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Irreversibility lines and morphologies of BiPbSrCaCuO silver sheathed wires
Physiea C 185-189 (1991) 2363-2364 North-Holland
lrreversibility lines and morphologies of BiPbSrCaCuO silver sheathed wires
Takeshi Hikata, Ken-iehi Sato and Yukikazu iwasa" Osaka Research Laboratories, Sumitomo Electric Industries Ltd., Shimaya, 1-1-3, Konohana-ku, Osaka, 554, Japan 'Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A The irreversibility lines of BiPbSrCaCuO silver sheathed tapes were measured at temperatures from 33 K to t 10 K. It was determined that the irreversibility magnetic field, H~,(81 K) did not change with the sweep rate of magnetic field from 0.16 to 0.8 T/min. It was found that the irreversibility line was improved to higher magnetic field and temperature with the increase of Jo~- This suggests that the irreversihility line has a strong relationship to the morphology of BiPbSrCaCuO. 1. INTRODUCTION For the design of a superconducting magnet, irreversibility magnetic field I-I~.(T) and temperature T~,(I-I) are important because the critical current is dominated by the Hn,(T) rather than the mean field critical magnetic field Hm(T)J m In this paper we present H=(T) and Tu,(H) data of silversheathed Bit.sPbo.4Sr2Caz2CuxOx tapes in the temperature range from 33 to 110 Kand in the magnetic field range up to 30 T, measured at the Francis Bitter National Magnet Laboratory with the facility's 33-mm warm bore, 30-T hybrid magnet and at Sumitomo Electric Industries with an 8-T magnet.
2fX) mA (J=1.5 A/ram 2 ) fin samples 2, 3, 4, and 5, was used to measure voltage. H,, and T= were defined by a resistive electric field of 1 btV/cm. This electric field is equivalent to an effective resistivity of 7x10 "n ~.m, a value much lower than 3 x 1 0 -9 ff2.m, the resistivity of silver at 77 K.
3. RESULTS AND DISCUSSION Figure 1 shows ~aoH= vs T plots for tcs~ samples 1 (open symbols) and 2 {solid symbo 0 with Jco=300 A/mm 2. The sweep rate dependency of magncdc ,,.,,.+":'-"~or~ ,H~ was SO
2. EXPERIMENTS Five test samples with 3 levels of .]co at 77.3 K and zero magnetic field, (No. 1,2 and 3 : 3 0 0 A/ram 2, No. 4 : 2 2 0 A/mm 2 and No. 5:130 A/ram 2) were prepared. (Note that test samples 2 and 3 are from the same tape.) The critical temperature, T o of each tape was 106 K. The overall dimensions, including silver sheath, were - 4 mm wide, -0.15 mm thick. A sample holder, housed in a temperature controlled adiabatic chamber, was used fo~ these measurements. In the holder, test samples 1, 2, 4, and 5 were oriented to align each tape plane parallel to the applied magnetic field direction, while test sample 3 was aligned in such a way that the tape plane was pe +rpendicular to the applied field. The experimental procedure was as follows. For a given temperature, the applied magnetic field, H, was swept at a constant rate (iu0dH,/dt=0.16--I T/min) starting at a field considerably below H , corresponding to the temperature. For a given magnetic field setting, the temperature was increased at a constant rate from 4.2 K to 120 K. The 4-probe dc technique, with a constant measurement current of 100 mA 0=0.9 A/ram: over the superconductor cross section) for :<,mp~e I and
7'0
I0 7" ~7E O 0
40
80
-
Z
;20
" "K"
FIGURE 1 Irrcvcrsibilily tinc data for the sample,~ with Jc0 (77.3 K) =3(}0 A/ram: through five c~mdifions w'hich indicalc H,.,~.q-)by' the sweep m~c of 0.16 T'min(~'}. ~!4 T rain:(©). 0.S Train:(% ant] lT'min:(®}, and T,,{H}:(z). OWn svmNqs corrcspor~d It> sample 1, while ..oiid sxn-~N.~lco,,rc~Dmds t~ samp]c 2
0921-4534/91/$03.50 O 1991 - Elsevier Science ]~blishers B.V. .,M~rights reserved
2364
T. Hikata et al. / trreversibUity lines and morphologies of BiPbSrCaCuO silver sheathed wires
measured with 0.16(A), 0.4(0) and 0.8 T/min(v) for sample 1. T~,(H)(n) was evaluated with a temperature sweep rate of 5 K/min. For sample 2, I-ql'lt,, (®) was measured up to 30 T with a 1 T/min sweep rate. As shown in Fig.l, it was found that the irreversibility lines were not changed with the different measurement procedures. Figure 2 shows g0H~, vs T plots for test ~ample 2 (©), 3(o), 4(ra) and 5(~). Hm(55 K) values were obtained at 27.9 T for sample 2, 22.8 T for .~mlple 4 ,and 18.2 T for sample 5, with the magnetic field lxwaUel to the tape plane. The data clearly show that H,, increases with Je0- We have reported previously that ,an increase in l~ suggests an improvement of morphology in BiPbSrCaCuO caused by a decrease in weak links at groin boundaries and a fine dispersion of nonsuperconducting pha.~s. :'+-~ The.~ data suggest that H~ apparently increa.~s with improved morphology of the high-Tc superconducting section in the silver-sheathed tapes. The superconducting section is composed of polycrystalline platelet grains including the granular nonsupereonducting phases, while the transport current contains the c-axis component when it crosses through the grain boundaries. The local Lorentz force between c-axis component current and magnetic field is generated perpendicularly to the c-axis along grain boundaries with the weaker pinning force. Therefore the improvement in h-reversibility line suggests that the
-r-
2
,\ I0-
\
2
\
~,kJ
4. CONCLUSIONS The irreversibility lines of BiPbSrCaCuO silver-sheathed tapes were measured as a function of temperature; H~ was found to increase with Jco. For a sample with Jc~(77.3 K)=300 A/mm 2, goH~ was 27.9 T at 55 K. The dependence of H~ on Jco suggests that the superconductor's morphology has a strong effect on Ht~. ACKNOWLEDGMENTS This work was supported in part by the U.S. Department of Energy, Office of Conservation and Renewable Energy and in part by Sumltomo Electric Industries, Ltd.. The Francis Bitter National Magnet Laboratory is supported by the National Science Foundation. The authors are grateful to Larry Rubin for valuable advice; Bruce Brandt, Ping Zhao and Vincent Adzovie for their technical assistance.
30-
20-
c-axis component current across the grain boundaries decreases and the flux does not flow easily with the improvement of morphology in the superconducting phase. For test mtmples 2 and 3 from the same tape, with which the effect of field direction on ti,, was examined, the data clearly show anisotmpy in relation to field direction. With the tape phme perpendicular to applied field (test ~mple 3, solid circle in Fig. 2), tt,,(33 K) was 17 T, which shows a lower irreversibility field than that of s:hmple 2. The H~,, begins to increase steeply at about 50 K as temperature is lowered. With a parallel applied field (test sample 2, open circle in Fig.I), this steep increase begins at about 80 K. H,, follows a power law relationship, i.e, H~,(T)~x[1T(H~,~Tt.(P,)]*, where T,.(0)=I06 K. The data fit the power law relationship with n=2.8 for the parallel-field orientation and n=3.0 for the perpendicular-field orientation. These data are much larger than n-l.5 for Y-based superconductors. :~
N'k/
7(K)
FIGURE 2 goH~,(T) data for four test samples ( 2 : 0 , 3 : 0 , 4 : ~ , 5: zx). Open symboles indicate that the applied magnetic field is parallel to the tape planes, while the solid symbol indicates a perpendicular magnetic field. The lines previde a guide for the eye.
REFERENCES 1. T.Matsushita, T.Fujimori. K.Toko and K.Yamafuji, Appl. Phys. Lett. 56 (199~3) 2f~39. 2. Y.Xu and M.Suenaga, Phys. Rev. B43 (1991) 5516. 3. T.Hikata, M.Ueyama, H.Mukai and K.Sato, Cryogcnics 30 (1990) 924. 4. T.Hika:a, K.Sam and YAwasa, Jpn. L Appl. Phys., in press. 5. K.Sato, T.Hikata: H.Mukai+ M.Ueyama, N.Shibuta, T.Kato, T.Ma~uda, M.Nagata, KAwata and T.Mitsui, IEEE Trans. MAG. 27 (i99t) 1231.
lrreversibility lines and morphologies of BiPbSrCaCuO silver sheathed wires
Takeshi Hikata, Ken-iehi Sato and Yukikazu iwasa" Osaka Research Laboratories, Sumitomo Electric Industries Ltd., Shimaya, 1-1-3, Konohana-ku, Osaka, 554, Japan 'Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A The irreversibility lines of BiPbSrCaCuO silver sheathed tapes were measured at temperatures from 33 K to t 10 K. It was determined that the irreversibility magnetic field, H~,(81 K) did not change with the sweep rate of magnetic field from 0.16 to 0.8 T/min. It was found that the irreversibility line was improved to higher magnetic field and temperature with the increase of Jo~- This suggests that the irreversihility line has a strong relationship to the morphology of BiPbSrCaCuO. 1. INTRODUCTION For the design of a superconducting magnet, irreversibility magnetic field I-I~.(T) and temperature T~,(I-I) are important because the critical current is dominated by the Hn,(T) rather than the mean field critical magnetic field Hm(T)J m In this paper we present H=(T) and Tu,(H) data of silversheathed Bit.sPbo.4Sr2Caz2CuxOx tapes in the temperature range from 33 to 110 Kand in the magnetic field range up to 30 T, measured at the Francis Bitter National Magnet Laboratory with the facility's 33-mm warm bore, 30-T hybrid magnet and at Sumitomo Electric Industries with an 8-T magnet.
2fX) mA (J=1.5 A/ram 2 ) fin samples 2, 3, 4, and 5, was used to measure voltage. H,, and T= were defined by a resistive electric field of 1 btV/cm. This electric field is equivalent to an effective resistivity of 7x10 "n ~.m, a value much lower than 3 x 1 0 -9 ff2.m, the resistivity of silver at 77 K.
3. RESULTS AND DISCUSSION Figure 1 shows ~aoH= vs T plots for tcs~ samples 1 (open symbols) and 2 {solid symbo 0 with Jco=300 A/mm 2. The sweep rate dependency of magncdc ,,.,,.+":'-"~or~ ,H~ was SO
2. EXPERIMENTS Five test samples with 3 levels of .]co at 77.3 K and zero magnetic field, (No. 1,2 and 3 : 3 0 0 A/ram 2, No. 4 : 2 2 0 A/mm 2 and No. 5:130 A/ram 2) were prepared. (Note that test samples 2 and 3 are from the same tape.) The critical temperature, T o of each tape was 106 K. The overall dimensions, including silver sheath, were - 4 mm wide, -0.15 mm thick. A sample holder, housed in a temperature controlled adiabatic chamber, was used fo~ these measurements. In the holder, test samples 1, 2, 4, and 5 were oriented to align each tape plane parallel to the applied magnetic field direction, while test sample 3 was aligned in such a way that the tape plane was pe +rpendicular to the applied field. The experimental procedure was as follows. For a given temperature, the applied magnetic field, H, was swept at a constant rate (iu0dH,/dt=0.16--I T/min) starting at a field considerably below H , corresponding to the temperature. For a given magnetic field setting, the temperature was increased at a constant rate from 4.2 K to 120 K. The 4-probe dc technique, with a constant measurement current of 100 mA 0=0.9 A/ram: over the superconductor cross section) for :<,mp~e I and
7'0
I0 7" ~7E O 0
40
80
-
Z
;20
" "K"
FIGURE 1 Irrcvcrsibilily tinc data for the sample,~ with Jc0 (77.3 K) =3(}0 A/ram: through five c~mdifions w'hich indicalc H,.,~.q-)by' the sweep m~c of 0.16 T'min(~'}. ~!4 T rain:(©). 0.S Train:(% ant] lT'min:(®}, and T,,{H}:(z). OWn svmNqs corrcspor~d It> sample 1, while ..oiid sxn-~N.~lco,,rc~Dmds t~ samp]c 2
0921-4534/91/$03.50 O 1991 - Elsevier Science ]~blishers B.V. .,M~rights reserved
2364
T. Hikata et al. / trreversibUity lines and morphologies of BiPbSrCaCuO silver sheathed wires
measured with 0.16(A), 0.4(0) and 0.8 T/min(v) for sample 1. T~,(H)(n) was evaluated with a temperature sweep rate of 5 K/min. For sample 2, I-ql'lt,, (®) was measured up to 30 T with a 1 T/min sweep rate. As shown in Fig.l, it was found that the irreversibility lines were not changed with the different measurement procedures. Figure 2 shows g0H~, vs T plots for test ~ample 2 (©), 3(o), 4(ra) and 5(~). Hm(55 K) values were obtained at 27.9 T for sample 2, 22.8 T for .~mlple 4 ,and 18.2 T for sample 5, with the magnetic field lxwaUel to the tape plane. The data clearly show that H,, increases with Je0- We have reported previously that ,an increase in l~ suggests an improvement of morphology in BiPbSrCaCuO caused by a decrease in weak links at groin boundaries and a fine dispersion of nonsuperconducting pha.~s. :'+-~ The.~ data suggest that H~ apparently increa.~s with improved morphology of the high-Tc superconducting section in the silver-sheathed tapes. The superconducting section is composed of polycrystalline platelet grains including the granular nonsupereonducting phases, while the transport current contains the c-axis component when it crosses through the grain boundaries. The local Lorentz force between c-axis component current and magnetic field is generated perpendicularly to the c-axis along grain boundaries with the weaker pinning force. Therefore the improvement in h-reversibility line suggests that the
-r-
2
,\ I0-
\
2
\
~,kJ
4. CONCLUSIONS The irreversibility lines of BiPbSrCaCuO silver-sheathed tapes were measured as a function of temperature; H~ was found to increase with Jco. For a sample with Jc~(77.3 K)=300 A/mm 2, goH~ was 27.9 T at 55 K. The dependence of H~ on Jco suggests that the superconductor's morphology has a strong effect on Ht~. ACKNOWLEDGMENTS This work was supported in part by the U.S. Department of Energy, Office of Conservation and Renewable Energy and in part by Sumltomo Electric Industries, Ltd.. The Francis Bitter National Magnet Laboratory is supported by the National Science Foundation. The authors are grateful to Larry Rubin for valuable advice; Bruce Brandt, Ping Zhao and Vincent Adzovie for their technical assistance.
30-
20-
c-axis component current across the grain boundaries decreases and the flux does not flow easily with the improvement of morphology in the superconducting phase. For test mtmples 2 and 3 from the same tape, with which the effect of field direction on ti,, was examined, the data clearly show anisotmpy in relation to field direction. With the tape phme perpendicular to applied field (test ~mple 3, solid circle in Fig. 2), tt,,(33 K) was 17 T, which shows a lower irreversibility field than that of s:hmple 2. The H~,, begins to increase steeply at about 50 K as temperature is lowered. With a parallel applied field (test sample 2, open circle in Fig.I), this steep increase begins at about 80 K. H,, follows a power law relationship, i.e, H~,(T)~x[1T(H~,~Tt.(P,)]*, where T,.(0)=I06 K. The data fit the power law relationship with n=2.8 for the parallel-field orientation and n=3.0 for the perpendicular-field orientation. These data are much larger than n-l.5 for Y-based superconductors. :~
N'k/
7(K)
FIGURE 2 goH~,(T) data for four test samples ( 2 : 0 , 3 : 0 , 4 : ~ , 5: zx). Open symboles indicate that the applied magnetic field is parallel to the tape planes, while the solid symbol indicates a perpendicular magnetic field. The lines previde a guide for the eye.
REFERENCES 1. T.Matsushita, T.Fujimori. K.Toko and K.Yamafuji, Appl. Phys. Lett. 56 (199~3) 2f~39. 2. Y.Xu and M.Suenaga, Phys. Rev. B43 (1991) 5516. 3. T.Hikata, M.Ueyama, H.Mukai and K.Sato, Cryogcnics 30 (1990) 924. 4. T.Hika:a, K.Sam and YAwasa, Jpn. L Appl. Phys., in press. 5. K.Sato, T.Hikata: H.Mukai+ M.Ueyama, N.Shibuta, T.Kato, T.Ma~uda, M.Nagata, KAwata and T.Mitsui, IEEE Trans. MAG. 27 (i99t) 1231.