Abstract
Large single crystals of high-temperature superconductor YBa2Cu3O7-δ (Tc ∼ 90 K) have been successfully grown in the cavity of bulk materials with a CuO flux. Crystals with a typical size of 2×2×0.3 mm3 were obtained. As-grown single crystals do not show superconductivity at liquid nitrogen temperature. However, after annealing in O2 flow for three days, they become superconductive at Tc ∼ 90 K.