Bulk samples, with sub-micron Y2BaCuO5 (211) particles, were prepared under O partial pressures of 1 or 0.21atm by using the powder melting process. No twins could be found in as-grown samples prepared under an O partial pressure of 0.21atm, but twins were observed to nucleate at the 211/123 interface and sub-grain boundaries and extend into the interior of the matrix in as-grown samples produced under an O partial pressure of 1atm. The O contents were equal to 6.63 and 6.76 for the 2 samples, respectively. High densities of twins, with an average width of 60 to 80nm, were found in oxygenated samples prepared both under O partial pressures of 1atm or 0.21atm. A form of twin-domain boundary structure was observed.

TEM Study of the Formation of Twins in PMP-Processed YBCO Bulks with Submicron Y2BaCuO5 Particles. S.K.Chen, L.Zhou, K.G.Wang, X.Z.Wu, P.X.Zhang, Y.Feng: Physica C, 2002, 377[4], 571-7