Y211 particle refinement in YBCO bulk superconductors by CeO_{2 addition

The influence of preparation parameters as nominal composition (Y 2 O 3 and CeO 2 additions), particle size of starting Y123 powder, milling and mixing conditions and sintering temperature on the refinement of Y 2 BaCuO 5 (Y211) particles in the single-grain YBa 2 Cu 3 O 7 /Y 2 BaCuO 5 (Y123/Y211) bulk superconductors prepared by top-seeded melt-growth process has been studied. The microstructure was analysed after sintering and melt processing by polarised light microscopy and electron microscopy. It is shown that cerium is active in the Y211 particle refinement when it is solved in the peritectic melt, L p . When cerium is present as barium cerate, it has no refining effect. The addition of CeO 2 and barium cerate formation even leads to a faster growth of Y211 particles at the sintering stage due to intensive melt production. Refinement of Y211 particles in the samples with large Y123 particles is related to the formation of very dense Y211 skeleton which is resistant to melt formation at the sintering stage. Critical current density of these single-grain bulk superconductors is significantly influenced by final microstructure.