Microstructure of bulk PMP YBCO with submicrometre Y2BaCuO5 particles

The microstructure of bulk YBCO processed by the powder melting process using a submicrometre Y2BaCuO5 precursor in combination with the addition of CeO2 was characterized by scanning electron microscopy, transmission electron microscopy and high resolution electron microscopy. The mean diameter of the Y2BaCuO5 precursor was less than 500 nm. As a result, the mean diameter of the Y2BaCuO5 particles entrapped in the textured bulk YBCO is about 500 nm. Two types of Y2BaCuO5 were found within the bulk YBCO: one with one or two nanometric Y2O3 cores; the other, however, has no cores. The refinement mechanism for Y2BaCuO5 particles related to the employment of a submicrometre Y2BaCuO5 precursor and the minor addition of CeO2 is discussed. In addition, a high density of twins with an average spacing of about 60-80 nm was observed. Moreover, a twin domain boundary structure where domains with different orientation twins meet one another was found. The formation mechanisms for this high density of twins and the twin domain boundary structure are also discussed.