Growth of superconducting Bi2Sr2CaCu2O8+δ single crystals from a (KCl-Bi2O3) flux
Abstract
Since the discovery of the high-critical temperature superconductors (HTSCs), they have been prepared in different morphologies and shapes. Even though there have been numerous studies on these materials, high quality single crystals are still very much needed for the investigation of the intrinsic properties of superconductors. For one, single crystals do not have grain boundaries that complicate the features of superconductors. Also, their chief merits are high anisotropy and uniformity of composition. On the other hand, large single crystals are preferred since they are easier to handle for characterization and are more amenable to commercial purposes.
Among the Bi-based HTSCs discovered so far, Bi-2212 is the most extensively used since it is the most stable, whereas Bi-2223 will decompose into Bi-2212 and Bi-2201 while melting. Common techniques in the preparation of Bi-2212 single crystals are the traveling solvent floating zone technique (TSFZ), the KCl-flux method and the self-flux method. Among these three, the most widely used is the flux growth because it is one of the easiest techniques in growing Bi-2212 single crystals. Moreover, the furnace needed for the growth runs need not be elaborate and expensive. In general, it is difficult to produce large single crystals using any of the flux methods. A principal advantage of using a solvent (flux) is that crystal growth takes place at relatively lower temperatures as compared to that required by a pure melt. A reduction in temperature is essential to many materials especially (a) those which are incongruently melting (b) materials that have volatile constituents and (c) highly refractory materials that require expensive techniques for crystallization from the melt.
In this study, Bi-2212 single crystals were grown using the KCl-flux method and the KCl-Bi2O3 flux method. It was found out that larger crystals were obtained using the latter method.
