DISPERSION OF SILVER IN THE MELT GROWN YBA2CU3O6+X CRYSTAL

The effect of silver contents and heat pattern on the dispersion of si lver in the melt grown Y123 crystal was investigated. The silver free region, where no silver droplets exist, was observed in the initial gr owth region of the samples with relatively lower Ag2O contents. The cr itical Ag2O contents, below which the silver free region exist, is int erpreted as the same Ag concentration in the L1 (Ba-Cu rich) liquid; t he Ag concentration about 12.6 at.% in the L1 liquid is evaluated to b e the critical value when Y123 crystals grow at 965 degrees C. The rea son for the formation of the silver free region is attributed to the c omplete dissolution of Ag in the LI liquid at maximum temperature, i.e ., since no L2 (Ag rich liquid) phase exists in the LI liquid at the g rowth temperature, the Y123 crystal grows without capturing L2 phase t o form the silver free region. Consequently, to obtain Y123/silver com posites without the silver free region, we need to select the initial composition and/or the heat pattern as the conditions in which the L2 phase exists in the L1 liquid at the growth temperature from the initi al growth stage. (C) 1998 Elsevier Science B.V. All rights reserved.