharply occur at TC : From these
resistance and AC-susceptibility curves, the transition temperature TC has been determined. It is


N.H. Sinh / Journal of Magnetism and Magnetic Materials 262 (2003) 514–519

517

125

1.0
(a)

120
(a)

115

0.6

T (K)

R (T)/R (300 K)

0.8

(c)
(b)

110

a:x = 0.5

0. 4

105

b:x = 0.5
c:x = 0.5

0.2

0.1

0.3

0.5

0.7

Concentration

0.0

50

100

150

200

300

250

Fig. 5. Dependence of TC
Bi2.1ÀxPbxSr2Ca2Cu3Oy.

on the Pb-concentration in

(b)

χac (arb.u)

0

0:x = 0 (
1:x = 0.1 (
3:x = 0.3 (
4:x = 0.4 (
5:x = 0.5 (

60

100

140

)
)
)
)
)

-1

180

T (K)

Fig. 4. (a) Temperature dependence of the linear resistivity,
showing a zero-resistance temperature of 100.5, 99.5 and 98 K
for the samples with x ¼ 0:30; 0.40 and 0.50, respectively.
(b) Temperature dependence of the ac susceptibility of
Bi2.1ÀxPbxSr2Ca2Cu3Oy compounds.

confirmed that the substitution of Pb in the range
of x ¼ 0:2020:40 for Bi in Bi-surplus compounds
of Bi2.1ÀxPbxSr2Ca2Cu3Oy has increased TC : The
highest value of TC about 120 K has been reached
at x ¼ 0:40: The dependence of TC on the Pbsubstitution concentration (x) is shown in Fig. 5.
This figure shows a parabolic behaviour of TC as a
function of the doping hole concentration. Similar
behaviours in some other systems of ours have
been found and reported in Ref. [6].

In the Bi-based superconductors, the holes are
confined to the O2p orbitals in the CuO2 planes.
Therefore, the variation of holes by substitution in
Bi-based superconducting compounds will lead to
variation of TC as a function of holes concentration in CuO2 planes. With increasing hole concentration TC reaches to a maximum value and
starts to decrease at the higher doping level. This
character is accompanied by the changing valence
of Cu in Bi2.1ÀxPbxSr2Ca2Cu3Oy compounds, also.
The zero-resistance temperature monotonically
decreases from 100.5 K at x ¼ 0:30 to 97 K at x ¼
0:60: The fraction of 2223 phase increases by
increasing the Pb-concentration up to x ¼ 0:60
and reaches nearly the same values in samples with
x ¼ 0:3020:60:

2.4. Variation of properties of
Bi1.70Pb0.40Sr2Ca2Cu3Oy compound
The sample of x ¼ 0:40 has a highest value of
TC (120 K) when it was heat-treated in air. We
have investigated the properties of this sample by
annealing it in vacuum and in flowing oxygen at
720 C, both for 72 h. Results have been obtained
by measurements of XPD, resistivity, susceptibility
and SEM.
XPD patterns indicate that there is no peak
identifying a superconducting phase when the
sample is annealed in vacuum. The resistivity
versus temperature curve of this sample is shown


N.H. Sinh / Journal of Magnetism and Magnetic Materials 262 (2003) 514–519

518

725

BPSCCO

R (Ω)

700

675

(a)

650

50

100

150
200
T (K)

250

300

Fig. 6. Temperature dependence of electrical resistivity of
Bi1.7Pb0.40Sr2Ca2Cu3Oy compound with annealing in vacuum.

in Fig. 6. The XPD patterns of the otherwise heattreated samples can be identified with the Bi-2223
superconducting phase. The calculated lattice
( and c ¼ 37:245 A,
(
parameters are a ¼ b ¼ 5:402 A
(
resulting in a unit cell volume of V ¼ 1086:86 A3,
for the sample annealed in flowing oxygen. For
comparison, the corresponding values for the
(
sample annealed in air are a ¼ b ¼ 5:392 A,
3
(

(
c ¼ 37:285 A and V ¼ 1058:06 A . It is shown that
the unit cell volume of the air annealed sample is
smaller than that of the oxygen annealed sample.
The value of TC of the oxygen annealed sample
has been obtained from resistivity and susceptibility measurements to be about 120 K. This value
is the same as the one of the air annealed sample.
These results indicate the important role of oxygen
in the creation of superconductivity. The superconductivity has been destroyed by oxygen deficiency (annealing in vacuum), but there is no
influence on TC by the oxygen excess (annealing in
flowing oxygen).
Typical SEM pictures of Bi1.7Pb0.4Sr2Ca2Cu3Oy
are shown in Fig. 7a–c for the samples annealed in
vacuum (a), in air (b) and in flowing oxygen (c),
respectively. The SEM pictures show a clear
change of the grain size. The grain size and the
distribution of grains on the surface of the sample
are quite different. This indicates the influence of
the different annealing conditions on the properties of the sample.

(b)

(c)
Fig. 7. SEM micrographs showing the surface morphology
of the Bi1.7Pb0.40Sr2Ca2Cu3Oy compound with annealing in:
(a) air, (b) vacuum, and (c) flowing oxygen.

In conclusion, the formation process of the 2223
phase in our samples can be shortly described as
follows.

The liquid phase generated by sintering in the
powder reacts with 2212 regions via Ca, Cu, and
Pb ion diffusion, resulting in the nucleation of
the 2223 phase. The diffusion process controls
the nucleation growth. The dependence of TC on


N.H. Sinh / Journal of Magnetism and Magnetic Materials 262 (2003) 514–519

Pb-concentration in the Bi2.1ÀxPbxSr2Ca2Cu3Oy
compounds has a parabolic character, with the
highest TC value of about 120 K at x ¼ 0:40:
Pb appears to play an important role in the
formation of the 2223-superconducting phase. A
crucial role is found also for oxygen, in the
creation and destruction of superconductivity.
A strong effect of Pb on the properties of
Bi2.1ÀxPbxSr2Ca2Cu3Oy compounds has been observed. It is suggested that the substitution of most
of the Pb ions at the Bi-site, is responsible for the
identified behaviour.

Acknowledgements
The author wishes to acknowledge the great
interest of Dr. Nguyen The Hien and of Mr. Do

519

Hong Minh from the Cryogenic Laboratory for
their help in editing this paper. This work is
supported by National Fundamental research

program No. 421101/2002.

References
[1] Y.S. Sung, E.E. Hellstrom, Phys. C 252 (1995) 155.
[2] Peter Majewski, Stefanic Kaesche, Huang-Iung, Fritz
Aldinger, Phys. C 221 (1994) 295.
[3] K. Eaiprasertsak, I.M. Tang, W. Tontiwttana, Phys. Lett. A
142 (8, 9) (1989) 519.
[4] S.M. Green, C. Jiang, Y. Mei, H.L. LuO, C. politis, Phys.
Rev. B 38 (1988) 5016.
[5] H.K. Lue, S.X. Dou, N. Savvides, J.P. Zhou, N.X. Tan,
A.J. Bourdillon, M. Kviz, C.C. Sorrell, Phys. C 157
(1989) 93.
[6] N.H. Sinh, Phys. C 252 (1995) 147.