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Influence of the preparation technique on Tc in the high Tc superconductor Bi32Pb12Sr2CaCu2Oy
L25 Journal
of the Less-Common
Metak;,
147 (1989)
L25
- L29
Letter
on T, in the high T, super-
Influence of the preparation technique conductor Bi3,zPbl ,$3r,CaCu,O, A. EHMANN, S. KEMMLER-SACK, M. SCHLICHENMAIER Znstitut fiir Anorganische Tiibingen (F.R.G.)
Chemie
R. KIEMEL, der Universitiit,
S. L&CH, Auf
W. SCUFER
der Morgenstelle
and
18, D-7400
L. KAN and B. ELSCHNER Znstitut D-6100
fiir Festkb’rperphysik Darmstadt (F.R.G.)
R. GROSS,
K. HIPLER
der Technischen
2,
der Universitiit
Tiibingen
Auf
der Morgenstelle
14,
and CH. J. RAUB
Forschungsinstitut D-7070 Schwabisch (Received
Hochschulstrasse
and R. P. HUEBENER
Znstitut fiir Experimentalphysik D-7400 Tiibingen (F.R.G.) H. R. KHAN
Hochschule,
August
fiir Edelmetalle und Metallchemie, Gmiind (F.R.G.)
Katharinenstrasse
17,
31, 1988)
In the system Bi-Pb-Sr-Ca-Cu-0, the high T, superconductor Bi&‘bi ,&,CaCu,O, has been synthesized. Its composition corresponds to the lead-free 80 K superconductor Bi2Sr,CaCu20, (see, for example, refs. 1 and 2). For Bi3,2Pb,,,Sr,CaCu20,, T, depends on the conditions of preparation. This communication deals with the preparation and investigation of this new high T, superconductor. For the preparation of Bi3,zPb1,2SrzCaCuzOy, stoichiometric amounts of Bi(N0,)3-5H20 (DAB 6; Merck), PbO (DAB 6; Merck), Sr(NO& (p.A.; Merck), CaCO, (p.A.; Merck) and CuO (p.A.; Merck) were mixed in an agate mortar and then fired in air in corundum boats at 600 “C (1 h) and 840 850 “C (80 h). The material was reground several times. The deep black compound formed is well crystallized. Scanning electron microscopy (SEM) photomicrographs of Bi,,,Pb,,$3r,CaCuz0, are shown in Fig. 1. Plate-like grains are observed, lying mainly parallel with the surface plane. The energy dispersive X-ray analysis (EDXA) conducted on different areas, as well as on different grains indicated a homogeneous distribution of the elements bismuth, lead, strontium, calcium and copper. It should be noted that no deviation in the Bi:Pb ratio could be detected. This implies a statistical 0022~5088/89/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
L26
tb) Fig. 1. SEM photomicrographs
of Bi 3,2Pb1,2Sr&aCu~Oy
(air preparation).
distribution of both elements. The compound crystallizes in the orthorhombic system with a = 5.376, b = 5 X 5.403, c = 30.79 A. The unit cell dimensions are similar to that of Bi#r&aCu,O, (see, for example ref. 2). Pressed pellets show a strong preferred orientation with the c axis lying normal to the surface plane. This is indicated by the high intensity of the (001) X-ray diffraction reflections compared with the powder pattern of this compound. The SEM photomicrographs also indicate the preferred stacking (Fig. 1). The average oxidation state was determined according to the method in ref. 3. With the assumption that all the bismuth is in the trivalent state and all the lead is in the bivalent state, the average oxidation state of copper is +2.55. This is relatively high compared with about +2.33 for the 90 K superconductor YBazCu30,_,. The room-temperature (RT) resistivity of air-prepared Bi3,2Pbl ,2Sr&aCu,O, is about 1.2 ms2 cm (Fig. 2). A nearly linear decreasing
.s,
. . . .
.I.
..I
I
.2
-
++‘+ ++++
+
t+ ++
3
$’ c 5
lt’*
++++ ++++ ++++ t*++
4.6
4
s’
:f/
.3
Ot’ 50
+ + + +
::t
..I....
I..
100
I
150
I
.
.
..I.
200
Temperature
250
(K)
.1 300
Fig. 2. Resistivity us. temperature for Bi ~$‘b~,&CaCu~Os
(air preparation).
resistivity is observed from 300 K to about 110 K. At about 110 K a small kink becomes noticeable. A clear onset of superconductivity is observed at about 80 K. T;(midpoint) is about 70 K. The presence of two superconducting phases was confirmed by magnetic susceptibility and Meissner effect measurements (Fig. 3). The amount of 70 K superconducting phase is about 30%. A portion of the air-prepared sample Bi3,2Pb1,2Sr2CaCu20y was cooled in oxygen from 700 “C to 400 “C! within 4 h and subsequently furnace
(a)
Temperature
(K)
L28
y------” 8.88
“‘I” 4+*
-
*+44
+ 4
4
H
+
#+4+4t++&+++ t++ 4,444
-I
Irn *
1-
-1.89
-
E 2
I4 4
%
-6.BB:.,....... 8.1)B 2e.e (b)
(8. B
LB.1
80.9
111
120
140
Temperature (K)
Fig. 3. (a) Magnetic susceptibility and Meissner effect SrzCaCu20, (air preparation); (b) enlarged section.
measurement
for Bi3/zPbl/z-
cooled. The powder diffraction pattern shows a reduction of the orthorhombit distortion (a = 5.40, b = 5 X 5.40, c =:30.79 A). On the SEM photomicrographs (Fig. 4), the beginning of the deterioration of the plate-like grains is indicated. This is confirmed by EDXA, which now gives deviations in the Bi:Pb:Sr:Ca:Cu ratio between different grains. The RT resistivity (Fig. 5) goes up to 5.8 ms2 cm compared with 1.2 ms2 cm for the airprepared sample (Fig. 2). A nearly linear decrease in resistivity is observed between 300 K and about 110 K. At about 110 K a kink is visible again. A clear resistance drop is seen at about, 70 K but the resistivity never completely reaches zero. The average oxidation state goes up to +2.61, compared with +2.55 for the air preparation.
Fig. 4. SEM photomicrographs
of Bi 3,2Pbl,&CaCu20,
(02 preparation).
0 50
100
i5B
200
25%
300
Temperature {K)
Fig. 5. Resistivity
us. temperature
for “Bi~,~Pbl&r~CaCu~Oy”
(02 preparation).
A second portion of the air-prepared sample Bis,zPbI,&%zCaCuzO, was heated in argon at 600 “C for 30 h and subsequently furnace cooled. The cell constants of the uniform, well crystallized sample are a = 5.380, b = 5 X 5.407 and c = 30.82 a. The average oxidation state is reduced to +2.43, leading to an oxygen content of Bi3,2Pb1/2SrzGaGuzOs.~s in com(average oxidaparison with Bi3,2Pbl ,zSrzGaCu,Os.,O for the air preparation tion state = +2.55). The resistivity vs. temperature results are shown in Fig. 6. A resistivity drop is seen at around 110 K. The midpoint transition temperature is approximately 93 K and T,(zero) is about 90 K. Evidently, for Bi~,~Pb~,*Sr*GaCu~O~ the transition temperature T, (midpoint) is raised from about 70 K to about 90 K by reducing the oxygen content. Note that the kink for the air-prepared sample (Fig. 2) is situated in exactly the same region as T, (onset) for the argon preparation. The kink can be explained by the presence of a small sample portion with constant cation ratio but lower oxygen content, compared with the overall value. The presence of one superconducting phase with T, (midpoint) at around 93 K was confirmed by magnetic susceptibility and Meissner effect measurements. The amount of the superconducting phase is about 45%. The observed increase in Z’, with decreasing oxygen content for Bi,,aPb,,zSr&aCuzO, opposes the trend for the high T, superconductor YBa,CusO,_,, leading to a reduction in T, from around 90 K to about 60 K and below with increasing z (see, for example, ref. 4). In summary, we have shown that the transition temperature of Bi3,2Pb1,2Sr2CaCu20y is strongly influenced by the oxygen content. Preparation in air yields a high oxygen content (Os_30) and T, = 70 K. Argon
L30
+ 0
..:::~,...-,--..,-.-.,.... 50
I00
IS0
200
250
300
Temperature (K)
Fig. 6. Resistivity us. temperature for Bis,z Pb r ,#raCaCuzO,
treatment reduces mately 93 K.
the oxygen
content
(argon preparation).
to Os.,, and T, goes up to approxi-
This work was supported by the Bundesministerium fiir Forschung und Technologie (No. 13N5482), the Forschungsschwerpunkt 47 des Landes Baden-Wiirttemberg; the Daimler-Benz AG and the Verband der Chemischen Industrie. W. S. thanks the Landesgraduiertenfiirderung von Baden-Wiirttemberg for granting a scholarship. We want to thank Mrs. R. Hiipper for her helpful assistance. A. Sunshine, T. Siegrist, L. F. Schneemeyer, D. W. Murphy, R. J. Cava, B. Batlogg, R. B. van Dover, R. M. Fleming, S. H. Glarum, S. Nakahara, R. Farrow, J. J. Krajewski, S. M. Zahurak, J. V. Waszczak, J. H. Marshal, P. Marsh, L. W. Rupp, Jr., and W. F. Peck, Phys. Rev. B, 38 (1988) 893. A. K. Cheetham, A. M. Chippingdale and S. J. Hibble, Nature, 333 (1988) 21, and references therein. W. Schafer, J. Maier-Rosenkranz, S. Liiscb, R. Kiemel, W. Wischert, S. KemmlerSack, H. Kneissel and B. Elschner, J. Less-Common Met., 142 (1988) L5. R. J. Cava, B. Batlogg, C. H. Chen, E. A. Rietman, S. M. Zahurak and D. Werder, Nature, 329 (1987) 423.
of the Less-Common
Metak;,
147 (1989)
L25
- L29
Letter
on T, in the high T, super-
Influence of the preparation technique conductor Bi3,zPbl ,$3r,CaCu,O, A. EHMANN, S. KEMMLER-SACK, M. SCHLICHENMAIER Znstitut fiir Anorganische Tiibingen (F.R.G.)
Chemie
R. KIEMEL, der Universitiit,
S. L&CH, Auf
W. SCUFER
der Morgenstelle
and
18, D-7400
L. KAN and B. ELSCHNER Znstitut D-6100
fiir Festkb’rperphysik Darmstadt (F.R.G.)
R. GROSS,
K. HIPLER
der Technischen
2,
der Universitiit
Tiibingen
Auf
der Morgenstelle
14,
and CH. J. RAUB
Forschungsinstitut D-7070 Schwabisch (Received
Hochschulstrasse
and R. P. HUEBENER
Znstitut fiir Experimentalphysik D-7400 Tiibingen (F.R.G.) H. R. KHAN
Hochschule,
August
fiir Edelmetalle und Metallchemie, Gmiind (F.R.G.)
Katharinenstrasse
17,
31, 1988)
In the system Bi-Pb-Sr-Ca-Cu-0, the high T, superconductor Bi&‘bi ,&,CaCu,O, has been synthesized. Its composition corresponds to the lead-free 80 K superconductor Bi2Sr,CaCu20, (see, for example, refs. 1 and 2). For Bi3,2Pb,,,Sr,CaCu20,, T, depends on the conditions of preparation. This communication deals with the preparation and investigation of this new high T, superconductor. For the preparation of Bi3,zPb1,2SrzCaCuzOy, stoichiometric amounts of Bi(N0,)3-5H20 (DAB 6; Merck), PbO (DAB 6; Merck), Sr(NO& (p.A.; Merck), CaCO, (p.A.; Merck) and CuO (p.A.; Merck) were mixed in an agate mortar and then fired in air in corundum boats at 600 “C (1 h) and 840 850 “C (80 h). The material was reground several times. The deep black compound formed is well crystallized. Scanning electron microscopy (SEM) photomicrographs of Bi,,,Pb,,$3r,CaCuz0, are shown in Fig. 1. Plate-like grains are observed, lying mainly parallel with the surface plane. The energy dispersive X-ray analysis (EDXA) conducted on different areas, as well as on different grains indicated a homogeneous distribution of the elements bismuth, lead, strontium, calcium and copper. It should be noted that no deviation in the Bi:Pb ratio could be detected. This implies a statistical 0022~5088/89/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
L26
tb) Fig. 1. SEM photomicrographs
of Bi 3,2Pb1,2Sr&aCu~Oy
(air preparation).
distribution of both elements. The compound crystallizes in the orthorhombic system with a = 5.376, b = 5 X 5.403, c = 30.79 A. The unit cell dimensions are similar to that of Bi#r&aCu,O, (see, for example ref. 2). Pressed pellets show a strong preferred orientation with the c axis lying normal to the surface plane. This is indicated by the high intensity of the (001) X-ray diffraction reflections compared with the powder pattern of this compound. The SEM photomicrographs also indicate the preferred stacking (Fig. 1). The average oxidation state was determined according to the method in ref. 3. With the assumption that all the bismuth is in the trivalent state and all the lead is in the bivalent state, the average oxidation state of copper is +2.55. This is relatively high compared with about +2.33 for the 90 K superconductor YBazCu30,_,. The room-temperature (RT) resistivity of air-prepared Bi3,2Pbl ,2Sr&aCu,O, is about 1.2 ms2 cm (Fig. 2). A nearly linear decreasing
.s,
. . . .
.I.
..I
I
.2
-
++‘+ ++++
+
t+ ++
3
$’ c 5
lt’*
++++ ++++ ++++ t*++
4.6
4
s’
:f/
.3
Ot’ 50
+ + + +
::t
..I....
I..
100
I
150
I
.
.
..I.
200
Temperature
250
(K)
.1 300
Fig. 2. Resistivity us. temperature for Bi ~$‘b~,&CaCu~Os
(air preparation).
resistivity is observed from 300 K to about 110 K. At about 110 K a small kink becomes noticeable. A clear onset of superconductivity is observed at about 80 K. T;(midpoint) is about 70 K. The presence of two superconducting phases was confirmed by magnetic susceptibility and Meissner effect measurements (Fig. 3). The amount of 70 K superconducting phase is about 30%. A portion of the air-prepared sample Bi3,2Pb1,2Sr2CaCu20y was cooled in oxygen from 700 “C to 400 “C! within 4 h and subsequently furnace
(a)
Temperature
(K)
L28
y------” 8.88
“‘I” 4+*
-
*+44
+ 4
4
H
+
#+4+4t++&+++ t++ 4,444
-I
Irn *
1-
-1.89
-
E 2
I4 4
%
-6.BB:.,....... 8.1)B 2e.e (b)
(8. B
LB.1
80.9
111
120
140
Temperature (K)
Fig. 3. (a) Magnetic susceptibility and Meissner effect SrzCaCu20, (air preparation); (b) enlarged section.
measurement
for Bi3/zPbl/z-
cooled. The powder diffraction pattern shows a reduction of the orthorhombit distortion (a = 5.40, b = 5 X 5.40, c =:30.79 A). On the SEM photomicrographs (Fig. 4), the beginning of the deterioration of the plate-like grains is indicated. This is confirmed by EDXA, which now gives deviations in the Bi:Pb:Sr:Ca:Cu ratio between different grains. The RT resistivity (Fig. 5) goes up to 5.8 ms2 cm compared with 1.2 ms2 cm for the airprepared sample (Fig. 2). A nearly linear decrease in resistivity is observed between 300 K and about 110 K. At about 110 K a kink is visible again. A clear resistance drop is seen at about, 70 K but the resistivity never completely reaches zero. The average oxidation state goes up to +2.61, compared with +2.55 for the air preparation.
Fig. 4. SEM photomicrographs
of Bi 3,2Pbl,&CaCu20,
(02 preparation).
0 50
100
i5B
200
25%
300
Temperature {K)
Fig. 5. Resistivity
us. temperature
for “Bi~,~Pbl&r~CaCu~Oy”
(02 preparation).
A second portion of the air-prepared sample Bis,zPbI,&%zCaCuzO, was heated in argon at 600 “C for 30 h and subsequently furnace cooled. The cell constants of the uniform, well crystallized sample are a = 5.380, b = 5 X 5.407 and c = 30.82 a. The average oxidation state is reduced to +2.43, leading to an oxygen content of Bi3,2Pb1/2SrzGaGuzOs.~s in com(average oxidaparison with Bi3,2Pbl ,zSrzGaCu,Os.,O for the air preparation tion state = +2.55). The resistivity vs. temperature results are shown in Fig. 6. A resistivity drop is seen at around 110 K. The midpoint transition temperature is approximately 93 K and T,(zero) is about 90 K. Evidently, for Bi~,~Pb~,*Sr*GaCu~O~ the transition temperature T, (midpoint) is raised from about 70 K to about 90 K by reducing the oxygen content. Note that the kink for the air-prepared sample (Fig. 2) is situated in exactly the same region as T, (onset) for the argon preparation. The kink can be explained by the presence of a small sample portion with constant cation ratio but lower oxygen content, compared with the overall value. The presence of one superconducting phase with T, (midpoint) at around 93 K was confirmed by magnetic susceptibility and Meissner effect measurements. The amount of the superconducting phase is about 45%. The observed increase in Z’, with decreasing oxygen content for Bi,,aPb,,zSr&aCuzO, opposes the trend for the high T, superconductor YBa,CusO,_,, leading to a reduction in T, from around 90 K to about 60 K and below with increasing z (see, for example, ref. 4). In summary, we have shown that the transition temperature of Bi3,2Pb1,2Sr2CaCu20y is strongly influenced by the oxygen content. Preparation in air yields a high oxygen content (Os_30) and T, = 70 K. Argon
L30
+ 0
..:::~,...-,--..,-.-.,.... 50
I00
IS0
200
250
300
Temperature (K)
Fig. 6. Resistivity us. temperature for Bis,z Pb r ,#raCaCuzO,
treatment reduces mately 93 K.
the oxygen
content
(argon preparation).
to Os.,, and T, goes up to approxi-
This work was supported by the Bundesministerium fiir Forschung und Technologie (No. 13N5482), the Forschungsschwerpunkt 47 des Landes Baden-Wiirttemberg; the Daimler-Benz AG and the Verband der Chemischen Industrie. W. S. thanks the Landesgraduiertenfiirderung von Baden-Wiirttemberg for granting a scholarship. We want to thank Mrs. R. Hiipper for her helpful assistance. A. Sunshine, T. Siegrist, L. F. Schneemeyer, D. W. Murphy, R. J. Cava, B. Batlogg, R. B. van Dover, R. M. Fleming, S. H. Glarum, S. Nakahara, R. Farrow, J. J. Krajewski, S. M. Zahurak, J. V. Waszczak, J. H. Marshal, P. Marsh, L. W. Rupp, Jr., and W. F. Peck, Phys. Rev. B, 38 (1988) 893. A. K. Cheetham, A. M. Chippingdale and S. J. Hibble, Nature, 333 (1988) 21, and references therein. W. Schafer, J. Maier-Rosenkranz, S. Liiscb, R. Kiemel, W. Wischert, S. KemmlerSack, H. Kneissel and B. Elschner, J. Less-Common Met., 142 (1988) L5. R. J. Cava, B. Batlogg, C. H. Chen, E. A. Rietman, S. M. Zahurak and D. Werder, Nature, 329 (1987) 423.