Zn doping in YBCO single crystal by the solute-rich liquid-crystal pulling method
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Zn doping in YBCO single crystal by the solute-rich liquid-crystal pulling method X. Yao, K. Ohtsu, S. Tajima, H. Zama, F. Wang, and Y. Shiohara Superconductivity Research Laboratory, ISTEC, 1-10-13 Shinonome Koto-ku, Tokyo 135, Japan (Received 20 July 1995; accepted 5 October 1995)
Zn-doped YBa2 Cu3 O61d (YBCO) single crystals were fabricated by the solute-rich liquid-crystal pulling (SRL-CP) method. The Zn content of x ranged from 0.0035–0.029 and almost uniformly distributed in YBa2 (Cu12x Znx )3 O61d . There is a nearly linear relationship between the added Zn content in the liquid and the analyzed Zn content in the liquid/in the crystal. When the added Zn content Cl was 1.086 at. %, decreasing of growth temperature led to increasing growth rate. However, growth temperature had no obvious effect on the doped Zn content in the crystal Cs , the Zn content in the flux Cl , and the effective distribution ratio of k 0 . In addition, growth spirals on the grown crystal surface were observed by atomic force microscopy (AFM). X-ray Laue pattern and RBS measurements are indicative of good crystallinity of YBa2 (Cu12x Znx )3 O61d . Critical temperatures of Tc changed from 89 to 57 K when the Zn content x ranged 0.0035 to 0.029 after appropriate oxygenation.
I. INTRODUCTION
Numerous investigations of the influence of doping on the structural and physical properties of YBa2 (Cu12x Mx )3 O61d (where M is Fe, Co, Al, Zn, and Ni) have been reported.1–5 This has become an important aspect for revealing the high temperature superconductivity mechanism, which is very different from that of conventional superconductors. The substitutions of M elements have resulted in single phase materials. A significant feature of this substitution is depression of Tc . Typically, this depression is about 2–5 Kyat. %1 for trivalent dopants (M Fe, Co, and Al); however, the substitution of divalent Zn for Cu led to an unusual rapid drop of Tc to nearly 11 Kyat. %.1,2 In addition, YBa2 (Cu12x Mx )3 O61d has also been characterized for their structural, magnetic, and superconducting properties,1–5 which showed a unique behavior for Zn substitution case as well. By using the continuous crystal pulling method, we selected Zn as a doping element to fabricate Zn-doped YBCO single crystal since Zn is one of the most sensitive elements to affect crystal structure and physical properties among these M elements. The aim of this work is to investigate Zn doping behaviors and growth processes of YBa2 (Cu12x Znx )3 O61d single crystals. Our attention was focused on the influence of the added Zn content and the influence of the growth temperature on the doped Zn content in the crystal, the crystal growth rate, and the effective distribution ratio. Crystal growth surfaces were observed for revealing growth mechanism. The effects of Zn-doping 1120
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J. Mater. Res., Vol. 11, No. 5, May 1996
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content on crystal structure and physical properties were also charac
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