Refinement mechanism of CeO₂ addition on Y₂BaCuO₅ particles in PMP YBCO bulks

YBCO bulk samples with a nominal composition of YBa₂Cu₃O_6+x+15 wt.% Y₂BaCuO₅+0.5 wt.% CeO₂ have been prepared by the powder melting process technique and the microstructure has been investigated by using scanning electron microscopy and transmission electron microscopy. An obvious refinement effect resulting in Y₂BaCuO₅ particles with a mean diameter about 500 nm in textured YBCO bulks has been achieved by CeO₂ addition. About one-fourth of the Y₂BaCuO₅ particles were observed to contain at least one nanometric core which was proved to be Y₂O₃ by selected area diffraction. In addition, a BaCeO₃ phase with a square shape was found. Our experimental results provide further evidence for the heterogeneous nucleation mechanism of Y₂BaCuO₅ particles on Y₂O₃ previously generated through a reaction between CeO₂ and precursors, which was first proposed by Piñol et al. for the melt texture growth process.