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Microstructure anisotropy and critical currents in silver-sheathed Bi2223 tapes
__EB
J&g
-
PHY SICA
ELSEVIER
Physica C 282-287
Microstructure
8
(I 997) 1995-1996
anisotropy and critical currents in silver-sheathed Bi2223 tapes
Q.Y. Hu, H.K. Liu, H.W. Weber’ and S.X. Dou Center for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2500. Australia
?? Atominstitut
der osterreichischen Universitlten, A-1020 Wien, Austria
The effective misalignment angle of the Bi2223 tape, (peg,can be derived by transport measurement in a magnetic field. By SEM observation, this angle was found to be identical to the average crystallographic grain misalignment angle. Also, the angle is not influenced by fast neutron radiation. These facts prove that the crystallographic misalignment of the grains determines the critical current anisotropy of the tape. A model is proposed that this typical value is mainly determined by intrinsic mechanical properties of the Bi2223 compound and is a result of the mechanical deformation of the tape during the tape fabrication. 1. INTRODUCTION
3. RESULTS AND DISCUSSIONS
According to Lawrence and Doniach [l], a dimensional crossover from 3D to 2D appears in layered superconductors under the condition that the coherence length & perpendicular to the superconducting layers is smaller than the distance between these layers. Bi2212.has been confirmed to have 2D behavior by Raffy et al. [2] and Schmitt et al. [3] in their expenments on Bi2212 thin films. Schalk et al [4] have also found that Bi2223 is two dimensional in the critical current behavior. In the following, we use the 2D description to study our Bi2223 tapes.
The critical current of the tapes was measured in a rotating field. The data are plotted as a function of the field component perpendicular to the tape (Fig. 1). It can be seen that the curves. obtained from the rotation measurement at different magnetic fields, are overlapped into one except for the low field region. The magnetic field dependence of the critical current measured with B//c is also plotted in the same figure. We can see that IJB&B,e)) coincides with ]e(B//c) in the high field region. This demonstrates that the dissipative behavior of Bi2223 at 77.3 K results from B//c. i.e., the tape does behaves 2D. The low field deviation of the curve I,(B,0) from the curve IJB//c) can be explained by the existence of the misalignment of the grains. In this case, the grains see a perpendicular field even when the field is parallel to the tape plane. Thus the misalignment angle can be calculated by ‘py~= Arcsin[Bl(//ab)&(//c)], where I&3 ,(//ab))=I,(B2(//c)>. The angle is around 10” for different tapes. From SEM, the misalignment of the grain can be observed and the misalignment angle can be estimated, which is quite close to Q, for various samples (Fig. 2). The 2D behavior can be briefly described as follows: (1) L(B//ab) is constant for different B and (2) IJB,e) = I, (Bsine), where 8 is the angle between the a,b-plane and B. As all know, the first
2. EXPERIMENTAL The tapes were fabricated by the well established powder in tube technique. The critical current Ic was measured as a function of the angle between the broad face of the tape and the magnetic field direction in different magnetic fields and as a function of field for B//tape and B-L tape, keeping the field and the current perpendicular to each other. A criterion of lO%/cm was used for the definition of Z. The angular resolution of the rotation is better than 1”. The microstructure of the tape (cross sectional direction) was determined with a Leica Stereoscan S440 scanning electron microscope (SEM). Og21-4534/97/$17.00
0 Elsevier Science B.V. All tights reserved.
PII SO921-4534(97)01068-X
1996
Q.K Hu et al./Physica
#I93824
ha< 3 6-
C 282-287 (1997) 1995-1996
$
47.5mT 59.2mT -93mT -3WmT -w/c
42-
o! . , -50 0
, . , , , , 50 loo 150 200 250 B*sitM(mT)
, . , J 300
350
Fig. 1 Critical currents of the tape as a function of B&V3) and B//c. condition does not satisfy for the Bi2223 tapes, i.e. I,(B//ab) is not parallel to the B axis. This is obviously not caused by weak links, in which case the b(B//ab)) will never scale with L(B//c) (the tape shows a scale factor of such kind of cp& because the Josephson penetration depth is different for the two different B orientations, which determines the dissipation of the current. The neutron was used to treat the samples after the rotation measurement. The radiation suppresses the low field critical current and increases high field critical current. However, the cptff remains the same following the radiation. Fast neutron irradiation is isotropic or the defect tracks are randomly oriented in the sample, which does not change the anisotropy of the material. Thus ‘ptifl can only be attributed to the crystallographic misalignment of the grains. Therefore, cpeflis an intrinsic property of the tape. When fabricating the tape, the mechanical deformation is used to obtain the desirable dimensions of the tape. We think the deformation also plays an important role in aligning grains. That is, during the deformation, the grains inside the colony slips along their a,b-plane because of the weak bonding of the Bi-0 layers. In such a way, the colony tends to tilt its a,b plane to parallel to the tape plane. The resultant thickness and width of the grains determine the misalignment
Fig. 2 Cross sectional micrograph of the tape and therefore the misalignment angle. That is, cpcti is determined by the intrinsic mechanical property of the garins. 4. CONCLUSION Based on the 2D behavior of Ag sheathed Bi2223 tapes with regard to their critical currents. the effective grain misalignment angle, cpcfi has been studied. The data of &(B,0) measurements on different samples show, that this value is around to the average loo, which is identical crystallographic grain misalignment angle of the tape. REFERENCES 1. W.E. Lawrence and S. Doniach, Proceedings of the 12th International Conference on Low Temperature Physics? Kyoto. 1970. Keipaku. Tokyo, 1971, p.361. 2. H. Raffy, S. Labdi, 0. Laborde. and P. Monceau, Phys. Rev. Lett., 66 (199 1) 25 15. 3. P. Schmitt, P. Kummeth, L. Schultz and G. Saemann-Ischenko, Phys. Rev. Lett. 67,267 (1991). 4. R.M. Schalk, G. Samadi Hosseinali, H.W. Weber, S. Griindorfer, D. BZuerle, S. Proyer, P. Wagner, U. Frey and H. Adrian. Physica C 235 240, (1994) 2625.
J&g
-
PHY SICA
ELSEVIER
Physica C 282-287
Microstructure
8
(I 997) 1995-1996
anisotropy and critical currents in silver-sheathed Bi2223 tapes
Q.Y. Hu, H.K. Liu, H.W. Weber’ and S.X. Dou Center for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2500. Australia
?? Atominstitut
der osterreichischen Universitlten, A-1020 Wien, Austria
The effective misalignment angle of the Bi2223 tape, (peg,can be derived by transport measurement in a magnetic field. By SEM observation, this angle was found to be identical to the average crystallographic grain misalignment angle. Also, the angle is not influenced by fast neutron radiation. These facts prove that the crystallographic misalignment of the grains determines the critical current anisotropy of the tape. A model is proposed that this typical value is mainly determined by intrinsic mechanical properties of the Bi2223 compound and is a result of the mechanical deformation of the tape during the tape fabrication. 1. INTRODUCTION
3. RESULTS AND DISCUSSIONS
According to Lawrence and Doniach [l], a dimensional crossover from 3D to 2D appears in layered superconductors under the condition that the coherence length & perpendicular to the superconducting layers is smaller than the distance between these layers. Bi2212.has been confirmed to have 2D behavior by Raffy et al. [2] and Schmitt et al. [3] in their expenments on Bi2212 thin films. Schalk et al [4] have also found that Bi2223 is two dimensional in the critical current behavior. In the following, we use the 2D description to study our Bi2223 tapes.
The critical current of the tapes was measured in a rotating field. The data are plotted as a function of the field component perpendicular to the tape (Fig. 1). It can be seen that the curves. obtained from the rotation measurement at different magnetic fields, are overlapped into one except for the low field region. The magnetic field dependence of the critical current measured with B//c is also plotted in the same figure. We can see that IJB&B,e)) coincides with ]e(B//c) in the high field region. This demonstrates that the dissipative behavior of Bi2223 at 77.3 K results from B//c. i.e., the tape does behaves 2D. The low field deviation of the curve I,(B,0) from the curve IJB//c) can be explained by the existence of the misalignment of the grains. In this case, the grains see a perpendicular field even when the field is parallel to the tape plane. Thus the misalignment angle can be calculated by ‘py~= Arcsin[Bl(//ab)&(//c)], where I&3 ,(//ab))=I,(B2(//c)>. The angle is around 10” for different tapes. From SEM, the misalignment of the grain can be observed and the misalignment angle can be estimated, which is quite close to Q, for various samples (Fig. 2). The 2D behavior can be briefly described as follows: (1) L(B//ab) is constant for different B and (2) IJB,e) = I, (Bsine), where 8 is the angle between the a,b-plane and B. As all know, the first
2. EXPERIMENTAL The tapes were fabricated by the well established powder in tube technique. The critical current Ic was measured as a function of the angle between the broad face of the tape and the magnetic field direction in different magnetic fields and as a function of field for B//tape and B-L tape, keeping the field and the current perpendicular to each other. A criterion of lO%/cm was used for the definition of Z. The angular resolution of the rotation is better than 1”. The microstructure of the tape (cross sectional direction) was determined with a Leica Stereoscan S440 scanning electron microscope (SEM). Og21-4534/97/$17.00
0 Elsevier Science B.V. All tights reserved.
PII SO921-4534(97)01068-X
1996
Q.K Hu et al./Physica
#I93824
ha< 3 6-
C 282-287 (1997) 1995-1996
$
47.5mT 59.2mT -93mT -3WmT -w/c
42-
o! . , -50 0
, . , , , , 50 loo 150 200 250 B*sitM(mT)
, . , J 300
350
Fig. 1 Critical currents of the tape as a function of B&V3) and B//c. condition does not satisfy for the Bi2223 tapes, i.e. I,(B//ab) is not parallel to the B axis. This is obviously not caused by weak links, in which case the b(B//ab)) will never scale with L(B//c) (the tape shows a scale factor of such kind of cp& because the Josephson penetration depth is different for the two different B orientations, which determines the dissipation of the current. The neutron was used to treat the samples after the rotation measurement. The radiation suppresses the low field critical current and increases high field critical current. However, the cptff remains the same following the radiation. Fast neutron irradiation is isotropic or the defect tracks are randomly oriented in the sample, which does not change the anisotropy of the material. Thus ‘ptifl can only be attributed to the crystallographic misalignment of the grains. Therefore, cpeflis an intrinsic property of the tape. When fabricating the tape, the mechanical deformation is used to obtain the desirable dimensions of the tape. We think the deformation also plays an important role in aligning grains. That is, during the deformation, the grains inside the colony slips along their a,b-plane because of the weak bonding of the Bi-0 layers. In such a way, the colony tends to tilt its a,b plane to parallel to the tape plane. The resultant thickness and width of the grains determine the misalignment
Fig. 2 Cross sectional micrograph of the tape and therefore the misalignment angle. That is, cpcti is determined by the intrinsic mechanical property of the garins. 4. CONCLUSION Based on the 2D behavior of Ag sheathed Bi2223 tapes with regard to their critical currents. the effective grain misalignment angle, cpcfi has been studied. The data of &(B,0) measurements on different samples show, that this value is around to the average loo, which is identical crystallographic grain misalignment angle of the tape. REFERENCES 1. W.E. Lawrence and S. Doniach, Proceedings of the 12th International Conference on Low Temperature Physics? Kyoto. 1970. Keipaku. Tokyo, 1971, p.361. 2. H. Raffy, S. Labdi, 0. Laborde. and P. Monceau, Phys. Rev. Lett., 66 (199 1) 25 15. 3. P. Schmitt, P. Kummeth, L. Schultz and G. Saemann-Ischenko, Phys. Rev. Lett. 67,267 (1991). 4. R.M. Schalk, G. Samadi Hosseinali, H.W. Weber, S. Griindorfer, D. BZuerle, S. Proyer, P. Wagner, U. Frey and H. Adrian. Physica C 235 240, (1994) 2625.