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A new procedure for the isolation of large YBCO superconducting single crystals
Journal of Crystal Growth 106 (1990) 487—489 North-Holland
487
PRIORITY COMMUNICATION A NEW PROCEDURE FOR THE ISOLATION OF LARGE YBCO SUPERCONDUCTING SINGLE CRYSTALS Yaoshui WANG, L.W.M. SCHREURS, P. VAN DER LINDEN, Yuan LI and P. BENNEMA Research Institute for Materials, University of Nzjmegen, Toernooiveld, NL-6525 ED N:pnegen, The Netherlands Received 23 March 1990; manuscript received in final form 20 July 1990
A new procedure, the liquid flow method, is reported for the separation of large YBCO superconducting single crystals from the flux. We used a shallow alumina boat with a slope of 20°—30°. The slope of the boat could be changed without disturbing the temperature. Single crystals up to 5—10 mm have been obtained; the superconducting transition occurs at about 90 K. The liquid flow method is one of the best techniques for a smooth separation of the flux and the detachment of the as-grown crystals from the crucible.
I. Introduction There is great interest in the growth of YBCO superconducting single crystals which show a superconducting transition temperature above the boiling point of liquid nitrogen. Several thousands of publications have been reported. However, this compound has a low thermal and chemical stability, melts incongruently in the temperature range of 850 to 1000°Cand decomposes at low oxygen partial pressure. It is recognized that YBCO crystals are impossible to grow from high temperature solutions. However, some fluxes which have been successfully used for the growth of single crystals similar to YBCO were reported by Elwell and Scheel [1]. The growth of high 7~ YBCO superconducting single crystals by liquid phase separation has been reported by several authors [2—9]. In order to obtain large high 7~crystals of good quality, the separation of as-grown crystals from residual flux is one of the critical problems which must be solved, Recently, techniques such as the decanting procedure and the liquid suction method were reported by Scheel, Licci, Boutellier et al. [10—12]. These techniques significantly improved the sep. aration of the as-grown crystals from the flux. However, the decanting procedure has a few nega0022-0248/90/$03.50
©
1990
—
tive aspects. For instance, the hot crucibie has to be removed from the furnace very quickly to allow the pour off of the flux; the as-grown crystals undergo a thermal shock which may be harmful for the crystals and the as-grown crystal surfaces may be contaminated by droplets of the flux due to the pouring process. The smooth flux separation by suction technique seems much improved. However, the flux suction also has a disadvantage, namely the damage or destruction of the crystals by the porous piece. Here we report a new liquid flow technique for the growth of large YBCO single crystals which facilitates the separation of the as-grown crystals from the flux.
2. Crystal growth procedure The procedure for the growth of YBCO single crystals employed a shallow boat with 200_300 of slope, as shown in fig. 1. The starting materials were prepared from a mixture of high purity Y203, BaCO3 and CuO, with a molar ratio of Y : Ba: Cu = 1 : 4: 10. Presintered polycrystalline ceramic material or powder of the raw materials were placed on the high position of the alumina boat. The mixture was heated up to 1000°Cand kept at this temperature for a period of 2 h. The liquid
Elsevier Science Publishers B.V. (North-Holland)
488
Y. Wang et aL
/ Newprocedure for isolation
of large YBCO superconducting single crystals
~03O.
iL_ /ps~,—______
0
-..
20-3~~~’
~
b
Fig. 1. Schematic of the liquid flow method for the growth of YBCO single crystals: (a) liquid phase separated from high melting koint solid phase; (b) the remaining hot flux separated from the as-grown YBCO crystals.
phase flowed down along the slope to the low side of the alumina boat and was separated from the high melting point solid phase, which was still on the high side of the boat. The melt was then slowly cooled at a rate of 2°C/hto 900°C.Single crystals were grown from the flux at the low side of the boat. The remaining liquid phase was separated from the as-grown crystals by changing the slope in the opposite direction and holding the temperature at 900°Cfor a period of 2 h. Single crystals with a flat surface were left on the high side of the boat, which facilitated the mechanical detachment of the as-grown crystals from the shallow alumina boat. The experiments were carried out in air.
g _____________________________ 0
20
40 60 Temperature (K)
80
100
Fig. 3. Magnetization versus temperature of the as-grown YBCO crystals.
We used both a horizontal tube furnace and chamber furnace for the liquid flow method cxperiments. Large superconducting single crystals were successfully grown by this technique. An as-grown crystal with dimensions up to 5—10 mm in size is shown in fig. 2. The superconducting transition occurred at 90 K (see fig. 3). The use of alumina boats in YBCO crystal growth certainly influences the crystal quality and surface morphology as was indicated in previous work [13—15]. However, an alumina crucible or boat can be used for the growth of large YBCO superconducting single crystals.
I Fig. 2. YBCO single crystals which were grown by the liquid flow method (each grid interval represents 1 mm).
Y. Wang et al.
/ Newprocedurefor isolation
3. Results and discussion Large size crystals with a flat surface of superconducting YBCO have been grown using the liquid flow method. The dimensions of the asgrown crystals are 5—10 mm. The superconducting transition occurs at about 90 K. Electron probe microanalysis shows that the as-grown crystals have an approximate cation ratio of Y : Ba: Cu = 1: 2: 3. In summary, we have developed a new procedure for the separation of large superconducting YBCO single crystals from the melt. As compared with other liquid separation methods, the liquid flow method could be one of the best techniques for a smooth flux separation and the detachment of the as-grown crystals from the crucible. It is not necessary to remove the hot crucible during the growth process, so the as-grown crystals do not undergo a thermal shock. There is no contammation of the crystal surface and no mechanical damage or destruction of the as-grown crystals during the flux separation.
of large YBCO superconducting single crystals
489
References [1] D. Elwell and H.J. Scheel. Crystal Growth from High Temperature Solutions (Academic Press, London, 1975). [2] D.L. Kaiser, F. Holtzberg, B.A. Scott and T.R. McGuire, AppI. Phys. Letters 51(1987) 1040. [3] L.F. Schneemeyer, J.V. Waszczak, T. Siegrist, R.B. van Dover, L.W. Rupp, B. Batlogg, R.J. Cava and D.W. Murphy, Nature 328 (1987) 601. [4] H.J. Scheel and F. Licci, J. Crystal Growth 85 (1987) 607. [5] Y. Hidaka, Y. Enomoto, M. Suzuki, M. Oda, A. Katsui and T. Murahami, Japan. J. AppI. Phys. 26 (1987) L726. [61H.J. Scheel and F. Licci, Mater. Res. Bull. 13 (1988) 56. [7] E. Walker and V. Sadowski, Helv. Phys. Acta 61 (1988) 470. [81Wang Yaoshui, P. Bennema, L.W.M. Schreurs, P.J.M. van Bentum, H. van Kempen, L.J.C. van Leemput. Ji. Wnuk and P. van der Linden, J. Crystal Growth 99 (1990) 933. and H.J. Scheel, Physica C153—155 (1988) 44. F. Licci, H.J. Scheel and T. Besagni, Physica C153—155 (1988) 431. R. Boutellier, B.N. Sun, H.J. Scheel and H. Schmid, J. Crystal Growth 96 (1989) 465. L.E.C. van de Leemput. P.J.M. van Bentum, L.W.M. Schreurs and H. van Kempen, Physica C152 (1988) 99.
[91Wang Yaoshui, L.W.M.Growth, Schreurs,to P. der Linden P. Bennema, J. Crystal bevan published.
[10] [11] [12] [13]
[14] L.E.C. van de Leemput, P.J.M. van Bentum, F.A.J.M. Driessen, J.W. Gerritsen, H. van Kempen. L.W.M.
Acknowledgements The authors would like to thank Dr. A.L.H. Stols for the electron probe microanalysis and J. van Kessel for the technical support. This work was supported by Dc Stichting Scheikundig Onderzoek (SON) and Dc Stichting voor Fundamenteel Onderzoek der Materie (FOM).
Schreurs and P. Bennema, J. Crystal Growth 98 (1989) 551. [15] R.L. T. Siegrist, Schneemeyer, Waszczak, N.P. Singh, Opila, L.F. B. Batlogg, L.W. J.V. Rupp and D.W. Murphy, Phys. Rev. B36 (1987) 8365.
487
PRIORITY COMMUNICATION A NEW PROCEDURE FOR THE ISOLATION OF LARGE YBCO SUPERCONDUCTING SINGLE CRYSTALS Yaoshui WANG, L.W.M. SCHREURS, P. VAN DER LINDEN, Yuan LI and P. BENNEMA Research Institute for Materials, University of Nzjmegen, Toernooiveld, NL-6525 ED N:pnegen, The Netherlands Received 23 March 1990; manuscript received in final form 20 July 1990
A new procedure, the liquid flow method, is reported for the separation of large YBCO superconducting single crystals from the flux. We used a shallow alumina boat with a slope of 20°—30°. The slope of the boat could be changed without disturbing the temperature. Single crystals up to 5—10 mm have been obtained; the superconducting transition occurs at about 90 K. The liquid flow method is one of the best techniques for a smooth separation of the flux and the detachment of the as-grown crystals from the crucible.
I. Introduction There is great interest in the growth of YBCO superconducting single crystals which show a superconducting transition temperature above the boiling point of liquid nitrogen. Several thousands of publications have been reported. However, this compound has a low thermal and chemical stability, melts incongruently in the temperature range of 850 to 1000°Cand decomposes at low oxygen partial pressure. It is recognized that YBCO crystals are impossible to grow from high temperature solutions. However, some fluxes which have been successfully used for the growth of single crystals similar to YBCO were reported by Elwell and Scheel [1]. The growth of high 7~ YBCO superconducting single crystals by liquid phase separation has been reported by several authors [2—9]. In order to obtain large high 7~crystals of good quality, the separation of as-grown crystals from residual flux is one of the critical problems which must be solved, Recently, techniques such as the decanting procedure and the liquid suction method were reported by Scheel, Licci, Boutellier et al. [10—12]. These techniques significantly improved the sep. aration of the as-grown crystals from the flux. However, the decanting procedure has a few nega0022-0248/90/$03.50
©
1990
—
tive aspects. For instance, the hot crucibie has to be removed from the furnace very quickly to allow the pour off of the flux; the as-grown crystals undergo a thermal shock which may be harmful for the crystals and the as-grown crystal surfaces may be contaminated by droplets of the flux due to the pouring process. The smooth flux separation by suction technique seems much improved. However, the flux suction also has a disadvantage, namely the damage or destruction of the crystals by the porous piece. Here we report a new liquid flow technique for the growth of large YBCO single crystals which facilitates the separation of the as-grown crystals from the flux.
2. Crystal growth procedure The procedure for the growth of YBCO single crystals employed a shallow boat with 200_300 of slope, as shown in fig. 1. The starting materials were prepared from a mixture of high purity Y203, BaCO3 and CuO, with a molar ratio of Y : Ba: Cu = 1 : 4: 10. Presintered polycrystalline ceramic material or powder of the raw materials were placed on the high position of the alumina boat. The mixture was heated up to 1000°Cand kept at this temperature for a period of 2 h. The liquid
Elsevier Science Publishers B.V. (North-Holland)
488
Y. Wang et aL
/ Newprocedure for isolation
of large YBCO superconducting single crystals
~03O.
iL_ /ps~,—______
0
-..
20-3~~~’
~
b
Fig. 1. Schematic of the liquid flow method for the growth of YBCO single crystals: (a) liquid phase separated from high melting koint solid phase; (b) the remaining hot flux separated from the as-grown YBCO crystals.
phase flowed down along the slope to the low side of the alumina boat and was separated from the high melting point solid phase, which was still on the high side of the boat. The melt was then slowly cooled at a rate of 2°C/hto 900°C.Single crystals were grown from the flux at the low side of the boat. The remaining liquid phase was separated from the as-grown crystals by changing the slope in the opposite direction and holding the temperature at 900°Cfor a period of 2 h. Single crystals with a flat surface were left on the high side of the boat, which facilitated the mechanical detachment of the as-grown crystals from the shallow alumina boat. The experiments were carried out in air.
g _____________________________ 0
20
40 60 Temperature (K)
80
100
Fig. 3. Magnetization versus temperature of the as-grown YBCO crystals.
We used both a horizontal tube furnace and chamber furnace for the liquid flow method cxperiments. Large superconducting single crystals were successfully grown by this technique. An as-grown crystal with dimensions up to 5—10 mm in size is shown in fig. 2. The superconducting transition occurred at 90 K (see fig. 3). The use of alumina boats in YBCO crystal growth certainly influences the crystal quality and surface morphology as was indicated in previous work [13—15]. However, an alumina crucible or boat can be used for the growth of large YBCO superconducting single crystals.
I Fig. 2. YBCO single crystals which were grown by the liquid flow method (each grid interval represents 1 mm).
Y. Wang et al.
/ Newprocedurefor isolation
3. Results and discussion Large size crystals with a flat surface of superconducting YBCO have been grown using the liquid flow method. The dimensions of the asgrown crystals are 5—10 mm. The superconducting transition occurs at about 90 K. Electron probe microanalysis shows that the as-grown crystals have an approximate cation ratio of Y : Ba: Cu = 1: 2: 3. In summary, we have developed a new procedure for the separation of large superconducting YBCO single crystals from the melt. As compared with other liquid separation methods, the liquid flow method could be one of the best techniques for a smooth flux separation and the detachment of the as-grown crystals from the crucible. It is not necessary to remove the hot crucible during the growth process, so the as-grown crystals do not undergo a thermal shock. There is no contammation of the crystal surface and no mechanical damage or destruction of the as-grown crystals during the flux separation.
of large YBCO superconducting single crystals
489
References [1] D. Elwell and H.J. Scheel. Crystal Growth from High Temperature Solutions (Academic Press, London, 1975). [2] D.L. Kaiser, F. Holtzberg, B.A. Scott and T.R. McGuire, AppI. Phys. Letters 51(1987) 1040. [3] L.F. Schneemeyer, J.V. Waszczak, T. Siegrist, R.B. van Dover, L.W. Rupp, B. Batlogg, R.J. Cava and D.W. Murphy, Nature 328 (1987) 601. [4] H.J. Scheel and F. Licci, J. Crystal Growth 85 (1987) 607. [5] Y. Hidaka, Y. Enomoto, M. Suzuki, M. Oda, A. Katsui and T. Murahami, Japan. J. AppI. Phys. 26 (1987) L726. [61H.J. Scheel and F. Licci, Mater. Res. Bull. 13 (1988) 56. [7] E. Walker and V. Sadowski, Helv. Phys. Acta 61 (1988) 470. [81Wang Yaoshui, P. Bennema, L.W.M. Schreurs, P.J.M. van Bentum, H. van Kempen, L.J.C. van Leemput. Ji. Wnuk and P. van der Linden, J. Crystal Growth 99 (1990) 933. and H.J. Scheel, Physica C153—155 (1988) 44. F. Licci, H.J. Scheel and T. Besagni, Physica C153—155 (1988) 431. R. Boutellier, B.N. Sun, H.J. Scheel and H. Schmid, J. Crystal Growth 96 (1989) 465. L.E.C. van de Leemput. P.J.M. van Bentum, L.W.M. Schreurs and H. van Kempen, Physica C152 (1988) 99.
[91Wang Yaoshui, L.W.M.Growth, Schreurs,to P. der Linden P. Bennema, J. Crystal bevan published.
[10] [11] [12] [13]
[14] L.E.C. van de Leemput, P.J.M. van Bentum, F.A.J.M. Driessen, J.W. Gerritsen, H. van Kempen. L.W.M.
Acknowledgements The authors would like to thank Dr. A.L.H. Stols for the electron probe microanalysis and J. van Kessel for the technical support. This work was supported by Dc Stichting Scheikundig Onderzoek (SON) and Dc Stichting voor Fundamenteel Onderzoek der Materie (FOM).
Schreurs and P. Bennema, J. Crystal Growth 98 (1989) 551. [15] R.L. T. Siegrist, Schneemeyer, Waszczak, N.P. Singh, Opila, L.F. B. Batlogg, L.W. J.V. Rupp and D.W. Murphy, Phys. Rev. B36 (1987) 8365.