Structural and physical properties of Cd doped
Bi1.64Pbo.36 Sr2Ca2-xCdxCu3Oy superconductor
S. E. Mousavi Ghahfarokhi* and M. Zargar Shoushtari
Physics Department, Shahid Chamran University, Ahvaz, I. R. Iran
musavi_ebrahim@yahoo.co.uk
m_zargar@scu.ac.ir
Abstract
The effect of Cd doping on the structure and physical properties of the Bi-Pb-Sr-Ca-Cu-O
system with a nominal starting composition of Bi1.64Pbo.36Sr2Ca2-xCdxCu3Oy (BPSCCC)
(x = 0.0, 0.02, 0.04, 0.1, 0.5, 1 and 2) was studied. The BPSCCC superconductor was
made by a solid state reaction method. The structural analysis was carried out using
XRD, SEM and EDX measurements. The critical temperature, critical current density and
flux pinning energy were measured by the standard four-probe method. The resistivity of
Cd-doped samples at room temperature increased in proportion to the increase in the
amounts of Cd. On the contrary, it decreased as the annealing time increased. Also for all
samples the relation between the current and voltage in the mixed state was found to
follow the model relationship V = I. In addition, small amount of doping (x = 0.04) has
been found to improve the superconducting properties of the Bi-Pb-Sr-Ca-Cu-O system.
Keywords: Superconductor; Cd substitution; magnetic susceptibility
PACS: 74.72.Hs
*
Corresponding
author:
S.
E.
Mousavi
Ghahfarokhi
musavi_ebrahim@yahoo.co.uk, Phone: +986113331040, Fax: +98611333104
1
e-mail:
1. Introduction
The critical temperature of the Bi-Sr-Ca-Cu-O system was shown to be 105 K by Meada
[1]. The Bi2Sr2Can-1CunOy system has layered structure, and according to their chemical
compositions it has three different phases which are called the Bi-2201 phases (n = 1, Tc
20K), the Bi-2212 phase (n = 2, Tc 85K) and the Bi-2223 phase (n = 3, Tc 110 K).
Here, we have used the abbreviation Bi-2201, Bi-2212 and Bi-2223 phases for n =1, 2
and 3, respectively. In these series, the Bi-2223 phase is the most attractive, because it
has the highest critical temperature, Tc, about 110 K [2, 3]. It is generally known that
chemical doping plays a very important role in high-Tc superconductivity. A large
number of elements have been doped into the Bi-Sr-Ca-Cu-O system [4]. However, the
preparation of the Bi-2223 Phase is too difficult and its formation is influenced by many
preparation conditions such as, composition, annealing time and temperature, atmosphere
and pressure during sintering, type and quantity of the dopant, heat-treatment method,
and operational procedures. Takano and et al showed that the incorporation of Pb in the
nominal composition of this system is very effective in increasing the volume fraction of
the high Tc phase [5-12]. Since the discovery of Bi-2223 superconductor, great progress
has been achieved in enhancing transport properties of this high-Tc superconductor.
However, the major limitations of the Bi-based superconductor application are the
intergrain weak links and weak flux pinning capability. The one of the major current
limiting factors in Bi-2223 phase is the presence of residual secondary phases. The
analysis of samples revealed that the Bi-2201 phase was located mainly between the
superconducting grains and preventing the super current flow [13]. The partial
replacements of Ca by Y and Gd in the Bi-2212 and Bi-2223 phases decreased carrier
concentration due to structural modulations and changes in the valence of Cu
2
[14-16]. The tremendous effort has been applied to improving the links between the
grains and the properties of the Bi-based superconductor, such as doping of them by Sn
and Sb [17,18], Ag [19, 20], Cd [21, 22] and Zr, Hf, Mo, and W [23]. In this work the
effects of Cd substitution instead of Ca in Bi1.64Pbo.36Sr2Ca2-xCdxCu3Oy (x = 0.0, 0.02,
0.04, 0.1, 0.5, 1 and 2) system was studied. The critical temperature, critical current
density, flux pinning energy, magnetic susceptibility, and microstructure properties of a
series of samples were studied.
2. Material and methods
Samples of Bi1.64Pbo.36Sr2Ca2-xCdxCu3Oy with x = 0.0, 0.02, 0.04, 0.1, 0.5, 1 and 2, were
prepared by the solid state reaction method. The fine powders of Bi2O3, PbO, SrCO3,
CaCO3, CuO and CdO with high purity were used. The required quantities of reagents
were weighed (m = 10-4mg). In order to prevent the growth of additional phases during
the process, the powders were ground and milled for an hour. The mixed powders were
calcined at 1093 K for 15 hours in air. Then they were taken out from the furnace,
re-ground, and pressed (with 250 bars) into the shape of pellets and bars. Then, they were
put in an alumina crucible and placed in the furnace and the procedure of sintering was
done at 1118 K in an air atmosphere. All of the samples were given the Meissner effect
test in liquid nitrogen. The critical temperature (at a constant DC current of 40 mA), flux
pinning energy, and the critical current density of the samples were measured by the
standard four-probe method. The AC magnetic susceptibility measurements were
performed using a Lake Shore AC susceptometer, Model 7000. The X-ray diffraction
(XRD) patterns of the samples were taken with a Philips X-ray diffractometer Model
3
PW1840. The microstructure characterization was performed, by SEM and EDX using a
scanning electron microscope Model 1455VP made by of the LEO Company.
3. Results and discussion
The XRD measurements of the samples are shown in figure 1. Based on the XRD
measurements, as is observed that by substitution of Cd instead of Ca up to an amount of
x = 0.04, the Bi-2223 phase increases in the sample and Cd seems to act as a phase
stabilizer. As one can see, the samples consist of a mixture of Bi-2223, Bi-2212 and
Bi-2201 phases as the major constituents. Also the XRD measurements shows that the
volume of Bi-2223 phase decreases with increasing Cd content (sample c) and the
optimum amount of cadmium is about x = 0.04 (sample b), which has the highest volume
fraction of Bi-2223 phase. The volume fraction of the phases can be estimated by various
methods.
The
all
of
the
peaks
Bi 21.8112  Bi1.6 Pb0.04 Sr1.81CaCu2 O8.716
of
the
Bi-2223,
Bi-2212,
Bi-2201,
CdO and Cd phases have used for the estimation
of the volume fractions of the phases and ignored the voids peaks.
The percentage of each phase in the samples was calculated as follows:
Bi (2223)(%) 
 I Bi 2223  100
Bi (2201)(%) 
 I Bi 2201  100
Cd (%) 
Bi (2212)(%) 
A
Bi 21.8112%  
A
 I Cd   100
 I Bi 2212  100
 I Bi 21.8112  100
CdO%  
A
4
A
A
 I CdO  100
A
where
A   I Bi 2223   I Bi 2212   I Bi 2201   I Bi 21.8112   I Cd    I CdO
and "I" is the
intensity of the phases present in the sample. The volume fractions of the phases for all
the samples were given in the table 1. As is shown in the table 1, the maximum volume
fraction of Bi-2223 phase is obtained for the sample with x = 0.04 (sample b). By
increasing the amounts of Cd to more than 0.04, the volume fraction of the Bi-2223 phase
will decrease. By decreasing x to amounts less than 0.04, the volume fraction of the
Bi-2223 phase also will decrease.
Figure 2 shows that the temperature dependencies of the real,   , and imaginary,   , are
parts of the AC magnetic susceptibility for samples with amounts of x = 0.0 and 0.04 in
ac field of 50 A/m with a frequency of 333 Hz which is applied parallel to the long
dimension of samples. In particular, the imaginary component,   , of the AC magnetic
susceptibility has been widely used to probe the nature of weak links in polycrystalline
superconductors. They are also employed to estimate some of the important physical
properties, such as the critical current density and the effective volume fraction of the
superconducting grains [24]. The real part of the AC magnetic susceptibility,   , in
polycrystalline samples shows two drops as the temperature is lowered below the onset of
the diamagnetic transition and correspondingly the derivative of the   (T) and displays
two peaks. The first sharp drop at the critical temperature is due to the transition within
the grains and the second gradual change is due to the occurrence of the superconducting
coupling between grains. The imaginary part,   , shows a peak which is a measure of the
dissipation in the sample. When the peak of   shifts to lower temperatures and broadens,
the interganular coupling between the grains, the critical current density and the flux
pinning energy will decrease. The curves shows that the interganular coupling between
the grains, the critical current density, and the flux pinning energy of the samples are
5
increased by increasing the amount of cadmium up to x = 0.04. Therefore, the
interganular coupling between grains, the critical current density and the flux pinning
energy in the sample x = 0.04 is better than the sample x = 0.0.
The results of AC-magnetic susceptibility measurements are shown in figure 3 – (a), (b)
and (c) for the samples with x = 0.0, 0.02 and 0.04 with and an annealing time of 270
hours for various ac fields. The diamagnetic onset temperature of the intrinsic
superconducting transition for these samples is about 107.5 K. It is clear from figure 3
that as the field increases the peak of   shifts to lower temperatures and will broaden.
Also, the effect of field on the intergranular component in the real part (   ) shifts to
lower temperatures. The amount of shift is as a function of the field amplitude, HAC,
which is proportional to the strength of the pinning force. When the pinning force
becomes smaller, it shows that the critical current will decrease. As seen in the figure 3
by increasing the HAC of the sample with x = 0.04, is more stabilized than the others. This
is not only dose of Cd act as a Bi-2223 phase stabilizer; it is also caused some
improvement in connectivity between the grains.
As figure 4 shows that by increasing x = 0.0 to = 0.04, Tc (onset) and Tc (offset) of the
samples will increase. When the amount of cadmium is more than 0.04, Tc (onset) and
Tc (offset) of the samples are decrease. The -T curves are shown in figure 5 for the
sample with x = 0.04 at different annealing time. One can observe that by increasing the
annealing time (t) up to 270 hours, Tc (onset) and Tc (offset) of the samples will increase.
The results of measurements show that the maximum Tc (onset) and Tc (offset) were
found for sample of the Bi1.64Pb0.36Sr2Ca1.96 Cd0.04Cu3Oy, which annealed for 270 hours.
The Tc (offset) versus the Cd content is shown in tables 2, 3 and 4 for different sintering
times. Clearly show that the Tc (offset) of the samples increase by increasing the amount
of Cd up to x = 0.04 and then the Tc (offset) extremely decreases for x  0.04. Also, by
6
increasing the sintering time up to 270 hours, the Tc (offset) of the sample will increase.
The enhancement of the Bi-2223 phase in the sample will increase the Tc (offset). In
addition, the XRD data show that by increasing the Cd content to more than 0.04, the
amounts of the other phases in the Bi-Sr-Ca-Cu-O system will increase, which causes a
decrease in the Tc (offset). Therefore, the maximum of the Tc (offset) were observed for
the sample with Cd content of 0.04 and sintering time of 270 hours. In tables 2, 3 and 4
also are shown that by increasing the sintering time up to 270 hours, the Tc (offset) of all
the samples will increase. The results of this investigation are consistent with the results
of the XRD measurements shown in Fig. 1.
The curves V – J are shown in figure 6 for the sample with x = 0.04 at different annealing
time. One can observe that by increasing the annealing time, the critical current densities
of the samples will increase. As annealing time is increases, the pinning energy will also
increase. Figure 7 shows that the V-J curves for doped samples with different amounts of
Cd after an annealing time of 270 hours.
The critical current density (Jc) versus the amount of Cd in the samples is shown in tables
2, 3 and 4 for different annealing times. Our observations suggested that not only dose Cd
(x = 0.04) act as a Bi-2223 phase stabilizer, but also is causes some improvement in
connectivity between the grains. Tables 2, 3 and 4 show that if the Cd content up to 0.04;
the
Jc
will
increase
as
well.
The
maximum
Jc
was
found
for
Bi1.64Pb0.36Sr2Ca1.96Cd0.04Cu3Oy, annealed for 270 hours. When the amount of cadmium is
more than 0.04, the
amount
of
unwanted phases,
such as
Bi-2212
and
Bi-2201, are increase in the sample. These unwanted phases play the role of weak links
and will decrease the critical current density. It is shown that the Bi-2201 phase locates
mainly between the superconducting grains, and preventing the super-current flow. It was
also shown that Jc was raised as the Bi-2212 phase decreased in Bi-2223 tapes [25].
7
The room temperature V–I curves are shown in figure 8 for the sample with x = 0.04 at
different annealing times. One can see that the normal state resistance of the samples will
decrease by increasing the annealing time. This means that the junctions between the
grains have been improved in the sample by increasing the annealing time.
The curves V-I are shown in figure 9 for different amounts of Cd after an annealing time
of 270 hours at room temperature. It can conclude that for the amounts of cadmium are
more than 0.04, the resistance of normal state of the samples will increase. Because, by
adding a higher amount of CdO to the samples, the other unwanted phases would form.
These phases will weaken the junctions between the grains and therefore, the electrical
resistance of normal state will increase.
The resistance (R) of the doped samples as a function of the cadmium content is shown in
tables 2, 3 and 4 for different annealing times at room temperature. By increasing the
annealing time up to 270 hours, the R will decrease as well. So, the minimum R was
found for Bi1.64Pb0.36Sr2Ca1.96Cd0.04Cu3Oy sample, annealed for 270 hours. When the
amount of cadmium is more than 0.04 the R of the samples will increase. Because, by
adding a higher amount of CdO to the samples, other unwanted phases would form.
These phases will weaken the junctions between the grains and therefore, the electrical
resistance of the normal state will increase
Moreover, for all samples, the relation between the current and voltage in the region
between Jco (onset of resistive state) and Jc (onset of normal state) follows the power law
model of V I [26, 27] which one of the sample curves is shown in Fig. 10. These
results have been derived from of curves logV- logI (see Figs. 11 and 12) which are
plotted in the region between Jco and Jc. The value of  for each sample is calculated.
Considering the value of  and the relationship of  = U/kBT [28], where U is the pinning
potential, it can be concluded that prolongation of annealing time, leads to an increase in
8
flux pinning energy. In other words, the average force on the flux for depinning will
increase.
The flux pinning energy (U) versus the amount of Cd in the samples are shown in tables
2, 3 and 4 for different annealing times. These tables show that if increase the Cd content,
U also will increases. Also, by increasing the annealing time up to 270 hours, U, will
increases as well. So, the maximum U was found for Bi1.64Pb0.36Sr2Ca1.96Cd0.04Cu3Oy
annealed for 270 hours. When the amount of cadmium is more than 0.04, the amounts of
unwanted phases, such as Bi-2212 and Bi-2201, will increase in the sample. These
unwanted phases play the role of weak links and decrease the flux pinning energy.
The result of EDX measurements show that there is no unwanted element in the samples,
which means, the samples are not contaminated during the synthesis process (see Fig.
13).
The SEM micrographs are shown in figure 14- (a), (b) and (c) for the samples, with
amounts of cadmium (x) = 0.0, 0.04 and 2 and with annealing time of 270 hours. It
shown that the sample with x = 2 (c) is partially melted. It seems increasing the amount
of Cd leads to the formation of a liquid phase that act as an insulating layer around the
superconductor grain. Also, for the amount of x = 0.0 (b) leads to the formation of more
pores. These pores act as a weak links between the grains. These pores and insulators
layers destroy grains connectivity and disrupt current flow. These results are in
agreement with the results of the X-ray diffraction measurements and the critical current
densities.
Figure 15- (a) and (b) show that the SEM micrographs for samples with the annealing
time 90 and 270 hours with cadmium content of 0.04. It seems that the increasing of
annealing time leads to the formation of the larger grains and also fewer pores. So that,
9
the gradual increase of the critical current density is observed with increasing the
annealing time.
Conclusion
In this work the role of Cd in the synthesis of Bi1.64Pb0.36Sr2Ca2-xCdxCu3Oy
superconductor with x = 0.0, 0.02, 0.04, 0.1, 0.5, 1 and 2 was investigated. The samples
were prepared by solid state reaction method using different annealing times. The results
of magnetic susceptibility measurements for the samples show that the diamagnetic
fraction of the sample with x = 0.04 is greater than the other samples. From the results, It
can conclude that the sample doped with cadmium having x = 0.04 and with annealing
time of 270 hours, has an increase in percentage of the Bi-2223 phase. The measurement
also are shown that the maximum value of the critical current density, the flux pinning
energy and the critical temperature were obtained for the sample with annealing time of
270 hours and Cd content of 0.04. Also the results are shown that the Bi-2223 phase is
converted to Bi-2212 phase for concentrations x  0.1, this due to the strong phase
transition occurred at x = 0.1 with consequent decrease in Tc (offset) due to the formation
of the weak links.
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14
Fig. 1: XRD patterns of samples with different cadmium amounts: 0.0 (a), 0.04 (b) and
0.1 (c) with annealing time of 270 hours.
15
-5
Susceptibility(cu. m/kg)
5.0x10
0.0

-5

-5.0x10
-4
-1.0x10
-4
-1.5x10
X = 0.0
-4
-2.0x10
X = 0.04
-4
-2.5x10

-4

-3.0x10
-4
-3.5x10
80
90
100
110
120
T(K)
Fig. 2: Temperature dependence of the magnetic susceptibility for samples with cadmium
content of 0.0 and 0.04 with annealing time 270 hours.
-5
5.0x10
Susceptibility(SI)
0.0


Hac = 50A/m
X = 0.0
-5
-5.0x10
-4
-1.0x10
Hac = 5A/m
X = 0.0
-4
-1.5x10
-4
-2.0x10
-4
-2.5x10


a
-4
-3.0x10
80
85
90
95
100 105 110 115 120
T(K)
16
-5
5.0x10
0.0


-5
Susceptibility(SI)
-5.0x10
-4
-1.0x10
-4
-1.5x10
Hac = 50 A/m
X = 0.02
-4
-2.0x10
-4
-2.5x10
Hac = 5 A/m
X = 0.02
-4
-3.0x10
-4
-3.5x10
-4
-4.0x10


b
80
85
90
95
100
105
110
115
120
T(K)
-5
5.0x10
0.0


-5
Susceptibility(SI)
-5.0x10
-4
-1.0x10
Hac = 50A/m
X = 0.04
-4
-1.5x10
-4
-2.0x10
Hac = 5A/m
X = 0.04
-4
-2.5x10
-4
-3.0x10
-4
-3.5x10


c
-4
-4.0x10
80
85
90
95
100 105 110 115 120
T(K)
Fig. 3– (a), (b) and (c): Temperature dependence of the magnetic susceptibility with
fields 5A/m and 50A/m for samples with cadmium contents: 0.0 (a), 0.02 (b) and 0.04 (c)
with annealing time 270 hours.
17
1.0
0.8

0.6
0.4
0.2
0.0
80
100
120
140
160
180
200
T (K)
T (K)
Fig. 4: The -T curves for different amounts of cadmium: 0.0 (■), 0.02 (●) and 0.04 (▲)
with annealing time 270 hours.
1.0
0.8

0.6
0.4
0.2
0.0
80
100
120
140
160
180
200
T (K)
Fig. 5: The -T curves for different annealing times: 90 (), 180 () and 270
() hours, for the sample with Cd content of 0.04.
18
-4
8.0x10
-5
4.0x10
-5
T = 77 K
V (v)
1.2x10
0.0
0
10
20
30
40
50
2
J (A/cm )
Fig. 6: The V-J curves for different annealing times: 90 (), 180 () and 270 () hours,
V (v)
for the sample with Cd content of 0.04.
8.0x10
-5
6.0x10
-5
4.0x10
-5
2.0x10
-5
T = 77 K
0.0
0
10
20
30
40
50
2
J (A/cm )
Fig. 7: The V-J curves for different amounts of cadmium: 0.0 (■), 0.02 (●) and 0.04 (▲)
with annealing time 270 hours.
19
V (v)
1.0x10
-4
8.0x10
-5
6.0x10
-5
4.0x10
-5
2.0x10
-5
0.0
0.0
-3
-3
-2
-2
4.0x10 8.0x10 1.2x10 1.6x10 2.0x10
-2
I (A)
Fig. 8: The V-I curves for different annealing times: 90(), 180() and 270() hours for
V (v)
the sample with 0.04 cadmium at room temperature.
1.6x10
-4
1.2x10
-4
8.0x10
-5
4.0x10
-5
0.0
0.00
0.01
0.02
0.03
0.04
0.05
I (A)
Fig. 9: The V-I curves for different amounts of cadmium: 0.02 (), 0.04 (▲), 0.1 (●)
and 0.5 (■) at room temperature with annealing time of 270 hours.
20
V (v)
T = 77 K
1.2x10
-4
8.0x10
-5
4.0x10
-5
Jco
Jc
0.0
0
10
20
30
40
50
60
2
J (A/cm )
Fig. 10: The V –J curves for the sample with Cd content of 0.04 and annealing
time of 270 hours.
-4.4
-4.6
log V
-4.8
-5.0
-5.2
-5.4
-5.6
-5.8
0.4
0.5
0.6
0.7
0.8
log I
Fig. 11: The log V-log I curves for the samples with Cd content: 0.0 (■), 0.02 (●) and
0.04 (▲) with annealing time of 270 hours.
21
-4.2
-4.4
-4.6
log V
-4.8
-5.0
-5.2
-5.4
-5.6
-5.8
0.4
0.5
0.6
0.7
0.8
log I
Fig. 12: The log V-log I curves for different annealing times: 90 (), 180 () and 270
() hours for the sample with Cd content of 0.04
Fig. 13: The EDX image of the sample with the amount of cadmium = 0.04 with
annealing time of 270 hours.
22
Fig. 14: The SEM micrographs of samples with different amounts of cadmium: 0.04 (a),
0.0 (b) and 2 (c) with annealing time of 270 hours.
23
Fig. 15: The SEM micrographs of samples with the annealing time 90 (a) and 270 (b)
hours with cadmium content of 0.04.
24
Table 1: Relative volume fractions of Bi-2223, Bi-2212, Bi-2201, CdO, Cd and
Bi-21.8112 with annealing time 270 hours.
Sample
a
b
c
Amount of Cd
0.0
0.04
0.1
Bi-2223 (%)
48.37
74.08
14.18
Bi-2212 (%)
31.57
22.89
19.65
Bi-21.8112 (%)
5.20
0
30.55
Bi-2201 (%)
14.86
0
15.18
CdO (%)
0
3.06
18.61
Cd (%)
0
0
17.01
Table 2: The critical temperature, critical current density, flux pinning energy and room
temperature resistance with annealing time of 90 hours.
x
0.0
0.02
0.04
0.1
0.5
1
2
Tc (Onset) (K)
92
98
103
77
77
77
77
Jc (A/cm2)
7.12
9.24
26.25
0.0
0.0
0.0
0.0
0.00625
0.0225
0.0475
0.425
0.634
9.79
0.0
0.0
0.0
0.0
R ()
U (J)10+21
0.108 0.0245
2.33
4.53
25
Table 3: The critical temperature, critical current density, flux pinning energy and room
temperature resistance with annealing time of 180 hours.
x
0.0
0.02
0.04
0.1
0.5
1
2
Tc (Onset) (K)
97
101.5
104
77
77
77
77
Jc (A/cm2)
18.26
19.25
34.67
0.0
0.0
0.0
0.0
0.00445
0.0152
0.0321
0.328
0.526
18.93
0.0
0.0
0.0
0.0
R ()
U (J)10+21
0.0884 0.00694
5.85
9.96
Table 4: The critical temperature, critical current density, flux pinning energy and room
temperature resistance with annealing time of 270 hours.
x
0.0
0.02
0.04
0.1
0.5
1
2
Tc (Onset) (K)
101.3
102.8
106.5
77
77
77
77
Jc (A/cm2)
24.26
27.21
39.86
0.0
0.0
0.0
0.0
0.00271
0.01
0.0245
0.121
0.221
22.34
0.0
0.0
0.0
0.0
R ()
U (J)10+21
0.0102 0.0045
8.60
14.11
26
Figures
Fig. 1: XRD patterns of samples with different cadmium amounts: 0.0 (a), 0.04 (b) and
0.1 (c) with annealing time of 270 hours.
Fig. 2: Temperature dependence of the magnetic susceptibility for samples with cadmium
content of 0.0 and 0.04 with annealing time 270 hours.
Fig. 3– (a), (b) and (c): Temperature dependence of the magnetic susceptibility with
fields 5A/m and 50A/m for samples with cadmium contents: 0.0 (a), 0.02 (b) and 0.04 (c)
with annealing time 270 hours.
Fig. 4: The -T curves for different amounts of cadmium: 0.0 (■), 0.02 (●) and 0.04 (▲)
with annealing time 270 hours.
Fig. 5: The -T curves for different annealing times: 90 (), 180 () and 270
()
hours, for the sample with Cd content of 0.04.
Fig. 6: The V-J curves for different annealing times: 90 (), 180 () and 270 () hours,
for the sample with Cd content of 0.04.
Fig. 7: The V-J curves for different amounts of cadmium: 0.0 (■), 0.02 (●) and 0.04 (▲)
with annealing time 270 hours.
Fig. 8: The V-I curves for different annealing times: 90(), 180() and 270() hours for
the sample with 0.04 cadmium at room temperature.
Fig. 9: The V-I curves for different amounts of cadmium: 0.02 (), 0.04 (▲), 0.1 (●) and
0.5 (■) at room temperature with annealing time of 270 hours.
Fig. 10: The V –J curves for the sample with Cd content of 0.04 and annealing time of
270 hours.
Fig. 11: The log V-log I curves for the samples with Cd content: 0.0 (■), 0.02 (●) and
0.04 (▲) with annealing time of 270 hours.
27
Fig. 12: The logV-logI curves for different annealing times: 90 (), 180 () and 270 ()
hours for the sample with Cd content of 0.04
Fig. 13: The EDX image of the sample with the amount of cadmium = 0.04 with
annealing time of 270 hours.
Fig. 14: The SEM micrographs of samples with different amounts of cadmium: 0.04 (a),
0.0 (b) and 2 (c) with annealing time of 270 hours.
Fig. 15: The SEM micrographs of samples with the annealing time 90 (a) and 270 (b)
hours with cadmium content of 0.04.
Tables
Table 1: Relative volume fractions of Bi-2223, Bi-2212, Bi-2201, CdO, Cd and
Bi-21.8112 with annealing time 270 hours.
Table 2: The critical temperature, critical current density, flux pinning energy and room
temperature resistance with annealing time of 90 hours.
Table 3: The critical temperature, critical current density, flux pinning energy and room
temperature resistance with annealing time of 180 hours.
Table 4: The critical temperature, critical current density, flux pinning energy and room
temperature resistance with annealing time of 270 hours.
28