International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2012) Jan. 7-8, 2012 Dubai
Effect of Magnesium on the Bi-based
(2212) superconductors
N. Boussoufa, M. -F. Mosbaha, F. Bouaichaa , Amiraa, b
Abstract- A series of Mg-doped bismuth (2212)
superconducting materials with nominal composition
Bi1.8Pb0.4Sr2MgxCa1.1Cu2.1Oy and Bi2Sr2MgxCaCu2O8+ (x =
0, 0.05) were synthesized by simple solid-state reaction route.
The effect of magnesium on structural properties and
superconducting behaviour has been investigated by X-ray
diffraction (XRD), Scanning Electron Microscopy (SEM),
electrical resistivity X-ray diffraction experiments and SEM
observations revealed the degree of texture in the
superconductor. SEM photographs show that the addition of
MgO affects the mechanism of the grains growth. In all
samples, the a-lattice parameter remains the same, but the cparameter decreases slightly with the content of MgO. All the
samples appear to have a multiphase character as shown by
AC magnetic susceptibility and XRD data. Mg was found to
be effective in the formation of the high-Tc phase at 5% of
doping in this system. The onset temperature Tc (onset) of all
the samples remains within the temperature range 80–86 K.
I. INTRODUCTION
in fully processed samples of Bi2223 and on its Ic value and
machinability [2]. For superconductivity, however, oxygen
(O)-rich secondary phases, particularly MgO, may be of
great importance and yield a positive effect for transport
properties. A recent study indicates also that the formations
of the (Bi, Pb)-2223 phases are greatly re-enhanced by
adding PbO during the final sintering .The PbO added was
found also to reduces the onset of the partial melting
temperature and produces more liquid phase during
sintering, which in turn improved the rate of (Bi,Pb)-2223
formation[3,4].In order to improve transition temperature
and critical current densities in Bi-2212 high temperature
Tc, introduction of effective pinning centres into the
superconductors is needed 5.
In this article, we discuss the effect of Mg doping on the
crystal
structures,
the
electrical
properties
of
superconducting BiSrCaCuO, BiPbSrCaCuO ceramics.
Keywords—Bi-based high-Tc superconductors; Scanning
electron microscopy; X-ray diffraction.
T
HE bismuth-based family of high-Tc superconductors
(HTS) has been extensively studied in the past 22 years,
both from the point of view of its fundamental physical
properties and from that of the thermodynamical stability of
its different components. In fact, it is well known that the
BSCCO material consists of at least three phases:
Bi2Sr2CuO6+γ (Bi- 2201), Bi2Sr2CaCu2O8+δ (Bi-2212) and
Bi2Sr2Ca2Cu3O10 (Bi-2223). The thermodynamical stability
limits between them have been investigated in
polycrystalline samples of macroscopic sizes [1] and this
information has been exploited in order to design the most
suitable processes for the synthesis of pure samples in the
different phases. The critical current density (Jc) and critical
temperature (Tc) are the parameters of primary importance
for potential applications of HTS and the Jc value is
primarily limited due to the insufficient flux pinning
properties. Therefore numerous efforts have been made to
enhance the flux pinning properties of Bi-based systems,
and hence the Jc value, by introducing effective pinning
sites, several alloying elements, such as Ag, MgO, BaSO4,
SrSO4, etc., can be added to improve both the electrical
properties and mechanical integrity of polycrystalline 2212,
and the addition of MgO was reported to have beneficial
effects on the grain connectivity and grain alignment
Boussouf. Noraa. Université Mentouri de Constantine, Laboratoire
Couches Minces et Interfaces, Campus de Chaabet-Erssas- B.P. 325 Route
d’Ain El Bey, 25000 Constantine. Algeria. (phone : (031) 81 86 04;
fax :213(031) 81 86 04; [email protected]).
Mosbah Mohamed Fayçala. Université Mentouri de Constantine,
Laboratoire Couches Minces et Interfaces, Campus de Chaabet-Erssas- B.P.
325
Route
d’Ain
El
Bey,
25000
Constantine.
Algeria.
([email protected]).
Bouaicha. Faizaa. Université Mentouri de Constantine, Laboratoire
Couches Minces et Interfaces, Campus de Chaabet-Erssas- B.P. 325 Route
d’Ain El Bey, 25000 Constantine. Algeria.( [email protected]).
Amira Abderrazakb Laboratoire des Essais Non Destructifs (LEND),
Université
de
Jijel.
B.P.
98,
18000
Jijel,
Algeria.
([email protected]).
318
II.EXPERIMENTAL PROCEDURE
The Mg doped (BSCCO; BPSCCO) ceramics were
prepared by the conventional ceramic method.
Predetermined amounts of high purity starting chemicals
(Bi2O3; SrCO3, CaCO3, CuO, PbO) were used for the
preparation of the ceramics of fixed nominal composition of
Bi1.8Pb0.4Sr2MgxCa1.1Cu2.1Oy.
These
Bi2Sr2CaCu2Oy;
powders were well mixed and ground by using an agate
mortar and pestle and were further calcined at 800°C for 30
and 820°C for 30 hours in a furnace. Calcined powders
were ground again to form a fine powder. Pellets 13 mm in
diameter and 1 mm in thicknesses were pressed by uniaxial
compaction in a die at 5 ton/cm2. These pellets were sintered
at 860°C for 60 hours in air and then furnace cooled to room
temperature. The obtained Bi-2212, Bi(Pb)-2212 powders
were mixed with MgO particles. The additional amount of
MgO in this case varying from (x = 0- 5%) of the total mass
of the sample. The mixed powders were pressed into pellets
under 5 ton/cm2 then sintered at 860°C for 60 hours.
Phase identification was carried out with an X-ray
diffractometer (DRX). The cell parameters were calculated
from XRD patterns using Dicvol 06. Resistance-temperature
data obtained by using four point probe AC method.
9 00
8 00
7 00
4 00
1 00
200
3 00
1115
2010
113
4 00
220
117
0012
008
006
Intensity (u-a)
5 00
2 00
(2010)
-1 00
10
20
30
40
50
2
200
*
100
Fig.2. X-ray diffraction patterns of Bi2212 sample:
doped with y=0.05.
(0010)
0
1600
0% Mg Bi(Pb)2212
1400
1200
1000
800
(1115)
(220)
(2010)
(117)
(200)
(0012)
400

(008)
(113)
(115)

600
(006)
Intensity (a-u)
0% M g B i2212
7 00
0
(1115)
300
115
0010
0
-1 00
8 00
1 00
(113)
400
(006)
500
(0012)
600
(220)
700
Intensity (a-u)
(115)
(0010)
(117)
(200)
(008)
800
220
3 00
6 00
5% Mg Bi(Pb)2212
1115
113
006
5 00
2010
6 00
2 00
1000
900
5% M g B i2212
117
200
115
10 00
0012
008
11 00
Intensity (u-a)
III. RESULTS
All the samples appear to have a multiphase structure
which indicates the difficulty in obtaining a single phase
material by the conventional ceramic method. X-ray powder
diffraction patterns of samples with 0% and 5% are shown
in Fig. 1. The peak positions and intensities show that
samples are essentially a mixture of Bi-2201, Bi-2212. Few
small peaks may be indexed to CuO and MgO. Our
synthesizing process described above produces, without
MgO, but the reflection of MgO can not be detected by
XRD. Bi-2212 with a minor amount of secondary phases.
The peaks of the added Bi(Pb)2212 sample show dominancy
of (00l) plans indicating a preferential orientation parallel to
ab plans which implies that a single phase Bi-2212 is
obtained.
0010
International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2012) Jan. 7-8, 2012 Dubai
200
0
-200
10
20
30
40
50
60

Fig.1 . X-ray diffraction patterns of Bi(Pb)2212 sample:
doped with y=0.05.
This figure 1 shows also that the peak at 2 =29.08° for the
Bi (Pb)-2212 increases with addition. This shows a
remarkable improvement of the high-Tc phase fraction. A
nearly single phase material could be synthesized in this
way. Some Bi-2201 phase peaks [2θ = 21.2◦, 30◦, 36.6◦
319
were obtained in the Mg-added composition. This is due to
the fact that Mg particles added to the prepared Bi-80 K
phase superconductor did not react with superconducting
grains. The other secondary phase attributed to Ca2PbO4
phase is denoted by (*) symbol. It is detected at 17.5°.
The main X-ray peaks in Fig 2 may be indexed assuming a
tetragonal cell with a = b= 5, 40079 A°, c = 30,82036 A° as
expected for the Bi-2212 structure. It can be found that the
content of Bi2212 increases with increasing MgO
concentration, indicating MgO addition in the samples
accelerate the reaction rate of Bi2212.
The lattice parameters of the Bi(Pb)2212 phase of sample
can be compared with those of the other samples prepared
by adding MgO. Calcinations of the samples at a
temperature higher than the melting point of Bi2O3 (818°C)
causes loss of some of the Bi atoms, which results in the
formation of the off-stoichiometric compound. For this
reason, we preferred to add MgO rather than substituting it
to the Bi site. There is a good possibility of vacant Bi sites
being occupied by these atoms, thus offering which has
serious implications for conductivity within the
Bi2212/MgO.
Figure.3. shows SEM photographs of two samples, without
magnesium (y = 0) and doped with magnesium (y = 0.05).
The SEM photograph of the undoped sample shows the
layered structure which characterizes the growth of Bi2212
grains. The grains appear rather dense and well connected.
The average size of the grains is about 4 μm. The grain
samples containing lead have a larger size and aspect very
different. Their orientation seems less random and porosity
60
International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2012) Jan. 7-8, 2012 Dubai
eveen smaller. Plaatelets have a strong
s
cohesionn. The additionn
of MgO appears to increase thee porosity whicch is manifestedd
in larger spaces between the grains. MgO particles cause
aggglomeration inn heat treatemeent and lead too weak links at
a
graains boundariess 8, 9.
Thhe electrical ressistivity was measured
m
with a standard AC
C
fouur-probe methood (Fig.4.). Eleectrical leads were
w attached too
thee samples by silver paint andd heat treated at
a 300 C° in aiir
forr half an hour, which gave coontact resistannces of order 1––
2
. The transitioon temperaturess Tc with zero resistance for
5%
% Bi2212/MgO
O and 5% Bi(Pbb)2212/MgO. changed due to
thee fact that Mg atoms in the samples
s
with 5 wt% Mg werre
sub
bstituted for the elements that composee the Bi-22122
sinngle-phase supperconductor6. This is connfirmed by thhe
XR
RD patterns off figure 1, whicch do not exhiibit an impurityy
phase but only a few Bi-2201 phase
p
peaks.
of the saamples. We caan observe thee resistance att normal
state at rooom temperaturre is higher forr pure samples than for
added one. The higher resistivity is due to new sccattering
which are introoduced in the system by thee dopant
centers, w
7 .
IV
V. CONCLUSION
N
nd, to the synthhesis and
We deevoted our worrk, on one han
the charracterization of supercond
ducting ceram
mics of
Bi2Sr2CaC
Cu2Mg0;05O8+δ, Bi1,8Pb0,4Srr2,0Ca1,1Cu2,1Mg0;05O8+δ
(y = 0,0.005) and, on the other handd, to the studyy of the
effect of substitution of Cu by Znn. The samples were
olid state reactiion. The
prepared with the usuall method of so
XRD resuults show the obbtaining
(a)Bi2212
2+5%
(a) Bi2212
(d)(Bi,Pb))2212+5%MgO
(c)(Bi,P
Pb)2212
Fig. 3. SEM Micrographs
M
of an
a undoped and
d a doped samplees (y=0.05), (a) Bi
B 2Sr2Ca1Cu2O8+δ, (b) Bi1,8Pb0,4Sr2,0Ca1,1Cu2,1O8+δ
.
o the electricaal resistivity of
o
Thhe temperature dependence of
thee Bi2Mg0.05Srr2Ca1Cu2Oy Bi
B 1.8Pb0:4Mg0.05Sr2Ca1.1Cu2.1Oy
Thhe temperature dependence of
o the electricaal resistivity of
o
thee Bi2Mg0.05Srr2Ca1Cu2Oy Bi
B 1.8Pb0:4Mg0.05Sr2Ca1.1Cu2.1Oy
cerramics additionn by x=0.05 Mg
M is given inn Figure 3.Thhe
onset temperaturre for two sam
mples is approxximately 80 K,
K
82 K. The resisttivity-temperatture curve is linear up to thhe
onset temperature, in accordancce with the meetallic characteer
320
with a majority fracction, of thee Bi(Pb)22122 phase
O parasitic phaases. By
accompannied by Bi2201 and Ca PbO
2
4
adding maagnesium, the proportion of Bi2201
B
parasittic phase
seems to initially decrrease then to increase slighhtly. The
indexing by Dicvol04 software connfirms the teetragonal
EM microphottographs
structure for the various samples.SE
g
of
highlight the lamellar sstructure characterizing the grains
Bi(Pb)22112.
International Conference on Electronics, Biomedical Engineering and its Applications (ICEBEA'2012) Jan. 7-8, 2012 Dubai
0,018
(a)
pur
5% MgO
0,016
0,014
Résistivité (mOhm.m)
Linear dependence of the electrical resistivity above the
onset temperature of superconductivity Tc (onset) is
showing the good quality of sample composition
Bi2Sr2CaCu2Mg0;05O8+δ.
A Bi1.8Pb0.4MgxSr2Ca1.1Cu2.1Oδ superconductor was sintered
by the solid state reaction method with Mg concentrations
varying x=0 to 0.05. It was found that the addition of MgO
enhances the high Tc Bi(Pb)2212 formation phase and
transport properties. The normal state of resistivity of
addition sample with 5% Mg is enhanced. An increase of the
resistivity from the overdoped regime to the underdoped
doped one is observed. Their measurements showed that
there was a large difference in the carrier concentration
between the inner and outer CuO2 planes due to the doping.
0,012
0,010
0,008
0,006
0,004
0,002
0,000
The addition of MgO particles may possibly affect the
oxygenation, the distribution of oxygen deficient regions in the
sample 10.
-0,002
20
40
60
80 100 120 140 160 180 200 220 240 260 280 300
T(K°)
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pur
5% MgO
0,12
0,10
0,08
0,06
0,04
0,02
0,00
50
60
70
80
90
100
110
120
130
150
Fig.4. Temperature dependence of Resistivity for two phases: (a)
Bi2Sr2CaCu2O8+δ, (b)Bi1,8Pb0,4Sr2,0Ca1,1Cu2,1O8+δ.
321
140
T(K°)