Growth of large and untwinned single crystals of YBCO

Large (up to 5x4x1.5 mm3) single crystals of YBa2Cu3O7-delta with perfect orthorhombic morphology were successfully grown from favourable flux composition in alumina crucibles. The number of nucleation centres was reduced by using smooth inner wall crucibles and a temperature oscillation method. The crystals could be isolated from the CuO flux by tipping the crucible over while remaining in the furnace at 970-degrees-C. By applying a uniaxial stress at the annealing temperature. both macro- and micro-twin domains in the thick crystals could be removed and a single untwinned domain was obtained. The structures of both twin- and single-domain crystals were characterised by means of high resolution electron microscopy. We also report the magnetic property of the as-grown single crystals.