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Fabrication of NdBaCuO single crystal by a flux method
PHYSICA © ELSEVIER
Physica C 282-287 (1997) 469--470
Fabrication of NdBaCuO single crystal by a flux method Shangmin Gonga,c, Donglu Shib, Guien Zhouc, Chuanbin Caia,c, Yaoxian Fua,c, Hong Zhanga aShanghai Institute of Metallurgy, CAS, Shanghai 200050, China bUniversity of Cincinnati, Cincinnati, OH 45221-0012, USA cStructure Research Laboratory, USTC, Hefei 230026, China NdBa2CU30y single crystal was fabricated by a flux method. X-ray powder diffraction pattern and Laue pattern show that the grown crystal is nearly perfect and has perovskite structure with the lattice constant of a=b=0.391nm, c=1.17nm.
1. INTRODUCTION
method are given.
Recently, it is very attractive to develop NdBa2Cu307.y crystal for the fundamental and application of research superconductivity. It was found that the melt-textured NdBa2Cu307.y processed under a reduced oxygen atmosphere has Tc of 96K and high critical current density at higher fields. Finely distributed Nd(Ndl.xBax)2CU307.y phase provides strong pinning centers in the good superconductive matrix[1-2]. It is contrary to MTG-YBCO, in which the Y2BaCu05 and related defects play the role of the pinning center. It is very interested to know what happens in the single crystal. Meanwhile, compared with YBa2Cu307.y, NdBa2Cu307.y has same perovskite structure but higher peritectic temperature[3], the NdBa2Cu307.y is an excellent seed for growing MTG-YBCO with large domains. As well known, in melt-growth process, Nd123 is obtained by a peritectic reaction[4]:
2. EXPERIMENTAL
Nd4Ba2Cu20 10+ Liquid(Cu -Ba)~ NdBruCu307.y here Nd422 has a tetragonal structure unlike the Y2BaCu05. Nd4Ba2Cu201O is always remained in the NdBaCuO matrix. At present, the influence of Nd4Ba2Cu201O in NdBaCuO, especially in larger size, on the MTG-YBCO growth is not clear. Some researchers prefer to use single crystal without Nd4Ba2Cu201O for growing MTGYBCO samples. The flux process is a conventional one. In this report some results about the single crystal of NdBaCuO by a flux 0921-4534/97/$17.00 © Elsevier Science B.Y. All rights reserved. PH S0921-4534(97)00322-5
The powders of Nrl203, BaC03 and CuO in a certain ratio were mixed and ground thoroughly then the mixture was pressed into pellets. The pellets were preheated in zirconia crucible at 940°C for 24 hs, then ramped near to 1080°C at a rate of 60°CIh, hold for 48hs. This heated mixture was slowly cooled to 1000°C in air at a rate of l°CIh followed by quenched on a copper plate at room temperature. Then the crystals were separated from the mixture of the crystals and solidified Cu-Ba phase. The crystals were identified by x-ray diffraction (XRD) and scanning electron microscopy (SEM).
3. RESULTS AND DISCUSSION The obtained crystal shows a surface with metallic luster, but rough with terraces and steps. Its shape is cubic or plate-like, which is dependent on the precursor composition and growing conditions. The dimension of the broad surface typically is about 2-3 mm. Fig. 1 is the Laue pattern with the x-ray perpendicular to the broad surface of the sample. The fine and sharp diffraction spots indicate that it is a single crystal with high perfection and the normal of the broad surface is a four-fold axis. The powder diffraction pattern of the crushed crystal is shown in figure 2. All the peaks can be well
470
S. Gong et al. / Physica C 282-287 (1997) 469-470
assigned to the peaks of the perovskite structure with the lattice constant: a=b=0.391nm, c=1.17nm. Other phases are not found. It means that the crystal with the perovskite structure is a pure NdBaCuO without Nd4Ba2Cu201O as expected. It can be deduced the broad plane is corresponding to the (ab) base plane.
temperature. It may be related to that the growing of the single crystals was in air, the oxygen partial pressure is too high[5]. The further work on increasing Tc and obtaining larger plate-like crystals is undertaken. The single crystal has been used to fabricate MTG-YBCO with large domains.
Fig. 1 Laue pattern of the sample Fig. 3 The Nd123 crystal under SEM 100 103
In conclusion, Nd123 single crystal with dimension of 2-3 mm without Nd422 phase can be fabricated by a flux method. The shape of the grown crystal can be controlled by adjusting the composition of the Cu-Ba liquid.
006
80 116 005 014
60
..0 ~
~
ACKNOWLEDGMENTS
003
40
113
to t 5 20
25
30 35 40
45
60
55
60
The authors acknowledge the support from the National Center for R&D on Superconductivity in China and from the Youth Funds in Shanghai Institute of Metallurgy.
219
Fig. 2 X-ray diffraction pattern ofthe sample A lot of growth terraces and steps in the surface of single crystal can be found by SEM observation as shown in fig. 3. The growing spiral is not found. It implies that the screw dislocation mechanism does not operate in the crystal growth and the others may operate. From the picture, the growing rate in a-b plane is higher than in c axis direction. Tc is lower than 77.3K for the crystal grown in this experiments even after oxygenating at low
Reference 1. S.I.Yoo et aI., Appi. Phys. Lett. 65(5), 1 August 1994, 633--635 2. M.Murakami et aI., Jpn.J.Appi. Phys., VoI.33(1994) pp.L715-L717 3. V.R.Todt et aI., Journal of Electronic Materials, Vo1.23, No. 11, 1994, 1127-1130 4. X.Yao et al., Journal of Materials Research, Vol. 10, No. 12, Dec. 1995, 3003-3008 5. Yoo et aI., Jpn.J.Appi. Phys., Vol.33(1994) pp.L1000-L1003
Physica C 282-287 (1997) 469--470
Fabrication of NdBaCuO single crystal by a flux method Shangmin Gonga,c, Donglu Shib, Guien Zhouc, Chuanbin Caia,c, Yaoxian Fua,c, Hong Zhanga aShanghai Institute of Metallurgy, CAS, Shanghai 200050, China bUniversity of Cincinnati, Cincinnati, OH 45221-0012, USA cStructure Research Laboratory, USTC, Hefei 230026, China NdBa2CU30y single crystal was fabricated by a flux method. X-ray powder diffraction pattern and Laue pattern show that the grown crystal is nearly perfect and has perovskite structure with the lattice constant of a=b=0.391nm, c=1.17nm.
1. INTRODUCTION
method are given.
Recently, it is very attractive to develop NdBa2Cu307.y crystal for the fundamental and application of research superconductivity. It was found that the melt-textured NdBa2Cu307.y processed under a reduced oxygen atmosphere has Tc of 96K and high critical current density at higher fields. Finely distributed Nd(Ndl.xBax)2CU307.y phase provides strong pinning centers in the good superconductive matrix[1-2]. It is contrary to MTG-YBCO, in which the Y2BaCu05 and related defects play the role of the pinning center. It is very interested to know what happens in the single crystal. Meanwhile, compared with YBa2Cu307.y, NdBa2Cu307.y has same perovskite structure but higher peritectic temperature[3], the NdBa2Cu307.y is an excellent seed for growing MTG-YBCO with large domains. As well known, in melt-growth process, Nd123 is obtained by a peritectic reaction[4]:
2. EXPERIMENTAL
Nd4Ba2Cu20 10+ Liquid(Cu -Ba)~ NdBruCu307.y here Nd422 has a tetragonal structure unlike the Y2BaCu05. Nd4Ba2Cu201O is always remained in the NdBaCuO matrix. At present, the influence of Nd4Ba2Cu201O in NdBaCuO, especially in larger size, on the MTG-YBCO growth is not clear. Some researchers prefer to use single crystal without Nd4Ba2Cu201O for growing MTGYBCO samples. The flux process is a conventional one. In this report some results about the single crystal of NdBaCuO by a flux 0921-4534/97/$17.00 © Elsevier Science B.Y. All rights reserved. PH S0921-4534(97)00322-5
The powders of Nrl203, BaC03 and CuO in a certain ratio were mixed and ground thoroughly then the mixture was pressed into pellets. The pellets were preheated in zirconia crucible at 940°C for 24 hs, then ramped near to 1080°C at a rate of 60°CIh, hold for 48hs. This heated mixture was slowly cooled to 1000°C in air at a rate of l°CIh followed by quenched on a copper plate at room temperature. Then the crystals were separated from the mixture of the crystals and solidified Cu-Ba phase. The crystals were identified by x-ray diffraction (XRD) and scanning electron microscopy (SEM).
3. RESULTS AND DISCUSSION The obtained crystal shows a surface with metallic luster, but rough with terraces and steps. Its shape is cubic or plate-like, which is dependent on the precursor composition and growing conditions. The dimension of the broad surface typically is about 2-3 mm. Fig. 1 is the Laue pattern with the x-ray perpendicular to the broad surface of the sample. The fine and sharp diffraction spots indicate that it is a single crystal with high perfection and the normal of the broad surface is a four-fold axis. The powder diffraction pattern of the crushed crystal is shown in figure 2. All the peaks can be well
470
S. Gong et al. / Physica C 282-287 (1997) 469-470
assigned to the peaks of the perovskite structure with the lattice constant: a=b=0.391nm, c=1.17nm. Other phases are not found. It means that the crystal with the perovskite structure is a pure NdBaCuO without Nd4Ba2Cu201O as expected. It can be deduced the broad plane is corresponding to the (ab) base plane.
temperature. It may be related to that the growing of the single crystals was in air, the oxygen partial pressure is too high[5]. The further work on increasing Tc and obtaining larger plate-like crystals is undertaken. The single crystal has been used to fabricate MTG-YBCO with large domains.
Fig. 1 Laue pattern of the sample Fig. 3 The Nd123 crystal under SEM 100 103
In conclusion, Nd123 single crystal with dimension of 2-3 mm without Nd422 phase can be fabricated by a flux method. The shape of the grown crystal can be controlled by adjusting the composition of the Cu-Ba liquid.
006
80 116 005 014
60
..0 ~
~
ACKNOWLEDGMENTS
003
40
113
to t 5 20
25
30 35 40
45
60
55
60
The authors acknowledge the support from the National Center for R&D on Superconductivity in China and from the Youth Funds in Shanghai Institute of Metallurgy.
219
Fig. 2 X-ray diffraction pattern ofthe sample A lot of growth terraces and steps in the surface of single crystal can be found by SEM observation as shown in fig. 3. The growing spiral is not found. It implies that the screw dislocation mechanism does not operate in the crystal growth and the others may operate. From the picture, the growing rate in a-b plane is higher than in c axis direction. Tc is lower than 77.3K for the crystal grown in this experiments even after oxygenating at low
Reference 1. S.I.Yoo et aI., Appi. Phys. Lett. 65(5), 1 August 1994, 633--635 2. M.Murakami et aI., Jpn.J.Appi. Phys., VoI.33(1994) pp.L715-L717 3. V.R.Todt et aI., Journal of Electronic Materials, Vo1.23, No. 11, 1994, 1127-1130 4. X.Yao et al., Journal of Materials Research, Vol. 10, No. 12, Dec. 1995, 3003-3008 5. Yoo et aI., Jpn.J.Appi. Phys., Vol.33(1994) pp.L1000-L1003