Microstructure of bulk PMP YBCO with submicrometre Y2BaCuO5 particles

The microstructure of bulk YBCO processed by the powder melting process usi ng a submicrometre Y2BaCuO5 precursor in combination with the addition of C eO2 was characterized by scanning electron microscopy, transmission electro n 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 refinemen t mechanism for Y2BaCuO5 particles related to the employment of a submicrom etre Y2BaCuO5 precursor and the minor addition of CeO2 is discussed. In add ition, a high density of twins with an average spacing of about 60-80 nm wa s observed. Moreover, a twin domain boundary structure where domains with d ifferent orientation twins meet one another was found. The formation mechan isms for this high density of twins and the twin domain boundary structure are also discussed.