04_Herrera


51

Synthesis of Pb-doped Bi-2223

* Corresponding author

ABSTRACT

Science Diliman (July-December 2002) 14:2, 51-58

Synthesis of Pb-doped Bi-2223 from Pb-doped Bi-2212,
Ca

2
CuO

3
,
 
and CuO Above the Glass Transition Temperature

of Bi-2212

Marvin U. Herrera1* and  Roland V. Sarmago2
1Materials Science and Engineering Program, College of Science

University of the Philippines, Diliman
2Condensed Matter Physics Laboratory

National Institute of Physics, College of Science
University of the Philippines, Diliman
Tel No.: 434-4260; Fax No. 920-5474
Email: 1mherrera@nip.upd.edu.ph

Synthesis of Pb-doped Bi-2223 from Pb-doped Bi-2212 (Pb=0.3),  Ca
2
CuO

3
,
 
and CuO was done by sintering

at the glass-phase temperature of Pb-doped Bi-2212. The sample sintered at 850°C possesses nearly 100%
Pb-doped Bi-2223, as revealed from the XRD pattern and magnetic susceptibility data. The presence of
holes, terrace-like features, and magma-like flow features in the SEM micrographs of the sample strongly
support a glass-state Pb-doped Bi-2223 formation.

Key words: Pb-doped Bi-2223,  glass transition temperature

INTRODUCTION

Bi-2223 has the highest critical temperature (110K)
among the superconducting phases of the Bi-Sr-Ca-
Cu-O system, but it is the most difficult to synthesize
(Khaled et al., 1996; Murayama et al., 1988; Shimojima
et al., 1989). The difficulty of preparing Bi-2223 lies in
the complexity of its structure and its narrow phase
stability. Considerable effort has been made in order to
synthesize single-phase Bi-2223 (Zhu et al., 1999).
Methods of increasing the volume fraction of Bi-2223
includes long sintering time (Yu et al., 1996; Hadano et
al., 1988), reduced oxygen partial pressure (Oka et al.,
1989; Hadano et al., 1988), control of composition (Endo
et al., 1989; Hadano et al., 1988), and Pb-doping (Hadano

et al., 1988). Although Bi-2223 in pure form is quite
difficult to achieve, substitution of lead enhances its
formation, and it is the most common way to increase
the volume fraction of Bi-2223. The role of lead in the
formation of Bi-2223, however, is still obscure.

Studies on Bi-2223 revealed that: (1) Bi-2212 precedes
the formation of Bi-2223 (Holesinger et al., 1996); and
(2) the presence of a liquid phase (Ono, 1988) and the
occurrence of partial melting (Hadano et al., 1988; Oka
et al., 1989) enhances its formation. Intercalation models
take into account that Bi-2223 comes from Bi-2212 via
insertion of Ca-Cu-O units. One variation of this model
states that CuO

2
/Ca bilayers are inserted into the CuO

2
/

Ca/CuO
2
 blocks of Bi-2212 to form Bi-2223 (Garnier

et al., 2000). Another states that insertion of CaCuO
2

slab into Bi-2212 results in the formation of Bi-2223
(Zhu et al., 1999). Nucleation and growth models are
about the involvement of a liquid phase in Bi-2223



52

Herrera and Sarmago

formation. Dissolution precipitation, low-level mobile
liquid droplet, partial molten-phase precipitation, and two-
dimensional nucleation growth describe the role of the
liquid in Bi-2223 formation (Garnier et al., 2000).

Since it was observed that Bi-2212 precedes Bi-2223
formation, using Bi-2212 as the starting material would
offer easier reaction since it would readily transform to
Bi-2223, as opposed to using carbonate and oxides as
precursors. The observed fluid-like movement that is
associated with increased Bi-2223 formation could be
Bi-2212 in its glassy phase. We use the term “glassy
phase” to describe the state in which a substance retains
some degree of crystallinity but possesses fluid-like
mobility. Glass state occurs above the glass transition
temperature and below the melting point. We expect
that a substance is more mobile in glassy phase, which
gives them the ability for faster reaction, than in solid
phase. The melting point of Bi-2212 (for certain Pb-
doped level ) is below the melting point of Bi-2223, so it
is possible to synthesize Bi-2223 at the glassy state of
Bi-2212. Differential thermal analysis (DTA) curves
of Bi-2212 is presented in the works of Liu et al. (1988).
Other substances which precedes Bi-2223 formation,
such as those belonging to the CaO-CuO system, have
melting points higher than that of the Bi-2223 system.
The phase diagram of  the CaO-CuO system is
presented in the works of Risold  et al. (1995).

The possibility of having a glassy state in Bi-2212 lies
in its structural anisotropy. The a,b plane of the
superconducting phases of the Bi-Sr-Ca-Cu-O system
(Bi-2212 and Bi-2223) are weakly bonded between the
neighboring BiO layers (Majewski, 2000). The weaker
bonding of a,b planes are dissociated at a lower
temperature (glass transition temperature) than the
bonding at other directions (that dissociates at the
melting point). When the bonding between the BiO layer
are dissociated, the a,b plane layers can move more
freely. There is still crystallinity within a layer since the
bonding between the b,c planes and a,c planes are still
present.

The concept previously stated indicates that to facilitate
the formation of Bi-2223, it is necessary to sinter the
sample at a temperature just below the melting point
where the glassy state is expected and has optimum
effect. For Pb-doped Bi-2223 (Pb=0.3), the candidate

sintering temperature for a fast-forming Bi-2223  would
be at 850°C. This temperature corresponds to the
position of the pre-peak of Bi-2212 endothermic curve
(Liu et al., 1998), which also corresponds to melting.

In this paper, Pb-doped Bi-2223 was synthesized from
Pb-doped Bi-2212 via partial melting in the glass state.
By avoiding decomposition, results indicate that Bi-2223
formation becomes faster and more homogeneous.
Magnetic Susceptibility measurements suggest that
conversion of Bi-2212 phase to the Bi-2223 is almost
100% complete.

METHODOLOGY

Stoichiometric amounts of oxide/carbonate precursor
powder were used to prepare Pb-doped Bi-2212
(Pb=0.3) and Ca

2
CuO

3 
via solid state reaction. These

were used as precursors for the formation of Pb-doped
Bi-2223. These were mixed with CuO to achieve a
stoichiometric amount of Bi-2223. The mixture was then
sintered at 830°C, 840°C, and 850°C for 50 to 150 hours.

The presence of Bi-2223 was detected using x-ray
diffraction (XRD) and was verified using Magnetic
Susceptibility. Confirmation using susceptibility
measurements was preferred over resistivity since the
former does not rely on granular connectivity to manifest
a signal. The samples were observed using a scanning
electron microscope (SEM).

RESULTS AND DISCUSSION

Our success in producing Bi-2223 from Bi-2212
(Pb=0.3), Ca

2
CuO

3
,
 
and CuO is verified by the magnetic

susceptibility data (Fig. 1) and the XRD patterns (Fig.
2). From the magnetic susceptibility measurements (Fig.
1B), the sample sintered at 850°C shows an almost
single phase Bi-2223, with a critical temperature of
103K.

The sample sintered at 830°C shows small amounts of
Bi-2223 (Fig. 2A). The sample is composed of
unreacted Bi-2212. Increasing the sintering time up to
150 hours does not show any significant increase in Bi-
2223 volume fraction. Fig. 2B shows the XRD pattern
of the sample sintered at 840°C, which shows



53

Synthesis of Pb-doped Bi-2223

Fig. 1. Magnetic Susceptibility of samples sintered for 50 hrs at (A) 840°C and (B) 850°C.

-2.5

-3.5

-4.5

-5.5

-6.5

-7.5

0 20 40 60 80 100 120

Temperature (oK)

S
u

s
c

e
p

ti
b

il
it

y
 (

A
rb

. 
u

n
it

s
)

A

-8.5
0 20 40 60 80 100 120

Temperature (oK)

-2.5

-3.5

-4.5

-5.5

-6.5

S
u

s
c

e
p

ti
b

il
it

y
 (

A
rb

. 
u

n
it

s
) B

proportionate amounts of Bi-2212 and Bi-2223 (the
volume fraction of Bi-2223 is approximately 40%).
Large Bi-2223 volume fraction is exhibited by the
sample sintered at 850°C (Fig. 2C). Practically, most
Bi-2212 is reacted to form Bi-2223. The volume
fraction at 830°C shows very slow reaction rate. In
fact, Bi-2223 is known to have a sluggish phase
formation (Zhu et al., 1999). Sintering at 850°C
greatly improved the volume fraction of Bi-2223.
The temperature 850°C is at the pre-peak of Bi-
2212 endothermic curve (Liu et al., 1998), which2QQQQQ

R
e

la
ti

v
e

 I
n

te
n

s
it

y

0

0.5

1

20 25 30 35

2QQQQQ

2
2
1
2 2
2
1
2

2
2
1
2

2
2
1
2

2
2
1
2

2
2
2
3

2
2
1
2

2
2
2
3

2
2
1
2

C
a 2

C
uO

3

A

0

0.5

1

R
e

la
ti

v
e

 I
n

te
n

s
it

y

20 25 30
0

0.5

1

C

2
2
2
3

2
2
2
3

2
2
1
2

2
2
2
3

2
2
2
3

2
2
2
3

2
2
2
3

C
a 2

C
uO

3

35

2
2
2
3

Fig. 2. XRD pattern of samples sintered for 50 hrs at (A)
830°C, (B) 840°C, and (C) 850°C.

20 25 30 35

2QQQQQ

2
2
1
2

2
2
2
3

2
2
1
2

2
2
2
3

2
2
1
2

2
2
1
2
, 2

2
2
3 2

2
1
2

2
2
2
3

2
2
1
2
, 2

2
2
3

2
2
2
3

2
2
1
2
, 2

2
2
3

C
a 2

C
uO

3

B



54

Herrera and Sarmago

corresponds to melting. In this temperature, Bi-2212 is
expected to be at its glassy phase, which possesses
higher mobility than the Bi-2212 in the solid phase.

The corresponding SEM images of the three samples
are presented in Fig. 3. The image in Fig. 3A is the
sample sintered at 830°C, showing unreacted
precursors. The grains are smaller in comparison with
Bi-2223 grains in the sample sintered at 850°C (Fig.

3C). The grain size of the samples sintered at 850°C is
the largest since it is sintered at a higher temperature.

Owing to the anisotropy of the superconducting phases
of Bi-Sr-Ca-Cu-O (Bi-2212 and Bi-2223), the rate of
crystallization about the a,b planes is much faster
(1000x) than in the c-direction (Majewski, 2000). Due
to the slow crystallization rate, the c-direction would
have the thinnest part in the grain. For comparison with

Fig. 3. SEM images of samples sintered for 50 hrs at (A)
830°C, (B) 840°C, and (C) 850°C.

2 mmmmmm

2 mmmmmm

2 mmmmmm

Fig. 4. (A) Crystallographic axis of Bi-Sr-Ca-Cu-O grain; (B)
SEM image of grains sintered at 830°C; and (C) SEM image
of grains sintered at 840°C.

b

a
c A

b

a

c

1mm
Acc. V.    Spot    Magn    Det                          WD    Exp
6.00kV     3.0    20000x   SE                          10.0    415

a

c
b

a b

c

B

5mm
Acc. V.    Spot    Magn    Det                          WD    Exp
6.00kV     3.0     4000x    SE                          15.0    429

a-b plane

C



55

Synthesis of Pb-doped Bi-2223

SEM images, the crystallographic direction of Bi-Sr-
Ca-Cu-O grains is presented in Fig. 4A. The a- and b-
directions could be treated isotropically. They can be
labeled arbitrarily in any direction in the plane
perpendicular to c-direction.

The relative proportions of both Bi-2212 and Bi-2223
phases from samples sintered at 840°C suggest that it
would be possible to observe the transformation of Bi-
2212 (frozen in the sample) to Bi-2223. Since the
reaction at  840°C is slower than the reaction at 850°C
(because the later temperature is higher), it is possible
to see remnants of Bi-2212 movements. These
movements are no longer apparent in samples sintered
at 850°C due to the rapid reaction rate.

By comparing the SEM images of the samples sintered
at 830°C and 840°C (Fig. 4B and Fig. 4C, respectively),
we could see the difference between the grains of
mostly unreacted sample (sample sintered at 830°C)
and those of the sample which reacted (sample sintered
at 840°C). The grains of samples sintered at 830°C are
unfused and stacked with other grains, while the grains
of the samples sintered at 840°C are fused with other
grains. These observations indicate that at 840°C the
sample becomes very soft and attain fluid-like movement
as compared with samples at 830°C, which are solid.
This agrees with the idea that the presence of fluid
enhances Bi-2223 formation (Khaled et al., 1996; Ono,
1988).

5 mm
Acc.V     Spot     Magn     Det      WD    Exp
6.00kV     3.0     4000x     SE      19.5    429

Terrace-like feature

Hole

Magma-like flow

Fig. 5.  SEM image of sample sintered at 840°C showing
terrace-like feature, magma-like flow, and holes.

Further examination of the sample sintered at 840°C
reveals the presence of terrace-like structures, fluid-
like movements, and holes (Figs. 5, 6, and 7). Two
important characteristics of these features include: (1)
movement between planes that are manifested by the
displacement of one layer with respect to other layers;
and (2) there exists a degree of order within a plane as
exemplified by the layered orientation of the plane.
These are the features of a substance in the glassy
state. Fig. 6 shows the layered structure where one
layer is displaced with respect to other layers, resembling
a terrace. Fig. 7 shows the presence of a magma-like
flow feature (Fig. 7A) and holes (Figs. 7B, 7C, and
7D). Holes also have a structure similar to a terrace.
Fig. 8 shows the possible mechanism, which happens
to the Bi-2212 grains. Fig. 8A shows the initial condition
of Bi-2212. The bonding in all directions is still intact.
When Bi-2212 is brought above the glass transition
temperature (Fig. 8B), the bonding between the Bi-O
layers (a-b planes) is dissociated. When this happens,
the a-b planes can move freely with respect to each
other. Since the bonding in the other directions is still
intact, a degree of order still exists within a plane.

The fast formation of Bi-2223 from the glassy phase of
Bi-2212 could explain the relationship between the
existence of fluid-like movement and large Bi-2223
volume fraction. The increase in the rate of Bi-2223
formation is a result of the higher mobility of Bi-2212,
due to the freely moving a-b planes of Bi-2212 above
the glass transition temperature. This allows Bi-2212
to move faster and react with other reactants to form
Bi-2223. This shows the importance of fluid-like
movement in Bi-2223 formation.

The above concept offers a possible explanation
regarding the relationship between the increase in Bi-
2223 volume fraction and the increase in Pb-doping.
Likewise, it could also explain the existence of an
optimum value of Pb-doping in Bi-2223. The melting
point of Bi-2212 decreases with an increase in Pb-
doping. DTA of Bi-2212 with different Pb-doping levels
is presented in the works of Liu et al. (1998). For a
sample sintered at a particular sintering temperature
(below the melting point of undoped Bi-2212), increasing
the amount of  Pb-doping entails the glass state to be
nearer the sintering temperature, which results in faster
reaction. Optimum Pb-doping exists when the melting



56

Herrera and Sarmago

temperature of Pb-doped Bi-2212 is just below the
sintering temperature. Further increase in the amount
of Pb will result in the melting of the sample.

SUMMARY AND CONCLUSION

Pb-doped Bi-2223 (Pb=0.3) from Pb-doped Bi-2212
(Pb=0.3), Ca

2
CuO

3
,
 
and CuO, at the glassy phase of

Bi-2212, was successfully prepared. The Bi-2212
phase dominates the samples sintered at 830oC. At
840°C, Bi-2212 and Bi-2223 phases coexist at almost
equal proportions. At 850°C, Bi-2223 dominates such
that the presence of Bi-2212 is no longer discernible
from the susceptibility measurements. SEM
investigation reveals the presence of frozen, fluid-like
movement in the material, which is attributed to the
formation of a glassy phase of the sample sintered at
840°C and above. This glassy phase is responsible
for the enhancement of Bi-2223 formation because
Bi-2212 can move freely to react with Ca

2
CuO

3 
and

CuO.

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Endo, U., S. Koyama, & T. Kawai, 1989. Composition
dependence on the superconducting properties of Bi-Pb-
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Fig 6. SEM image of sample sintered at 840°C showing
terrace-like feature.

5 mmmmmm

2 mmmmmm

5 mmmmmm

2     mmmmmm



57

Synthesis of Pb-doped Bi-2223

Khaled, J., T. Komatsu,  & K. Matusita, 1996. A new model
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Sr

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O

x
 glass-ceramics. J. Mater. Sci. Mater.

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O

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-SrO-CaO-CuO system. J. Mat. Res.

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B
Hole

c

A

c

aa

Fig 8. (A) Bi-2212 grains below glass transition
temperature; and (B) movement of Bi-2212 above the glass
transition temperature.

2 mmmmmm 5 mmmmmm

5 mmmmmm
2 mmmmmm

Fig 7.  SEM image of sample sintered at 840°C showing magma-like flow feature (A) and holes (B-D).



58

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