Prakt. Met. Sonderband 38 (2006) 515 
n be seen small second particles non-uniformly distributed in Y123 grains. Many circular-type of 
der. Many second particle-free areas are observed with the addition of BaCeO3; and segregation also 
h a size of observed at the liquid phase remained at the high angle grain boundary as shown in (d). 
in size are These results indicate that the segregation of the second particles with/without BaCeOs is 
iin. to 150 general phenomena. 
les in size 
nilling, the 
(d). 
1a Fr 
(C) (d) 
Fig. 3: the microstructures of the Y123 sample melt-textured with (a) no addition, 
(b) 5 wt.%, (c) 10 wt.%, and (d) 20 wt.% BaCeO3 addition. 
3.2.2 Variation of the mixed powder size 
In order to study the influence of the particle size of the Y123 and the second phase on the 
microstructure and superconducting properties of the melt-textured Y123 samples, the 
w.- Y123 calcined powders were mixed with 10 wt.% BaCeO3z and melt textured. Figure 4 
show optical micrographs of the melt-textured Y123 samples from the powder of (a) as 
calcined Y123 mixture, (b) attrition milled for 30 min, (c) attrition milled for 150 min., and 
(d) attrition milled for 270 min. As can be seen in Fig. 4, the size distribution of the Y211 
ied in the within the Y123 matrix of the sample (a) is very wide, while Y211 becomes finer with 
t.% to 20 attriton milling. The Y211 and the BaCeO;s is relatively homogeneously distributed within 
ith (a) no the textured Y123 matrix in (a), but many small spherical second particle-free regions are 
racks due also observed. This type of Y211-free regions are formed by liquid filling into the preformed 
structure spherical pores at the incongruent melting state of Y211 + liquid phase [5]. The second 
It is also particles tend to segregate more as the particles attrition-milled as shown (b)-(d). In these 
creased, samples, the small spherical Y211-free regions are also observed. As the attrition milling 
x 
iw