Two classes of growth spirals on single crystals of YBCO

A detailed examination of the (001) surfaces of CuO-flux grown single crystals of YBCO (YBa 2Cu 3O 7− x ) has shown the presence of two types of growth feature. The first of these consists of relatively large growth steps which can be in the form of spirals, arcs, instabilities or complex intergrowths which are similar to those reported by a number of workers. The second type involves much more conventional growth spirals with a step height close to the limit of optical DIC detection and which only become readily visible after decoration. The nature of these two classes of growth feature is discussed.