Effects of Y2O3 additions on the oxygen diffusion in top-seeded melt growth processed YBa2Cu3O7−y superconductors

► The effect of Y2BaCuO5 (Y211)/YBa2Cu3O7-y (Y123) interfaces on the oxygen diffusion in single grain YBa2Cu3O7-y superconductors was examined. ► The Y211/Y123 interfacial area in Y123 grains was successfully controlled by Y2O3 additions. ► The Tc value of surface region was higher than those of interior regions, which indicates the presence of more oxygen at the bulk surface. ► The Y211/Y123 interfaces promoted the oxygen diffusion into Y123 single grain. ► In spite of the promoted oxygen diffusion by Y2O3 addition, the large Tc difference among the regions still existed, which suggests sluggish oxygen diffusion into single Y123 grains.