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Critical current densities in sintered Ba-Y-Cu-O compound
Volume 124, number 6,7
CRITICAL CURRENT DENSITIES
PHYSICS LETTERS A
IN SINTERED
Ba-Y-Cu-0
5 October 1987
COMPOUND
H. KUMAKURA, M. UEHARA, Y. YOSHIDA and K. TOGANO National Research Institutefor Metals, Tukuba Laboratories, l-2-1, Sengen, Sakura-mura, Niihari-gun, Ibaraki 305. Japan
Received 1 May 1987; revised manuscript received 30 June 1987; accepted for publication 20 August 1987 Communicated by J.I. Budnick
Critical current densities J, of Ba-Y-Cu-0 compounds were measured at 77 K by the magnetization method and the resistive method. The JC’s derived from magnetization are much larger than those obtained by the resistive method. The origin of this J, difference is discussed in relation to the microstructure of the samples.
The discovery of high temperature superconductivity in La-Ba-Cu-0 [ 1] and La-Sr-Cu-0 [ 2,3] compounds with K2NiF4 structure has strongly encouraged the search of new superconducting materials having higher transition temperature T,. Recently, Wu et al. reported superconductivity in an unidentified phase in the Ba-Y-Cu-0 compound system at 93 K [ 41. It seemed that high temperature superconductivity was not related to the KINiF, structure for this system. The authors have prepared a series of compounds having nominal composition (Ba, +.Y,)CuOJ_,, which corresponds to perovskite structure, and have found superconductivity in the range x=0.2-0.6 with maximum T, of N 120 K (onset) and 92.5 K (offset) for x=0.4 [5]. Very recently, Cava et al. reported that oxygen-deficient perovskite of stoichiometric (Ba,Y, ) Cu309 _,, is responsible for high T, for the Ba-Y-Cu-0 system
[61. In this letter, magnetization measurements were carried out for the stoichiometric ( Ba*Y, ) CU~O~_~ and the compound x=0.4 in our previous investigation. Critical current densities J, were estimated from obtained magnetization curves, and were compared to those directly measured by the resistive method. The samples investigated were prepared by the solid state reaction method using BaC03, Y,03 and CuO powders of 99.99% purity. The nominal composition was and (Ba2YI)Cu309--y (Ba1.8YI.2)Cu309_~ The samples have a porous
structure with a packing factor of 72% assuming y= 2.1 [ 61. The details of the sample preparation are described elsewhere [ 51. The transition temperaturesof(Ba2Y1)Cu309_yare 110,92and91SKfor onset, midpoint and offset, respectively. X-ray diffraction shows that the ( Ba2Y1)Cu309_-y sample consists of a single phase which is identified as oxygen-deficient perovskite with a small orthorhombic distortion, while (Ba, ,sY, .2)CU~O~_~contains a second and/or a third phase. The details of the X-ray diffraction analysis will be described elsewhere. The magnetization measurements were performed on a rectangular sample of dimensions 4x 2.4x0.8 mm3 using a vibrating sample magnometer in fields up to f 10 kOe. The magnetization curves were measured in liquid nitrogen at a constant sweep rate of applied field of 2-10 Oe/s. Examples of obtained magnetization curves for ( Ba,Y, ) Cu309 _-y compound are shown in figs. 1 and 2. Similar magnetization curves were also obtained for the (Ba1.8Y,.2)Cu309_-y compound. In fig. 1 the results of the first run (I) and the second run (II) are shown. Magnetization measurements at room temperature indicate that the compounds are paramagnetic in the normal state. Magnetization curves at 77 K clearly indicate that the compounds are typical type II superconductors. From the slope of the initial magnetization curves near zero field, the volume fraction of the superconducting phase can be estimated. About 55% of the sample is superconducting at 77 K for (BazY,)CusOg_,, which is rather smaller than
0375-9601/87/$ 03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
367
Volume
124, number
PHYSICS
6,7
LETTERS
A
5 October
1987
From Magnetization 4
*
%.#l.,)Cu3O9-,
Fig. 1. Magnetization curves for the ( BazY i )Cu109_ vcompound measured at 77 K. First (I) and second (II) runs are shown.
the packing factor of the sample mentioned above. This indicates that a rather large amount of the sample is not superconducting at 77 K in spite of the single phase, which may be attributed to the fluctuation of oxygen concentration. Magnetization measurement at a constant field for 3 hours indicates that the magnitude of magnetization is time independent expect for a slight decrease at early times. From the hysteresis of the magnetization curves, .I, can be estimated using the critical state model [ 71. Fig. 3 shows the calcualted Jc’s as a function of the magnetic field. The Jc’s extrapolated to zero field are above lo3 A/cm2 for both samples. Direct J, measurements by a standard four-probe resistive method
F..
A
..,’
50-
,:.-
E zl
-
s
-
= 5
o-
-2
,+._~*,...._‘.
77K ( Ba2Y1)Cu,09_,
.:I;.-_.,._._,._____ + “I -..___..._.__.__,i,.: ~
-1.2
-0.4
0.4
1.2 H (kOe)
Fig. 2. Magnetization curve for the ( BazYI )Cus09measured at 77 K (second run in fig. 1) .
368
-
,, compound
2
77K
Resistive Method
0
5
10 H(kOe)
Fig. and tion also
3. Critical current densities J, at 77 K for ( BazYI)Cu,Og_, (Ba,,sY, Z)Cu309_-y compounds derived from magnetizacurves. J, values obtained by a direct resistive method are shown for comparison.
are also carried out at 77 K. Current and voltage leads were attached to the samples using silver paste. J, was defined as the current density at which 0.1 uV was induced across the 10 mm of the sample. The results obtained are shown in fig. 3. J, decreases rapidly with increasing magnetic field. The Jc’s directly measured by the resistive method are much smaller than those estimated from magnetization curves. A similar result was reported by Wtihl et al. for the Ba-Y-Cu-0 system [S] and by Larbaiestier et al. for the La-Sr-Cu-0 system [ 91. This J, difference can be partly explained by the morphological feature of these samples. Fig. 4 shows a scanning electron micrograph of the (Ba,Y ,)CU~O~_~compound. The sample has a large porosity as mentioned above, which results in a significant reduction of the contact area between the grains. Such a microstructural feature reduces the macroscopic transfer current which flows throughout the sample, resulting in a smaller J, by the resistive method. Another possible reason is the presence of a non-superconducting phase
PHYSICS LETTERS A
Volume 124, number6,7
5 October1987
The authors are grateful to K. Itoh of the National Research Institute for Metals for helpful discussions.
References
Fig. 4. Scanning electron compound.
micrograph
of (Ba2Y,)Cu@_,
between grains which results in a weak coupling between grains, and hence, significant reduction in superconducting transport current as indicated by Finnemore et al. for the La-Sr-Cu-0 system [ IO] .) It is expected that J, by the resistive method is significantly increased by improving the quality of the samples. In summary, we have estimated J, for
(Ba2Y1)Cu309-, and (Bal.8YI.ZP309-y cornpounds from the magnetization measurement at 77 K. The Jc’s deduced from magnetization are much larger than those directly obtained by a resistive method. The porous structure and non-superconducting phase between grains in the samples are responsible to this J, difference.
[ 1] J.G. Bednorz and K.A. Milller, Z. Phys. B 64 (1986) 189. [2] C.W. Chu, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang and Y.Q. Wang, Phys. Rev. Lett. 58 (1987) 405. K. Kishino, K. Kitazawa, S. Kanbe, I. Yasuda, N. Sugii, H. Takagi, S. Uchida, K. Fueki and S. Tanaka, Chem. Lett. (1987) 429. M.K. Wu, J.R. Ashburn, C.J. Tomg, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.Q. Wang and C.W. Chu, Phys. Rev. Lett. 58 (1987) 908. K. Togano, H. Kumakura, K. Fukutomi and K. Tachikawa, Appl. Phys. Lett., to be published. [ 6 ] R.J. Cava, B. Batlogg, R.B. van Dover, D.W. Murphy, S. Sunshine, T. Siegrist, J.P. Remeika, E.A. Rietman, S. Zahurak and G.P. Espinosa, Phys. Rev. Lett. 58 (1987) 1676. [ 71 A.M. Campbell and J.E. Evetts, Critical currents in superconductors (Taylor and Francis, London, 1972) ch. 3. [8] H. Wiihl, I. Apfelstedt, M. Dietrich, J. Ecke, W.H. Fietz, J. Fink, R. Flukiger, E. Gering, F. Gompf, H. Kupfer, N. Nucker, B. Obst, C. Politis, W. Reichardt, B. Renker, H. Rietschel, W. Schauer and F. Weiss, presented at the Spring Meeting of Materials Research Society in Anaheim, CA, April 1987. [ 91 D.C. Larbalestier, M. Daeumling, P.J. Lee, T.F. Kelly, J. Seuntjens, C. Meingast, X. Cai, J. McKinnell, R.D. Ray, R.G. Dillenburg and E.E. Hellstrom, Cryogenics 27 (1987) 411. [ lo] D.K. Finnemore, R.N. Shelton, J.R. Clem, R.W. McCallum, H.C. Ku, R.E. McCarley, S.C. Chen, P. Klavins and V. Kogan, Phys. Rev. B 35 (1987) 53 19.
369
CRITICAL CURRENT DENSITIES
PHYSICS LETTERS A
IN SINTERED
Ba-Y-Cu-0
5 October 1987
COMPOUND
H. KUMAKURA, M. UEHARA, Y. YOSHIDA and K. TOGANO National Research Institutefor Metals, Tukuba Laboratories, l-2-1, Sengen, Sakura-mura, Niihari-gun, Ibaraki 305. Japan
Received 1 May 1987; revised manuscript received 30 June 1987; accepted for publication 20 August 1987 Communicated by J.I. Budnick
Critical current densities J, of Ba-Y-Cu-0 compounds were measured at 77 K by the magnetization method and the resistive method. The JC’s derived from magnetization are much larger than those obtained by the resistive method. The origin of this J, difference is discussed in relation to the microstructure of the samples.
The discovery of high temperature superconductivity in La-Ba-Cu-0 [ 1] and La-Sr-Cu-0 [ 2,3] compounds with K2NiF4 structure has strongly encouraged the search of new superconducting materials having higher transition temperature T,. Recently, Wu et al. reported superconductivity in an unidentified phase in the Ba-Y-Cu-0 compound system at 93 K [ 41. It seemed that high temperature superconductivity was not related to the KINiF, structure for this system. The authors have prepared a series of compounds having nominal composition (Ba, +.Y,)CuOJ_,, which corresponds to perovskite structure, and have found superconductivity in the range x=0.2-0.6 with maximum T, of N 120 K (onset) and 92.5 K (offset) for x=0.4 [5]. Very recently, Cava et al. reported that oxygen-deficient perovskite of stoichiometric (Ba,Y, ) Cu309 _,, is responsible for high T, for the Ba-Y-Cu-0 system
[61. In this letter, magnetization measurements were carried out for the stoichiometric ( Ba*Y, ) CU~O~_~ and the compound x=0.4 in our previous investigation. Critical current densities J, were estimated from obtained magnetization curves, and were compared to those directly measured by the resistive method. The samples investigated were prepared by the solid state reaction method using BaC03, Y,03 and CuO powders of 99.99% purity. The nominal composition was and (Ba2YI)Cu309--y (Ba1.8YI.2)Cu309_~ The samples have a porous
structure with a packing factor of 72% assuming y= 2.1 [ 61. The details of the sample preparation are described elsewhere [ 51. The transition temperaturesof(Ba2Y1)Cu309_yare 110,92and91SKfor onset, midpoint and offset, respectively. X-ray diffraction shows that the ( Ba2Y1)Cu309_-y sample consists of a single phase which is identified as oxygen-deficient perovskite with a small orthorhombic distortion, while (Ba, ,sY, .2)CU~O~_~contains a second and/or a third phase. The details of the X-ray diffraction analysis will be described elsewhere. The magnetization measurements were performed on a rectangular sample of dimensions 4x 2.4x0.8 mm3 using a vibrating sample magnometer in fields up to f 10 kOe. The magnetization curves were measured in liquid nitrogen at a constant sweep rate of applied field of 2-10 Oe/s. Examples of obtained magnetization curves for ( Ba,Y, ) Cu309 _-y compound are shown in figs. 1 and 2. Similar magnetization curves were also obtained for the (Ba1.8Y,.2)Cu309_-y compound. In fig. 1 the results of the first run (I) and the second run (II) are shown. Magnetization measurements at room temperature indicate that the compounds are paramagnetic in the normal state. Magnetization curves at 77 K clearly indicate that the compounds are typical type II superconductors. From the slope of the initial magnetization curves near zero field, the volume fraction of the superconducting phase can be estimated. About 55% of the sample is superconducting at 77 K for (BazY,)CusOg_,, which is rather smaller than
0375-9601/87/$ 03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
367
Volume
124, number
PHYSICS
6,7
LETTERS
A
5 October
1987
From Magnetization 4
*
%.#l.,)Cu3O9-,
Fig. 1. Magnetization curves for the ( BazY i )Cu109_ vcompound measured at 77 K. First (I) and second (II) runs are shown.
the packing factor of the sample mentioned above. This indicates that a rather large amount of the sample is not superconducting at 77 K in spite of the single phase, which may be attributed to the fluctuation of oxygen concentration. Magnetization measurement at a constant field for 3 hours indicates that the magnitude of magnetization is time independent expect for a slight decrease at early times. From the hysteresis of the magnetization curves, .I, can be estimated using the critical state model [ 71. Fig. 3 shows the calcualted Jc’s as a function of the magnetic field. The Jc’s extrapolated to zero field are above lo3 A/cm2 for both samples. Direct J, measurements by a standard four-probe resistive method
F..
A
..,’
50-
,:.-
E zl
-
s
-
= 5
o-
-2
,+._~*,...._‘.
77K ( Ba2Y1)Cu,09_,
.:I;.-_.,._._,._____ + “I -..___..._.__.__,i,.: ~
-1.2
-0.4
0.4
1.2 H (kOe)
Fig. 2. Magnetization curve for the ( BazYI )Cus09measured at 77 K (second run in fig. 1) .
368
-
,, compound
2
77K
Resistive Method
0
5
10 H(kOe)
Fig. and tion also
3. Critical current densities J, at 77 K for ( BazYI)Cu,Og_, (Ba,,sY, Z)Cu309_-y compounds derived from magnetizacurves. J, values obtained by a direct resistive method are shown for comparison.
are also carried out at 77 K. Current and voltage leads were attached to the samples using silver paste. J, was defined as the current density at which 0.1 uV was induced across the 10 mm of the sample. The results obtained are shown in fig. 3. J, decreases rapidly with increasing magnetic field. The Jc’s directly measured by the resistive method are much smaller than those estimated from magnetization curves. A similar result was reported by Wtihl et al. for the Ba-Y-Cu-0 system [S] and by Larbaiestier et al. for the La-Sr-Cu-0 system [ 91. This J, difference can be partly explained by the morphological feature of these samples. Fig. 4 shows a scanning electron micrograph of the (Ba,Y ,)CU~O~_~compound. The sample has a large porosity as mentioned above, which results in a significant reduction of the contact area between the grains. Such a microstructural feature reduces the macroscopic transfer current which flows throughout the sample, resulting in a smaller J, by the resistive method. Another possible reason is the presence of a non-superconducting phase
PHYSICS LETTERS A
Volume 124, number6,7
5 October1987
The authors are grateful to K. Itoh of the National Research Institute for Metals for helpful discussions.
References
Fig. 4. Scanning electron compound.
micrograph
of (Ba2Y,)Cu@_,
between grains which results in a weak coupling between grains, and hence, significant reduction in superconducting transport current as indicated by Finnemore et al. for the La-Sr-Cu-0 system [ IO] .) It is expected that J, by the resistive method is significantly increased by improving the quality of the samples. In summary, we have estimated J, for
(Ba2Y1)Cu309-, and (Bal.8YI.ZP309-y cornpounds from the magnetization measurement at 77 K. The Jc’s deduced from magnetization are much larger than those directly obtained by a resistive method. The porous structure and non-superconducting phase between grains in the samples are responsible to this J, difference.
[ 1] J.G. Bednorz and K.A. Milller, Z. Phys. B 64 (1986) 189. [2] C.W. Chu, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang and Y.Q. Wang, Phys. Rev. Lett. 58 (1987) 405. K. Kishino, K. Kitazawa, S. Kanbe, I. Yasuda, N. Sugii, H. Takagi, S. Uchida, K. Fueki and S. Tanaka, Chem. Lett. (1987) 429. M.K. Wu, J.R. Ashburn, C.J. Tomg, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.Q. Wang and C.W. Chu, Phys. Rev. Lett. 58 (1987) 908. K. Togano, H. Kumakura, K. Fukutomi and K. Tachikawa, Appl. Phys. Lett., to be published. [ 6 ] R.J. Cava, B. Batlogg, R.B. van Dover, D.W. Murphy, S. Sunshine, T. Siegrist, J.P. Remeika, E.A. Rietman, S. Zahurak and G.P. Espinosa, Phys. Rev. Lett. 58 (1987) 1676. [ 71 A.M. Campbell and J.E. Evetts, Critical currents in superconductors (Taylor and Francis, London, 1972) ch. 3. [8] H. Wiihl, I. Apfelstedt, M. Dietrich, J. Ecke, W.H. Fietz, J. Fink, R. Flukiger, E. Gering, F. Gompf, H. Kupfer, N. Nucker, B. Obst, C. Politis, W. Reichardt, B. Renker, H. Rietschel, W. Schauer and F. Weiss, presented at the Spring Meeting of Materials Research Society in Anaheim, CA, April 1987. [ 91 D.C. Larbalestier, M. Daeumling, P.J. Lee, T.F. Kelly, J. Seuntjens, C. Meingast, X. Cai, J. McKinnell, R.D. Ray, R.G. Dillenburg and E.E. Hellstrom, Cryogenics 27 (1987) 411. [ lo] D.K. Finnemore, R.N. Shelton, J.R. Clem, R.W. McCallum, H.C. Ku, R.E. McCarley, S.C. Chen, P. Klavins and V. Kogan, Phys. Rev. B 35 (1987) 53 19.
369