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Crystal growth of high Tc superconductors YBa2Cu3Ox, Bi3Sr3CaCu2.5Ox and Pb0.6Bi3Sr2CaCu3Ox
Journal of Crystal Growth 99 (1990) 929-932 North-Holland
929
CRYSTAL GROWTH OF HIGH Tc S U P E R C O N D U C T O R S YBa2CuaOx, Bi3Sr3CaCu2.50 x A N D Pho.6 Bi 3Sr2CaCu 3Ox W A N G Hong, S H A N G Shuxia, Y A N G Zhaohe, W A N G Zhuo, SHEN Xiaonong, Z H A O Huansui, J I A N G Minhua and CHEN Huanchu Institute of Crystal Materials, Shandong University, Jinan, Shandong, People's Rep, of China
Single crystals of YBa2Cu30 x, Bi3SraCaCu2.50 x and Pb0.6Bi3Sr2CaCu30:, have been grown by the flux method. The crystals obtained have sizes varying from 2.5 × 2.0×0.1 mm 3 to 1 0 x 4 × 3 mm 3. These crystals have an orthorhombic structure with cell parameters a = 3.838(1) A, b = 3.871(1) ,~ and e=11.738(4) A (YBazCu3Ox); a = 5 . 3 9 A, b = 5 . 3 7 ,~ and c = 31.01 (Bi3Sr3CaCu2.5Ox); and a = 5.38 A, b = 5.34 A, c = 30.55 A (Pb0.6Bi3Sr2CaCu3Ox). Measurements of resistivity and AC susceptibility confirmed that these crystals are bulk superconductors with Tc (zero) of 91.4, 90 and 82 K, respectively. Differential thermal analysis (DTA) measurements were made to study the crystal growth process and thermal properties of these crystals.
1. Introduction Since the discovery of superconductivity phenomena in the system R - B a - C u - O (R is a rare earth) [1,2], there has been considerable activity in the search for other superconducting oxides and an understanding of the superconductivity phenomenon in these oxide systems. Recently high T~ superconductivity has been found in the B i - S r - C a - C u - O oxide system by several groups, and crystal growth experiments have also been reported [3,4]. Sunshine et al. have prepared single crystals of the 84 K superconductor Bi2.2SrzCa0. ~ Cu 2O [6], and reported that the chemical substitution of Pb in B i - S r - C a - C u oxides results in an increase of T~ to 107 K. To understand the superconductivity phenomenon in these systems as well as to apply the crystal for practical use, it is necessary to obtain single crystals with a large size and high quality.
We report here the crystal growth of YBa 2Cu 3Ox (YBCO), Bi3Sr3CaCu 2.50x (BSCCO) and Pb0.6Bi3Sr2CaCu30 x (PBSCCO) by the flux method. The crystals were separated mechanically and had well developed faces. The size of the crystals ranged from 2.5 × 2.0 × 0.1 mm 3 to 10 × 4 × 3 mm 3. Measurements of electrical resistivity and AC susceptibility confirmed that these crystals are bulk superconductors with critical temperature Tc (zero) of 91.4, 90 and 82 K respectively. X-ray diffraction analysis shows that these three materials all have the orthorombic structure.
2. Crystal growth and characterization The single crystals were grown by the flux method in a vertical tubular furnace. An A1203 crucible was used for crystal growth. The chemical
Table 1 The chemical compositions, lattice constants and melting point of the three crystals Crystal
YBCO BSCCO PBSCCO
Starting composition
Y:Ba:Cu =1:4:10 Bi:Sr:Ca:Cu = 4:3:2:3 Bi:Sr:Ca:Cu:Pb = 4:3:2:3 : 1
0022-0248/90/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
Crystal composition
1:2:3 3:3:1:2.5 3:2:1:3:0.6
Melting point
Lattice constants (A) a
b
3.838 5.39 5,38
5.871 5.37 5,34
(°c) 11.738 31..01 30.55
1012 866 829
Wang Hong et aL / Growth of high T¢ superconductors YBCO, BSCCO and PBSCCO
930
Fig. 1. Single crystals of (a) YBCO, (b) BSCCO and (c) PBSCCO.
compositions of the starting materials and the grown crystals are listed in table 1. The crystals of YBCO, BSCCO and PBSCCO were separated mechanically and were heavily darkly colored with shiny cleaved faces. The c-axis was perpendicular to the cleaved face. Figs. l a - l c show crystals of YBCO (fig. la), BSCCO (fig. lb), and PBSCCO (fig. lc), respectively. Crystal symmetry and lattice constants were examined using a four-circle X-ray diffractometer and by powder X-ray diffraction. This shows that these crystals all have orthorhombic structure. The lattice constants are listed in table 1. The electrical resistivity measurements were performed by a standard DC four-probe technique•
Fig. 2 shows the temperature dependences of resistivity of the BSCCO and PBSCCO crystals. In the normal state, the samples had a typical metallic behaviour and the superconductivity transition appeared at 110 and 103 K, with zero resistance observed at 90 and 82 K, respectively. The AC magnetic susceptibility is also shown in fig. 2. It is confirmed that these crystals are bulk superconductors. The differential thermal analysis (DTA) measurements (fig. 3) were made to study the crystal growth process and the thermal properties of these crystals. The melting points of the three crystals are listed in table 1.
3. Discussion
i
ud o
(bl// Cc~)/
z
tla
t~
q.a
~0
90
11o
1t0
150
ITO
TEMPERATUP.E(K) Fig. 2. Temperature dependence of electrical resistance and AC susceptibility of single crystals: (a) YBCO, (b) BSCCO and (c) PBSCCO.
For the Y - B a - C u - O system, the DTA measurements suggested that in the BaCO3-CuO system a binary eutectic exists, while in the Y - B a - C u ternary system, with Y : Ba : Cu = 1 : 4 : 10, a wide peak of thermal absorption appeared between 900 and 1000 o C. This suggests that the raw materials were partially melting at 900 o C. Crystal growth appeared to be most favorable around 1000 o C. A scanning electron micrograph of as-grown YBCO single crystals is shown in fig. la. The well developed crystals have a plate-like form with square corners. The habit face is normal to the c axis, and many growth steps were observed on these surfaces. The developing crystals have round
Wang Hong et al. / Growth of high Te superconductors YBCO, BSCCO and PBSCCO
931
SlNeLE CRYSTAL
yBco tota °e qO0~
y 6a4 C~,oO~ ~/
tO°°°d/
~
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£21
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20.00 d~/mbt
,~rt4osp/-fY~qE ,
,4zR
990
II00
/300
7"Et4PegArURE ( ° d ) Fig. 3. DTA measurements on the Y - B a - C u - O system.
corners and growth steps could be found on the (111) face (as indicated by the arrow). This suggests that the crystal growth is a non-linear growth process. During growth, the (111) face disappeared, since the growth rate is fast along the (111) direction. The lowest growth rate is along the c axis, so that the largest face is the (001) face.
It is found, in our experiments, that the ratio of the S r : C a ions is very important for high T~ superconductivity in the B i - S r - C a - C u - O compounds. The crystals grown from the B i - S r - C a C u - O system may have different contents of Sr and Ca if the ratio of S r / C a in starting composition is varied. The lattice parameter c increases
932
Wang Hong et al. / Growth of high Tc superconductors YBCO, BSCCO and PBSCCO
with an increase in the ratio S r : C a from 2 / 1 to 3/1, and the superconducting transition temperature Tc also increases [8]. Up to now, all the crystals grown from B i - S r - C a - C u - O system have been found to belong to the low temperature phase family (2212) and the critical temperature Tc (zero) reported is around 80-84 K [5-7]. We reported in this paper that crystals of Bi3Sr3CaCu 2.50~ have a larger lattice parameter c and a higher T~ (zero) of 90 K. This result is important for understanding the superconductivity phenomenon in B i - S r - C a - C u - O system.
Acknowledgements The authors would like to thank Professor B. Xiu and W. Yui for X-ray analysis. This work was supported by the National Research and Development Center on Superconductivity.
References [1] J.G. Bednorz and K.A. Miiller, Z. Physik B64 (1986) 189. [2] Z.X. Zhao, L.Q. Chen, Q.S. Yang, Y.Z. Huang, G.G. Chen, R.M. Tang, G.R. Liu, C.G. Cui, L. Chen, L.Z. Wang, S.Q. Guo, S.L. Li and J.Q. Bi, Kexue Tongbao 6 (1987) 421. [3] H. Maeda, Y. Tanaka, H. Fukutomi and T. Asano, Japan. J. Appl. Phys. Letters 27 (1988) L209. [4] J.M. Tarascon, Y. Le Page, B.G. Bagley, L.H. Greene, W.R. McKinnon, C.W. Hull, M. Giroud and D.M. Hwang, Phys. Rev. B37 (1988) 9382. [5] M. Hikita, T. lwata, Y. Tajima and A. Katsui, J. Crystal Growth 91 (1988) 282. [6] S.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. Nakabara, R. Farrow, J.J. Krajewski, S.M. Zahurak, J.V. Waszczak, J.H. Marshall, P. Marsh, L.W. Rupp. Jr and W.F. Peck, Phys. Rev. B1 (1988) 584. [7] A. Katsui and H. Ohtsuka, J. Crystal Growth 91 (1988) 261. [8] Wang Hong et al., to be submitted.
929
CRYSTAL GROWTH OF HIGH Tc S U P E R C O N D U C T O R S YBa2CuaOx, Bi3Sr3CaCu2.50 x A N D Pho.6 Bi 3Sr2CaCu 3Ox W A N G Hong, S H A N G Shuxia, Y A N G Zhaohe, W A N G Zhuo, SHEN Xiaonong, Z H A O Huansui, J I A N G Minhua and CHEN Huanchu Institute of Crystal Materials, Shandong University, Jinan, Shandong, People's Rep, of China
Single crystals of YBa2Cu30 x, Bi3SraCaCu2.50 x and Pb0.6Bi3Sr2CaCu30:, have been grown by the flux method. The crystals obtained have sizes varying from 2.5 × 2.0×0.1 mm 3 to 1 0 x 4 × 3 mm 3. These crystals have an orthorhombic structure with cell parameters a = 3.838(1) A, b = 3.871(1) ,~ and e=11.738(4) A (YBazCu3Ox); a = 5 . 3 9 A, b = 5 . 3 7 ,~ and c = 31.01 (Bi3Sr3CaCu2.5Ox); and a = 5.38 A, b = 5.34 A, c = 30.55 A (Pb0.6Bi3Sr2CaCu3Ox). Measurements of resistivity and AC susceptibility confirmed that these crystals are bulk superconductors with Tc (zero) of 91.4, 90 and 82 K, respectively. Differential thermal analysis (DTA) measurements were made to study the crystal growth process and thermal properties of these crystals.
1. Introduction Since the discovery of superconductivity phenomena in the system R - B a - C u - O (R is a rare earth) [1,2], there has been considerable activity in the search for other superconducting oxides and an understanding of the superconductivity phenomenon in these oxide systems. Recently high T~ superconductivity has been found in the B i - S r - C a - C u - O oxide system by several groups, and crystal growth experiments have also been reported [3,4]. Sunshine et al. have prepared single crystals of the 84 K superconductor Bi2.2SrzCa0. ~ Cu 2O [6], and reported that the chemical substitution of Pb in B i - S r - C a - C u oxides results in an increase of T~ to 107 K. To understand the superconductivity phenomenon in these systems as well as to apply the crystal for practical use, it is necessary to obtain single crystals with a large size and high quality.
We report here the crystal growth of YBa 2Cu 3Ox (YBCO), Bi3Sr3CaCu 2.50x (BSCCO) and Pb0.6Bi3Sr2CaCu30 x (PBSCCO) by the flux method. The crystals were separated mechanically and had well developed faces. The size of the crystals ranged from 2.5 × 2.0 × 0.1 mm 3 to 10 × 4 × 3 mm 3. Measurements of electrical resistivity and AC susceptibility confirmed that these crystals are bulk superconductors with critical temperature Tc (zero) of 91.4, 90 and 82 K respectively. X-ray diffraction analysis shows that these three materials all have the orthorombic structure.
2. Crystal growth and characterization The single crystals were grown by the flux method in a vertical tubular furnace. An A1203 crucible was used for crystal growth. The chemical
Table 1 The chemical compositions, lattice constants and melting point of the three crystals Crystal
YBCO BSCCO PBSCCO
Starting composition
Y:Ba:Cu =1:4:10 Bi:Sr:Ca:Cu = 4:3:2:3 Bi:Sr:Ca:Cu:Pb = 4:3:2:3 : 1
0022-0248/90/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
Crystal composition
1:2:3 3:3:1:2.5 3:2:1:3:0.6
Melting point
Lattice constants (A) a
b
3.838 5.39 5,38
5.871 5.37 5,34
(°c) 11.738 31..01 30.55
1012 866 829
Wang Hong et aL / Growth of high T¢ superconductors YBCO, BSCCO and PBSCCO
930
Fig. 1. Single crystals of (a) YBCO, (b) BSCCO and (c) PBSCCO.
compositions of the starting materials and the grown crystals are listed in table 1. The crystals of YBCO, BSCCO and PBSCCO were separated mechanically and were heavily darkly colored with shiny cleaved faces. The c-axis was perpendicular to the cleaved face. Figs. l a - l c show crystals of YBCO (fig. la), BSCCO (fig. lb), and PBSCCO (fig. lc), respectively. Crystal symmetry and lattice constants were examined using a four-circle X-ray diffractometer and by powder X-ray diffraction. This shows that these crystals all have orthorhombic structure. The lattice constants are listed in table 1. The electrical resistivity measurements were performed by a standard DC four-probe technique•
Fig. 2 shows the temperature dependences of resistivity of the BSCCO and PBSCCO crystals. In the normal state, the samples had a typical metallic behaviour and the superconductivity transition appeared at 110 and 103 K, with zero resistance observed at 90 and 82 K, respectively. The AC magnetic susceptibility is also shown in fig. 2. It is confirmed that these crystals are bulk superconductors. The differential thermal analysis (DTA) measurements (fig. 3) were made to study the crystal growth process and the thermal properties of these crystals. The melting points of the three crystals are listed in table 1.
3. Discussion
i
ud o
(bl// Cc~)/
z
tla
t~
q.a
~0
90
11o
1t0
150
ITO
TEMPERATUP.E(K) Fig. 2. Temperature dependence of electrical resistance and AC susceptibility of single crystals: (a) YBCO, (b) BSCCO and (c) PBSCCO.
For the Y - B a - C u - O system, the DTA measurements suggested that in the BaCO3-CuO system a binary eutectic exists, while in the Y - B a - C u ternary system, with Y : Ba : Cu = 1 : 4 : 10, a wide peak of thermal absorption appeared between 900 and 1000 o C. This suggests that the raw materials were partially melting at 900 o C. Crystal growth appeared to be most favorable around 1000 o C. A scanning electron micrograph of as-grown YBCO single crystals is shown in fig. la. The well developed crystals have a plate-like form with square corners. The habit face is normal to the c axis, and many growth steps were observed on these surfaces. The developing crystals have round
Wang Hong et al. / Growth of high Te superconductors YBCO, BSCCO and PBSCCO
931
SlNeLE CRYSTAL
yBco tota °e qO0~
y 6a4 C~,oO~ ~/
tO°°°d/
~
92rOe po~-ri~me~t~ 1£ ~2 ua
~ss "d
£21
__f-v'fqSo°~
B~C03 /
811°~ p h ~ e /'~nni~ion
5oo
700
ScAN gATE..
20.00 d~/mbt
,~rt4osp/-fY~qE ,
,4zR
990
II00
/300
7"Et4PegArURE ( ° d ) Fig. 3. DTA measurements on the Y - B a - C u - O system.
corners and growth steps could be found on the (111) face (as indicated by the arrow). This suggests that the crystal growth is a non-linear growth process. During growth, the (111) face disappeared, since the growth rate is fast along the (111) direction. The lowest growth rate is along the c axis, so that the largest face is the (001) face.
It is found, in our experiments, that the ratio of the S r : C a ions is very important for high T~ superconductivity in the B i - S r - C a - C u - O compounds. The crystals grown from the B i - S r - C a C u - O system may have different contents of Sr and Ca if the ratio of S r / C a in starting composition is varied. The lattice parameter c increases
932
Wang Hong et al. / Growth of high Tc superconductors YBCO, BSCCO and PBSCCO
with an increase in the ratio S r : C a from 2 / 1 to 3/1, and the superconducting transition temperature Tc also increases [8]. Up to now, all the crystals grown from B i - S r - C a - C u - O system have been found to belong to the low temperature phase family (2212) and the critical temperature Tc (zero) reported is around 80-84 K [5-7]. We reported in this paper that crystals of Bi3Sr3CaCu 2.50~ have a larger lattice parameter c and a higher T~ (zero) of 90 K. This result is important for understanding the superconductivity phenomenon in B i - S r - C a - C u - O system.
Acknowledgements The authors would like to thank Professor B. Xiu and W. Yui for X-ray analysis. This work was supported by the National Research and Development Center on Superconductivity.
References [1] J.G. Bednorz and K.A. Miiller, Z. Physik B64 (1986) 189. [2] Z.X. Zhao, L.Q. Chen, Q.S. Yang, Y.Z. Huang, G.G. Chen, R.M. Tang, G.R. Liu, C.G. Cui, L. Chen, L.Z. Wang, S.Q. Guo, S.L. Li and J.Q. Bi, Kexue Tongbao 6 (1987) 421. [3] H. Maeda, Y. Tanaka, H. Fukutomi and T. Asano, Japan. J. Appl. Phys. Letters 27 (1988) L209. [4] J.M. Tarascon, Y. Le Page, B.G. Bagley, L.H. Greene, W.R. McKinnon, C.W. Hull, M. Giroud and D.M. Hwang, Phys. Rev. B37 (1988) 9382. [5] M. Hikita, T. lwata, Y. Tajima and A. Katsui, J. Crystal Growth 91 (1988) 282. [6] S.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. Nakabara, R. Farrow, J.J. Krajewski, S.M. Zahurak, J.V. Waszczak, J.H. Marshall, P. Marsh, L.W. Rupp. Jr and W.F. Peck, Phys. Rev. B1 (1988) 584. [7] A. Katsui and H. Ohtsuka, J. Crystal Growth 91 (1988) 261. [8] Wang Hong et al., to be submitted.