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MATERIALS RESEARCH

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Growth of high-quality Bi2 Sr2 CaCu2 Oz crystal and characterization H. Faqir and G. Vacquier ´ Laboratoire de Physico-Chimie des Mat´eriaux-Equipe de Chimie du Solide, Universit´e de Provence– Centre St-Charles, 13331 Marseille Cedex 3, France

H. Chiba, M. Kikuchi, Y. Muraoka, and Y. Syono Institute for Materials Research, Tohoku University, Katahira, Sendai 980, Japan (Received 17 May 1996; accepted 12 May 1997)

We report growth of high-quality Bi2 Sr2 CaCu2 Oz single crystals with dimensions 2 3 1 3 0.03 mm3 with a melt and growth technique. The composition of this crystal is homogeneous and very close to the stoichiometric composition. Structure characterization of a single crystal was realized by measuring the (001) x-ray diffraction. The lattice parameters of a typical crystal ˚ The superconducting ˚ and c ­ 30.823s10d A. ˚ b ­ 5.413s2d A, are a ­ 5.414s2d A, temperature Tc ­ 95 K with a sharp transition width (10–90% level) between 6 and 10 K was determined from resistivity and dc susceptibility. We have measured the magnetization of Bi2 Sr2 CaCu2 Oz single crystal under magnetic field applied along the c-axis. The anomalous second peak effect appeared between 20 and 30 K. We discuss the qualities of these crystals.

I. INTRODUCTION 1,2

Since the discovery of its superconductivity, the Bi2 Sr2 CaCu2 Oz (2212) bismuth cuprate superconductor has been the subject of many papers owing to its rather high critical temperature close to 85 K for ceramic and 90 K for single crystals. However, a large number of investigations have been carried out in recent years about the elaboration of 2212 superconducting ceramics and single crystals. Achieving single crystals with good superconducting properties is really difficult owing to the incongruent character of its melting, the growth mechanism complexity, and the intergrowth propensity of the 2212 with other cuprate superconductors like Bi2 Sr2 CuOz (2201) or precipitation of other impurities. In order to obtain a reproducible transition temperature from one sample to another, the phase diagram of the bismuth cuprate has been studied first.3,4 To grow sizeable single crystals of 2212, several growth techniques have been reported. Mostly, the crystals are grown from the melt with floating zone5 and flux growth6 techniques. Single crystals 2212 were also grown from the melt 2212 stoichiometry composition7,9 or not.8 We have tried to develop crystals by slow cooling of completely or partially melted mixtures of 2212 stoichiometry. Magnetic measurements have played an important role in understanding the behavior of the 2212 superconductor. Recently, the second peak of the magnetization in the 2212 single crystal has been the subject of many papers.10,11 It was also noted that the characteristic second peak effect was observed in the overdoped sample and this anomaly becomes small in an optimally 2522

http://journals.cambridge.org

J. Mater. Res., Vol. 12, No. 10, Oct 1997

Downloaded: 12 Apr 2015

doped 2212 single crystal.10 T