- Email: [email protected]
Intergrain magnetic properties and critical currents of T1-1223 bulk and tape superconductors
PHYSlCA® ELSEVIER
Physica C 341-348 (2000) 2 0 4 9 - 2 0 5 0 www.elsevier.nl/locate/physc
Intergrain magnetic properties and critical currents of T1-1223 bulk and tape superconductors* R. Zalecki a, A. Kolodziejczyka, J. Chmist a, W. K6nigb, G. Gritzner b a Department of Solid State Physics, University of Mining and Metallurgy, PL-30-059 Cracow, Poland bJohannes Kepler Universit~t, Institut f'tir Chemische Technologie Anorganischer Stoffe, A-4040 Linz, Austria The magnetic field and the temperature dependencies of the dispersive and the absorption components of the low frequency a c magnetic susceptibility for Pb and Bi single doped bulk superconductors as well as for Pb and Bi co-doped Ag-sheathed superconducting T1-1223 tapes have been measured and analyzed. The studies were accompanied by optical and electron microscopic observations of the microstructure. The ac susceptibility measured at various ac magnetic field amplitudes showed both intergrain and intragrain features. The temperature dependencies of the intergrain critical current densities were extracted from the absorption susceptibility via a modified Bean model. They were at relevant temperatures one order of magnitude larger for the tape than for the bulk specimens. 1. INTRODUCTION Some magnetic and electrical properties of hightemperature superconductors are controlled by the superconducting intergrain weak link system (SWL), which may be treated as Josephson junctions (SWL-JJ) [1]. The total critical current density Jc is thus limited by the Josephson critical current density J~j. Upon lowering the temperature the grains become superconducting first, followed by the intergrain junctions. This results in a twostep behavior in the dispersive and absorption a c magnetic susceptibility. Substitution of Pb and/or Bi into the T1 sites in T11223 bulk phase superconductors leads to improved flux pinning properties and to an increase in the J~j [2,3]. In this paper we show by a c susceptibility measurements that Pb and Bi co-doped T1-1223 tapes are suitable materials for technical applications because of their high Jcj values.
2. EXPERIMENTAL (Tlo.74Bio.3)(Sro.gBao.1)2Ca2Cu3Oy and (Tlo.oPbo.5) (Sro.aBao.l)2CazCuaOy superconductors were
prepared with Tc values of 121 K and 118 K, respectively, by a procedure described elsewhere [2-4]. The Ag-sheathed tape of (Tlo.6Bio.16Pbo.z4) (Sro.aBao.0zCa2CuaOy with a T~ of 118 K was fabricated from precursors prepared either by the spray-drying of nitrates technique or by the tartrate gel techn!que [4]. Following the addition of TI2Oa, PbO and' BizOa the powders were compacted and sintered into superconducting pellets. The resultant pellets were milled, filled in silver tubes, drawn to wires and then rolled to 0.25 minx 2 nun tapes. Final sintering was carried out in air at 850 °C for 0.5 h followed by annealing at 750 °C for 50 h in flowing oxygen. The phase purity and the microstructure of the sample were investigated by a number of methods [2-4]. The degree of grain alignment in the tape was about 95%. A c susceptibility measurements were carried out in a standard mutual inductance bridge for the a c magnetic field amplitude Bac from 1 pT to about 1 mT at 189 Hz in the zero field cooling procedure (ZFC). The a c field was applied along the bulk needle- like shaped sample with diameter d _=2 mm and in parallel direction to the plane of the tape sample with cross section about 0.2 x 0.2 nun2.
*This study was financiallysupported by the KBN, Poland (project no 2P03B 147 17), the Fonds zur F6rdemng der wissenschaflichen Forschung in Osterreich (project 11 873) and by the Osterreichischer Akademischer Austauschdienst, Wissenschafllich-technischeZusammenarbeitmit Polen (project 3/99). 0921-4534/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII S0921-4534(00)01008-X
R. Zalecki et al./Physica C 341-348 (2000) 2049-2050
2050
3. RESULTS AND DISCUSSION Figures 1 and 2 show typical temperature dependencies of ac absorption susceptibilities Z".
(TI,Bi)-1223
600pT
" ~
200pT801~
\
T
I
1
.
2O.T '/
"
Jcj, d_=_ 2 mm is the sample diameter perpendicular to Bp. For intragrain Jog, d is an average grain diameter [2,5]. Some values of Jog were estimated in 15]. The calculated values of J~j were plotted versus the respective peak temperatures in Fig. 2. The linear extrapolation of Jcj (T) for the tape resulted in values of J~j(100 K) : 3.85 kA cmz and J~j(77 K) = 10.2 kA cmz about one order of magnitude larger than for the bulk sample. Latter value agrees well with the direct transport critical current density of 10 kA cm-z [2].
1 . . . .
0
,? o
,
.
..~
,
.
.
.
.
,
(Tl,Bi,Pb)-1223
3
300'
~
B
. . . .
,
tape
II ( a , b )
1500
,t"-' "7
200,
2
1000
600~T
"'E
200~T
500
~ = 1 O0 •
400~T 5OpT
0
lOO . . . .
lt~5 . . . .
0
1{o . . . .
1{5 . . . .
1~o
TIK
Figure 2. Plot of J~j (7') for samples as indicated. 3
Bacll
(a,b)
11001~T
0
/880.T ~
55OPT
f
220~T
~ 100
105
110
115
120
TIK Figure 1. Plot o f X "
(T) for samples as indicated.
The low temperature intergrain peak and the high temperature intragrain peaks in Fig. 1 resulted from the flux movement in the SWL-JJ system and in the grains, respectively [5]. For the tape only one intergrain peak was observed. The ac field Ba~ penetrates into the grains at the higher temperature peak while it penetrates into the center of the intergrain junctions at the lower temperature peak. The induced supercurrents are equal to the intra- and the intergrain critical currents, respectively. J~(T) may be derived from the dependence of the position of the inter- and intragrain peaks of Z"(T) on different ac fields. The critical currents were derived from the Bean model and its modifications [6-9] as Jc(B)=gB/d, where Bp is the penetration field and d is the average penetration depth. We assumed Bp equal to Bac which is only an approximation [6-9]. For intergrain
4. SUMMARY AND CONCLUSIONS Intergrain critical current densities J~j of Pb and Bi single-doped T1-1223 bulk superconductors as well as for a Pb and Bi co-doped Ag-sheathed tape were estimated from the absorption ac susceptibility. The intergrain Jcj for the tape was enhanced due to improvement of the flux pinning and the grain connectivity by Bi and Pb co-doping. REFERENCES 1. G. Deutscher, Springer Series in Solid State Sciences, eds. J.C. Bednorz and K.A. Miiller, Springer-Verlag, Berlin, vol.90 (1990) 174. 2. W. Kbnig, G. Gritzner, M. Reissner and W. Steiner, Physica C, 258 (1996) 175. 3. M. Mair, W. K6nig and G. Gritzner, Supercond. Sci. Techn., 8 (1995) 894. 4. W. K6nig et al., J. Mater. Chem., 5 (1995) 879 and J. Supercond., 11 (1998) 107, 5. A. Kolodziejczyk et al., Mater. Engin. Bull., 4 (105) (1998) 1226. 6. C.P. Bean, Phys. Rev. Lett., 8 (1962) 250. 7. L. Ji, R.H. Sohn, G.C. Spalding, C.J.Lobb, and M. Tinkham, Phys. Rev., B 40, (1989) 10936. 8. Y.B. Kim etal., Phys. Rev., 131 (1963) 2486. 9. J.R. Clem, Physica C, 153-155 (1988) 50.
Physica C 341-348 (2000) 2 0 4 9 - 2 0 5 0 www.elsevier.nl/locate/physc
Intergrain magnetic properties and critical currents of T1-1223 bulk and tape superconductors* R. Zalecki a, A. Kolodziejczyka, J. Chmist a, W. K6nigb, G. Gritzner b a Department of Solid State Physics, University of Mining and Metallurgy, PL-30-059 Cracow, Poland bJohannes Kepler Universit~t, Institut f'tir Chemische Technologie Anorganischer Stoffe, A-4040 Linz, Austria The magnetic field and the temperature dependencies of the dispersive and the absorption components of the low frequency a c magnetic susceptibility for Pb and Bi single doped bulk superconductors as well as for Pb and Bi co-doped Ag-sheathed superconducting T1-1223 tapes have been measured and analyzed. The studies were accompanied by optical and electron microscopic observations of the microstructure. The ac susceptibility measured at various ac magnetic field amplitudes showed both intergrain and intragrain features. The temperature dependencies of the intergrain critical current densities were extracted from the absorption susceptibility via a modified Bean model. They were at relevant temperatures one order of magnitude larger for the tape than for the bulk specimens. 1. INTRODUCTION Some magnetic and electrical properties of hightemperature superconductors are controlled by the superconducting intergrain weak link system (SWL), which may be treated as Josephson junctions (SWL-JJ) [1]. The total critical current density Jc is thus limited by the Josephson critical current density J~j. Upon lowering the temperature the grains become superconducting first, followed by the intergrain junctions. This results in a twostep behavior in the dispersive and absorption a c magnetic susceptibility. Substitution of Pb and/or Bi into the T1 sites in T11223 bulk phase superconductors leads to improved flux pinning properties and to an increase in the J~j [2,3]. In this paper we show by a c susceptibility measurements that Pb and Bi co-doped T1-1223 tapes are suitable materials for technical applications because of their high Jcj values.
2. EXPERIMENTAL (Tlo.74Bio.3)(Sro.gBao.1)2Ca2Cu3Oy and (Tlo.oPbo.5) (Sro.aBao.l)2CazCuaOy superconductors were
prepared with Tc values of 121 K and 118 K, respectively, by a procedure described elsewhere [2-4]. The Ag-sheathed tape of (Tlo.6Bio.16Pbo.z4) (Sro.aBao.0zCa2CuaOy with a T~ of 118 K was fabricated from precursors prepared either by the spray-drying of nitrates technique or by the tartrate gel techn!que [4]. Following the addition of TI2Oa, PbO and' BizOa the powders were compacted and sintered into superconducting pellets. The resultant pellets were milled, filled in silver tubes, drawn to wires and then rolled to 0.25 minx 2 nun tapes. Final sintering was carried out in air at 850 °C for 0.5 h followed by annealing at 750 °C for 50 h in flowing oxygen. The phase purity and the microstructure of the sample were investigated by a number of methods [2-4]. The degree of grain alignment in the tape was about 95%. A c susceptibility measurements were carried out in a standard mutual inductance bridge for the a c magnetic field amplitude Bac from 1 pT to about 1 mT at 189 Hz in the zero field cooling procedure (ZFC). The a c field was applied along the bulk needle- like shaped sample with diameter d _=2 mm and in parallel direction to the plane of the tape sample with cross section about 0.2 x 0.2 nun2.
*This study was financiallysupported by the KBN, Poland (project no 2P03B 147 17), the Fonds zur F6rdemng der wissenschaflichen Forschung in Osterreich (project 11 873) and by the Osterreichischer Akademischer Austauschdienst, Wissenschafllich-technischeZusammenarbeitmit Polen (project 3/99). 0921-4534/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII S0921-4534(00)01008-X
R. Zalecki et al./Physica C 341-348 (2000) 2049-2050
2050
3. RESULTS AND DISCUSSION Figures 1 and 2 show typical temperature dependencies of ac absorption susceptibilities Z".
(TI,Bi)-1223
600pT
" ~
200pT801~
\
T
I
1
.
2O.T '/
"
Jcj, d_=_ 2 mm is the sample diameter perpendicular to Bp. For intragrain Jog, d is an average grain diameter [2,5]. Some values of Jog were estimated in 15]. The calculated values of J~j were plotted versus the respective peak temperatures in Fig. 2. The linear extrapolation of Jcj (T) for the tape resulted in values of J~j(100 K) : 3.85 kA cmz and J~j(77 K) = 10.2 kA cmz about one order of magnitude larger than for the bulk sample. Latter value agrees well with the direct transport critical current density of 10 kA cm-z [2].
1 . . . .
0
,? o
,
.
..~
,
.
.
.
.
,
(Tl,Bi,Pb)-1223
3
300'
~
B
. . . .
,
tape
II ( a , b )
1500
,t"-' "7
200,
2
1000
600~T
"'E
200~T
500
~ = 1 O0 •
400~T 5OpT
0
lOO . . . .
lt~5 . . . .
0
1{o . . . .
1{5 . . . .
1~o
TIK
Figure 2. Plot of J~j (7') for samples as indicated. 3
Bacll
(a,b)
11001~T
0
/880.T ~
55OPT
f
220~T
~ 100
105
110
115
120
TIK Figure 1. Plot o f X "
(T) for samples as indicated.
The low temperature intergrain peak and the high temperature intragrain peaks in Fig. 1 resulted from the flux movement in the SWL-JJ system and in the grains, respectively [5]. For the tape only one intergrain peak was observed. The ac field Ba~ penetrates into the grains at the higher temperature peak while it penetrates into the center of the intergrain junctions at the lower temperature peak. The induced supercurrents are equal to the intra- and the intergrain critical currents, respectively. J~(T) may be derived from the dependence of the position of the inter- and intragrain peaks of Z"(T) on different ac fields. The critical currents were derived from the Bean model and its modifications [6-9] as Jc(B)=gB/d, where Bp is the penetration field and d is the average penetration depth. We assumed Bp equal to Bac which is only an approximation [6-9]. For intergrain
4. SUMMARY AND CONCLUSIONS Intergrain critical current densities J~j of Pb and Bi single-doped T1-1223 bulk superconductors as well as for a Pb and Bi co-doped Ag-sheathed tape were estimated from the absorption ac susceptibility. The intergrain Jcj for the tape was enhanced due to improvement of the flux pinning and the grain connectivity by Bi and Pb co-doping. REFERENCES 1. G. Deutscher, Springer Series in Solid State Sciences, eds. J.C. Bednorz and K.A. Miiller, Springer-Verlag, Berlin, vol.90 (1990) 174. 2. W. Kbnig, G. Gritzner, M. Reissner and W. Steiner, Physica C, 258 (1996) 175. 3. M. Mair, W. K6nig and G. Gritzner, Supercond. Sci. Techn., 8 (1995) 894. 4. W. K6nig et al., J. Mater. Chem., 5 (1995) 879 and J. Supercond., 11 (1998) 107, 5. A. Kolodziejczyk et al., Mater. Engin. Bull., 4 (105) (1998) 1226. 6. C.P. Bean, Phys. Rev. Lett., 8 (1962) 250. 7. L. Ji, R.H. Sohn, G.C. Spalding, C.J.Lobb, and M. Tinkham, Phys. Rev., B 40, (1989) 10936. 8. Y.B. Kim etal., Phys. Rev., 131 (1963) 2486. 9. J.R. Clem, Physica C, 153-155 (1988) 50.