Growth of single crystals of selected cuprates by the optical Floating Zone Technique

Cuprates are complicated oxides with fascinating properties. They often disclose a layered type structure and are anisotropic, so to reliably investigate their physical, crystallographic and optical properties high quality single crystals are essential. The optical Floating Zone [FZ] technique and the related Travelling Solvent Floating Zone [TSFZ] technique are among the newest, most sophisticated crucible-free methods for the growth of various single crystals of cuprates. Using optical heating, it is possible to crystallize congruently [e.g. CuGeO3] as well as incongruently melting materials [e.g. high temperature superconductor SrxLaCuO4 or the Shastry-Sutherland 2-x material SrCu(BO)]. Copper oxide tends to react with all common crucible materials (refractory metals and ceramics) at elevated temperatures, so a crucible-free method is essential to obtain single crystals of cuprates. Careful control of the partial pressure of oxygen is important in order to sustain the proper oxidation state of copper cations. This presentation discusses the application of both the FZ and the TSFZ methods in growth of high quality single crystals of selected cuprates. The materials grown require either very slow (slower than 0.3 mm/h) or very fast (faster than 25 mm/h) growth speed each presenting its own challenges. The relevant processes and reactions are explained on the basis of known phase diagrams. The growth of high quality single crystals of SrCu2(80)(2), and CuGeO3 as well as some high temperature superconductors [LaSr CuO4 and LaBa CuO] is discussed in detail.