Optimization of Y₂BaCuO₅ phase morphology for the growth of large bulk YBCO grains

YBCO samples were prepared using different types of precursor powders: quenched, or YBa₂Cu₃O_7−x and Y₂BaCuO₅ commercial powders, with and without Pt addition. Two stoichiomctrics, corresponding to 0 and 40% molar excess of the Y₂BaCuO₅ phase, were adopted. The behavior of the Y₂BaCuO₅ phase through thermal treatments, typical of melt processes, was observed by quenching the samples at various stages. YBa₂Cu₃O_7−x grain growth kinetics was enhanced and liquid phase losses were limited by optimizing the morphology of the Y₂BaCuO₅ phase in the partially melted state, with the simultaneous presence of round particles ≤1 μm and needle-like particles with very high aspect ratio. The optimized processing conditions were adopted, together with a seeding technique, to grow YBCO samples. At 77 K, a magnetic levitation force of 2.5 kg was measured for a sample with 18 mm diameter, and magnetization critical current densities over 10⁴ A/cm² were reached at 1 T.