DISTRIBUTION OF AG AND Y2BACUO5 IN SUPERCONDUCTING YBCO AG COMPOSITE FABRICATED BY UNIDIRECTIONAL SOLIDIFICATION/

The distribution of 211 (Y2BaCuO5) and Ag particles in the columnar 12 3 (YBa2Cu3O7-x) crystal of YBCO/Ag composites solidified unidirectiona lly was investigated to clarify the peritecto-monotectic solidificatio n mechanism. The fabricated 123 crystal has a faceted cell and a band structure of 211 particles at the center of the cell, because of radia l solute diffusion layer at the cell tip where 211 particles can't suf ficiently dissolve into the melt. Ag-free region was also formed at th e same central region of the 123 cell by pushing of Ag particles, whic h sizes are under a critical radius (r(c)), by the 123 growth interfac e. The relation between r(0) and growth rate R-i (: the following R-a or R-c) of faceted planes was given by the equation: R-i = 0.52/r(c). In the Ag added hyperperitectic YBCO, the amount of the 211 particles in the 123 phase was larger in the Ag-rich region than in the Ag-free region because the amount of 123 phase in the Ag-rich region was small er than that in the Ag-free region. Therefore, the distribution of 211 particles in the 123 phase takes a duplicated structure. The growth d irection of the cell tip was obtained by analyzing the above band stru ctures of Ag-free regions or 211-rich regions which correspond to the growth trace of cell edges. From the measured crystallographic orienta tion of the cell, the relation between R-a, R-c and R are R-a (R-b) = 0.66R and R-c = 0.54R, where R (mu m/s), R-a, and R-c (mu m/s) are mac ro-growth rate of each faceted plane, respectively.