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.