Study on microstructure of PMP-processed YBCO containing submicron Y2BaCuO5 particles

The microstructure of a PMP-processed YBCO single domain sample with a nominal composition of 123 + 15%211 + 0.5%CeO2 fabricated by using 211 precursor powder smaller than 500 nm has been studied by SEM, TEM and HREM. The results show that the single domain contained a large amount of 211 particles with an average diameter of about 500 nm. The 211 particles were spherical, about one-fourth of which had one or more global cores smaller than 100 nm. Electron diffraction patterns proved that the cores were Y2O3. In addition, a tretragonal-shaped phase with a size about I mum was also observed. This phase was proved to be BaCeO3 by ED and EDA. Therefore, the refinement mechanism of CeO2 addition on 211 was believed to lie in a reaction between CeO2 and part of 211 precursor yielding nanometer Y2O3, and by-product BaCeO3. The nanometer Y2O3 acted as an inhomogeneous nucleation site for 211, providing more nucleation sites and suppressing the over-growth of 211. A high density of twins with spacing about 60 nmsimilar to80 nm was found. Additionally, a kind of twin domain boundary structure was observed. The formation mechanism of the, twin domain boundary was discussed. Similar to the sample without CeO2 addition, no impurity phases were found at the 211/123 boundaries by HREM.